Achondroplasia is the most common cause of disproportionate short stature. Affected individuals have rhizomelic shortening of the limbs, macrocephaly, and characteristic facial features with frontal bossing and midface retrusion. In infancy, hypotonia is typical, and acquisition of developmental motor milestones is often both aberrant in pattern and delayed. Intelligence and life span are usually near normal, although craniocervical junction compression increases the risk of death in infancy. Additional complications include obstructive sleep apnea, middle ear dysfunction, kyphosis, and spinal stenosis.

Apert syndrome is characterized by the presence of multisuture craniosynostosis, midface retrusion, and syndactyly of the hands with fusion of the second through fourth nails. Almost all affected individuals have coronal craniosynostosis, and a majority also have involvement of the sagittal and lambdoid sutures. The midface in Apert syndrome is underdeveloped as well as retruded; a subset of affected individuals have cleft palate. The hand in Apert syndrome always includes fusion of the middle three digits; the thumb and fifth finger are sometimes also involved. Feeding issues, dental abnormalities, hearing loss, hyperhidrosis, and progressive synostosis of multiple bones (skull, hands, feet, carpus, tarsus, and cervical vertebrae) are also common. Multilevel airway obstruction may be present and can be due to narrowing of the nasal passages, tongue-based airway obstruction, and/or tracheal anomalies. Nonprogressive ventriculomegaly is present in a majority of individuals, with a small subset having true hydrocephalus. Most individuals with Apert syndrome have normal intelligence or mild intellectual disability; moderate-to-severe intellectual disability has been reported in some individuals. A minority of affected individuals have structural cardiac abnormalities, true gastrointestinal malformations, and anomalies of the genitourinary tract.

Cleidocranial dysplasia (CCD) spectrum disorder is a skeletal dysplasia that represents a clinical continuum ranging from classic CCD (triad of delayed closure of the cranial sutures, hypoplastic or aplastic clavicles, and dental abnormalities) to mild CCD to isolated dental anomalies without the skeletal features. Most individuals come to diagnosis because they have classic features. At birth, affected individuals typically have abnormally large, wide-open fontanelles that may remain open throughout life. Clavicular hypoplasia can result in narrow, sloping shoulders that can be opposed at the midline. Moderate short stature may be observed, with most affected individuals being shorter than their unaffected sibs. Dental anomalies may include supernumerary teeth, eruption failure of the permanent teeth, and presence of the second permanent molar with the primary dentition. Individuals with CCD spectrum disorder are at increased risk of developing recurrent sinus infections, recurrent ear infections leading to conductive hearing loss, and upper-airway obstruction. Intelligence is typically normal.

Clubfoot is a congenital limb deformity defined as fixation of the foot in cavus, adductus, varus, and equinus (i.e., inclined inwards, axially rotated outwards, and pointing downwards) with concomitant soft tissue abnormalities (Cardy et al., 2007). Clubfoot may occur in isolation or as part of a syndrome (e.g., diastrophic dysplasia, 222600). Clubfoot has been reported with deficiency of long bones and mirror-image polydactyly (Gurnett et al., 2008; Klopocki et al., 2012).

Fucosidosis is an autosomal recessive lysosomal storage disease caused by defective alpha-L-fucosidase with accumulation of fucose in the tissues. Clinical features include angiokeratoma, progressive psychomotor retardation, neurologic signs, coarse facial features, and dysostosis multiplex. Fucosidosis has been classified into 2 major types. Type 1 is characterized by rapid psychomotor regression and severe neurologic deterioration beginning at about 6 months of age, elevated sweat sodium chloride, and death within the first decade of life. Type 2 is characterized by milder psychomotor retardation and neurologic signs, the development of angiokeratoma corporis diffusum, normal sweat salinity, and longer survival (Kousseff et al., 1976).

Glycogen storage disease type III (GSD III) is characterized by variable liver, cardiac muscle, and skeletal muscle involvement. GSD IIIa is the most common subtype, present in about 85% of affected individuals; it manifests with liver and muscle involvement. GSD IIIb, with liver involvement only, comprises about 15% of all affected individuals. In infancy and early childhood, liver involvement presents as hepatomegaly and failure to thrive, with fasting ketotic hypoglycemia, hyperlipidemia, and elevated hepatic transaminases. In adolescence and adulthood, liver disease becomes less prominent. Most individuals develop cardiac involvement with cardiac hypertrophy and/or cardiomyopathy. Skeletal myopathy manifesting as weakness may be evident in childhood and slowly progresses, typically becoming prominent in the third to fourth decade. The overall prognosis is favorable but cannot be predicted on an individual basis. Long-term complications such as muscular and cardiac symptoms as well as liver fibrosis/cirrhosis and hepatocellular carcinoma may have a severe impact on prognosis and quality of life. To date, it is unknown if long-term complications can be alleviated and/or avoided by dietary interventions.

Orofaciodigital syndrome II (OFD2), also known as Mohr syndrome, is characterized by cleft lip/palate, lobulated tongue with nodules, dental anomalies including tooth agenesis, maxillary hypoplasia, conductive hearing loss, and poly-, syn-, and brachydactyly. Mesomelic shortening of the limbs has also been observed (Mohr, 1941; Gorlin, 1982; Monroe et al., 2016).

Mucopolysaccharidosis type I (MPS I) is a progressive multisystem disorder with features ranging over a continuum of severity. While affected individuals have traditionally been classified as having one of three MPS I syndromes (Hurler syndrome, Hurler-Scheie syndrome, or Scheie syndrome), no easily measurable biochemical differences have been identified and the clinical findings overlap. Affected individuals are best described as having either a phenotype consistent with either severe (Hurler syndrome) or attenuated MPS I, a distinction that influences therapeutic options. Severe MPS I. Infants appear normal at birth. Typical early manifestations are nonspecific (e.g., umbilical or inguinal hernia, frequent upper respiratory tract infections before age 1 year). Coarsening of the facial features may not become apparent until after age one year. Gibbus deformity of the lower spine is common and often noted within the first year. Progressive skeletal dysplasia (dysostosis multiplex) involving all bones is universal, as is progressive arthropathy involving most joints. By age three years, linear growth decreases. Intellectual disability is progressive and profound but may not be readily apparent in the first year of life. Progressive cardiorespiratory involvement, hearing loss, and corneal clouding are common. Without treatment, death (typically from cardiorespiratory failure) usually occurs within the first ten years of life. Attenuated MPS I. Clinical onset is usually between ages three and ten years. The severity and rate of disease progression range from serious life-threatening complications leading to death in the second to third decade, to a normal life span complicated by significant disability from progressive joint manifestations and cardiorespiratory disease. While some individuals have no neurologic involvement and psychomotor development may be normal in early childhood, learning disabilities and psychiatric manifestations can be present later in life. Hearing loss, cardiac valvular disease, respiratory involvement, and corneal clouding are common.

Mucopolysaccharidosis type VI (MPS6) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of arylsulfatase B. Clinical features and severity are variable, but usually include short stature, hepatosplenomegaly, dysostosis multiplex, stiff joints, corneal clouding, cardiac abnormalities, and facial dysmorphism. Intelligence is usually normal (Azevedo et al., 2004).

An autosomal dominant inherited condition caused by mutations in the lamin B receptor gene. It is characterized by defects in the neutrophil lobulation, resulting in the presence of dumbbell-shaped neutrophils with bilobed nuclei in the peripheral blood smear.

Disorders of GNAS inactivation include the phenotypes pseudohypoparathyroidism Ia, Ib, and Ic (PHP-Ia, -Ib, -Ic), pseudopseudohypoparathyroidism (PPHP), progressive osseous heteroplasia (POH), and osteoma cutis (OC). PHP-Ia and PHP-Ic are characterized by: End-organ resistance to endocrine hormones including parathyroid hormone (PTH), thyroid-stimulating hormone (TSH), gonadotropins (LH and FSH), growth hormone-releasing hormone (GHRH), and CNS neurotransmitters (leading to obesity and variable degrees of intellectual disability and developmental delay); and The Albright hereditary osteodystrophy (AHO) phenotype (short stature, round facies, and subcutaneous ossifications) and brachydactyly type E (shortening mainly of the 4th and/or 5th metacarpals and metatarsals and distal phalanx of the thumb). Although PHP-Ib is characterized principally by PTH resistance, some individuals also have partial TSH resistance and mild features of AHO (e.g., brachydactyly). PPHP, a more limited form of PHP-Ia, is characterized by various manifestations of the AHO phenotype without the hormone resistance or obesity. POH and OC are even more restricted variants of PPHP: POH consists of dermal ossification beginning in infancy, followed by increasing and extensive bone formation in deep muscle and fascia. OC consists of extra-skeletal ossification that is limited to the dermis and subcutaneous tissues.

Proteus syndrome is characterized by progressive segmental or patchy overgrowth most commonly affecting the skeleton, skin, adipose, and central nervous systems. In most individuals Proteus syndrome has modest or no manifestations at birth, develops and progresses rapidly beginning in the toddler period, and relentlessly progresses through childhood, causing severe overgrowth and disfigurement. It is associated with a range of tumors, pulmonary complications, and a striking predisposition to deep vein thrombosis and pulmonary embolism.

Mucopolysaccharidosis type I (MPS I) is a progressive multisystem disorder with features ranging over a continuum of severity. While affected individuals have traditionally been classified as having one of three MPS I syndromes (Hurler syndrome, Hurler-Scheie syndrome, or Scheie syndrome), no easily measurable biochemical differences have been identified and the clinical findings overlap. Affected individuals are best described as having either a phenotype consistent with either severe (Hurler syndrome) or attenuated MPS I, a distinction that influences therapeutic options. Severe MPS I. Infants appear normal at birth. Typical early manifestations are nonspecific (e.g., umbilical or inguinal hernia, frequent upper respiratory tract infections before age 1 year). Coarsening of the facial features may not become apparent until after age one year. Gibbus deformity of the lower spine is common and often noted within the first year. Progressive skeletal dysplasia (dysostosis multiplex) involving all bones is universal, as is progressive arthropathy involving most joints. By age three years, linear growth decreases. Intellectual disability is progressive and profound but may not be readily apparent in the first year of life. Progressive cardiorespiratory involvement, hearing loss, and corneal clouding are common. Without treatment, death (typically from cardiorespiratory failure) usually occurs within the first ten years of life. Attenuated MPS I. Clinical onset is usually between ages three and ten years. The severity and rate of disease progression range from serious life-threatening complications leading to death in the second to third decade, to a normal life span complicated by significant disability from progressive joint manifestations and cardiorespiratory disease. While some individuals have no neurologic involvement and psychomotor development may be normal in early childhood, learning disabilities and psychiatric manifestations can be present later in life. Hearing loss, cardiac valvular disease, respiratory involvement, and corneal clouding are common.

Mucopolysaccharidosis type III (MPS III) is a multisystem lysosomal storage disease characterized by progressive central nervous system degeneration manifest as severe intellectual disability (ID), developmental regression, and other neurologic manifestations including autism spectrum disorder (ASD), behavioral problems, and sleep disturbances. Disease onset is typically before age ten years. Disease course may be rapidly or slowly progressive; some individuals with an extremely attenuated disease course present in mid-to-late adulthood with early-onset dementia with or without a history of ID. Systemic manifestations can include musculoskeletal problems (joint stiffness, contractures, scoliosis, and hip dysplasia), hearing loss, respiratory tract and sinopulmonary infections, and cardiac disease (valvular thickening, defects in the cardiac conduction system). Neurologic decline is seen in all affected individuals; however, clinical severity varies within and among the four MPS III subtypes (defined by the enzyme involved) and even among members of the same family. Death usually occurs in the second or third decade of life secondary to neurologic regression or respiratory tract infections.

Mucopolysaccharidosis type I (MPS I) is a progressive multisystem disorder with features ranging over a continuum of severity. While affected individuals have traditionally been classified as having one of three MPS I syndromes (Hurler syndrome, Hurler-Scheie syndrome, or Scheie syndrome), no easily measurable biochemical differences have been identified and the clinical findings overlap. Affected individuals are best described as having either a phenotype consistent with either severe (Hurler syndrome) or attenuated MPS I, a distinction that influences therapeutic options. Severe MPS I. Infants appear normal at birth. Typical early manifestations are nonspecific (e.g., umbilical or inguinal hernia, frequent upper respiratory tract infections before age 1 year). Coarsening of the facial features may not become apparent until after age one year. Gibbus deformity of the lower spine is common and often noted within the first year. Progressive skeletal dysplasia (dysostosis multiplex) involving all bones is universal, as is progressive arthropathy involving most joints. By age three years, linear growth decreases. Intellectual disability is progressive and profound but may not be readily apparent in the first year of life. Progressive cardiorespiratory involvement, hearing loss, and corneal clouding are common. Without treatment, death (typically from cardiorespiratory failure) usually occurs within the first ten years of life. Attenuated MPS I. Clinical onset is usually between ages three and ten years. The severity and rate of disease progression range from serious life-threatening complications leading to death in the second to third decade, to a normal life span complicated by significant disability from progressive joint manifestations and cardiorespiratory disease. While some individuals have no neurologic involvement and psychomotor development may be normal in early childhood, learning disabilities and psychiatric manifestations can be present later in life. Hearing loss, cardiac valvular disease, respiratory involvement, and corneal clouding are common.

Hypohidrotic ectodermal dysplasia (HED) is characterized by hypotrichosis (sparseness of scalp and body hair), hypohidrosis (reduced ability to sweat), and hypodontia (congenital absence of teeth). The cardinal features of classic HED become obvious during childhood. The scalp hair is thin, lightly pigmented, and slow growing. Sweating, although present, is greatly deficient, leading to episodes of hyperthermia until the affected individual or family acquires experience with environmental modifications to control temperature. Only a few abnormally formed teeth erupt, at a later-than-average age. Physical growth and psychomotor development are otherwise within normal limits. Mild HED is characterized by mild manifestations of any or all the characteristic features.

Smith-Lemli-Opitz syndrome (SLOS) is a congenital multiple-anomaly / cognitive impairment syndrome caused by an abnormality in cholesterol metabolism resulting from deficiency of the enzyme 7-dehydrocholesterol (7-DHC) reductase. It is characterized by prenatal and postnatal growth restriction, microcephaly, moderate-to-severe intellectual disability, and multiple major and minor malformations. The malformations include distinctive facial features, cleft palate, cardiac defects, underdeveloped external genitalia in males, postaxial polydactyly, and 2-3 syndactyly of the toes. The clinical spectrum is wide; individuals with normal development and only minor malformations have been described.

Sotos syndrome is characterized by a distinctive facial appearance (broad and prominent forehead with a dolichocephalic head shape, sparse frontotemporal hair, downslanting palpebral fissures, malar flushing, long and narrow face, long chin); learning disability (early developmental delay, mild-to-severe intellectual impairment); and overgrowth (height and/or head circumference =2 SD above the mean). These three clinical features are considered the cardinal features of Sotos syndrome. Major features of Sotos syndrome include behavioral problems (most notably autistic spectrum disorder), advanced bone age, cardiac anomalies, cranial MRI/CT abnormalities, joint hyperlaxity with or without pes planus, maternal preeclampsia, neonatal complications, renal anomalies, scoliosis, and seizures.

Williams syndrome (WS) is characterized by cardiovascular disease (elastin arteriopathy, peripheral pulmonary stenosis, supravalvar aortic stenosis, hypertension), distinctive facies, connective tissue abnormalities, intellectual disability (usually mild), a specific cognitive profile, unique personality characteristics, growth abnormalities, and endocrine abnormalities (hypercalcemia, hypercalciuria, hypothyroidism, and early puberty). Feeding difficulties often lead to poor weight gain in infancy. Hypotonia and hyperextensible joints can result in delayed attainment of motor milestones.

The FLNB disorders include a spectrum of phenotypes ranging from mild to severe. At the mild end are spondylocarpotarsal synostosis (SCT) syndrome and Larsen syndrome; at the severe end are the phenotypic continuum of atelosteogenesis types I (AOI) and III (AOIII) and Piepkorn osteochondrodysplasia (POCD). SCT syndrome is characterized by postnatal disproportionate short stature, scoliosis and lordosis, clubfeet, hearing loss, dental enamel hypoplasia, carpal and tarsal synostosis, and vertebral fusions. Larsen syndrome is characterized by congenital dislocations of the hip, knee, and elbow; clubfeet (equinovarus or equinovalgus foot deformities); scoliosis and cervical kyphosis, which can be associated with a cervical myelopathy; short, broad, spatulate distal phalanges; distinctive craniofacies (prominent forehead, depressed nasal bridge, malar flattening, and widely spaced eyes); vertebral anomalies; and supernumerary carpal and tarsal bone ossification centers. Individuals with SCT syndrome and Larsen syndrome can have midline cleft palate and hearing loss. AOI and AOIII are characterized by severe short-limbed dwarfism; dislocated hips, knees, and elbows; and clubfeet. AOI is lethal in the perinatal period. In individuals with AOIII, survival beyond the neonatal period is possible with intensive and invasive respiratory support. Piepkorn osteochondrodysplasia (POCD) is a perinatal-lethal micromelic dwarfism characterized by flipper-like limbs (polysyndactyly with complete syndactyly of all fingers and toes, hypoplastic or absent first digits, and duplicated intermediate and distal phalanges), macrobrachycephaly, prominant forehead, hypertelorism, and exophthalmos. Occasional features include cleft palate, omphalocele, and cardiac and genitourinary anomalies. The radiographic features at mid-gestation are characteristic.

Pfeiffer syndrome is an autosomal dominant craniosynostosis syndrome with characteristic anomalies of the hands and feet. Three clinical subtypes, which have important diagnostic and prognostic implications, have been identified. Type 1, the classic syndrome, is compatible with life and consists of craniosynostosis, midface deficiency, broad thumbs, broad great toes, brachydactyly, and variable syndactyly. Type 2 consists of cloverleaf skull with Pfeiffer hands and feet, together with ankylosis of the elbows. Type 3 is similar to type 2 but without cloverleaf skull. Ocular proptosis is severe, and the anterior cranial base is markedly short. Various visceral malformations have been found in association with type 3. Early demise is characteristic of types 2 and 3 (Cohen, 1993). Cohen and Barone (1994) further tabulated the findings in the 3 types of Pfeiffer syndrome.

Blepharophimosis, ptosis, and epicanthus inversus syndrome (BPES) is defined by a complex eyelid malformation characterized by four major features, all present at birth: blepharophimosis, ptosis, epicanthus inversus, and telecanthus. BPES type I includes the four major features and primary ovarian insufficiency; BPES type II includes only the four major features. Other ophthalmic manifestations that can be associated with BPES include dysplastic eyelids, lacrimal duct anomalies, strabismus, refractive errors, and amblyopia. Other craniofacial features may include a broad nasal bridge and low-set ears.

A rare developmental anomaly, affecting primarily the anterior part of the maxilla and nasal complex. Affected individuals typically have an unusually flat, underdeveloped midface, with an abnormally short nose and flat nasal bridge, underdeveloped upper jaw, relatively protruding lower jaw and/or a ''reverse overbite'' (or class III malocclusion). Hypoplasia of distal phalanges of fingers was reported in some cases. The pathogenesis remains uncertain, most reported cases were sporadic.

The most basic description of Moebius syndrome is a congenital facial palsy with impairment of ocular abduction. The facial nerve (cranial nerve VII) and abducens nerve (CN VI) are most frequently involved, but other cranial nerves may be involved as well. Other variable features include orofacial dysmorphism and limb malformations. Mental retardation has been reported in a subset of patients. Most cases of Moebius syndrome are sporadic, but familial occurrence has been reported (Verzijl et al., 2003). The definition of and diagnostic criteria for Moebius syndrome have been controversial and problematic. The syndrome has most frequently been confused with hereditary congenital facial paresis (HCFP; see 601471), which is restricted to involvement of the facial nerve and no other abnormalities. Verzijl et al. (2003) and Verzijl et al. (2005) concluded that HCFP and Moebius syndrome are distinct disorders, and that Moebius syndrome is a complex developmental disorder of the brainstem. Moebius syndrome was defined at the Moebius Syndrome Foundation Research Conference in 2007 as congenital, nonprogressive facial weakness with limited abduction of one or both eyes. Additional features can include hearing loss and other cranial nerve dysfunction, as well as motor, orofacial, musculoskeletal, neurodevelopmental, and social problems (summary by Webb et al., 2012). Kumar (1990) provided a review of Moebius syndrome, which was critiqued by Lipson et al. (1990). Briegel (2006) provided a review of Moebius sequence with special emphasis on neuropsychiatric findings.

EZH2-related overgrowth includes EZH2-related Weaver syndrome at one end of the spectrum and tall stature at the other. Although most individuals diagnosed with a heterozygous EZH2 pathogenic variant have been identified because of a clinical suspicion of Weaver syndrome, a minority have been identified through molecular genetic testing of family members of probands or individuals with overgrowth who did not have a clinical diagnosis of Weaver syndrome. Thus, the extent of the phenotypic spectrum associated with a heterozygous EZH2 pathogenic variant is not yet known. Weaver syndrome is characterized by tall stature, variable intellect (ranging from normal intellect to severe intellectual disability), characteristic facial appearance, and a range of associated clinical features including advanced bone age, poor coordination, soft doughy skin, camptodactyly of the fingers and/or toes, umbilical hernia, abnormal tone, and hoarse low cry in infancy. Brain MRI has identified abnormalities in a few individuals with EZH2-related overgrowth. Neuroblastoma occurs at a slightly increased frequency in individuals with a heterozygous EZH2 pathogenic variant but data are insufficient to determine absolute risk. There is currently no evidence that additional malignancies (including hematologic malignancies) occur with increased frequency.

The Marshall-Smith syndrome (MRSHSS) is a malformation syndrome characterized by accelerated skeletal maturation, relative failure to thrive, respiratory difficulties, mental retardation, and unusual facies, including prominent forehead, shallow orbits, blue sclerae, depressed nasal bridge, and micrognathia (Adam et al., 2005).

GLI3-related Pallister-Hall syndrome (GLI3-PHS) is characterized by a spectrum of anomalies ranging from polydactyly, asymptomatic bifid epiglottis, and hypothalamic hamartoma at the mild end to laryngotracheal cleft with neonatal lethality at the severe end. Individuals with mild GLI3-PHS may be incorrectly diagnosed as having isolated postaxial polydactyly type A. Individuals with GLI3-PHS can have pituitary insufficiency and may die as neonates from undiagnosed and untreated adrenal insufficiency.

Schinzel-Giedion syndrome is a highly recognizable syndrome characterized by severe mental retardation, distinctive facial features, and multiple congenital malformations including skeletal abnormalities, genitourinary and renal malformations, and cardiac defects, as well as a higher-than-normal prevalence of tumors, notably neuroepithelial neoplasia (summary by Hoischen et al., 2010).

Marshall syndrome (MRSHS) is characterized by midfacial hypoplasia, cleft palate, ocular anomalies including high myopia and cataracts, sensorineural hearing loss, short stature with spondyloepiphyseal dysplasia, and arthropathy. In contrast to Stickler syndrome type II, it has less severe eye findings but striking ocular hypertelorism, more pronounced maxillary hypoplasia, and ectodermal abnormalities (summary by Shanske et al., 1997 and Ala-Kokko and Shanske, 2009).

The NSDHL-related disorders include: CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, an X-linked condition that is usually male lethal during gestation and thus predominantly affects females; and CK syndrome, an X-linked disorder that affects males. CHILD syndrome is characterized by unilateral distribution of ichthyosiform (yellow scaly) skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb. Intellect is usually normal. The ichthyosiform skin lesions are usually present at birth or in the first weeks of life; new lesions can develop in later life. Nail changes are also common. The heart, lung, and kidneys can also be involved. CK syndrome (named for the initials of the original proband) is characterized by mild to severe cognitive impairment and behavior problems (aggression, attention deficit hyperactivity disorder, and irritability). All affected males reported have developed seizures in infancy and have cerebral cortical malformations and microcephaly. All have distinctive facial features, a thin habitus, and relatively long, thin fingers and toes. Some have scoliosis and kyphosis. Strabismus is common. Optic atrophy is also reported.

The term achondrogenesis has been used to characterize the most severe forms of chondrodysplasia in humans, invariably lethal before or shortly after birth. Achondrogenesis type I is a severe chondrodystrophy characterized radiographically by deficient ossification in the lumbar vertebrae and absent ossification in the sacral, pubic and ischial bones and clinically by stillbirth or early death (Maroteaux and Lamy, 1968; Langer et al., 1969). In addition to severe micromelia, there is a disproportionately large cranium due to marked edema of soft tissues. Classification of Achondrogenesis Achondrogenesis was traditionally divided into 2 types: type I (Parenti-Fraccaro) and type II (Langer-Saldino). Borochowitz et al. (1988) suggested that achondrogenesis type I of Parenti-Fraccaro should be classified into 2 distinct disorders: type IA, corresponding to the cases originally published by Houston et al. (1972) and Harris et al. (1972), and type IB (600972), corresponding to the case originally published by Fraccaro (1952). Analysis of the case reported by Parenti (1936) by Borochowitz et al. (1988) suggested the diagnosis of achondrogenesis type II, i.e., the Langer-Saldino type (200610). Type IA would be classified as lethal achondrogenesis, Houston-Harris type; type IB, lethal achondrogenesis, Fraccaro type; and type II, lethal achondrogenesis-hypochondrogenesis, Langer-Saldino type. Superti-Furga (1996) suggested that hypochondrogenesis should be considered separately from achondrogenesis type II because the phenotype can be much milder. Genetic Heterogeneity of Achondrogenesis Achondrogenesis type IB (ACG1B; 600972) is caused by mutation in the DTDST gene (606718), and achondrogenesis type II (ACG2; 200610) is caused by mutation in the COL2A1 gene (120140).

Kniest dysplasia is characterized by skeletal and craniofacial anomalies. Skeletal anomalies include disproportionate dwarfism, a short trunk and small pelvis, kyphoscoliosis, short limbs, and prominent joints and premature osteoarthritis that restrict movement. Craniofacial manifestations include midface hypoplasia, cleft palate, early-onset myopia, retinal detachment, and hearing loss. The phenotype is severe in some patients and mild in others. There are distinct radiographic changes including coronal clefts of vertebrae and dumbbell-shaped femora. The chondrooseous morphology is pathognomonic with perilacunar 'foaminess' and sparse, aggregated collagen fibrils resulting in an interterritorial matrix with a 'Swiss-cheese' appearance (summary by Wilkin et al., 1999).

The autosomal dominant TRPV4 disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported. The three autosomal dominant neuromuscular disorders (mildest to most severe) are: Charcot-Marie-Tooth disease type 2C. Scapuloperoneal spinal muscular atrophy. Congenital distal spinal muscular atrophy. The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six autosomal dominant skeletal dysplasias (mildest to most severe) are: Familial digital arthropathy-brachydactyly. Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened. Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias.

The autosomal dominant TRPV4 disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported. The three autosomal dominant neuromuscular disorders (mildest to most severe) are: Charcot-Marie-Tooth disease type 2C. Scapuloperoneal spinal muscular atrophy. Congenital distal spinal muscular atrophy. The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six autosomal dominant skeletal dysplasias (mildest to most severe) are: Familial digital arthropathy-brachydactyly. Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened. Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias.

The FLNB disorders include a spectrum of phenotypes ranging from mild to severe. At the mild end are spondylocarpotarsal synostosis (SCT) syndrome and Larsen syndrome; at the severe end are the phenotypic continuum of atelosteogenesis types I (AOI) and III (AOIII) and Piepkorn osteochondrodysplasia (POCD). SCT syndrome is characterized by postnatal disproportionate short stature, scoliosis and lordosis, clubfeet, hearing loss, dental enamel hypoplasia, carpal and tarsal synostosis, and vertebral fusions. Larsen syndrome is characterized by congenital dislocations of the hip, knee, and elbow; clubfeet (equinovarus or equinovalgus foot deformities); scoliosis and cervical kyphosis, which can be associated with a cervical myelopathy; short, broad, spatulate distal phalanges; distinctive craniofacies (prominent forehead, depressed nasal bridge, malar flattening, and widely spaced eyes); vertebral anomalies; and supernumerary carpal and tarsal bone ossification centers. Individuals with SCT syndrome and Larsen syndrome can have midline cleft palate and hearing loss. AOI and AOIII are characterized by severe short-limbed dwarfism; dislocated hips, knees, and elbows; and clubfeet. AOI is lethal in the perinatal period. In individuals with AOIII, survival beyond the neonatal period is possible with intensive and invasive respiratory support. Piepkorn osteochondrodysplasia (POCD) is a perinatal-lethal micromelic dwarfism characterized by flipper-like limbs (polysyndactyly with complete syndactyly of all fingers and toes, hypoplastic or absent first digits, and duplicated intermediate and distal phalanges), macrobrachycephaly, prominant forehead, hypertelorism, and exophthalmos. Occasional features include cleft palate, omphalocele, and cardiac and genitourinary anomalies. The radiographic features at mid-gestation are characteristic.

Pallister-Killian syndrome (PKS) is a dysmorphic condition involving most organ systems, but is also characterized by a tissue-limited mosaicism; most fibroblasts have 47 chromosomes with an extra small metacentric chromosome, whereas the karyotype of lymphocytes is normal. The extra metacentric chromosome is an isochromosome for part of the short arm of chromosome 12: i(12)(p10) (Peltomaki et al., 1987; Warburton et al., 1987).

Aspartylglucosaminuria (AGU) is a severe autosomal recessive lysosomal storage disorder that involves the central nervous system and causes skeletal abnormalities as well as connective tissue lesions. The most characteristic feature is progressive mental retardation. The disorder is caused by deficient activity of the lysosomal enzyme glycosylasparaginase, which results in body fluid and tissue accumulation of a series of glycoasparagines, i.e., glycoconjugates with an aspartylglucosamine moiety at the reducing end. AGU belongs to the group of disorders commonly referred to as the Finnish disease heritage (summary by Mononen et al., 1993 and Arvio and Arvio, 2002).

PLOD1-related kyphoscoliotic Ehlers-Danlos syndrome (kEDS) is an autosomal recessive generalized connective tissue disorder characterized by hypotonia, early-onset kyphoscoliosis, and generalized joint hypermobility in association with skin fragility and ocular abnormality. Intelligence is normal. Life span may be normal, but affected individuals are at risk for rupture of medium-sized arteries. Adults with severe kyphoscoliosis are at risk for complications from restrictive lung disease, recurrent pneumonia, and cardiac failure.

Prolidase deficiency is characterized by skin lesions (typically severe, chronic, recalcitrant, and painful skin ulcers of the lower extremities and telangiectasias of the face and hands), recurrent infections (particularly of the skin and respiratory tract), dysmorphic facial features, variable intellectual disability, and organomegaly (typically splenomegaly but occasionally associated with hepatomegaly) with elevated liver enzymes. Skeletal anomalies, chronic pulmonary disease, anemia, thrombocytopenia, hypergammaglobulinemia, and hypocomplementemia are observed in a minority of affected individuals. An association between prolidase deficiency and autoimmune conditions – particularly systemic lupus erythematosus (SLE) – has been described.

Multiple acyl-CoA dehydrogenase deficiency (MADD) represents a clinical spectrum in which presentations can be divided into type I (neonatal onset with congenital anomalies), type II (neonatal onset without congenital anomalies), and type III (late onset). Individuals with type I or II MADD typically become symptomatic in the neonatal period with severe metabolic acidosis, which may be accompanied by profound hypoglycemia and hyperammonemia. Many affected individuals die in the newborn period despite metabolic treatment. In those who survive the neonatal period, recurrent metabolic decompensation resembling Reye syndrome and the development of hypertrophic cardiomyopathy can occur. Congenital anomalies may include dysmorphic facial features, large cystic kidneys, hypospadias and chordee in males, and neuronal migration defects (heterotopias) on brain MRI. Individuals with type III MADD, the most common presentation, can present from infancy to adulthood. The most common symptoms are muscle weakness, exercise intolerance, and/or muscle pain, although metabolic decompensation with episodes of rhabdomyolysis can also be seen. Rarely, individuals with late-onset MADD (type III) may develop severe sensory neuropathy in addition to proximal myopathy.

A type of central congenital hypothyroidism, a permanent thyroid deficiency that is present from birth, characterized by low levels of thyroid hormones due to a deficiency in TSH synthesis.

Pallister-Hall-like syndrome (PHLS) is a pleiotropic autosomal recessive disorder characterized by phenotypic variability. Patients exhibit postaxial polydactyly as well as hypothalamic hamartoma, cardiac and skeletal anomalies, and craniofacial dysmorphisms. Hirschsprung disease has also been observed (Rubino et al., 2018; Le et al., 2020). Pallister-Hall syndrome (146510) is an autosomal dominant disorder with features overlapping those of PHLS, caused by mutation in the GLI3 gene (165240).

Fumarate hydratase (FH) deficiency results in severe neonatal and early infantile encephalopathy that is characterized by poor feeding, failure to thrive, hypotonia, lethargy, and seizures. Dysmorphic facial features include frontal bossing, depressed nasal bridge, and widely spaced eyes. Many affected individuals are microcephalic. A spectrum of brain abnormalities are seen on magnetic resonance imaging, including cerebral atrophy, enlarged ventricles and generous extra-axial cerebral spinal fluid (CSF) spaces, delayed myelination for age, thinning of the corpus callosum, and an abnormally small brain stem. Brain malformations including bilateral polymicrogyria and absence of the corpus callosum can also be observed. Development is severely affected: most affected individuals are nonverbal and nonambulatory, and many die during early childhood. Less severely affected individuals with moderate cognitive impairment and long-term survival have been reported.

D-bifunctional protein deficiency is a disorder of peroxisomal fatty acid beta-oxidation. See also peroxisomal acyl-CoA oxidase deficiency (264470), caused by mutation in the ACOX1 gene (609751) on chromosome 17q25. The clinical manifestations of these 2 deficiencies are similar to those of disorders of peroxisomal assembly, including X-linked adrenoleukodystrophy (ALD; 300100), Zellweger cerebrohepatorenal syndrome (see 214100) and neonatal adrenoleukodystrophy (NALD; see 601539) (Watkins et al., 1995). DBP deficiency has been classified into 3 subtypes depending upon the deficient enzyme activity. Type I is a deficiency of both 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase; type II is a deficiency of hydratase activity alone; and type III is a deficiency of dehydrogenase activity alone. Virtually all patients with types I, II, and III have a severe phenotype characterized by infantile-onset of hypotonia, seizures, and abnormal facial features, and most die before age 2 years. McMillan et al. (2012) proposed a type IV deficiency on the basis of less severe features; these patients have a phenotype reminiscent of Perrault syndrome (PRLTS1; 233400). Pierce et al. (2010) noted that Perrault syndrome and DBP deficiency overlap clinically and suggested that DBP deficiency may be underdiagnosed.

PMM2-CDG, the most common of a group of disorders of abnormal glycosylation of N-linked oligosaccharides, is divided into three clinical stages: infantile multisystem, late-infantile and childhood ataxia–intellectual disability, and adult stable disability. The clinical manifestations and course are highly variable, ranging from infants who die in the first year of life to mildly affected adults. Clinical findings tend to be similar in sibs. In the infantile multisystem presentation, infants show axial hypotonia, hyporeflexia, esotropia, and developmental delay. Feeding problems, vomiting, faltering growth, and developmental delay are frequently seen. Subcutaneous fat may be excessive over the buttocks and suprapubic region. Two distinct clinical courses are observed: (1) a nonfatal neurologic course with faltering growth, strabismus, developmental delay, cerebellar hypoplasia, and hepatopathy in infancy followed by neuropathy and retinitis pigmentosa in the first or second decade; and (2) a more severe neurologic-multivisceral course with approximately 20% mortality in the first year of life. The late-infantile and childhood ataxia–intellectual disability stage, which begins between ages three and ten years, is characterized by hypotonia, ataxia, severely delayed language and motor development, inability to walk, and IQ of 40 to 70; other findings include seizures, stroke-like episodes or transient unilateral loss of function, coagulopathy, retinitis pigmentosa, joint contractures, and skeletal deformities. In the adult stable disability stage, intellectual ability is stable; peripheral neuropathy is variable, progressive retinitis pigmentosa and myopia are seen, thoracic and spinal deformities with osteoporosis worsen, and premature aging is observed; females may lack secondary sexual development and males may exhibit decreased testicular volume. Hypogonadotropic hypogonadism and coagulopathy may occur. The risk for deep venous thrombosis is increased.

The branchiooculofacial syndrome (BOFS) is characterized by: branchial (cervical or infra- or supra-auricular) skin defects that range from barely perceptible thin skin or hair patch to erythematous "hemangiomatous" lesions to large weeping erosions; ocular anomalies that can include microphthalmia, anophthalmia, coloboma, and nasolacrimal duct stenosis/atresia; and facial anomalies that can include ocular hypertelorism or telecanthus, broad nasal tip, upslanted palpebral fissures, cleft lip or prominent philtral pillars that give the appearance of a repaired cleft lip (formerly called "pseudocleft lip") with or without cleft palate, upper lip pits, and lower facial weakness (asymmetric crying face or partial 7th cranial nerve weakness). Malformed and prominent pinnae and hearing loss from inner ear and/or petrous bone anomalies are common. Intellect is usually normal.

Wiedemann-Rautenstrauch syndrome (WDRTS) is a rare autosomal recessive neonatal progeroid disorder characterized by intrauterine growth retardation, failure to thrive, short stature, a progeroid appearance, hypotonia, and variable mental impairment (summary by Toriello, 1990). Average survival in WDRTS is 7 months, although survival into the third decade of life has been reported (Akawi et al., 2013).

EEC syndrome is a genetic developmental disorder characterized by ectrodactyly, ectodermal dysplasia, and orofacial clefts (cleft lip/palate).

GAPO syndrome is the acronymic designation for a complex of growth retardation, alopecia, pseudoanodontia (failure of tooth eruption), and progressive optic atrophy (Tipton and Gorlin, 1984). Ilker et al. (1999) and Bayram et al. (2014) noted that optic atrophy is not a consistent feature of the disorder.

Hypochondroplasia is a skeletal dysplasia characterized by short stature; stocky build; disproportionately short arms and legs; broad, short hands and feet; mild joint laxity; and macrocephaly. Radiologic features include shortening of long bones with mild metaphyseal flare; narrowing of the inferior lumbar interpedicular distances; short, broad femoral neck; and squared, shortened ilia. The skeletal features are very similar to those seen in achondroplasia but tend to be milder. Medical complications common to achondroplasia (e.g., spinal stenosis, tibial bowing, obstructive apnea) occur less frequently in hypochondroplasia but intellectual disability and epilepsy may be more prevalent. Children usually present as toddlers or at early school age with decreased growth velocity leading to short stature and limb disproportion. Other features also become more prominent over time.

Wolcott-Rallison syndrome is a rare autosomal recessive disorder characterized by permanent neonatal or early infancy insulin-dependent diabetes. Epiphyseal dysplasia, osteoporosis, and growth retardation develop at a later age. Other frequent multisystem manifestations include hepatic and renal dysfunction, mental retardation, and cardiovascular abnormalities (summary by Delepine et al., 2000).

Opsismodysplasia (OPSMD) is a rare skeletal dysplasia involving delayed bone maturation. Clinical signs observed at birth include short limbs, small hands and feet, relative macrocephaly with a large anterior fontanel, and characteristic craniofacial abnormalities including a prominent brow, depressed nasal bridge, a small anteverted nose, and a relatively long philtrum. Death in utero or secondary to respiratory failure during the first few years of life has been reported, but there can be long-term survival. Typical radiographic findings include shortened long bones with delayed epiphyseal ossification, severe platyspondyly, metaphyseal cupping, and characteristic abnormalities of the metacarpals and phalanges (summary by Below et al., 2013 and Fradet and Fitzgerald, 2017).

A rare primary bone dysplasia characterized, radiologically, by short, stubby long bones, severely angulated femurs and lesser bowing of other long bones (mild, moderate or no bowing), short and wide iliac wings with horizontal acetabular roofs, platyspondyly and a narrow thorax, clinically manifesting with severe, disproportionate short stature. Regression of femora angulation is observed with advancing age.

Osteoglophonic dysplasia (OGD) is characterized by rhizomelic dwarfism, nonossifying bone lesions, craniosynostosis, prominent supraorbital ridge, and depressed nasal bridge (summary by White et al., 2005).

Monosomy 18q is a partial deletion of the long arm of chromosome 18 characterized by highly variable phenotype, most commonly including hypotonia, developmental delay, short stature, growth hormone deficiency, hearing loss and external ear anomalies, intellectual disability, palatal defects, dysmorphic facial features, skeletal anomalies (foot deformities, tapering fingers, scoliosis) and mood disorders.

Mulibrey nanism (MUL) is a rare autosomal recessive growth disorder with prenatal onset, including occasional progressive cardiomyopathy, characteristic facial features, failure of sexual maturation, insulin resistance with type 2 diabetes, and an increased risk for Wilms tumor (summary by Hamalainen et al., 2006).

While the majority of individuals with Costello syndrome share characteristic findings affecting multiple organ systems, the phenotypic spectrum is wide, ranging from a milder or attenuated phenotype to a severe phenotype with early lethal complications. Costello syndrome is typically characterized by failure to thrive in infancy as a result of severe postnatal feeding difficulties; short stature; developmental delay or intellectual disability; coarse facial features (full lips, large mouth, full nasal tip); curly or sparse, fine hair; loose, soft skin with deep palmar and plantar creases; papillomata of the face and perianal region; diffuse hypotonia and joint laxity with ulnar deviation of the wrists and fingers; tight Achilles tendons; and cardiac involvement including: cardiac hypertrophy (usually typical hypertrophic cardiomyopathy), congenital heart defect (usually valvar pulmonic stenosis), and arrhythmia (usually supraventricular tachycardia, especially chaotic atrial rhythm/multifocal atrial tachycardia or ectopic atrial tachycardia). Relative or absolute macrocephaly is typical, and postnatal cerebellar overgrowth can result in the development of a Chiari I malformation with associated anomalies including hydrocephalus or syringomyelia. Individuals with Costello syndrome have an approximately 15% lifetime risk for malignant tumors including rhabdomyosarcoma and neuroblastoma in young children and transitional cell carcinoma of the bladder in adolescents and young adults.

Ophthalmo-acromelic syndrome is a condition that results in malformations of the eyes, hands, and feet. The features of this condition are present from birth. The eyes are often absent or severely underdeveloped (anophthalmia), or they may be abnormally small (microphthalmia). Usually both eyes are similarly affected in this condition, but if only one eye is small or missing, the other eye may have a defect such as a gap or split in its structures (coloboma).\n\nThe most common hand and foot malformation seen in ophthalmo-acromelic syndrome is missing fingers or toes (oligodactyly). Other frequent malformations include fingers or toes that are fused together (syndactyly) or extra fingers or toes (polydactyly). These skeletal malformations are often described as acromelic, meaning that they occur in the bones that are away from the center of the body. Additional skeletal abnormalities involving the long bones of the arms and legs or the spinal bones (vertebrae) can also occur. Affected individuals may have distinctive facial features, an opening in the lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate), or intellectual disability.

Recombinant chromosome 8 syndrome (Rec8 syndrome) is a chromosomal disorder found among individuals of Hispanic descent with ancestry from the San Luis Valley of southern Colorado and northern New Mexico. Affected individuals typically have impaired intellectual development, congenital heart defects, seizures, a characteristic facial appearance with hypertelorism, thin upper lip, anteverted nares, wide face, and abnormal hair whorl, and other manifestations (Sujansky et al., 1993, summary by Graw et al., 2000).

A rare chromosomal anomaly with characteristics of psychomotor developmental delay, facial dysmorphism (trigonocephaly, midface hypoplasia, upslanting palpebral fissures, dysplastic small ears, flat nasal bridge with anteverted nostrils and long philtrum, micrognathia, choanal atresia, short neck), single umbilical artery, omphalocele, inguinal or umbilical hernia, genital abnormalities (hypospadia, cryptorchidism), muscular hypotonia and scoliosis.

Jacobsen syndrome (JBS) is a contiguous gene deletion syndrome with major clinical features of growth retardation, psychomotor retardation, trigonocephaly, divergent intermittent strabismus, epicanthus, telecanthus, broad nasal bridge, short nose with anteverted nostrils, carp-shaped upper lip, retrognathia, low-set dysmorphic ears, bilateral camptodactyly, hammertoes, and isoimmune thrombocytopenia (Fryns et al., 1986, Epstein, 1986).

Cantú syndrome is characterized by congenital hypertrichosis; distinctive coarse facial features (including broad nasal bridge, wide mouth with full lips and macroglossia); enlarged heart with enhanced systolic function or pericardial effusion and in many, a large patent ductus arteriosus (PDA) requiring repair; and skeletal abnormalities (thickening of the calvaria, broad ribs, scoliosis, and flaring of the metaphyses). Other cardiovascular abnormalities may include dilated aortic root and ascending aorta with rare aortic aneurysm, tortuous vascularity involving brain and retinal vasculature, and pulmonary arteriovenous communications. Generalized edema (which may be present at birth) spontaneously resolves; peripheral edema of the lower extremities (and sometimes arms and hands) may develop at adolescence. Developmental delays are common, but intellect is typically normal; behavioral problems can include attention-deficit/hyperactivity disorder, autism spectrum disorder, obsessive-compulsive disorder, anxiety, and depression.

Syndrome with characteristics of psychomotor delay, brachycephaly with flat face, small nose, microstomia, cleft palate, cataract, hearing loss, hypoplastic scrotum and digital anomalies. Less than 10 patients have been described in the literature so far. Although the majority of reported cases were sporadic, the syndrome has been reported in one pair of siblings (a brother and sister) with an apparently autosomal recessive inheritance pattern.

An extremely rare disorder of methionine cycle and sulfur amino acid metabolism with characteristics of increased urine excretion of beta-mercaptolactate-cysteine disulfide (due to deficiency of mercaptopyruvate sulfurtransferase activity in erythrocytes), leading to a positive cyanide nitroprusside test. Association with intellectual disability, congenital lens dislocation, and behavioral abnormalities has been reported, however the causal link remains to be established. There have been no further descriptions in the literature since 1981.

The cardinal findings of Neuhauser syndrome, also known as MMR syndrome, are impaired intellectual development or developmental delay, megalocornea, hypotonia, prominent forehead, micrognathia, prominent nasal bridge, and thin upper lip or carp-like mouth (Naritomi et al., 1997). Reviews Gutierrez-Amavizca et al. (2013) reviewed published reports and tabulated the clinical features of 35 patients with Neuhauser syndrome. Primary megalocornea and psychomotor delay were present in all patients. Characteristics observed in more than half of patients included hypotonia, growth retardation, abnormal electroencephalography (EEG) and/or seizures, micro- or macrocephaly, brain malformations such as cerebral atrophy and hypoplastic corpus callosum, craniofacial dysmorphisms, cardiac anomalies, osteoarticular abnormalities, and refractive errors. Additional features found at low frequency included primary hypothyroidism, recurrent infections, feeding difficulties, cerebral hypomyelination, dyslipidemia, sensorineural deafness, laryngomalacia, large fleshy and cup-shaped ears, obesity, and cryptorchidism. The authors stated that the classification suggested by Verloes et al. (1993) did not seem to be applicable, and proposed that the diagnosis of Neuhauser syndrome should be made in the presence of intellectual disability and megalocornea in the absence of elevated intraocular pressure, with at least 1 minor feature from among those observed in more than half of patients.

A rare multiple congenital malformation syndrome with characteristics of blepharophimosis, ptosis, dental hypoplasia, hearing impairment and intellectual disability. Abnormal ears, microcephaly, and growth retardation have been reported occasionally. Male patients may show cryptorchidism and scrotal hypoplasia. Most reported cases are sporadic, except the original cases of Ohdo who described two affected sisters and a first cousin, suggesting autosomal recessive inheritance. Autosomal dominant, X-linked- and mitochondrial inheritance have also been suggested.

Perlman syndrome (PRLMNS) is an autosomal recessive congenital overgrowth syndrome with similarities to Beckwith-Wiedemann syndrome (BWS; 130650). Affected children are large at birth, are hypotonic, and show organomegaly, characteristic facial dysmorphisms (inverted V-shaped upper lip, prominent forehead, deep-set eyes, broad and flat nasal bridge, and low-set ears), renal anomalies (nephromegaly and hydronephrosis), frequent neurodevelopmental delay, and high neonatal mortality. Perlman syndrome is associated with a high risk of Wilms tumor, with a 64% incidence in infants surviving beyond the neonatal period. The tumor is diagnosed at an earlier age in these individuals compared with sporadic cases (less than 2 years and 3-4 years of age, respectively), and there is a high frequency of bilateral tumors (55%). Histologic examination of the kidneys in children with Perlman syndrome shows frequent nephroblastomatosis, which is a precursor lesion for Wilms tumor (summary by Astuti et al., 2012).

Primrose syndrome is characterized by macrocephaly, hypotonia, developmental delay, intellectual disability with expressive speech delay, behavioral issues, a recognizable facial phenotype, radiographic features, and altered glucose metabolism. Additional features seen in adults: sparse body hair, distal muscle wasting, and contractures. Characteristic craniofacial features include brachycephaly, high anterior hairline, deeply set eyes, ptosis, downslanted palpebral fissures, high palate with torus palatinus, broad jaw, and large ears with small or absent lobes. Radiographic features include calcification of the external ear cartilage, multiple Wormian bones, platybasia, bathrocephaly, slender bones with exaggerated metaphyseal flaring, mild epiphyseal dysplasia, and spondylar dysplasia. Additional features include hearing impairment, ocular anomalies, cryptorchidism, and nonspecific findings on brain MRI.

Simpson-Golabi-Behmel syndrome type 1 (SGBS1) is characterized by pre- and postnatal macrosomia; distinctive craniofacial features (including macrocephaly, coarse facial features, macrostomia, macroglossia, and palatal abnormalities); and commonly, mild-to-severe intellectual disability with or without structural brain anomalies. Other variable findings include supernumerary nipples, diastasis recti / umbilical hernia, congenital heart defects, diaphragmatic hernia, genitourinary defects, and gastrointestinal anomalies. Skeletal anomalies can include vertebral fusion, scoliosis, rib anomalies, and congenital hip dislocation. Hand anomalies can include large hands and postaxial polydactyly. Affected individuals are at increased risk for embryonal tumors including Wilms tumor, hepatoblastoma, adrenal neuroblastoma, gonadoblastoma, hepatocellular carcinoma, and medulloblastoma.

A very rare syndrome described in three siblings of one Japanese family with main features of congenital heart disease, round face with depressed nasal bridge, small mouth, short stature, and relatively dark skin and typical dermatoglyphic anomalies, and intellectual deficit.

A rare primary bone dysplasia disorder with characteristics of severe short stature, coarse facies, thoracolumbar kyphoscoliosis and enlarged joints with contractures. Psychomotor delay and intellectual disability may also be associated. Radiographic features include flat vertebral bodies, lacy ossification of the metaphyses of long bones and iliac crests, and marked sclerosis of the skull base.

Spondyloperipheral dysplasia is a disorder that impairs bone growth. This condition is characterized by flattened bones of the spine (platyspondyly) and unusually short fingers and toes (brachydactyly), with the exception of the first (big) toes. Other skeletal abnormalities associated with spondyloperipheral dysplasia include short stature, shortened long bones of the arms and legs, exaggerated curvature of the lower back (lordosis), and an inward- and upward-turning foot (clubfoot). Additionally, some affected individuals have nearsightedness (myopia), hearing loss, and intellectual disability.

Toriello-Carey syndrome is a multiple congenital anomaly disorder with variable systemic manifestations, most commonly including mental retardation, agenesis of the corpus callosum, postnatal growth delay, cardiac defects, usually septal defects, distal limb defects, and urogenital anomalies in affected males. Patients have facial dysmorphic features, micrognathia, including full cheeks, hypertelorism, flattened nasal bridge, anteverted nares, and short neck. Not all features are found in all patients and some patients may have additional features such as anal anomalies or hernias (summary by Toriello et al., 2003). In a review of the Toriello-Carey syndrome, Toriello et al. (2016) stated that while corpus callosum abnormalities and micrognathia with highly arched or cleft palate are seen in most patients, other manifestations are widely variable. They noted that etiologic heterogeneity has been observed in reported patients, with at least 20% of patients having chromosome anomalies, and that no good candidate genes have been identified by exome sequencing. The authors commented that this condition might not be a unitary diagnostic entity. They recommended chromosome microarray for any child suspected of having the condition, followed by standard of care by genetic testing.

X-linked intellectual developmental disorder-9 (XLID9) is characterized by moderately to severely impaired intellectual development. Some patients have also been reported with delayed motor development, seizures, and/or behavioral problems (Hamel et al., 1999; Froyen et al., 2007).

Bohring-Opitz syndrome (BOS) is characterized by distinctive facial features and posture, growth failure, variable but usually severe intellectual disability, and variable anomalies. The facial features may include microcephaly or trigonocephaly / prominent (but not fused) metopic ridge, hypotonic facies with full cheeks, synophrys, glabellar and eyelid nevus flammeus (simplex), prominent globes, widely set eyes, palate anomalies, and micrognathia. The BOS posture, which is most striking in early childhood and often becomes less apparent with age, is characterized by flexion at the elbows with ulnar deviation and flexion of the wrists and metacarpophalangeal joints. Feeding difficulties in early childhood, including cyclic vomiting, have a significant impact on overall health; feeding tends to improve with age. Seizures are common and typically responsive to standard epileptic medications. Minor cardiac anomalies and transient bradycardia and apnea may be present. Affected individuals may experience recurrent infections, which also tend to improve with age. Isolated case reports suggest that individuals with BOS are at greater risk for Wilms tumor than the general population, but large-scale epidemiologic studies have not been conducted.

Schimke immunoosseous dysplasia (SIOD) is characterized by spondyloepiphyseal dysplasia (SED) resulting in short stature, nephropathy, and T-cell deficiency. Radiographic manifestations of SED include ovoid and mildly flattened vertebral bodies, small ilia with shallow dysplastic acetabular fossae, and small deformed capital femoral epiphyses. Nearly all affected individuals have progressive steroid-resistant nephropathy, usually developing within five years of the diagnosis of growth failure and terminating with end-stage renal disease. The majority of tested individuals have T-cell deficiency and an associated risk for opportunistic infection, a common cause of death. SIOD involves a spectrum that ranges from an infantile or severe early-onset form with a greater risk of death during childhood to a juvenile or milder later-onset form with likely survival into adulthood if renal disease is appropriately treated.

Cardiofaciocutaneous (CFC) syndrome is characterized by cardiac abnormalities (pulmonic stenosis and other valve dysplasias, septal defects, hypertrophic cardiomyopathy, rhythm disturbances), distinctive craniofacial appearance, and cutaneous abnormalities (including xerosis, hyperkeratosis, ichthyosis, keratosis pilaris, ulerythema ophryogenes, eczema, pigmented moles, hemangiomas, and palmoplantar hyperkeratosis). The hair is typically sparse, curly, fine or thick, woolly or brittle; eyelashes and eyebrows may be absent or sparse. Nails may be dystrophic or fast growing. Some form of neurologic and/or cognitive delay (ranging from mild to severe) is seen in all affected individuals. Neoplasia, mostly acute lymphoblastic leukemia, has been reported in some individuals.

Transaldolase deficiency (TALDOD) is a rare inborn error of pentose metabolism. Typical features include intrauterine growth restriction, triangular face, loose wrinkly skin at birth, and development of progressive liver failure (summary by Lee-Barber et al., 2019).

Mucopolysaccharidosis type IX (MPS9) is a rare progressive lysosomal storage disorder caused by the deficiency of the enzyme hyaluronoglucosaminidase-1, which degrades hyaluronan (summary by Imundo et al., 2011).

Phosphoribosylaminoimidazole carboxylase deficiency (PAICSD) is an autosomal recessive disorder characterized by multiple congenital anomalies and early neonatal death (Pelet et al., 2019).

Sponastrime dysplasia is an autosomal recessive spondyloepimetaphyseal dysplasia (SEMD) named for characteristic clinical and radiographic findings, including spine (spondylar) abnormalities, midface hypoplasia with a depressed nasal bridge, and striation of the metaphyses. Additional features include disproportionate short stature with exaggerated lumbar lordosis, scoliosis, coxa vara, limited elbow extension, small dysplastic epiphyses, childhood cataracts, short dental roots, and hypogammaglobulinemia. Radiographically, the abnormalities of the lumbar vertebral bodies are suggested to be the most specific finding because the characteristic metaphyseal striations may not be apparent at young ages. Striking clinical variability in presentation, severity, and associated features has been observed (summary by Burrage et al., 2019).

Transient neonatal hyperparathyroidism is characterized by interference with placental maternal-fetal calcium transport, causing fetal calcium deficiency resulting in hyperparathyroidism and metabolic bone disease. Because 80% of calcium is transferred during the third trimester, abnormalities may not be detected on second-trimester ultrasounds. Affected infants present at birth with prenatal fractures, shortened ribs, and bowing of long bones, as well as respiratory and feeding difficulties. Postnatal recovery or improvement is observed once calcium is provided orally, with most patients showing complete resolution of skeletal abnormalities by 2 years of age (Suzuki et al., 2018).

The focal dermal dysplasias (FFDDs) are a group of related developmental defects characterized by bitemporal or preauricular skin lesions resembling aplasia cutis congenita. FFFD3 is an autosomal recessive disorder characterized by bitemporal skin lesions with variable facial findings, including thin and puckered periorbital skin, distichiasis and/or absent eyelashes, upslanting palpebral fissures, a flat nasal bridge with a broad nasal tip, large lips, and redundant facial skin (summary by Slavotinek et al., 2013). FFDD2 (614973) is characterized by the same facial features as FFDD3, but the inheritance is autosomal dominant. For a classification and a discussion of genetic heterogeneity of FFDD, see FFDD1 (136500).

The TP63-related disorders comprise six overlapping phenotypes: Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome (which includes Rapp-Hodgkin syndrome). Acro-dermo-ungual-lacrimal-tooth (ADULT) syndrome. Ectrodactyly, ectodermal dysplasia, cleft lip/palate syndrome 3 (EEC3). Limb-mammary syndrome. Split-hand/foot malformation type 4 (SHFM4). Isolated cleft lip/cleft palate (orofacial cleft 8). Individuals typically have varying combinations of ectodermal dysplasia (hypohidrosis, nail dysplasia, sparse hair, tooth abnormalities), cleft lip/palate, split-hand/foot malformation/syndactyly, lacrimal duct obstruction, hypopigmentation, hypoplastic breasts and/or nipples, and hypospadias. Findings associated with a single phenotype include ankyloblepharon filiforme adnatum (tissue strands that completely or partially fuse the upper and lower eyelids), skin erosions especially on the scalp associated with areas of scarring, and alopecia, trismus, and excessive freckling.

Congenital disorders of glycosylation (CDGs) are a genetically heterogeneous group of autosomal recessive disorders caused by enzymatic defects in the synthesis and processing of asparagine (N)-linked glycans or oligosaccharides on glycoproteins. Type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein. These disorders can be identified by a characteristic abnormal isoelectric focusing profile of plasma transferrin (Leroy, 2006). CDG1D is a type I CDG that generally presents with severe neurologic involvement associated with dysmorphism and visual impairment. Liver involvement is sometimes present (summary by Marques-da-Silva et al., 2017). For a discussion of the classification of CDGs, see CDG1A (212065).

Aymé-Gripp syndrome is classically defined as the triad of bilateral early cataracts, sensorineural hearing loss, and characteristic facial features in combination with neurodevelopmental abnormalities. The facial features are often described as "Down syndrome-like" and include brachycephaly, flat facial appearance, short nose, long philtrum, narrow mouth, and low-set and posteriorly rotated ears. Hearing loss is often congenital. Other features may include postnatal short stature, seizure disorder, nonspecific brain abnormalities on head imaging, skeletal abnormalities, and joint limitations. A subset of individuals have been found to have pericarditis or pericardial effusion during the neonatal or infantile period. All affected individuals have had developmental delay, but the degree of cognitive impairment is extremely variable. Other features including gastrointestinal and endocrine abnormalities, ectodermal dysplasia (i.e., nail dystrophy and mammary gland hypoplasia), dental anomalies, and chronic glomerulopathy with proteinuria have been reported in rare affected individuals.

The first identified CACNA1C-related disorder, referred to as Timothy syndrome, consists of the combination of prolonged QT interval, autism, and cardiovascular malformation with syndactyly of the fingers and toes. Infrequent findings also include developmental and speech delay, seizures, and recurrent infections. With increased availability of molecular genetic testing, a wider spectrum of pathogenic variants and clinical findings associated with CACNA1C-related disorders has been recognized. Because CACNA1C is associated with calcium channel function, all individuals with a pathogenic variant in this gene are at risk for cardiac arrhythmia of a specific type. The clinical manifestations of a CACNA1C-related disorder include three phenotypes: Timothy syndrome with or without syndactyly. QT prolongation (QTc >480 ms) and arrhythmias in the absence of other syndromic features. Short QT syndrome (QTc <350 ms) or Brugada syndrome with short QT interval. These three phenotypes can be separated into two broad categories on the basis of the functional consequences of the pathogenic variants in CACNA1C: QT prolongation with or without a Timothy syndrome-associated phenotype associated with pathogenic variants inducing a gain of function at the cellular level (i.e., increased calcium current). Short QT interval with or without Brugada syndrome EKG pattern associated with pathogenic variants causing loss of function (i.e., reduced calcium current).

Van den Ende-Gupta syndrome (VDEGS) is an autosomal recessive disorder characterized by severe contractual arachnodactyly from birth and distinctive facial dysmorphism, including triangular face, malar hypoplasia, narrow nose, everted lips, and blepharophimosis. Skeletal anomalies include slender ribs, hooked clavicles, and dislocated radial head. There is no neurologic involvement (summary by Patel et al., 2014).

Craniosynostosis (CRS) is a primary abnormality of skull growth involving premature fusion of the cranial sutures such that the growth velocity of the skull often cannot match that of the developing brain. This produces skull deformity and, in some cases, raises intracranial pressure, which must be treated promptly to avoid permanent neurodevelopmental disability (summary by Fitzpatrick, 2013). Craniosynostosis-4 (CRS4) includes lambdoid, sagittal, metopic, coronal, and multisuture forms. For a discussion of genetic heterogeneity of craniosynostosis, see CRS1 (123100).

Syndrome with characteristics of facial (telecanthus, flat nasal bridge, retrognathia), oral (cleft palate, vestibular frenula) and digital (oligodactyly, preaxial polydactyly) features, associated with remarkable radial shortening, fibular agenesis and coalescence of tarsal bones. The syndrome has been described in one 10-month-old girl. No new cases have been described since 1993.

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant form of recurrent focal neuropathy characterized clinically by acute, recurrent episodes of brachial plexus neuropathy with muscle weakness and atrophy preceded by severe pain in the affected arm.

Delayed membranous cranial ossification is a rare, genetic primary bone dysplasia characterized by absent ossification of calvarial bones at birth and characteristic facial dysmorphisms (frontal bossing, hypertelorism, downward-slanting palpebral fissures, proptosis, flat nasal bridge, low-set ears, midface retrusion). Patients present a soft skull at birth which, over time, progressively ossifies and in adulthood typically results in a deformed skull (with brachycephaly and prominent occiput). No other skeletal abnormalities are associated and patients have normal cognitive and motor development.

Microcephaly with or without chorioretinopathy, lymphedema, or impaired intellectual development (MCLMR) is an autosomal dominant disorder that involves an overlapping but variable spectrum of central nervous system and ocular developmental anomalies. Microcephaly ranges from mild to severe and is often associated with mild to moderate developmental delay and a characteristic facial phenotype with upslanting palpebral fissures, broad nose with rounded tip, long philtrum with thin upper lip, prominent chin, and prominent ears. Chorioretinopathy is the most common eye abnormality, but retinal folds, microphthalmia, and myopic and hypermetropic astigmatism have also been reported, and some individuals have no overt ocular phenotype. Congenital lymphedema, when present, is typically confined to the dorsa of the feet, and lymphoscintigraphy reveals the absence of radioactive isotope uptake from the webspaces between the toes (summary by Ostergaard et al., 2012). Robitaille et al. (2014) found that MCLMR includes a broader spectrum of ocular disease, including retinal detachment with avascularity of the peripheral retina, and noted phenotypic overlap with familial exudative vitreoretinopathy (FEVR; see EVR1, 133780). Birtel et al. (2017) observed intrafamilial and intraindividual variability in retinal phenotype, and noted that syndromic manifestations in some patients are too subtle to be detected during a routine ophthalmologic evaluation. Variable expressivity and reduced penetrance have also been observed in some families (Jones et al., 2014; Li et al., 2016). Autosomal recessive forms of microcephaly with chorioretinopathy have been reported (see 251270). See also Mirhosseini-Holmes-Walton syndrome (autosomal recessive microcephaly with pigmentary retinopathy and impaired intellectual development; 268050), which has been mapped to chromosome 8q21.3-q22.1.

The Torrance type of platyspondylic lethal skeletal dysplasia (PLSDT) is an autosomal dominant disorder characterized by varying platyspondyly, short ribs with anterior cupping, hypoplasia of the lower ilia with broad ischial and pubic bones, and shortening of the tubular bones with splayed and cupped metaphyses. Histology of the growth plate typically shows focal hypercellularity with slightly enlarged chondrocytes in the resting cartilage and relatively well-preserved columnar formation and ossification at the chondroosseous junction. Though generally lethal in the perinatal period, longer survival has been reported (summary by Zankl et al., 2005).

Holoprosencephaly-9 refers to a disorder characterized by a wide phenotypic spectrum of brain developmental defects, with or without overt forebrain cleavage abnormalities. It usually includes midline craniofacial anomalies involving the first branchial arch and/or orbits, pituitary hypoplasia with panhypopituitarism, and postaxial polydactyly. The disorder shows incomplete penetrance and variable expressivity (summary by Roessler et al., 2003 and Bertolacini et al., 2012). For general phenotypic information and a discussion of genetic heterogeneity of holoprosencephaly, see HPE1 (236100).

Cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma syndrome (CEDNIK) refers to a unique constellation of clinical manifestations including global developmental delay with hypotonia, roving eye movements or nystagmus, poor motor skills, and impaired intellectual development with speech delay. More variable features include microcephaly, feeding difficulties, seizures, ocular anomalies, hearing loss, and nonspecific dysmorphic facial features. Palmoplantar keratoderma and ichthyosis or neuropathy develop in some patients. Brain magnetic resonance imaging (MRI) shows varying degrees of cerebral dysgenesis, including absence of the corpus callosum and cortical dysplasia, as well as hypomyelination, white matter loss, and white matter signal anomalies suggestive of a leukodystrophy. Some patients may show developmental regression; many die in childhood (Fuchs-Telem et al., 2011; Mah-Som et al., 2021). With more patients being reported, several authors (Diggle et al., 2017; Llaci et al., 2019; Mah-Som et al., 2021) have observed that the dermatologic features and peripheral neuropathy show reduced penetrance and are more variable manifestations of this disorder, as they are not observed in all patients with biallelic SNAP29 mutations.

Alpha-N-acetylgalactosaminidase (NAGA) deficiency is a very rare lysosomal storage disorder with atypical features. It is clinically heterogeneous with 3 main phenotypes: type I is an infantile-onset neuroaxonal dystrophy (609241); type II, also known as Kanzaki disease, is an adult-onset disorder characterized by angiokeratoma corporis diffusum and mild intellectual impairment; and type III is an intermediate disorder (see 609241) with mild to moderate neurologic manifestations (Desnick and Schindler, 2001).

Distal arthrogryposis type 4 (DA4) is distinguished by the presence of scoliosis (summary by Bamshad et al., 2009). For a phenotypic description and a discussion of genetic heterogeneity of distal arthrogryposis, see DA1 (108120).

Congenital disorders of glycosylation (CDGs) are metabolic deficiencies in glycoprotein biosynthesis that usually cause severe mental and psychomotor retardation. Different forms of CDGs can be recognized by altered isoelectric focusing (IEF) patterns of serum transferrin. For a general discussion of CDGs, see CDG Ia (212065) and CDG Ib (602579).

CODAS is an acronym for cerebral, ocular, dental, auricular, and skeletal anomalies. CODAS syndrome is a rare disorder characterized by a distinctive constellation of features that includes developmental delay, craniofacial anomalies, cataracts, ptosis, median nasal groove, delayed tooth eruption, hearing loss, short stature, delayed epiphyseal ossification, metaphyseal hip dysplasia, and vertebral coronal clefts (summary by Strauss et al., 2015).

Oculoectodermal syndrome (OES) is characterized by the association of epibulbar dermoids and aplasia cutis congenita. Affected individuals exhibit congenital scalp lesions which are atrophic, nonscarring, hairless regions that are often multiple and asymmetric in distribution, and may have associated hamartomas. Ectodermal changes include linear hyperpigmentation that may follow the lines of Blaschko and, rarely, epidermal nevus-like lesions. Epibulbar dermoids may be uni- or bilateral. Additional ocular anomalies such as skin tags of the upper eyelid and rarely optic nerve or retinal changes or microphthalmia can be present. Phenotypic expression is highly variable, and various other abnormalities have occasionally been reported, including growth failure, lymphedema, and cardiovascular defects, as well as neurodevelopmental symptoms such as developmental delay, epilepsy, learning difficulties, and behavioral abnormalities. Benign tumor-like lesions such as nonossifying fibromas of the long bones and giant cell granulomas of the jaws have repeatedly been observed and appear to be age-dependent, becoming a common manifestation in individuals aged 5 years or older (summary by Boppudi et al., 2016).

A rare disorder caused by mutations in the TGIF gene mapped to chromosome 18p11.3. It is characterized by semilobar holoprosencephaly, hypotelorism, and ptosis.

Any holoprosencephaly in which the cause of the disease is a mutation in the SHH gene.

Nablus mask-like facial syndrome (NMLFS) is a rare entity defined by distinctive facial features, including blepharophimosis, tight-appearing glistening facial skin, an abnormal hair pattern with an upswept frontal hairline, sparse arched eyebrows, flat and broad nose, long philtrum, distinctive ears, and a happy demeanor (summary by Jain et al., 2010).

Classic Joubert syndrome (JS) is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. Additional findings can include retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen.

Pontocerebellar hypoplasia (PCH) refers to a heterogeneous group of disorders characterized by an abnormally small cerebellum and brainstem. Clinical features vary, but usually include severe developmental delay, dysmorphic features, seizures, and early death (summary by Durmaz et al., 2009). For a phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1 (607596).

Diaphanospondylodysostosis is a rare, recessively inherited, perinatal lethal skeletal disorder. The primary skeletal characteristics include small chest, abnormal vertebral segmentation, and posterior rib gaps containing incompletely differentiated mesenchymal tissue. Consistent craniofacial features include ocular hypertelorism, epicanthal folds, depressed nasal bridge with short nose, and low-set ears. The most commonly described extraskeletal finding is nephroblastomatosis with cystic kidneys, but other visceral findings have been described in some cases (summary by Funari et al., 2010).

Gaucher disease (GD) encompasses a continuum of clinical findings from a perinatal lethal disorder to an asymptomatic type. The identification of three major clinical types (1, 2, and 3) and two other subtypes (perinatal-lethal and cardiovascular) is useful in determining prognosis and management. GD type 1 is characterized by the presence of clinical or radiographic evidence of bone disease (osteopenia, focal lytic or sclerotic lesions, and osteonecrosis), hepatosplenomegaly, anemia and thrombocytopenia, lung disease, and the absence of primary central nervous system disease. GD types 2 and 3 are characterized by the presence of primary neurologic disease; in the past, they were distinguished by age of onset and rate of disease progression, but these distinctions are not absolute. Disease with onset before age two years, limited psychomotor development, and a rapidly progressive course with death by age two to four years is classified as GD type 2. Individuals with GD type 3 may have onset before age two years, but often have a more slowly progressive course, with survival into the third or fourth decade. The perinatal-lethal form is associated with ichthyosiform or collodion skin abnormalities or with nonimmune hydrops fetalis. The cardiovascular form is characterized by calcification of the aortic and mitral valves, mild splenomegaly, corneal opacities, and supranuclear ophthalmoplegia. Cardiopulmonary complications have been described with all the clinical subtypes, although varying in frequency and severity.

The constitutional deletion of chromosome 1p36 results in a syndrome with multiple congenital anomalies and mental retardation (Shapira et al., 1997). Monosomy 1p36 is the most common terminal deletion syndrome in humans, occurring in 1 in 5,000 births (Shaffer and Lupski, 2000; Heilstedt et al., 2003). See also neurodevelopmental disorder with or without anomalies of the brain, eye, or heart (NEDBEH; 616975), which shows overlapping features and is caused by heterozygous mutation in the RERE gene (605226) on proximal chromosome 1p36. See also Radio-Tartaglia syndrome (RATARS; 619312), caused by mutation in the SPEN gene (613484) on chromosome 1p36, which shows overlapping features.

The X-linked otopalatodigital (X-OPD) spectrum disorders, characterized primarily by skeletal dysplasia, include the following: Otopalatodigital syndrome type 1 (OPD1). Otopalatodigital syndrome type 2 (OPD2). Frontometaphyseal dysplasia type 1 (FMD1). Melnick-Needles syndrome (MNS). Terminal osseous dysplasia with pigmentary skin defects (TODPD). In OPD1, most manifestations are present at birth; females can present with severity similar to affected males, although some have only mild manifestations. In OPD2, females are less severely affected than related affected males. Most males with OPD2 die during the first year of life, usually from thoracic hypoplasia resulting in pulmonary insufficiency. Males who live beyond the first year of life are usually developmentally delayed and require respiratory support and assistance with feeding. In FMD1, females are less severely affected than related affected males. Males do not experience a progressive skeletal dysplasia but may have joint contractures and hand and foot malformations. Progressive scoliosis is observed in both affected males and females. In MNS, wide phenotypic variability is observed; some individuals are diagnosed in adulthood, while others require respiratory support and have reduced longevity. MNS in males results in perinatal lethality in all recorded cases. TODPD, seen only in females, is characterized by a skeletal dysplasia that is most prominent in the digits, pigmentary defects of the skin, and recurrent digital fibromata.

Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is characterized by distinctive craniofacial features, genital anomalies, hypotonia, and mild-to-profound developmental delay / intellectual disability (DD/ID). Craniofacial abnormalities include small head circumference, telecanthus or widely spaced eyes, short triangular nose, tented upper lip, and thick or everted lower lip with coarsening of the facial features over time. While all affected individuals have a normal 46,XY karyotype, genital anomalies comprise a range from hypospadias and undescended testicles, to severe hypospadias and ambiguous genitalia, to normal-appearing female external genitalia. Alpha-thalassemia, observed in about 75% of affected individuals, is mild and typically does not require treatment. Osteosarcoma has been reported in a few males with germline pathogenic variants.

Additional features seen in some people with FG syndrome include widely set eyes (hypertelorism), an upswept frontal hairline, and a large head compared to body size (relative macrocephaly). Other health problems have also been reported, including heart defects, seizures, undescended testes (cryptorchidism) in males, and a soft out-pouching in the lower abdomen (an inguinal hernia).\n\nThe physical features of FG syndrome include weak muscle tone (hypotonia), broad thumbs, and wide first (big) toes. Abnormalities of the tissue connecting the left and right halves of the brain (the corpus callosum) are also common. Most affected individuals have constipation, and many have abnormalities of the anus such as an obstruction of the anal opening (imperforate anus). People with FG syndrome also tend to have a distinctive facial appearance including small, underdeveloped ears; a tall, prominent forehead; and outside corners of the eyes that point downward (down-slanting palpebral fissures).\n\nFG syndrome affects intelligence and behavior. Almost everyone with the condition has intellectual disability, which ranges from mild to severe. Affected individuals tend to be friendly, inquisitive, and hyperactive, with a short attention span. Compared to people with other forms of intellectual disability, their socialization and daily living skills are strong, while verbal communication and language skills tend to be weaker.\n\nFG syndrome is a genetic condition that affects many parts of the body and occurs almost exclusively in males. "FG" represents the surname initials of the first family diagnosed with the disorder.

X-linked intellectual disability, Stocco Dos Santos type is characterised by severe intellectual deficit with hyperactivity, language delay, congenital hip luxation, short stature, kyphosis and recurrent respiratory infections. Aggressive behaviour and frequent epileptic seizures may also be present. The syndrome has been described in four boys from the same family. Transmission is X-linked and is caused by mutations in the <i>KIAA1202</i> gene, localised to the Xp11.2 region.

The Cabezas type of X-linked syndromic intellectual developmental disorder is characterized primarily by short stature, hypogonadism, and abnormal gait, with other more variable features such as speech delay, prominent lower lip, and tremor (Cabezas et al., 2000).

IMAGe syndrome is an acronym for the major findings of intrauterine growth restriction (IUGR), metaphyseal dysplasia, adrenal hypoplasia congenita, and genitourinary abnormalities (in males). Findings reported in individuals with a clinical and/or molecular diagnosis include: IUGR; Some type of skeletal abnormality (most commonly delayed bone age and short stature, and occasionally, metaphyseal and epiphyseal dysplasia of varying severity); Adrenal insufficiency often presenting in the first month of life as an adrenal crisis or (rarely) later in childhood with failure to thrive and recurrent vomiting; Genital abnormalities in males (cryptorchidism, micropenis, and hypospadias) but not in females. Hypotonia and developmental delay are reported in some individuals; cognitive outcome appears to be normal in the majority of individuals.

MECP2 duplication syndrome is a severe neurodevelopmental disorder characterized by early-onset hypotonia, feeding difficulty, gastrointestinal manifestations including gastroesophageal reflux and constipation, delayed psychomotor development leading to severe intellectual disability, poor speech development, progressive spasticity, recurrent respiratory infections (in ~75% of affected individuals), and seizures (in ~50%). MECP2 duplication syndrome is 100% penetrant in males. Occasionally females have been described with a MECP2 duplication and a range of findings from mild intellectual disability to a phenotype similar to that seen in males. In addition to the core features, autistic behaviors, nonspecific neuroradiologic findings on brain MRI, mottled skin, and urogenital anomalies have been observed in several affected boys.

X-linked spondyloepimetaphyseal dysplasia with hypomyelinating leukodystrophy (SEMDHL) is an X-linked recessive developmental disorder characterized by slowly progressive skeletal and neurologic abnormalities, including short stature, large and deformed joints, significant motor impairment, visual defects, and sometimes cognitive deficits. Affected individuals typically have normal early development in the first year or so of life, followed by development regression and the development of symptoms. Brain imaging shows white matter abnormalities consistent with hypomyelinating leukodystrophy (summary by Miyake et al., 2017).

The AMME complex is an X-linked contiguous gene deletion syndrome with features of Alport syndrome, mental retardation, midface hypoplasia, and elliptocytosis in affected males (summary by Meloni et al., 2002).

Al-Gazali-Bakalinova syndrome (AGBK) is characterized by multiple epiphyseal dysplasia, macrocephaly, and distinctive facial features including frontal bossing, hypertelorism, flat malar regions, low-set ears, and short neck. Other features include pectus excavatum, spindle-shaped fingers, clinodactyly, prominent joints, and genu valgum (summary by Ali et al., 2012).

A rare, genetic disorder of amino acid absorption and transport, characterized by generalized hypotonia at birth, neonatal/infantile failure to thrive (followed by hyperphagia and rapid weight gain in late childhood), cystinuria type 1, nephrolithiasis, growth retardation due to growth hormone deficiency, and minor facial dysmorphism. Dysmorphic features mainly include dolichocephaly and ptosis. Nephrolithiasis occurs at variable ages.

CHIME syndrome, also known as Zunich neuroectodermal syndrome, is an extremely rare autosomal recessive multisystem disorder clinically characterized by colobomas, congenital heart defects, migratory ichthyosiform dermatosis, mental retardation, and ear anomalies (CHIME). Other clinical features include distinctive facial features, abnormal growth, genitourinary abnormalities, seizures, and feeding difficulties (summary by Ng et al., 2012). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Stickler syndrome is a connective tissue disorder that can include ocular findings of myopia, cataract, and retinal detachment; hearing loss that is both conductive and sensorineural; midfacial underdevelopment and cleft palate (either alone or as part of the Robin sequence); and mild spondyloepiphyseal dysplasia and/or precocious arthritis. Variable phenotypic expression of Stickler syndrome occurs both within and among families; interfamilial variability is in part explained by locus and allelic heterogeneity.

Cold-induced sweating syndrome (CISS) and its infantile presentation, Crisponi syndrome(CS) is characterized by dysmorphic features (distinctive facies, lower facial weakness, flexion deformity at the elbows, camptodactyly with fisted hands, misshapen feet, and overriding toes); intermittent contracture of facial and oropharyngeal muscles when crying or being handled with puckering of lips and drooling of foamy saliva often associated with laryngospasm and respiratory distress; excessive startling and opisthotonus-like posturing with unexpected tactile or auditory stimuli; poor suck reflex and severely impaired swallowing; and a scaly erythematous rash. During the first decade of life, children with CISS/CS develop profuse sweating of the face, arms, and chest with ambient temperatures below 18º to 22º C, and with other stimuli including nervousness or ingestion of sweets. Affected individuals sweat very little in hot environments and may feel overheated. Progressive thoracolumbar kyphoscoliosis occurs, requiring intervention in the second decade.

Spondyloepimetaphyseal dysplasia-short limb-abnormal calcification syndrome is a rare, genetic primary bone dysplasia disorder characterized by disproportionate short stature with shortening of upper and lower limbs, short and broad fingers with short hands, narrowed chest with rib abnormalities and pectus excavatum, abnormal chondral calcifications (incl. larynx, trachea and costal cartilages) and facial dysmorphism (frontal bossing, hypertelorism, prominent eyes, short flat nose, wide nostrils, high-arched palate, long philtrum). Platyspondyly (esp. of cervical spine) and abnormal epiphyses and metaphyses are observed on radiography. Atlantoaxial instability causing spinal compression and recurrent respiratory disease are potential complications that may result lethal.

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

Pulmonary lymphangiectasia is a rare congenital vascular dysplasia characterized by an increased number of dilated pulmonary lymphatics in the subpleural, peribronchial, and interlobular septa. Respiratory distress is usually noted immediately after birth (summary by Stevenson et al., 2006).

Peroxisomal acyl-CoA oxidase deficiency is a disorder of peroxisomal fatty acid beta-oxidation. See also D-bifunctional protein deficiency (261515), caused by mutation in the HSD17B4 gene (601860) on chromosome 5q2. The clinical manifestations of these 2 deficiencies are similar to those of disorders of peroxisomal assembly, including Zellweger cerebrohepatorenal syndrome (see 214100) and neonatal adrenoleukodystrophy (see 601539) (Watkins et al., 1995).

Raine syndrome (RNS) is a neonatal osteosclerotic bone dysplasia of early and aggressive onset that usually results in death within the first few weeks of life, although there have been some reports of survival into childhood. Radiographic studies show a generalized increase in the density of all bones and a marked increase in the ossification of the skull. The increased ossification of the basal structures of the skull and facial bones underlies the characteristic facial features, which include narrow prominent forehead, proptosis, depressed nasal bridge, and midface hypoplasia. Periosteal bone formation is also characteristic of this disorder and differentiates it from osteopetrosis and other known lethal and nonlethal osteosclerotic bone dysplasias. The periosteal bone formation typically extends along the diaphysis of long bones adjacent to areas of cellular soft tissue (summary by Simpson et al., 2009). Some patients survive infancy (Simpson et al., 2009; Fradin et al., 2011).

Omodysplasia-1 (OMOD1) is a rare autosomal recessive skeletal dysplasia characterized by severe congenital micromelia with shortening and distal tapering of the humeri and femora to give a club-like appearance. Typical facial features include a prominent forehead, frontal bossing, short nose with a depressed broad bridge, short columella, anteverted nostrils, long philtrum, and small chin. Variable findings are cryptorchidism, hernias, congenital heart defects, and cognitive delay (Elcioglu et al., 2004; Albano et al., 2007). Genetic Heterogeneity of Omodysplasia Also see omodysplasia-2 (OMOD2; 164745), an autosomal dominant form of the disorder in which abnormalities are limited to the upper limbs. The facial changes and typical growth defect of the distal humerus with complex deformity of the elbows appear to be similar in both entities (Baxova et al., 1994).

Mosaic variegated aneuploidy (MVA) syndrome is a rare disorder in which some cells in the body have an abnormal number of chromosomes instead of the usual 46 chromosomes, a situation known as aneuploidy. Most commonly, cells have an extra chromosome, which is called trisomy, or are missing a chromosome, which is known as monosomy. In MVA syndrome, some cells are aneuploid and others have the normal number of chromosomes, which is a phenomenon known as mosaicism. Typically, at least one-quarter of cells in affected individuals have an abnormal number of chromosomes. Because the additional or missing chromosomes vary among the abnormal cells, the aneuploidy is described as variegated.\n\nThere are at least three types of MVA syndrome, each with a different genetic cause. Type 1 is the most common and displays the classic signs and symptoms described above. Type 2 appears to have slightly different signs and symptoms than type 1, although the small number of affected individuals makes it difficult to define its characteristic features. Individuals with MVA syndrome type 2 grow slowly before and after birth; however, their head size is typically normal. Some people with MVA syndrome type 2 have unusually short arms. Individuals with MVA syndrome type 2 do not seem to have an increased risk of cancer. Another form of MVA syndrome is characterized by a high risk of developing Wilms tumor. Individuals with this form may also have other signs and symptoms typical of MVA syndrome type 1.\n\nIn MVA syndrome, growth before birth is slow (intrauterine growth restriction). After birth, affected individuals continue to grow at a slow rate and are shorter than average. In addition, they typically have an unusually small head size (microcephaly). Another common feature of MVA syndrome is an increased risk of developing cancer in childhood. Cancers that occur most frequently in affected individuals include a cancer of muscle tissue called rhabdomyosarcoma, a form of kidney cancer known as Wilms tumor, and a cancer of the blood-forming tissue known as leukemia.\n\nLess commonly, people with MVA syndrome have eye abnormalities or distinctive facial features, such as a broad nasal bridge and low-set ears. Some affected individuals have brain abnormalities, the most common of which is called Dandy-Walker malformation. Intellectual disability, seizures, and other health problems can also occur in people with MVA syndrome.

Clinical features of atelosteogenesis type 2 (AO2) include rhizomelic limb shortening with normal-sized skull, hitchhiker thumbs, small chest, protuberant abdomen, cleft palate, and distinctive facial features (midface retrusion, depressed nasal bridge, epicanthus, micrognathia). Other typical findings are ulnar deviation of the fingers, gap between the first and second toes, and clubfoot. AO2 is usually lethal at birth or shortly thereafter due to pulmonary hypoplasia and tracheobronchomalacia. However, it exists in a continuous phenotypic spectrum with diastrophic dysplasia, and long-term survivors have been reported.

Beare-Stevenson cutis gyrata syndrome (BSTVS) is an autosomal dominant condition characterized by the furrowed skin disorder of cutis gyrata, acanthosis nigricans, craniosynostosis, craniofacial dysmorphism, digital anomalies, umbilical and anogenital abnormalities, and early death (summary by Przylepa et al., 1996).

Craniofacial-deafness-hand syndrome (CDHS) is an autosomal dominant disorder characterized by dysmorphic facial features, hand abnormalities, absent or hypoplastic nasal and wrist bones, and severe sensorineural hearing impairment (summary by Gad et al., 2008).

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Macrocephaly/autism syndrome is an autosomal dominant disorder characterized by increased head circumference, abnormal facial features, and delayed psychomotor development resulting in autistic behavior or mental retardation (Herman et al., 2007). Some patients may have a primary immunodeficiency disorder with recurrent infections associated with variably abnormal T- and B-cell function (Tsujita et al., 2016).

Sedaghatian-type spondylometaphyseal dysplasia (SMDS) is a rare lethal disorder characterized by severe metaphyseal chondrodysplasia with mild limb shortening, platyspondyly, delayed epiphyseal ossification, irregular iliac crests, and pulmonary hemorrhage. Affected infants present with severe hypotonia and cardiorespiratory problems; most die within days of birth due to respiratory failure. Cardiac abnormalities include conduction defects, complete heart block, and structural anomalies. Half of infants with SMDS are reported to have central nervous system malformations consistent with abnormal neuronal migration, including agenesis of the corpus callosum, pronounced frontotemporal pachygyria, simplified gyral pattern, partial lissencephaly, and severe cerebellar hypoplasia (summary by Smith et al., 2014).

The primary characteristics of the Frank-ter Haar syndrome (FTHS) are brachycephaly, wide fontanels, prominent forehead, hypertelorism, prominent eyes, macrocornea with or without glaucoma, full cheeks, small chin, bowing of the long bones, and flexion deformity of the fingers. Protruding, simple ears and prominent coccyx are also regarded as important diagnostic signs (summary by Maas et al., 2004). Borrone syndrome was described as a severe progressive multisystem disorder with features overlapping those of FTHS, including thick skin, acne conglobata, osteolysis, gingival hypertrophy, brachydactyly, camptodactyly, and mitral valve prolapse. Although it was initially thought to be a distinct phenotype, mutations in the FTHS-associated gene SH3PXD2B have been identified in patients diagnosed with Borrone syndrome. The earlier differential description was attributed to phenotypic variability as well as to differences in the ages at which patients were examined (Wilson et al., 2014).

Keutel syndrome (KTLS) is an autosomal recessive disorder characterized by multiple peripheral pulmonary stenoses, brachytelephalangy, inner ear deafness, and abnormal cartilage ossification or calcification (summary by Khosroshahi et al., 2014).

Kaufman oculocerebrofacial syndrome (KOS) is characterized by developmental delay, severe intellectual disability, and distinctive craniofacial features. Most affected children have prenatal-onset microcephaly, hypotonia, and growth deficiency. Feeding issues, ocular abnormalities, hearing impairment, and respiratory tract abnormalities are common. Ocular abnormalities can include structural abnormalities (microcornea or microphthalmia, coloboma, optic nerve hypoplasia), refractive errors (myopia ± astigmatism, hyperopia), strabismus, and entropion. Both conductive and sensorineural hearing loss have been reported as well as mixed conductive-sensorineural hearing loss of variable severity. Breathing problems can lead to prolonged hospitalization after birth in more than half of individuals. Less common findings include ectodermal abnormalities, cardiac manifestations, urogenital abnormalities, seizures, and skeletal abnormalities.

With the current widespread use of multigene panels and comprehensive genomic testing, it has become apparent that the phenotypic spectrum of EPG5-related disorder represents a continuum. At the most severe end of the spectrum is classic Vici syndrome (defined as a neurodevelopmental disorder with multisystem involvement characterized by the combination of agenesis of the corpus callosum, cataracts, hypopigmentation, cardiomyopathy, combined immunodeficiency, microcephaly, and failure to thrive); at the milder end of the spectrum are attenuated neurodevelopmental phenotypes with variable multisystem involvement. Median survival in classic Vici syndrome appears to be 24 months, with only 10% of children surviving longer than age five years; the most common causes of death are respiratory infections as a result of primary immunodeficiency and/or cardiac insufficiency resulting from progressive cardiac failure. No data are available on life span in individuals at the milder end of the spectrum.

Hypoparathyroidism-retardation-dysmorphism syndrome (HRDS) is an autosomal recessive multisystem disorder characterized by intrauterine and postnatal growth retardation, infantile-onset hypoparathyroidism that can result in severe hypocalcemic seizures, dysmorphic facial features, and developmental delay (summary by Padidela et al., 2009 and Ratbi et al., 2015).

Hall-Riggs syndrome is a very rare syndrome consisting of microcephaly with facial dysmorphism, spondylometaepiphyseal dysplasia and severe intellectual deficit.

Rhizomelic chondrodysplasia punctata (RCDP) is a peroxisomal disorder characterized by disproportionately short stature primarily affecting the proximal parts of the extremities, a typical facial appearance including a broad nasal bridge, epicanthus, high-arched palate, dysplastic external ears, and micrognathia, congenital contractures, characteristic ocular involvement, dwarfism, and severe mental retardation with spasticity. Biochemically, plasmalogen synthesis and phytanic acid alpha-oxidation are defective. Most patients die in the first decade of life. RCDP1 (215100) is the most frequent form of RCDP (summary by Wanders and Waterham, 2005). Whereas RCDP1 is a peroxisomal biogenesis disorder (PBD), RCDP2 is classified as a single peroxisome enzyme deficiency (Waterham and Ebberink, 2012). For a discussion of genetic heterogeneity of rhizomelic chondrodysplasia punctata, see 215100.

Donnai-Barrow syndrome (DBS) is characterized by typical craniofacial features (large anterior fontanelle, wide metopic suture, widow's peak, markedly widely spaced eyes, enlarged globes, downslanted palpebral fissures, posteriorly rotated ears, depressed nasal bridge, and short nose. Ocular complications include high myopia, retinal detachment, retinal dystrophy, and progressive vision loss. Additional common features include agenesis of the corpus callosum, sensorineural hearing loss, intellectual disability, and congenital diaphragmatic hernia and/or omphalocele. Both inter- and intrafamilial phenotypic variability are observed.

A syndromic disorder with the association between Dandy-Walker malformation and postaxial polydactyly as a major feature. The Dandy-Walker malformation has a variable expression and characteristics of a posterior fossa cyst communicating with the fourth ventricle, the partial or complete absence of the cerebellar vermis, and facultative hydrocephalus. Postaxial polydactyly includes tetramelic postaxial polydactyly of hands and feet with possible enlargement of the fifth metacarpal and metatarsal bones, as well as bifid fifth metacarpals.

Neonatal diabetes mellitus with congenital hypothyroidism (NDH) syndrome is characterized by intrauterine growth retardation and onset of nonimmune diabetes mellitus within the first few weeks of life. Other features include renal parenchymal disease, primarily renal cystic dysplasia, and hepatic disease, with hepatitis in some patients and hepatic fibrosis and cirrhosis in others. Facial dysmorphism, when present, consistently involves low-set ears, epicanthal folds, flat nasal bridge, long philtrum, and thin upper lip. Most patients exhibit developmental delay (Dimitri et al., 2015).

Stickler syndrome is a connective tissue disorder that can include ocular findings of myopia, cataract, and retinal detachment; hearing loss that is both conductive and sensorineural; midfacial underdevelopment and cleft palate (either alone or as part of the Robin sequence); and mild spondyloepiphyseal dysplasia and/or precocious arthritis. Variable phenotypic expression of Stickler syndrome occurs both within and among families; interfamilial variability is in part explained by locus and allelic heterogeneity.

Poikiloderma with neutropenia (PN) is characterized by an inflammatory eczematous rash (ages 6-12 months) followed by post-inflammatory poikiloderma (age >2 years) and chronic noncyclic neutropenia typically associated with recurrent sinopulmonary infections in the first two years of life and (often) bronchiectasis. There is increased risk for myelodysplastic syndrome and, rarely, acute myelogenous leukemia. Other ectodermal findings include nail dystrophy and palmar/plantar hyperkeratosis. Most affected individuals also have reactive airway disease and some have short stature, hypogonadotropic hypogonadism, midfacial retrusion, calcinosis cutis, and non-healing skin ulcers.

Rhizomelic chondrodysplasia punctata type 1 (RCDP1), a peroxisome biogenesis disorder (PBD) has a classic (severe) form and a nonclassic (mild) form. Classic (severe) RCDP1 is characterized by proximal shortening of the humerus (rhizomelia) and to a lesser degree the femur, punctate calcifications in cartilage with epiphyseal and metaphyseal abnormalities (chondrodysplasia punctata, or CDP), coronal clefts of the vertebral bodies, and cataracts that are usually present at birth or appear in the first few months of life. Birth weight, length, and head circumference are often at the lower range of normal; postnatal growth deficiency is profound. Intellectual disability is severe, and the majority of children develop seizures. Most affected children do not survive the first decade of life; a proportion die in the neonatal period. Nonclassic (mild) RCDP1 is characterized by congenital or childhood cataracts, CDP or infrequently, chondrodysplasia manifesting only as mild epiphyseal changes, variable rhizomelia, and milder intellectual disability and growth restriction than classic RCDP1.

Blomstrand chondrodysplasia is an autosomal recessive disorder characterized by short limbs, polyhydramnios, hydrops fetalis, facial anomalies, increased bone density, and advanced skeletal maturation (summary by Loshkajian et al., 1997).

Bardet-Biedl syndrome-7 (BBS7) is an autosomal recessive disorder characterized by retinitis pigmentosa, postaxial polydactyly, mental retardation, obesity, renal anomalies, and hypogenitalism (Harville et al., 2010). Zaghloul and Katsanis (2009) estimated the contribution of BBS7 gene mutations to the total BBS mutational load to be 1.50%. For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).

Campomelic dysplasia (CD) is a skeletal dysplasia characterized by distinctive facies, Pierre Robin sequence with cleft palate, shortening and bowing of long bones, and clubfeet. Other findings include laryngotracheomalacia with respiratory compromise and ambiguous genitalia or normal female external genitalia in most individuals with a 46,XY karyotype. Many affected infants die in the neonatal period; additional findings identified in long-term survivors include short stature, cervical spine instability with cord compression, progressive scoliosis, and hearing impairment.

KAT6B disorders include genitopatellar syndrome (GPS) and Say-Barber-Biesecker-Young-Simpson variant of Ohdo syndrome (SBBYSS) which are part of a broad phenotypic spectrum with variable expressivity; individuals presenting with a phenotype intermediate between GPS and SBBYSS have been reported. Both phenotypes are characterized by some degree of global developmental delay / intellectual disability; hypotonia; genital abnormalities; and skeletal abnormalities including patellar hypoplasia/agenesis, flexion contractures of the knees and/or hips, and anomalies of the digits, spine, and/or ribs. Congenital heart defects, small bowel malrotation, feeding difficulties, slow growth, cleft palate, hearing loss, and dental anomalies have been observed in individuals with either phenotype.

Holoprosencephaly associated with mutations in the ZIC2 gene.

Spondyloepiphyseal dysplasia of the Genevieve type (SEMDG) is characterized by infantile-onset severe developmental delay and skeletal dysplasia, including short stature, premature carpal ossification, platyspondyly, longitudinal metaphyseal striations, and small epiphyses (summary by van Karnebeek et al., 2016).

Congenital glutamine deficiency is a severe autosomal recessive disorder characterized by onset at birth of encephalopathy, lack of normal development, seizures, and hypotonia associated with variable brain abnormalities (summary by Haberle et al., 2011).

Enlarged parietal foramina are characteristic symmetric, paired radiolucencies of the parietal bones, located close to the intersection of the sagittal and lambdoid sutures, caused by deficient ossification around the parietal notch, which is normally obliterated by the fifth month of fetal development. Enlarged parietal foramina are usually asymptomatic. Meningeal, cortical, and vascular malformations of the posterior fossa occasionally accompany the bone defects and may predispose to epilepsy. In a minority of individuals, headaches, vomiting, or intense local pain are sometimes associated with the defects, especially on application of mild pressure to the unprotected cerebral cortex.

PIK3CA-related overgrowth spectrum (PROS) encompasses a range of clinical findings in which the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia. Prior to the identification of PIK3CA as the causative gene, PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved (e.g., MCAP [megalencephaly-capillary malformation] syndrome and CLOVES [congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies] syndrome). The predominant areas of overgrowth include the brain, limbs (including fingers and toes), trunk (including abdomen and chest), and face, all usually in an asymmetric distribution. Generalized brain overgrowth may be accompanied by secondary overgrowth of specific brain structures resulting in ventriculomegaly, a markedly thick corpus callosum, and cerebellar tonsillar ectopia with crowding of the posterior fossa. Vascular malformations may include capillary, venous, and less frequently, arterial or mixed (capillary-lymphatic-venous or arteriovenous) malformations. Lymphatic malformations may be in various locations (internal and/or external) and can cause various clinical issues, including swelling, pain, and occasionally localized bleeding secondary to trauma. Lipomatous overgrowth may occur ipsilateral or contralateral to a vascular malformation, if present. The degree of intellectual disability appears to be mostly related to the presence and severity of seizures, cortical dysplasia (e.g., polymicrogyria), and hydrocephalus. Many children have feeding difficulties that are often multifactorial in nature. Endocrine issues affect a small number of individuals and most commonly include hypoglycemia (largely hypoinsulinemic hypoketotic hypoglycemia), hypothyroidism, and growth hormone deficiency.

Scalp-ear-nipple syndrome is characterized by aplasia cutis congenita of the scalp, breast anomalies that range from hypothelia or athelia to amastia, and minor anomalies of the external ears. Less frequent clinical characteristics include nail dystrophy, dental anomalies, cutaneous syndactyly of the digits, and renal malformations. Penetrance appears to be high, although there is substantial variable expressivity within families (Marneros et al., 2013).

Nasopalpebral lipoma-coloboma syndrome (NPLCS) is an autosomal dominant condition characterized by upper eyelid and nasopalpebral lipomas, colobomas of upper and lower eyelids, telecanthus, and maxillary hypoplasia (summary by Suresh et al., 2011).

Weill-Marchesani syndrome (WMS) is a connective tissue disorder characterized by abnormalities of the lens of the eye, short stature, brachydactyly, joint stiffness, and cardiovascular defects. The ocular problems, typically recognized in childhood, include microspherophakia (small spherical lens), myopia secondary to the abnormal shape of the lens, ectopia lentis (abnormal position of the lens), and glaucoma, which can lead to blindness. Height of adult males is 142-169 cm; height of adult females is 130-157 cm. Autosomal recessive WMS cannot be distinguished from autosomal dominant WMS by clinical findings alone.

Alagille syndrome (ALGS) is a multisystem disorder with a wide spectrum of clinical variability; this variability is seen even among individuals from the same family. The major clinical manifestations of ALGS are bile duct paucity on liver biopsy, cholestasis, congenital cardiac defects (primarily involving the pulmonary arteries), butterfly vertebrae, ophthalmologic abnormalities (most commonly posterior embryotoxon), and characteristic facial features. Renal abnormalities, growth failure, developmental delays, splenomegaly, and vascular abnormalities may also occur.

Noonan syndrome with multiple lentigines (NSML) is a condition in which the cardinal features consist of lentigines, hypertrophic cardiomyopathy, short stature, pectus deformity, and dysmorphic facial features including widely spaced eyes and ptosis. Multiple lentigines present as dispersed flat, black-brown macules, mostly on the face, neck, and upper part of the trunk with sparing of the mucosa. In general, lentigines do not appear until age four to five years but then increase to the thousands by puberty. Some individuals with NSML do not exhibit lentigines. Approximately 85% of affected individuals have heart defects, including hypertrophic cardiomyopathy (typically appearing during infancy and sometimes progressive) and pulmonary valve stenosis. Postnatal growth restriction resulting in short stature occurs in fewer than 50% of affected persons, although most affected individuals have a height that is less than the 25th centile for age. Sensorineural hearing deficits, present in approximately 20% of affected individuals, are poorly characterized. Intellectual disability, typically mild, is observed in approximately 30% of persons with NSML.

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Syndrome with characteristics of severe psychomotor retardation, failure to thrive and intolerance to wheat and dairy products. So far, only two cases have been described. The disease is caused by mutations in the COG8 gene, which encodes a subunit of the COG complex. This complex is involved vesicle transport in the Golgi apparatus.

Phosphoribosylpyrophosphate synthetase (PRS) superactivity comprises two phenotypes, both characterized by hyperuricemia and hyperuricosuria. The mild phenotype (~75% of affected males) with onset in the second or third decade of life is typically limited to these biochemical findings, whereas the severe phenotype (~25% of affected males) with onset in the first decade of life has in addition to these biochemical findings variable combinations of developmental delay (DD) / intellectual disability (ID), sensorineural hearing loss, hypotonia, and ataxia. In the mild phenotype, uric acid crystalluria or a urinary stone is commonly the first clinical finding, followed later by gouty arthritis if serum urate concentration is not controlled.

Stickler syndrome is a connective tissue disorder that can include ocular findings of myopia, cataract, and retinal detachment; hearing loss that is both conductive and sensorineural; midfacial underdevelopment and cleft palate (either alone or as part of the Robin sequence); and mild spondyloepiphyseal dysplasia and/or precocious arthritis. Variable phenotypic expression of Stickler syndrome occurs both within and among families; interfamilial variability is in part explained by locus and allelic heterogeneity.

GNPTAB-related disorders comprise the phenotypes mucolipidosis II (ML II) and mucolipidosis IIIa/ß (ML IIIa/ß), and phenotypes intermediate between ML II and ML IIIa/ß. ML II is evident at birth and slowly progressive; death most often occurs in early childhood. Orthopedic abnormalities present at birth may include thoracic deformity, kyphosis, clubfeet, deformed long bones, and/or dislocation of the hip(s). Growth often ceases in the second year of life; contractures develop in all large joints. The skin is thickened, facial features are coarse, and gingiva are hypertrophic. All children have cardiac involvement, most commonly thickening and insufficiency of the mitral valve and, less frequently, the aortic valve. Progressive mucosal thickening narrows the airways, and gradual stiffening of the thoracic cage contributes to respiratory insufficiency, the most common cause of death. ML IIIa/ß becomes evident at about age three years with slow growth rate and short stature; joint stiffness and pain initially in the shoulders, hips, and fingers; gradual mild coarsening of facial features; and normal to mildly impaired cognitive development. Pain from osteoporosis becomes more severe during adolescence. Cardiorespiratory complications (restrictive lung disease, thickening and insufficiency of the mitral and aortic valves, left and/or right ventricular hypertrophy) are common causes of death, typically in early to middle adulthood. Phenotypes intermediate between ML II and ML IIIa/ß are characterized by physical growth in infancy that resembles that of ML II and neuromotor and speech development that resemble that of ML IIIa/ß.

An extremely rare type of spondyloepiphyseal dysplasia described in about 5 patients to date with clinical signs including short stature, peculiar facies with blepharophimosis, upward slanted eyes, abundant eyebrows and eyelashes, coarse voice, and short hands and feet.

SADDAN dysplasia (severe achondroplasia with developmental delay and acanthosis nigricans) is a very rare skeletal dysplasia characterized by the constellation of these features. Radiology reveals 'ram's horn' shaped clavicles and reverse bowing of lower limbs. Approximately half of patients die before the fourth week of life secondary to respiratory failure (summary by Zankl et al., 2008).

Distal monosomy 6p is responsible for a distinct chromosome deletion syndrome with a recognizable clinical picture including intellectual deficit, ocular abnormalities, hearing loss, and facial dysmorphism.

Craniodiaphyseal dysplasia (CDD) is a severe bone dysplasia characterized by massive generalized hyperostosis and sclerosis, especially involving the skull and facial bones. Progressive bony encroachment upon cranial foramina leads to severe neurologic impairment in childhood (summary by Brueton and Winter, 1990). The sclerosis is so severe that the resulting facial distortion is referred to as 'leontiasis ossea' (leonine facies), and the bone deposition results in progressive stenosis of craniofacial foramina (summary by Kim et al., 2011).

1q41q42 microdeletion syndrome is a chromosomal anomaly characterized by a severe developmental delay and/or intellectual disability, typical facial dysmorphic features, brain anomalies, seizures, cleft palate, clubfeet, nail hypoplasia and congenital heart disease.

Chromosome 2p16.1-p15 deletion syndrome is a neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, and variable but distinctive dysmorphic features, including microcephaly, bitemporal narrowing, smooth and long philtrum, hypertelorism, downslanting palpebral fissures, broad nasal root, thin upper lip, and high palate. Many patients have behavioral disorders, including autistic features, as well as structural brain abnormalities, such as pachygyria or hypoplastic corpus callosum. Those with deletions including the BCL11A gene (606557) also have persistence of fetal hemoglobin (HbF), which is asymptomatic and does not affected hematologic parameters or susceptibility to infection (summary by Funnell et al., 2015). Point mutation in the BCL11A gene causes intellectual developmental disorder with persistence of fetal hemoglobin (617101), which shows overlapping features. See also fetal hemoglobin quantitative trait locus-5 (HBFQTL5; 142335).

The 1q21.1 recurrent microdeletion itself does not appear to lead to a clinically recognizable syndrome as some persons with the deletion have no obvious clinical findings and others have variable findings that most commonly include microcephaly (50%), mild intellectual disability (30%), mildly dysmorphic facial features, and eye abnormalities (26%). Other findings can include cardiac defects, genitourinary anomalies, skeletal malformations, and seizures (~15%). Psychiatric and behavioral abnormalities can include autism spectrum disorders, attention deficit hyperactivity disorder, autistic features, and sleep disturbances.

Ehlers-Danlos syndrome spondylodysplastic type 3 (EDSSPD3) is characterized by short stature, hyperelastic skin and hypermobile joints, protuberant eyes with bluish sclerae, finely wrinkled palms, and characteristic radiologic features (Giunta et al., 2008). For a discussion of genetic heterogeneity of the spondylodysplastic type of Ehlers-Danlos syndrome, see 130070.

SLC25A24 Fontaine progeroid syndrome is a multisystem connective tissue disorder characterized by poor growth, abnormal skeletal features, and distinctive craniofacial features with sagging, thin skin, and decreased subcutaneous fat suggesting an aged appearance that is most pronounced in infancy and improves with time. Characteristic radiographic features include turribrachycephaly with widely open anterior fontanelle, craniosynostosis, and anomalies of the terminal phalanges. Cardiovascular, genitourinary, ocular, and gastrointestinal abnormalities may also occur. To date, 13 individuals with a molecularly confirmed diagnosis of SLC25A24 Fontaine progeroid syndrome have been described.

This syndrome is characterized by congenital lymphedema of the lower limbs, atrial septal defect and a characteristic facies (a round face with a prominent forehead, a flat nasal bridge with a broad nasal tip, epicanthal folds, a thin upper lip and a cleft chin). It has been described in two brothers and a sister. Transmission appears to be autosomal recessive.

Syndrome with the association of toe syndactyly, facial dysmorphism including telecanthus and a broad nasal tip, urogenital malformations and anal atresia. Around ten cases have been reported so far. The syndrome is caused by mutations in the FAM58A gene (located on the X chromosome) encoding a protein of unknown function.

Turner-type X-linked syndromic intellectual developmental disorder (MRXST) is a neurodevelopmental disorder with a highly variable phenotype. Some affected families show X-linked recessive inheritance, with only males being affected and carrier females having no abnormal findings. In other affected families, males are severely affected, and female mutation carriers show milder cognitive abnormalities or dysmorphic features. In addition, there are female patients with de novo mutations who show the full phenotype, despite skewed X-chromosome inactivation. Affected individuals show global developmental delay from infancy, with variably impaired intellectual development and poor or absent speech, often with delayed walking. Dysmorphic features are common and can include macrocephaly, microcephaly, deep-set eyes, hypotelorism, small palpebral fissures, dysplastic, large, or low-set ears, long face, bitemporal narrowing, high-arched palate, thin upper lip, and scoliosis or mild distal skeletal anomalies, such as brachydactyly or tapered fingers. Males tend to have cryptorchidism. Other features, such as hypotonia, seizures, and delayed bone age, are more variable (summary by Moortgat et al., 2018).

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

Temple-Baraitser syndrome is a rare developmental disorder characterized by severe mental retardation and anomalies of the first ray of the upper and lower limbs with absence/hypoplasia of the nails. Most patients also have seizures; various dysmorphic facial features have been reported (summary by Jacquinet et al., 2010).

Roifman-Chitayat syndrome (ROCHIS) is an autosomal recessive digenic disorder characterized by global developmental delay, variable neurologic features such as seizures, ataxia, and optic atrophy, dysmorphic facial features, distal skeletal anomalies, and combined immunodeficiency manifest as recurrent infections (summary by Sharfe et al., 2018).

Autosomal recessive spondylometaphyseal dysplasia, Mégarbané type is a rare, primary bone dysplasia characterized by intrauterine growth retardation, pre- and postnatal disproportionate short stature with short, rhizomelic limbs, facial dysmorphism, a short neck and small thorax. Hypotonia, cardiomegaly and global developmental delay have also been associated. Several radiographic findings have been reported, including ribs with cupped ends, platyspondyly, square iliac bones, horizontal and trident acetabula, hypoplastic ischia, and delayed epiphyseal ossification.

Omodysplasia-2 (OMOD2) is a rare autosomal dominant skeletal dysplasia characterized by shortened humeri, dislocated radial heads, shortened first metacarpals, craniofacial dysmorphism, and variable genitourinary anomalies (Saal et al., 2015). For a discussion of genetic heterogeneity of OMOD, see 258315.

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Combined pituitary hormone deficiency (CPHD) in man denotes impaired production of growth hormone (GH; 139250) and one or more of the other 5 anterior pituitary hormones. Mutations of the POU1F1 gene in the human and Pit1 in the mouse are responsible for pleiotropic deficiencies of GH, prolactin (PRL; 176760), and thyroid-stimulating hormone (TSH; see 188540), while the production of adrenocorticotrophic hormone (ACTH; see 176830), luteinizing hormone (LH; 152780), and follicle-stimulating hormone (FSH; 136530) are preserved (Wu et al., 1998). Some patients exhibit only GH deficiency, although approximately 50% of isolated GH deficiency progresses to CPHD (Gergics et al., 2021). In infancy severe growth deficiency from birth as well as distinctive facial features with prominent forehead, marked midfacial hypoplasia with depressed nasal bridge, deep-set eyes, and a short nose with anteverted nostrils and hypoplastic pituitary gland by MRI examination can be seen (Aarskog et al., 1997). Some cases present with severe mental retardation along with short stature (Radovick et al., 1992). Reviews Voss and Rosenfeld (1992) reviewed the development and differentiation of the 5 pituitary cell types: galactotropes, gonadotropes, corticotropes, thyrotropes, and somatotropes. As indicated by the mutations in PIT1 described later, combined pituitary hormone deficiency can have either autosomal dominant or autosomal recessive inheritance, depending on the part of the PIT1 molecule affected by the mutation. Some mutations have a dominant-negative effect. Genetic Heterogeneity of Combined Pituitary Hormone Deficiency CPHD2 (262600), associated with hypogonadism, is caused by mutation in the PROP1 gene (601538). CPHD3 (221750), which is associated with rigid cervical spine and variable sensorineural deafness, is caused by mutation in the LHX3 gene (600577). CPHD4 (262700) is caused by mutation in the LHX4 gene (602146). CPHD5 (see septooptic dysplasia, 182230) is caused by mutation in the HESX1 gene (601802). CPHD6 (613986) is caused by mutation in the OTX2 gene (600037). CPHD7 (618160) is caused by mutation in the RNPC3 gene (618016).

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

An extremely rare genetic disorder characterized by corneal anesthesia, retinal abnormalities, bilateral hearing loss, distinct facies, patent ductus arteriosus, Hirschsprung disease, short stature and intellectual disability. The phenotype is variable. Some affected individuals have only mild disease manifestations. The etiology of this syndrome is not yet known. Mutations in an as of yet unidentified gene, involved in autonomic nervous system function, are suspected. Follows an autosomal dominant pattern of inheritance, probably with variable expressivity.

Ring chromosome 14 syndrome is a condition characterized by seizures and intellectual disability. Recurrent seizures (epilepsy) develop in infancy or early childhood. In many cases, the seizures are resistant to treatment with anti-epileptic drugs. Most people with ring chromosome 14 syndrome also have some degree of intellectual disability or learning problems. Development may be delayed, particularly the development of speech and of motor skills such as sitting, standing, and walking.\n\nAdditional features of ring chromosome 14 syndrome can include slow growth and short stature, a small head (microcephaly), puffy hands and/or feet caused by a buildup of fluid (lymphedema), and subtle differences in facial features. Some affected individuals have problems with their immune system that lead to recurrent infections, especially involving the respiratory system. Abnormalities of the retina, the specialized tissue at the back of the eye that detects light and color, have also been reported in some people with this condition. These changes typically do not affect vision. Major birth defects are rarely seen with ring chromosome 14 syndrome.

Congenital disorders of glycosylation (CDGs) that represent defects of dolichol-linked oligosaccharide assembly are classified as CDG type I. For a general description and a discussion of the classification of CDGs, see CDG1A (212065).

Greenberg dysplasia (GRBGD), also known as hydrops-ectopic calcification-moth-eaten (HEM) skeletal dysplasia, is a rare autosomal recessive osteochondrodysplasia characterized by gross fetal hydrops, severe shortening of all long bones with a moth-eaten radiographic appearance, platyspondyly, disorganization of chondroosseous calcification, and ectopic ossification centers. It is lethal in utero. Patient fibroblasts show increased levels of cholesta-8,14-dien-3-beta-ol, suggesting a defect of sterol metabolism (summary by Konstantinidou et al., 2008). Herman (2003) reviewed the cholesterol biosynthetic pathway and 6 disorders involving enzyme defects in postsqualene cholesterol biosynthesis: Smith-Lemli-Opitz syndrome (SLOS; 270400), desmosterolosis (602398), X-linked dominant chondrodysplasia punctata (CDPX2; 302960), CHILD syndrome (308050), lathosterolosis (607330), and HEM skeletal dysplasia.

A rare genetic multiple congenital anomalies/dysmorphic syndrome characterized by intellectual disability, obesity, macrocephaly, behavioral abnormalities (such as aggressive tantrums and autistic-like behavior), and delayed speech development. Dysmorphic facial features include large, square forehead, prominent supraorbital ridges, broad nasal tip, large ears, prominent lower lip, and minor dental anomalies such as small upper lateral incisors and central incisor gap.

An extremely rare syndrome with characteristics of radial ray hypoplasia, choanal atresia and convergent strabismus. It has been reported in a father and his two daughters. The radial ray involvement varies from absent radius, first metacarpal and thumb to hypoplastic thumb or triphalangeal thumb. Transmitted as an autosomal dominant trait.

A variant of neurofibromatosis type 1 characterized by the combination of features of neurofibromatosis type 1, such as café-au-lait spots, iris Lisch nodules, axillary and inguinal freckling, optic nerve glioma and multiple neurofibromas; and Noonan syndrome, with features such as short stature, typical facial features, congenital heart defects and unusual pectus deformity.

Patients with chromosome 2q37 deletion syndrome show highly variable clinical manifestations likely resulting from different deletion sizes and deletions of different genes. Variable clinical features included brachydactyly type E (BDE), affecting the metacarpals and metatarsals (in about 50% of patients), short stature, mild to moderate intellectual disability, behavioral abnormalities, and dysmorphic facial features. However, many individuals with deletions do not show cognitive deficits (summary by Villavicencio-Lorini et al., 2013, Wheeler et al., 2014, Jean-Marcais et al., 2015).

Disorders of GNAS inactivation include the phenotypes pseudohypoparathyroidism Ia, Ib, and Ic (PHP-Ia, -Ib, -Ic), pseudopseudohypoparathyroidism (PPHP), progressive osseous heteroplasia (POH), and osteoma cutis (OC). PHP-Ia and PHP-Ic are characterized by: End-organ resistance to endocrine hormones including parathyroid hormone (PTH), thyroid-stimulating hormone (TSH), gonadotropins (LH and FSH), growth hormone-releasing hormone (GHRH), and CNS neurotransmitters (leading to obesity and variable degrees of intellectual disability and developmental delay); and The Albright hereditary osteodystrophy (AHO) phenotype (short stature, round facies, and subcutaneous ossifications) and brachydactyly type E (shortening mainly of the 4th and/or 5th metacarpals and metatarsals and distal phalanx of the thumb). Although PHP-Ib is characterized principally by PTH resistance, some individuals also have partial TSH resistance and mild features of AHO (e.g., brachydactyly). PPHP, a more limited form of PHP-Ia, is characterized by various manifestations of the AHO phenotype without the hormone resistance or obesity. POH and OC are even more restricted variants of PPHP: POH consists of dermal ossification beginning in infancy, followed by increasing and extensive bone formation in deep muscle and fascia. OC consists of extra-skeletal ossification that is limited to the dermis and subcutaneous tissues.

Cytochrome P450 oxidoreductase deficiency (PORD) is a disorder of steroidogenesis with a broad phenotypic spectrum including cortisol deficiency, altered sex steroid synthesis, disorders of sex development (DSD), and skeletal malformations of the Antley-Bixler syndrome (ABS) phenotype. Cortisol deficiency is usually partial, with some baseline cortisol production but failure to mount an adequate cortisol response in stress. Mild mineralocorticoid excess can be present and causes arterial hypertension, usually presenting in young adulthood. Manifestations of altered sex steroid synthesis include ambiguous genitalia/DSD in both males and females, large ovarian cysts in females, poor masculinization and delayed puberty in males, and maternal virilization during pregnancy with an affected fetus. Skeletal malformations can manifest as craniosynostosis, mid-face retrusion with proptosis and choanal stenosis or atresia, low-set dysplastic ears with stenotic external auditory canals, hydrocephalus, radiohumeral synostosis, neonatal fractures, congenital bowing of the long bones, joint contractures, arachnodactyly, and clubfeet; other anomalies observed include urinary tract anomalies (renal pelvic dilatation, vesicoureteral reflux). Cognitive impairment is of minor concern and likely associated with the severity of malformations; studies of developmental outcomes are lacking.

Cytochrome P450 oxidoreductase deficiency (PORD) is a disorder of steroidogenesis with a broad phenotypic spectrum including cortisol deficiency, altered sex steroid synthesis, disorders of sex development (DSD), and skeletal malformations of the Antley-Bixler syndrome (ABS) phenotype. Cortisol deficiency is usually partial, with some baseline cortisol production but failure to mount an adequate cortisol response in stress. Mild mineralocorticoid excess can be present and causes arterial hypertension, usually presenting in young adulthood. Manifestations of altered sex steroid synthesis include ambiguous genitalia/DSD in both males and females, large ovarian cysts in females, poor masculinization and delayed puberty in males, and maternal virilization during pregnancy with an affected fetus. Skeletal malformations can manifest as craniosynostosis, mid-face retrusion with proptosis and choanal stenosis or atresia, low-set dysplastic ears with stenotic external auditory canals, hydrocephalus, radiohumeral synostosis, neonatal fractures, congenital bowing of the long bones, joint contractures, arachnodactyly, and clubfeet; other anomalies observed include urinary tract anomalies (renal pelvic dilatation, vesicoureteral reflux). Cognitive impairment is of minor concern and likely associated with the severity of malformations; studies of developmental outcomes are lacking.

17q23.1q23.2 microdeletion syndrome is a recently described syndrome characterized by developmental delay, microcephaly, short stature, heart defects and limb abnormalities.

Neurodevelopmental disorder with hypotonia, stereotypic hand movements, and impaired language (NEDHSIL) is characterized by global developmental delay with hypotonia, poor motor development with limited walking, impaired intellectual development with poor or absent speech, and behavioral abnormalities. Almost all affected individuals demonstrate repetitive stereotypic hand movements that can be categorized as hyperkinetic and resembling those of Rett syndrome (RTT; 312750). About 80% of patients develop various types of seizures that may be refractory to treatment. Additional features may include dysmorphic facial features, particularly dysplastic ears, poor eye contact, episodic hyperventilation, tendency to infection, and abnormalities on brain imaging, such as enlarged ventricles, thin corpus callosum, and delayed myelination (summary by Vrecar et al., 2017, Paciorkowski et al., 2013).

Frontonasal dysplasia-2 (FND2) is an autosomal recessive disorder characterized by variable degrees of alopecia, skull defects, hypertelorism, depressed nasal bridge and ridge with notched alae nasi, and abnormal central nervous system findings (summary by Kariminejad et al., 2014).

The congenital variant of Rett syndrome is a severe neurodevelopmental disorder with features of classic Rett syndrome (RTT; 312750), but earlier onset in the first months of life. Classic Rett syndrome shows later onset and is caused by mutation in the MECP2 gene (300005).

14q11.2 microdeletion syndrome is a recently described syndrome characterized by developmental delay, hypotonia and facial dysmorphism.

16p13.3 microduplication syndrome is a rare chromosomal anomaly syndrome resulting from a partial duplication of the short arm of chromosome 16 and manifesting with a variable phenotype which is mostly characterized by: mild to moderate intellectual deficit and developmental delay (particularly speech), normal growth, short, proximally implanted thumbs and other hand and feet malformations (such as camptodactyly, syndactyly, club feet), mild arthrogryposis and characteristic facies (upslanting, narrow palpebral fissures, hypertelorism, mid face hypoplasia, bulbous nasal tip and low set ears). Other reported manifestations include cryptorchidism, inguinal hernia and behavioral problems.

Noonan syndrome-like disorder is a developmental disorder resembling Noonan syndrome (NS1; 163950) and characterized by facial dysmorphism, a wide spectrum of cardiac disease, reduced growth, variable cognitive deficits, and ectodermal and musculoskeletal anomalies. There is extensive phenotypic heterogeneity and variable expressivity (summary by Martinelli et al., 2010). Patients with heterozygous germline CBL mutations have an increased risk for certain malignancies, particularly juvenile myelomonocytic leukemia (JMML; 607785), as also seen in patients with Noonan syndrome (summary by Niemeyer et al., 2010).

Cranioectodermal dysplasia (CED) is a ciliopathy with skeletal involvement (narrow thorax, shortened proximal limbs, syndactyly, polydactyly, brachydactyly), ectodermal features (widely spaced hypoplastic teeth, hypodontia, sparse hair, skin laxity, abnormal nails), joint laxity, growth deficiency, and characteristic facial features (frontal bossing, low-set simple ears, high forehead, telecanthus, epicanthal folds, full cheeks, everted lower lip). Most affected children develop nephronophthisis that often leads to end-stage kidney disease in infancy or childhood, a major cause of morbidity and mortality. Hepatic fibrosis and retinal dystrophy are also observed. Dolichocephaly, often secondary to sagittal craniosynostosis, is a primary manifestation that distinguishes CED from most other ciliopathies. Brain malformations and developmental delay may also occur.

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Noonan syndrome with multiple lentigines (NSML) is a condition in which the cardinal features consist of lentigines, hypertrophic cardiomyopathy, short stature, pectus deformity, and dysmorphic facial features including widely spaced eyes and ptosis. Multiple lentigines present as dispersed flat, black-brown macules, mostly on the face, neck, and upper part of the trunk with sparing of the mucosa. In general, lentigines do not appear until age four to five years but then increase to the thousands by puberty. Some individuals with NSML do not exhibit lentigines. Approximately 85% of affected individuals have heart defects, including hypertrophic cardiomyopathy (typically appearing during infancy and sometimes progressive) and pulmonary valve stenosis. Postnatal growth restriction resulting in short stature occurs in fewer than 50% of affected persons, although most affected individuals have a height that is less than the 25th centile for age. Sensorineural hearing deficits, present in approximately 20% of affected individuals, are poorly characterized. Intellectual disability, typically mild, is observed in approximately 30% of persons with NSML.

Osteogenesis imperfecta (OI) comprises a group of connective tissue disorders characterized by bone fragility and low bone mass. The disorder is clinically and genetically heterogeneous. OI type XII is an autosomal recessive form characterized by recurrent fractures, mild bone deformations, generalized osteoporosis, delayed teeth eruption, progressive hearing loss, no dentinogenesis imperfecta, and white sclerae (summary by Lapunzina et al., 2010).

Ogden syndrome (OGDNS) is an X-linked neurodevelopmental disorder characterized by postnatal growth failure, severely delayed psychomotor development, variable dysmorphic features, and hypotonia. Many patients also have cardiac malformations or arrhythmias (summary by Popp et al., 2015).

The Nascimento type of X-linked syndromic intellectual developmental disorder (MRXSN) is characterized by dysmorphic features, including large head, synophrys, prominent supraorbital ridges, almond-shaped and deep-set eyes, large ears, wide mouth, myxedematous appearance, hirsutism, abnormal hair whorls, micropenis, and onychodystrophy. Female carriers have normal cognition, but may show subtle facial features (summary by Budny et al., 2010).

Multiple congenital anomalies-hypotonia-seizures syndrome-2 (MCAHS2) is an X-linked recessive neurodevelopmental disorder characterized by dysmorphic features, neonatal hypotonia, early-onset myoclonic seizures, and variable congenital anomalies involving the central nervous, cardiac, and urinary systems. Some affected individuals die in infancy (summary by Johnston et al., 2012). The phenotype shows clinical variability with regard to severity and extraneurologic features. However, most patients present in infancy with early-onset epileptic encephalopathy associated with developmental arrest and subsequent severe neurologic disability; these features are consistent with a form of developmental and epileptic encephalopathy (DEE) (summary by Belet et al., 2014, Kato et al., 2014). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of nomenclature and genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Acrodysostosis-1 (ACRDYS1) is a form of skeletal dysplasia characterized by short stature, severe brachydactyly, facial dysostosis, and nasal hypoplasia. Affected individuals often have advanced bone age and obesity. Laboratory studies show resistance to multiple hormones, including parathyroid, thyrotropin, calcitonin, growth hormone-releasing hormone, and gonadotropin (summary by Linglart et al., 2011). However, not all patients show endocrine abnormalities (Lee et al., 2012). Genetic Heterogeneity of Acrodysostosis See also ACRDYS2 (614613), caused by mutation in the PDE4D gene (600129) on chromosome 5q12.

Fibrochondrogenesis is a severe, autosomal recessive, short-limbed skeletal dysplasia clinically characterized by a flat midface with a small nose and anteverted nares, significant shortening of all limb segments but relatively normal hands and feet, and a small bell-shaped thorax with a protuberant abdomen. Radiographically, the long bones are short and have broad metaphyseal ends, giving them a dumb-bell shape. The vertebral bodies are flat and, on lateral view, have a distinctive pinched appearance, with a hypoplastic posterior end and a rounded anterior end. The ribs are typically short and wide and have metaphyseal cupping at both ends (summary by Tompson et al., 2010). Genetic Heterogeneity of Fibrochondrogenesis Fibrochondrogenesis-2 (FBCG2; 614524) is caused by mutation in the COL11A2 gene (120290) on chromosome 6p21.3.

CHST3-related skeletal dysplasia is characterized by short stature of prenatal onset, joint dislocations (knees, hips, radial heads), clubfeet, and limitation of range of motion that can involve all large joints. Kyphosis and occasionally scoliosis with slight shortening of the trunk develop in childhood. Minor heart valve dysplasia has been described in several persons. Intellect and vision are normal.

Immunodeficiency, centromeric instability, and facial dysmorphism (ICF) syndrome is a rare autosomal recessive disorder characterized by facial dysmorphism, immunoglobulin deficiency resulting in recurrent infections, and mental retardation. Laboratory studies of patient cells show hypomethylation of satellite regions of chromosomes 1, 9, and 16, as well as pericentromeric chromosomal instability in response to phytohemagglutinin stimulation (summary by de Greef et al., 2011). For a discussion of genetic heterogeneity of immunodeficiency-centromeric instability-facial anomalies syndrome, see ICF1 (242860).

Multiple congenital anomalies-hypotonia-seizures syndrome is an autosomal recessive disorder characterized by neonatal hypotonia, lack of psychomotor development, seizures, dysmorphic features, and variable congenital anomalies involving the cardiac, urinary, and gastrointestinal systems. Most affected individuals die before 3 years of age (summary by Maydan et al., 2011). The disorder is caused by a defect in glycosylphosphatidylinositol biosynthesis; see GPIBD1 (610293). Genetic Heterogeneity of Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome MCAHS2 (300868) is caused by mutation in the PIGA gene (311770) on chromosome Xp22, MCAHS3 (615398) is caused by mutation in the PIGT gene (610272) on chromosome 20q13, and MCAHS4 (618548) is caused by mutation in the PIGQ gene (605754) on chromosome 16p13. Knaus et al. (2018) provided a review of the main clinical features of the different types of MCAHS, noting that patients with mutations in the PIGN, PIGA, and PIGT genes have distinct patterns of facial anomalies that can be detected by computer-assisted comparison. Some individuals with MCAHS may have variable increases in alkaline phosphatase (AP) as well as variable decreases in GPI-linked proteins that can be detected by flow cytometry. However, there was no clear correlation between AP levels or GPI-linked protein abnormalities and degree of neurologic involvement, mutation class, or gene involved. Knaus et al. (2018) concluded that a distinction between MCAHS and HPMRS1 (239300), which is also caused by mutation in genes involved in GPI biosynthesis, may be artificial and even inaccurate, and that all these disorders should be considered and classified together under the more encompassing term of 'GPI biosynthesis defects' (GPIBD).

Methylmalonate semialdehyde dehydrogenase deficiency is a rare autosomal recessive inborn error of metabolism with a highly variable phenotype. Some patients may be asymptomatic, whereas others show global developmental delay, nonspecific dysmorphic features, and delayed myelination on brain imaging. Laboratory studies typically show increased urinary 3-hydroxyisobutyric acid, although additional metabolic abnormalities may also be observed (summary by Marcadier et al., 2013).

Mosaic variegated aneuploidy syndrome is an autosomal recessive disorder characterized by poor growth and variable phenotypic manifestations, such as facial dysmorphism and congenital heart defects, associated with mosaic aneuploidies resulting from defects in cell division (summary by Snape et al., 2011). See also MVA1 (257300), caused by mutation in the BUB1B gene (602860) on chromosome 15q15.

CRSDA is an autosomal recessive disorder characterized by craniosynostosis, maxillary hypoplasia, and dental anomalies, including malocclusion, delayed and ectopic tooth eruption, and/or supernumerary teeth. Some patients also display minor digit anomalies, such as syndactyly and/or clinodactyly (summary by Nieminen et al., 2011).

Adams-Oliver syndrome (AOS) is characterized by aplasia cutis congenita (ACC) of the scalp and terminal transverse limb defects (TTLD). ACC lesions usually occur in the midline of the parietal or occipital regions, but can also occur on the abdomen or limbs. At birth, an ACC lesion may already have the appearance of a healed scar. ACC lesions less than 5 cm often involve only the skin and almost always heal over a period of months; larger lesions are more likely to involve the skull and possibly the dura, and are at greater risk for complications, which can include infection, hemorrhage, or thrombosis, and can result in death. The limb defects range from mild (unilateral or bilateral short distal phalanges) to severe (complete absence of all toes or fingers, feet or hands, or more, often resembling an amputation). The lower extremities are almost always more severely affected than the upper extremities. Additional major features frequently include cardiovascular malformations/dysfunction (23%), brain anomalies, and less frequently renal, liver, and eye anomalies.

Any autosomal recessive non-syndromic intellectual disability in which the cause of the disease is a mutation in the LINS1 gene.

EFEMP2-related cutis laxa, or autosomal recessive cutis laxa type 1B (ARCL1B), is characterized by cutis laxa and systemic involvement, most commonly arterial tortuosity, aneurysms, and stenosis; retrognathia; joint laxity; and arachnodactyly. Severity ranges from perinatal lethality as a result of cardiopulmonary failure to manifestations limited to the vascular and craniofacial systems.

Trigonocephaly occurs predominantly as a nonsyndromic craniosynostosis and has an estimated prevalence of between 1:15,000 and 1:68,000 live births (summary by Vissers et al., 2011). For a discussion of genetic heterogeneity of isolated trigonocephaly, see TRIGNO1 (190440). A syndromic form of trigonocephaly is associated with monosomy for an 8-Mb interval of chromosome 9p22.3 (see 158170).

The 17q12 recurrent deletion syndrome is characterized by variable combinations of the three following findings: structural or functional abnormalities of the kidney and urinary tract, maturity-onset diabetes of the young type 5 (MODY5), and neurodevelopmental or neuropsychiatric disorders (e.g., developmental delay, intellectual disability, autism spectrum disorder, schizophrenia, anxiety, and bipolar disorder). Using a method of data analysis that avoids ascertainment bias, the authors determined that multicystic kidneys and other structural and functional kidney anomalies occur in 85% to 90% of affected individuals, MODY5 in approximately 40%, and some degree of developmental delay or learning disability in approximately 50%. MODY5 is most often diagnosed before age 25 years (range: age 10-50 years).

The interstitial 16q22 deletion syndrome is a multiple congenital anomaly disorder associated with failure to thrive in infancy, poor growth, delayed psychomotor development, hypotonia, and dysmorphic features, including large anterior fontanel, high forehead, diastasis of the cranial sutures, broad nasal bridge, hypertelorism, low-set abnormal ears, and short neck. The phenotypic features and deletion sizes are variable, but deletion of 16q22 appears to be critical for manifestations of the syndrome (summary by Fujiwara et al., 1992).

Coffin-Siris syndrome (CSS) is classically characterized by aplasia or hypoplasia of the distal phalanx or nail of the fifth and additional digits, developmental or cognitive delay of varying degree, distinctive facial features, hypotonia, hirsutism/hypertrichosis, and sparse scalp hair. Congenital anomalies can include malformations of the cardiac, gastrointestinal, genitourinary, and/or central nervous systems. Other findings commonly include feeding difficulties, slow growth, ophthalmologic abnormalities, and hearing impairment.

Trichohepatoenteric syndrome (THES), generally considered to be a neonatal enteropathy, is characterized by intractable diarrhea (seen in almost all affected children), woolly hair (seen in all), intrauterine growth restriction, facial dysmorphism, and short stature. Additional findings include poorly characterized immunodeficiency, recurrent infections, skin abnormalities, and liver disease. Mild intellectual disability (ID) is seen in about 50% of affected individuals. Less common findings include congenital heart defects and platelet anomalies. To date 52 affected individuals have been reported.

Disorders of GNAS inactivation include the phenotypes pseudohypoparathyroidism Ia, Ib, and Ic (PHP-Ia, -Ib, -Ic), pseudopseudohypoparathyroidism (PPHP), progressive osseous heteroplasia (POH), and osteoma cutis (OC). PHP-Ia and PHP-Ic are characterized by: End-organ resistance to endocrine hormones including parathyroid hormone (PTH), thyroid-stimulating hormone (TSH), gonadotropins (LH and FSH), growth hormone-releasing hormone (GHRH), and CNS neurotransmitters (leading to obesity and variable degrees of intellectual disability and developmental delay); and The Albright hereditary osteodystrophy (AHO) phenotype (short stature, round facies, and subcutaneous ossifications) and brachydactyly type E (shortening mainly of the 4th and/or 5th metacarpals and metatarsals and distal phalanx of the thumb). Although PHP-Ib is characterized principally by PTH resistance, some individuals also have partial TSH resistance and mild features of AHO (e.g., brachydactyly). PPHP, a more limited form of PHP-Ia, is characterized by various manifestations of the AHO phenotype without the hormone resistance or obesity. POH and OC are even more restricted variants of PPHP: POH consists of dermal ossification beginning in infancy, followed by increasing and extensive bone formation in deep muscle and fascia. OC consists of extra-skeletal ossification that is limited to the dermis and subcutaneous tissues.

Hypohidrotic ectodermal dysplasia (HED) is characterized by hypotrichosis (sparseness of scalp and body hair), hypohidrosis (reduced ability to sweat), and hypodontia (congenital absence of teeth). The cardinal features of classic HED become obvious during childhood. The scalp hair is thin, lightly pigmented, and slow growing. Sweating, although present, is greatly deficient, leading to episodes of hyperthermia until the affected individual or family acquires experience with environmental modifications to control temperature. Only a few abnormally formed teeth erupt, at a later-than-average age. Physical growth and psychomotor development are otherwise within normal limits. Mild HED is characterized by mild manifestations of any or all the characteristic features.

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

Coffin-Siris syndrome is a congenital malformation syndrome characterized by developmental delay, intellectual disability, coarse facial features, feeding difficulties, and hypoplastic or absent fifth fingernails and fifth distal phalanges. Other more variable features may also occur. Patients with ARID1A mutations have a wide spectrum of manifestations, from severe intellectual disability and serious internal complications that could result in early death to mild intellectual disability (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900). The chromosome 1p36.11 duplication syndrome, in which the ARID1A gene is duplicated, is characterized by impaired intellectual development, microcephaly, dysmorphic facial features, and hand and foot anomalies.

Coffin-Siris syndrome is a congenital malformation syndrome characterized by developmental delay, intellectual disability, coarse facial features, feeding difficulties, and hypoplastic or absent fifth fingernails and fifth distal phalanges. Other more variable features may also occur. Patients with SMARCB1 mutations may have more severe neurodevelopmental deficits including severe intellectual disability, brain structural abnormalities, and no expressive words, as well as scoliosis (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Coffin-Siris syndrome is a congenital malformation syndrome characterized by developmental delay, intellectual disability, coarse facial features, feeding difficulties, and hypoplastic or absent fifth fingernails and fifth distal phalanges. Other more variable features may also occur. Patients with SMARCA4 mutations may have less coarse craniofacial appearances and fewer behavioral abnormalities than Coffin-Siris patients with mutations in other genes (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Acrodysostosis-2 (ACRDYS2) is a rare skeletal dysplasia characterized by brachydactyly, facial dysostosis, and spinal stenosis. Many patients have intellectual disability and some have hormone resistance (summary by Michot et al., 2012 and Lee et al., 2012). For a discussion of genetic heterogeneity of acrodysostosis, see ACRDYS1 (101800).

HCFP3 is an autosomal recessive congenital cranial dysinnervation disorder characterized by isolated dysfunction of the seventh cranial nerve resulting in facial palsy. Additional features may include orofacial anomalies, such as smooth philtrum, lagophthalmos, swallowing difficulties, and dysarthria, as well as hearing loss. There is some phenotypic overlap with Moebius syndrome (see, e.g., 157900), but patients with HCFP usually retain full eye motility or have esotropia without paralysis of the sixth cranial nerve (summary by Vogel et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of hereditary congenital facial paresis, see 601471.

The peroxisomal biogenesis disorder (PBD) Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 4 (CG4, equivalent to CG6 and CGC) have mutations in the PEX6 gene. For information on the history of PBD complementation groups, see 214100.

Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome resulting from disordered peroxisome biogenesis. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 13 (CG13, equivalent to CGH) have mutations in the PEX13 gene. For information on the history of PBD complementation groups, see 214100.

Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome resulting from disordered peroxisome biogenesis. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group K (CGK) have mutations in the PEX14 gene. For information on the history of PBD complementation groups, see 214100.

Carpenter syndrome-2 (CRPT2) is an autosomal recessive multiple congenital malformation disorder characterized by multisuture craniosynostosis and polysyndactyly of the hands and feet, in association with abnormal left-right patterning and other features, most commonly obesity, umbilical hernia, cryptorchidism, and congenital heart disease (summary by Twigg et al., 2012). For a discussion of genetic heterogeneity of Carpenter syndrome, see 201000.

Alazami syndrome is an autosomal recessive disorder characterized by severe growth restriction present at birth, severely impaired intellectual development, and distinctive facial features. Some patients have been reported with skeletal and behavioral features (summary by Imbert-Bouteille et al., 2019).

Patients with SSOAD exhibit a broad phenotypic spectrum involving short stature associated with advanced bone maturation and early-onset osteoarthritis (OA), as well as mild dysmorphic features consisting of midface hypoplasia, brachydactyly, broad great toes, and lumbar lordosis. Other features include intervertebral disc disease and osteochondritis dissecans, which is characterized by separation of articular cartilage and subchondral bone from the articular surface. Phenotypes are highly variable even among patients within the same family, and there are no apparent genotype-phenotype correlations (Dateki et al., 2017). The term 'dissecans' comes from 'dis' meaning 'from' and 'secare' meaning 'cut off,' and is not to be confused with 'desiccans' derived from 'desiccare' meaning to 'dry up.' Dissecans refers to the appearance of part of the bone having been cut away.

The FLNB disorders include a spectrum of phenotypes ranging from mild to severe. At the mild end are spondylocarpotarsal synostosis (SCT) syndrome and Larsen syndrome; at the severe end are the phenotypic continuum of atelosteogenesis types I (AOI) and III (AOIII) and Piepkorn osteochondrodysplasia (POCD). SCT syndrome is characterized by postnatal disproportionate short stature, scoliosis and lordosis, clubfeet, hearing loss, dental enamel hypoplasia, carpal and tarsal synostosis, and vertebral fusions. Larsen syndrome is characterized by congenital dislocations of the hip, knee, and elbow; clubfeet (equinovarus or equinovalgus foot deformities); scoliosis and cervical kyphosis, which can be associated with a cervical myelopathy; short, broad, spatulate distal phalanges; distinctive craniofacies (prominent forehead, depressed nasal bridge, malar flattening, and widely spaced eyes); vertebral anomalies; and supernumerary carpal and tarsal bone ossification centers. Individuals with SCT syndrome and Larsen syndrome can have midline cleft palate and hearing loss. AOI and AOIII are characterized by severe short-limbed dwarfism; dislocated hips, knees, and elbows; and clubfeet. AOI is lethal in the perinatal period. In individuals with AOIII, survival beyond the neonatal period is possible with intensive and invasive respiratory support. Piepkorn osteochondrodysplasia (POCD) is a perinatal-lethal micromelic dwarfism characterized by flipper-like limbs (polysyndactyly with complete syndactyly of all fingers and toes, hypoplastic or absent first digits, and duplicated intermediate and distal phalanges), macrobrachycephaly, prominant forehead, hypertelorism, and exophthalmos. Occasional features include cleft palate, omphalocele, and cardiac and genitourinary anomalies. The radiographic features at mid-gestation are characteristic.

X-linked chondrodysplasia punctata 1 (CDPX1) is characterized by chondrodysplasia punctata (stippled epiphyses), brachytelephalangy (shortening of the distal phalanges), and nasomaxillary hypoplasia. Although most affected males have minimal morbidity and skeletal findings that improve by adulthood, some have significant medical problems including respiratory involvement, cervical spine stenosis and instability, mixed conductive and sensorineural hearing loss, and intellectual disability.

MED12-related disorders include the phenotypes of FG syndrome type 1 (FGS1), Lujan syndrome (LS), X-linked Ohdo syndrome (XLOS), Hardikar syndrome (HS), and nonspecific intellectual disability (NSID). FGS1 and LS share the clinical findings of cognitive impairment, hypotonia, and abnormalities of the corpus callosum. FGS1 is further characterized by absolute or relative macrocephaly, tall forehead, downslanted palpebral fissures, small and simple ears, constipation and/or anal anomalies, broad thumbs and halluces, and characteristic behavior. LS is further characterized by large head, tall thin body habitus, long thin face, prominent nasal bridge, high narrow palate, and short philtrum. Carrier females in families with FGS1 and LS are typically unaffected. XLOS is characterized by intellectual disability, blepharophimosis, and facial coarsening. HS has been described in females with cleft lip and/or cleft palate, biliary and liver anomalies, intestinal malrotation, pigmentary retinopathy, and coarctation of the aorta. Developmental and cognitive concerns have not been reported in females with HS. Pathogenic variants in MED12 have been reported in an increasing number of males and females with NSID, with affected individuals often having clinical features identified in other MED12-related disorders.

X-linked intellectual developmental disorder-98 (XLID98) is a neurodevelopmental disorder characterized by delayed psychomotor development, poor speech, behavioral abnormalities, poor overall growth, dysmorphic facial features, and often early-onset seizures. Some carrier females are unaffected, whereas other females with mutations are affected; males tend to be more severely affected than females. It is believed that the phenotypic variability and disease manifestations in female carriers results from skewed X-inactivation or cellular mosaicism (summary by de Lange et al., 2016).

Multiple congenital anomalies-hypotonia-seizures syndrome is an autosomal recessive disorder characterized by neonatal hypotonia, lack of psychomotor development, seizures, dysmorphic features, and variable congenital anomalies involving the cardiac, urinary, and gastrointestinal systems. Most affected individuals die before 3 years of age (summary by Maydan et al., 2011). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

Van Maldergem syndrome is an autosomal recessive disorder characterized by intellectual disability, typical craniofacial features, auditory malformations resulting in hearing loss, and skeletal and limb malformations. Some patients have renal hypoplasia. Brain MRI typically shows periventricular nodular heterotopia (summary by Cappello et al., 2013). For a discussion of genetic heterogeneity of Van Maldergem syndrome, see 601390.

Intellectual disability-facial dysmorphism syndrome due to SETD5 haploinsufficiency is a rare, syndromic intellectual disability characterized by intellectual disability of various severity, hypotonia, feeding difficulties, dysmorphic features, autism and behavioral issues. Growth retardation, congenital heart anomalies, gastrointestinal and genitourinary defects have been rarely associated.

Hypohidrotic ectodermal dysplasia (HED) is characterized by hypotrichosis (sparseness of scalp and body hair), hypohidrosis (reduced ability to sweat), and hypodontia (congenital absence of teeth). The cardinal features of classic HED become obvious during childhood. The scalp hair is thin, lightly pigmented, and slow growing. Sweating, although present, is greatly deficient, leading to episodes of hyperthermia until the affected individual or family acquires experience with environmental modifications to control temperature. Only a few abnormally formed teeth erupt, at a later-than-average age. Physical growth and psychomotor development are otherwise within normal limits. Mild HED is characterized by mild manifestations of any or all the characteristic features.

Hennekam lymphangiectasia-lymphedema syndrome (HKLLS1) is an autosomal recessive disorder characterized by generalized lymphatic dysplasia affecting various organs, including the intestinal tract, pericardium, and limbs. Additional features of the disorder include facial dysmorphism and cognitive impairment (summary by Alders et al., 2014). Genetic Heterogeneity of Hennekam Lymphangiectasia-Lymphedema Syndrome See also HKLLS2 (616006), caused by mutation in the FAT4 gene (612411) on chromosome 4q28, and HKLLS3 (618154), caused by mutation in the ADAMTS3 gene (605011) on chromosome 4q13.

Desbuquois dysplasia (DBQD) is an autosomal recessive chondrodysplasia belonging to the multiple dislocation group and characterized by severe prenatal and postnatal growth retardation (stature less than -5 SD), joint laxity, short extremities, and progressive scoliosis. The main radiologic features are short long bones with metaphyseal splay, a 'Swedish key' appearance of the proximal femur (exaggerated trochanter), and advanced carpal and tarsal bone age with a delta phalanx (summary by Huber et al., 2009). Desbuquois dysplasia is clinically and radiographically heterogeneous, and had been classified into 2 types based on the presence (type 1) or absence (type 2) of characteristic hand anomalies, including an extra ossification center distal to the second metacarpal, delta phalanx, bifid distal thumb phalanx, and dislocation of the interphalangeal joints (Faivre et al., 2004). However, patients with and without these additional hand anomalies have been reported to have mutations in the same gene (see, e.g., CANT1); thus, these features are not distinctive criteria to predict the molecular basis of DBQD (Furuichi et al., 2011). In addition, Kim et al. (2010) described another milder variant of DBQD with almost normal outwardly appearing hands, but significant radiographic changes, including short metacarpals, elongated phalanges, and remarkably advanced carpal bone age. However, there is no accessory ossification center distal to the second metacarpal, and patients do not have thumb anomalies. Similar changes occur in the feet. These patients also tend to develop precocious osteoarthritis of the hand and spine with age. This phenotype is sometimes referred to as the 'Kim variant' of DBQD (Furuichi et al., 2011). Genetic Heterogeneity of Desbuquois Dysplasia DBQD2 (615777) is caused by mutation in the XYLT1 gene (608124) on chromosome 16p12. Two unrelated patients with immunodeficiency-23 (IMD23; 615816), due to mutation in the PGM3 gene (172100), were reported to have skeletal features reminiscent of DBQD.

Progressive microcephaly with seizures and cerebral and cerebellar atrophy is a severe autosomal recessive neurodevelopmental and neurodegenerative disorder with onset in the first days or months of life. Patients are born with microcephaly and soon develop intractable seizures, resulting in profoundly delayed development and hypotonia (summary by Zhang et al., 2014).

Desbuquois dysplasia, which belongs to the multiple dislocation group of disorders, is characterized by dislocations of large joints, severe pre- and postnatal growth retardation, joint laxity, and flat face with prominent eyes. Radiologic features include short long bones with an exaggerated trochanter that gives a 'monkey wrench' appearance to the proximal femur, and advanced carpal and tarsal ossification (summary by Bui et al., 2014). For a discussion of genetic heterogeneity of Desbuquois dysplasia, see DBQD1 (251450).

Short stature with microcephaly and distinctive facies (SSMCF) is characterized by pre- or postnatal growth retardation, frontal bossing, high forehead, sparse hair and eyebrows, and telecanthus. Patients also show skin dyspigmentation, with hyper- and/or hypopigmented areas (Leduc et al., 2016).

Neurodevelopmental disorder with dysmorphic features, spasticity, and brain abnormalities (NEDDSBA) is an autosomal recessive neurodevelopmental disorder characterized by severely delayed global development, with hypotonia, impaired intellectual development, and poor or absent speech. Most patients have spasticity with limb hypertonia and brisk tendon reflexes. Additional features include nonspecific dysmorphic facial features, structural brain abnormalities, and cortical visual impairment (summary by Bosch et al., 2015). Novarino et al. (2014) labeled the disorder 'spastic paraplegia-67' (SPG67). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Any mitochondrial complex III deficiency in which the cause of the disease is a mutation in the UQCC2 gene.

The main features of Xia-Gibbs syndrome (XGS), present in a majority of affected individuals, include delayed motor milestones, speech delay with severely limited or absent speech, moderate-to-severe cognitive impairment, hypotonia, structural brain anomalies, and nonspecific dysmorphic features. Other features may include sleep apnea, movement disorders (ataxia, tremors, and bradykinesias) that often become apparent in childhood or adolescence, short stature, seizures, eye anomalies, behavioral concerns, autism spectrum disorder, scoliosis, and laryngomalacia.

A rare genetic syndromic intellectual disability characterized by global developmental delay and borderline to severe intellectual disability, autism spectrum disorder with obsessive behavior, stereotypies, hyperactivity but frequently friendly and affable personality, feeding difficulties, short stature, muscular hypotonia, microcephaly, characteristic dysmorphic features (hypertelorism, high arched eyebrows, ptosis, deep and/or broad nasal bridge, broad/prominent nasal tip, short and/or upturned philtrum, narrow mouth, and micrognathia), and skeletal anomalies (kyphosis and/or scoliosis, arthrogryposis, slender habitus and extremities). Other clinical features may include hernias, congenital heart defects, cryptorchidism and seizures.

Intellectual developmental disorder with microcephaly and with or without ocular malformations or hypogonadotropic hypogonadism (IDDMOH) is characterized by mildly impaired intellectual development and microcephaly. Patients may also have ocular malformations, ocular apraxia, or hypogonadotropic hypogonadism. The disorder shows a unique DNA methylation signature (summary by Al-Jawahiri et al., 2022).

Any autosomal recessive non-syndromic intellectual disability in which the cause of the disease is a mutation in the METTL23 gene.

Hennekam lymphangiectasia-lymphedema syndrome is an autosomal recessive disorder characterized by generalized lymphatic dysplasia affecting various organs, including the intestinal tract, pericardium, and limbs. Additional features of the disorder include facial dysmorphism and cognitive impairment (summary by Alders et al., 2014). For a discussion of genetic heterogeneity of Hennekam lymphangiectasia-lymphedema syndrome, see HKLLS1 (235510).

CAGSSS, which comprises cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia, is an autosomal recessive multisystemic disorder with a highly variable phenotypic spectrum. Not all of these features are always present, and almost all the features may present at different times and/or become more apparent with age. The skeletal features are consistent with spondyloepimetaphyseal dysplasia (SEMD) (summary by Vona et al., 2018). One family had a distinctive presentation with infantile-onset intractable seizures and cortical abnormalities reminiscent of Leigh syndrome (see 256000). The correlation between genotype and phenotype remains unclear, but since the IARS2 gene is involved in mitochondrial function, heterogeneous manifestations can be expected (Takezawa et al., 2018).

Temple syndrome is a short stature disorder of imprinting. The cardinal features are low birth weight, hypotonia and motor delay, feeding problems early in life, early puberty, and significantly reduced final height. Facial features include a broad forehead and short nose with a wide nasal tip, and the majority of patients have small hands and feet. However, many of the clinical features are nonspecific, making diagnosis difficult. In addition, isodisomy may uncover recessive disorders, which may influence the phenotype in maternal uniparental disomy of chromosome 14 (UPD14mat) cases (summary by Ioannides et al., 2014).

Autosomal dominant Robinow syndrome (ADRS) is characterized by skeletal findings (short stature, mesomelic limb shortening predominantly of the upper limbs, and brachydactyly), genital abnormalities (in males: micropenis / webbed penis, hypoplastic scrotum, cryptorchidism; in females: hypoplastic clitoris and labia majora), dysmorphic facial features (widely spaced and prominent eyes, frontal bossing, anteverted nares, midface retrusion), dental abnormalities (including malocclusion, crowding, hypodontia, late eruption of permanent teeth), bilobed tongue, and occasional prenatal macrocephaly that persists postnatally. Less common findings include renal anomalies, radial head dislocation, vertebral abnormalities such as hemivertebrae and scoliosis, nail dysplasia, cardiac defects, cleft lip/palate, and (rarely) cognitive delay. When present, cardiac defects are a major cause of morbidity and mortality. A variant of Robinow syndrome, associated with osteosclerosis and caused by a heterozygous pathogenic variant in DVL1, is characterized by normal stature, persistent macrocephaly, increased bone mineral density with skull osteosclerosis, and hearing loss, in addition to the typical features described above.

Any Meier-Gorlin syndrome in which the cause of the disease is a mutation in the GMNN gene.

Hyperphosphatasia with impaired intellectual development syndrome-6 (HPMRS6) is an autosomal recessive multisystem disorder characterized by global developmental delay, dysmorphic features, seizures, and congenital cataracts. Severity is variable, and the disorder may show a range of phenotypic and biochemical abnormalities, including increased serum alkaline phosphatase levels (summary by Ilkovski et al., 2015). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of HPMRS, see HPMRS1 (239300). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Lamb-Shaffer syndrome is a neurodevelopmental disorder characterized by global developmental delay, intellectual disability, poor expressive speech, and mild dysmorphic facial features. Additional variable skeletal abnormalities may also be present (summary by Nesbitt et al., 2015).

Impaired intellectual development and distinctive facial features with or without cardiac defects (MRFACD) is an autosomal dominant, complex syndromic neurodevelopmental disorder characterized by delayed psychomotor development, poor speech acquisition, distinctive dysmorphic facial features, including frontal bossing, upslanting palpebral fissures, depressed nasal bridge with bulbous tip, and macrostomia. There is variable penetrance of cardiac malformations, ranging from no malformations to patent foramen ovale to septal defects and/or transposition of the great arteries (summary by Adegbola et al., 2015).

Congenital symmetric circumferential skin creases is characterized by the folding of excess skin, which leads to ringed creases, primarily of the limbs. Affected individuals also exhibit intellectual disability, cleft palate, and dysmorphic features (summary by Isrie et al., 2015). For a discussion of genetic heterogeneity of congenital symmetric circumferential skin creases, see CSCSC1 (156610).

Smith-Kingsmore syndrome (SKS) is a rare autosomal dominant syndromic intellectual disability syndrome characterized by macrocephaly, seizures, umbilical hernia, and facial dysmorphic features including frontal bossing, midface hypoplasia, small chin, hypertelorism with downslanting palpebral fissures, depressed nasal bridge, smooth philtrum, and thin upper lip (Smith et al., 2013; Baynam et al., 2015).

Kosaki overgrowth syndrome (KOGS) is characterized by a facial gestalt involving prominent forehead, proptosis, downslanting palpebral fissures, broad nasal bridge, thin upper lip, and pointed chin. Affected individuals are tall, with an elongated lower segment, and have large hands and feet. Skin is hyperelastic and fragile. Patients exhibit progressive dilatory and vascular changes in basilar/vertebral and coronary arteries starting in the teenage years (Takenouchi et al., 2015; Takenouchi et al., 2021).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia with or without polydactyly, see SRTD1 (208500).

Any lethal congenital contracture syndrome in which the cause of the disease is a mutation in the ADGRG6 gene.

Any autosomal dominant non-syndromic intellectual disability in which the cause of the disease is a mutation in the EEF1A2 gene.

White-Sutton syndrome is a neurodevelopmental disorder characterized by a wide spectrum of cognitive dysfunction, developmental delays (particularly in speech and language acquisition), hypotonia, autism spectrum disorder, and other behavioral problems. Additional features commonly reported include seizures, refractive errors and strabismus, hearing loss, sleep disturbance (particularly sleep apnea), feeding and gastrointestinal problems, mild genital abnormalities in males, and urinary tract involvement in both males and females.

Autosomal dominant Robinow syndrome (ADRS) is characterized by skeletal findings (short stature, mesomelic limb shortening predominantly of the upper limbs, and brachydactyly), genital abnormalities (in males: micropenis / webbed penis, hypoplastic scrotum, cryptorchidism; in females: hypoplastic clitoris and labia majora), dysmorphic facial features (widely spaced and prominent eyes, frontal bossing, anteverted nares, midface retrusion), dental abnormalities (including malocclusion, crowding, hypodontia, late eruption of permanent teeth), bilobed tongue, and occasional prenatal macrocephaly that persists postnatally. Less common findings include renal anomalies, radial head dislocation, vertebral abnormalities such as hemivertebrae and scoliosis, nail dysplasia, cardiac defects, cleft lip/palate, and (rarely) cognitive delay. When present, cardiac defects are a major cause of morbidity and mortality. A variant of Robinow syndrome, associated with osteosclerosis and caused by a heterozygous pathogenic variant in DVL1, is characterized by normal stature, persistent macrocephaly, increased bone mineral density with skull osteosclerosis, and hearing loss, in addition to the typical features described above.

Female-restricted X-linked syndromic intellectual developmental disorder-99 (MRXS99F) is an X-linked dominant neurodevelopmental disorder characterized by delayed psychomotor development and mild to moderate intellectual disability. Affected females can have a wide range of additional congenital anomalies, including scoliosis, postaxial polydactyly, mild cardiac or urogenital anomalies, dysmorphic facial features, and mild structural brain abnormalities (summary by Reijnders et al., 2016).

Van Esch-O'Driscoll syndrome (VEODS) is characterized by varying degrees of intellectual disability, moderate to severe short stature, microcephaly, hypogonadism, and variable congenital malformations (Van Esch et al., 2019).

LICS is an autosomal recessive chromosome breakage syndrome characterized by failure to thrive in infancy, immune deficiency, and fatal progressive pediatric lung disease induced by viral infection. Some patients may have mild dysmorphic features (summary by van der Crabben et al., 2016).

Combined oxidative phosphorylation deficiency-31 is an autosomal recessive multisystem disorder characterized by left ventricular noncompaction (LVNC), global developmental delay, and severe hypotonia. More variable features include seizures, cataract, and abnormal movements. The disorder becomes apparent soon after birth or in early infancy, and patients may die in early childhood. Biochemical studies are consistent with a defect in mitochondrial function (summary by Eldomery et al., 2016). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Chitayat syndrome (CHYTS) is a rare condition characterized by respiratory distress presenting at birth, bilateral accessory phalanx resulting in shortened index fingers with ulnar deviation, hallux valgus, and characteristic facial features including prominent eyes, hypertelorism, depressed nasal bridge, full lips, and upturned nose (summary by Balasubramanian et al., 2017).

A rare genetic, multiple congenital anomalies syndrome characterized by short stature, hand brachydactyly with hypoplastic distal phalanges, global development delay, intellectual disability, and more variably seizures, obesity, and craniofacial dysmorphism that includes microcephaly, high forehead, flat face, hypertelorism, deep set eyes, flat nasal bridge, averted nostrils, long philtrum, thin lip vermilion, and short neck.

ZTTK syndrome (ZTTKS) is a severe multisystem developmental disorder characterized by delayed psychomotor development and intellectual disability. Affected individuals have characteristic dysmorphic facial features, hypotonia, poor feeding, poor overall growth, and eye or visual abnormalities. Most patients also have musculoskeletal abnormalities, and some have congenital defects of the heart and urogenital system. Brain imaging usually shows developmental abnormalities such as gyral changes, cortical and/or cerebellar atrophy, and thin corpus callosum (summary by Kim et al., 2016).

Frontometaphyseal dysplasia (FMD) is a progressive sclerosing skeletal dysplasia characterized by supraorbital hyperostosis, undermodeling of the small bones, and small and large joint contractures, as well as extraskeletal developmental abnormalities, primarily of the cardiorespiratory system and genitourinary tract. Patients with FMD2 appear to have a propensity for keloid formation (summary by Wade et al., 2016). For a discussion of genetic heterogeneity of frontometaphyseal dysplasia, see FMD1 (305620).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia with or without polydactyly, see SRTD1 (208500).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). SRTD15 is characterized by narrow thorax, oral and cardiovascular anomalies, short long bones, and postaxial polydactyly, in addition to other congenital anomalies. Considerable variability in features and in severity has been reported, with some affected individuals succumbing shortly after birth and others living to adulthood, even within the same family. For a discussion of genetic heterogeneity of short-rib thoracic dysplasia with or without polydactyly, see SRTD1 (208500).

TRIO-related intellectual disability (ID) is characterized by delay in acquisition of motor and language skills, mild to borderline intellectual disability, and neurobehavioral problems (including autistic traits or autism spectrum disorder, attention-deficit/hyperactivity disorder, and/or aggression). Neonatal or infantile feeding difficulties including poor suck, impaired bottle feeding, and failure to thrive are common and are often the presenting finding. Other findings can include microcephaly, variable hand and dental abnormalities, and suggestive facial features. Only ten of the 20 individuals with a TRIO pathogenic variant reported to date had sufficient information to make preliminary generalizations about clinical manifestations; it is anticipated that the phenotype of this newly described disorder will continue to evolve.

PERCHING syndrome is an autosomal recessive multisystem disorder characterized by global developmental delay, dysmorphic facial features, feeding and respiratory difficulties with poor overall growth, axial hypotonia, and joint contractures. The features are variable, even within families, and may also include retinitis pigmentosa, cardiac or genitourinary anomalies, and abnormal sweating. Each letter of the PERCHING acronym represents 2 important phenotypic elements: Postural and Palatal abnormalities; Exophthalmos and Enteral-tube dependency/feeding issues; Respiratory distress and Retinitis pigmentosa; Contractures and Camptodactyly; Hypertelorism and Hirsutism; Intrauterine growth retardation (IUGR)/growth failure and Intellectual disability/developmental delay; Nevus flammeus and Neurologic malformations; and facial Gestalt/grimacing and Genitourinary abnormalities (Jeffries et al., 2019). Death in infancy or early childhood often occurs, although survival to the third decade has been reported. Some of the features, such as contractures, dysmorphic craniofacial features, and severe feeding difficulties, are reminiscent of Bohring-Opitz syndrome (605039) (summary by Kanthi et al., 2019 and Buers et al., 2020).

Coffin-Siris syndrome is a rare congenital disorder characterized by delayed psychomotor development, intellectual disability, coarse facial features, and hypoplasia of the distal phalanges, particularly the fifth digit. Other features may also be observed, including congenital heart defects, hypoplasia of the corpus callosum, and poor overall growth with short stature and microcephaly (summary by Wieczorek et al., 2013). Patients with SMARCE1 mutations have a wide spectrum of manifestations, including severe to moderate intellectual disability and heart defects (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Heart and brain malformation syndrome (HBMS) is a severe autosomal recessive multiple congenital anomaly syndrome characterized by profoundly delayed psychomotor development, dysmorphic facial features, microphthalmia, cardiac malformations, mainly septal defects, and brain malformations, including Dandy-Walker malformation (summary by Shaheen et al., 2016). Homozygous mutation in the SMG9 gene can also cause neurodevelopmental disorder with intention tremor, pyramidal signs, dyspraxia, and ocular anomalies (NEDITPDO; 619995), a less severe neurodevelopmental disorder.

Immunodeficiency-centromeric instability-facial anomalies syndrome-4 is an autosomal recessive disorder characterized by recurrent infections in childhood and variable dysmorphic facial features. Laboratory studies show hypomethylation of certain chromosomal regions. Additional features, including delayed development, are variable (summary by Thijssen et al., 2015). For a discussion of genetic heterogeneity of immunodeficiency-centromeric instability-facial anomalies syndrome, see ICF1 (242860).

Immunodeficiency-centromeric instability-facial anomalies syndrome-3 is an autosomal recessive disorder characterized by recurrent infections in childhood and variable dysmorphic facial features. Laboratory studies show hypomethylation of certain chromosomal regions. Additional features, including delayed development, are variable (summary by Thijssen et al., 2015). For a discussion of genetic heterogeneity of immunodeficiency-centromeric instability-facial anomalies syndrome, see ICF1 (242860).

A rare genetic multiple congenital anomalies/dysmorphic syndrome with characteristics of craniofacial dysmorphism (including an abnormal skull shape, hypertelorism, downslanting palpebral fissures, epicanthal folds, low-set ears, depressed nasal bridge, micrognathia), short stature, ectodermal anomalies (such as sparse eyebrows, eyelashes, and scalp hair, hypoplastic toenails), developmental delay, and intellectual disability. Additional features may include cerebral/cerebellar malformations and mild renal involvement.

Witteveen-Kolk syndrome (WITKOS) is an autosomal dominant disorder with characteristic distinctive facial features, microcephaly, short stature, and mildly impaired intellectual development with delayed cognitive and motor development and subtle anomalies on MRI-brain imaging (summary by Balasubramanian et al., 2021).

Midface hypoplasia, hearing impairment, elliptocytosis, and nephrocalcinosis is an X-linked recessive disorder with onset of features in early childhood. Anemia is sometimes present. Some patients may show mild early motor or speech delay, but cognition is normal (summary by Andreoletti et al., 2017).

GLYT1 encephalopathy is characterized in neonates by severe hypotonia, respiratory failure requiring mechanical ventilation, and absent neonatal reflexes; encephalopathy, including impaired consciousness and unresponsiveness, may be present. Arthrogryposis or joint laxity can be observed. Generalized hypotonia develops later into axial hypotonia with limb hypertonicity and a startle-like response to vocal and visual stimuli which should not be confused with seizures. To date, three of the six affected children reported from three families died between ages two days and seven months; the oldest reported living child is severely globally impaired at age three years. Because of the limited number of affected individuals reported to date, the phenotype has not yet been completely described.

SRD5A3-congenital disorder of glycosylation (SRD5A3-CDG, formerly known as congenital disorder of glycosylation type Iq) is an inherited condition that causes neurological and vision problems and other signs and symptoms. The pattern and severity of this condition's features vary widely among affected individuals.\n\nIndividuals with SRD5A3-CDG typically develop signs and symptoms of the condition during infancy or early childhood. Most individuals with SRD5A3-CDG have intellectual disability, vision problems, unusual facial features,low muscle tone (hypotonia), and problems with coordination and balance (ataxia). \n\nVision problems in SRD5A3-CDG often include involuntary side-side movements of the eyes (nystagmus), a gap or hole in one of the structures of the eye (coloboma), underdevelopment of the nerves that carry signals between the eyes and the brain(optic nerve hypoplasia), or vision loss early in life (early-onset severe retinal dystrophy). Over time, affected individuals may develop clouding of the lenses of the eyes (cataracts) or increased pressure in the eyes (glaucoma).\n\nOther features of SRD5A3-CDG can include skin rash, unusually small red blood cells (microcytic anemia),and liver problems.

Congenital heart defects and ectodermal dysplasia (CHDED) is a rare disorder characterized by these cardinal features, with additional variable features of microcephaly, craniofacial or skeletal dysmorphism, feeding difficulties, or hypotonia (Sifrim et al., 2016).

Some ectodermal dysplasias are here classified as congenital disorders characterized by abnormal development in 2 or more ectodermal structures (hair, nails, teeth, and sweat glands) without other systemic findings. Ectodermal dysplasia-13 of the hair/tooth type is characterized by severe oligodontia accompanied by anomalies of hair and skin (Issa et al., 2016).

BTDD is an autosomal dominant disorder characterized by brachycephaly, trichomegaly, and developmental delay. Although it is caused by dysfunction of the ribosome, patients do not have anemia (summary by Paolini et al., 2017).

Intellectual developmental disorder with neuropsychiatric features is an autosomal recessive disorder characterized by moderate intellectual disability, relatively mild seizures, and neuropsychiatric abnormalities, such as anxiety, obsessive-compulsive behavior, and autistic features. Mild facial dysmorphic features may also be present (summary by Srour et al., 2017).

EED-related overgrowth is characterized by fetal or early childhood overgrowth (tall stature, macrocephaly, large hands and feet, and advanced bone age) and intellectual disability that ranges from mild to severe. To date, EED-related overgrowth has been reported in eight individuals.

WDR26-related intellectual disability (ID) is characterized by developmental delay / intellectual disability, characteristic facial features, hypotonia, epilepsy, and infant feeding difficulties. To date 15 individuals, ages 24 months to 34 years, have been reported. Developmental delay is present in all individuals and ranges from mild to severe. All individuals have delayed speech. Although some begin to develop speech in the second year, others have remained nonverbal. Seizures, present in all affected individuals reported to date, can be febrile or non-febrile (tonic-clonic, absence, rolandic seizures); most seizures are self limited or respond well to standard treatment. Affected individuals are generally described as happy and socially engaging; several have stereotypies / autistic features (repetitive or rocking behavior, abnormal hand movements or posturing, and at times self-stimulation).

Vertebral, cardiac, renal, and limb defects syndrome-2 (VCRL2) is an autosomal recessive congenital malformation syndrome characterized by vertebral segmentation abnormalities, congenital cardiac defects, renal defects, and mild distal limb defects. Additional features are variable (summary by Shi et al., 2017). For a discussion of genetic heterogeneity of VCRL, see VCRL1 (617660).

Al Kaissi syndrome (ALKAS) is an autosomal recessive developmental disorder characterized by growth retardation, spine malformation, particularly of the cervical spine, dysmorphic facial features, and delayed psychomotor development with moderate to severe intellectual disability (summary by Windpassinger et al., 2017).

Joubert syndrome-32 (JBTS32) is an autosomal recessive developmental disorder characterized by delayed psychomotor development, intellectual disability, dysmorphic facial features, and postaxial polydactyly. Brain imaging shows cerebellar abnormalities consistent with the molar tooth sign (MTS) (summary by De Mori et al., 2017). For discussion of genetic heterogeneity of Joubert syndrome, see JBTS1 (213300).

Neurodevelopmental disorder with microcephaly, seizures, and cortical atrophy (NDMSCA) is an autosomal recessive disorder characterized by severe global developmental delay with poor motor and intellectual function apparent soon after birth, as well as postnatal progressive microcephaly. Most patients develop early-onset, frequent, and often intractable seizures, compatible with an epileptic encephalopathy. Other features include poor feeding, poor overall growth, absent speech, poor or absent eye contact, inability to achieve walking, hypotonia, and peripheral spasticity. Brain imaging usually shows progressive cerebral atrophy, thin corpus callosum, and abnormalities in myelination. Death in childhood may occur (summary by Siekierska et al., 2019).

NEDMIAL is a neurodevelopmental disorder characterized by delayed psychomotor development and hypotonia apparent from early infancy, resulting in feeding difficulties, ataxic gait or inability to walk, delayed or absent speech development, and impaired intellectual development, sometimes with behavioral abnormalities, such as hand-flapping. Additional common features may include sleep disorder, nonspecific dysmorphic facial features, and joint hyperlaxity (summary by Lessel et al., 2017 and Mannucci et al., 2021).

Coffin-Siris syndrome (CSS) is classically characterized by aplasia or hypoplasia of the distal phalanx or nail of the fifth and additional digits, developmental or cognitive delay of varying degree, distinctive facial features, hypotonia, hirsutism/hypertrichosis, and sparse scalp hair. Congenital anomalies can include malformations of the cardiac, gastrointestinal, genitourinary, and/or central nervous systems. Other findings commonly include feeding difficulties, slow growth, ophthalmologic abnormalities, and hearing impairment.

Geleophysic dysplasia, a progressive condition resembling a lysosomal storage disorder, is characterized by short stature, short hands and feet, progressive joint limitation and contractures, distinctive facial features, progressive cardiac valvular disease, and thickened skin. Intellect is normal. Major findings are likely to be present in the first year of life. Cardiac, respiratory, and lung involvement result in death before age five years in approximately 33% of individuals with ADAMTSL2-related geleophysic dysplasia.

Autosomal dominant Robinow syndrome (ADRS) is characterized by skeletal findings (short stature, mesomelic limb shortening predominantly of the upper limbs, and brachydactyly), genital abnormalities (in males: micropenis / webbed penis, hypoplastic scrotum, cryptorchidism; in females: hypoplastic clitoris and labia majora), dysmorphic facial features (widely spaced and prominent eyes, frontal bossing, anteverted nares, midface retrusion), dental abnormalities (including malocclusion, crowding, hypodontia, late eruption of permanent teeth), bilobed tongue, and occasional prenatal macrocephaly that persists postnatally. Less common findings include renal anomalies, radial head dislocation, vertebral abnormalities such as hemivertebrae and scoliosis, nail dysplasia, cardiac defects, cleft lip/palate, and (rarely) cognitive delay. When present, cardiac defects are a major cause of morbidity and mortality. A variant of Robinow syndrome, associated with osteosclerosis and caused by a heterozygous pathogenic variant in DVL1, is characterized by normal stature, persistent macrocephaly, increased bone mineral density with skull osteosclerosis, and hearing loss, in addition to the typical features described above.

Fraser syndrome is an autosomal recessive malformation disorder characterized by cryptophthalmos, syndactyly, and abnormalities of the respiratory and urogenital tract (summary by van Haelst et al., 2008). Genetic Heterogeneity of Fraser Syndrome Fraser syndrome-2 (FRASRS2) is caused by mutation in the FREM2 gene (608945) on chromosome 13q13, and Fraser syndrome-3 (FRASRS3; 617667) is caused by mutation in the GRIP1 gene (604597) on chromosome 12q14. See Bowen syndrome (211200) for a comparable but probably distinct syndrome of multiple congenital malformations.

SOST-related sclerosing bone dysplasias include sclerosteosis and van Buchem disease, both disorders of progressive bone overgrowth due to increased bone formation. The major clinical features of sclerosteosis are progressive skeletal overgrowth, most pronounced in the skull and mandible, and variable syndactyly, usually of the second (index) and third (middle) fingers. Affected individuals appear normal at birth except for syndactyly. Facial distortion due to bossing of the forehead and mandibular overgrowth is seen in nearly all individuals and becomes apparent in early childhood with progression into adulthood. Hyperostosis of the skull results in narrowing of the foramina, causing entrapment of the seventh cranial nerve (leading to facial palsy) with other, less common nerve entrapment syndromes including visual loss (2nd cranial nerve), neuralgia or anosmia (5th cranial nerve), and sensory hearing loss (8th cranial nerve). In sclerosteosis, hyperostosis of the calvarium reduces intracranial volume, increasing the risk for potentially lethal elevation of intracranial pressure. Survival of individuals with sclerosteosis into old age is unusual, but not unprecedented. The manifestations of van Buchem disease are generally milder than sclerosteosis and syndactyly is absent; life span appears to be normal.

Carpenter syndrome is a rare autosomal recessive disorder with the cardinal features of acrocephaly with variable synostosis of the sagittal, lambdoid, and coronal sutures; peculiar facies; brachydactyly of the hands with syndactyly; preaxial polydactyly and syndactyly of the feet; congenital heart defects; growth retardation; mental retardation; hypogenitalism; and obesity. In addition, cerebral malformations, oral and dental abnormalities, coxa valga, genu valgum, hydronephrosis, precocious puberty, and hearing loss may be observed (summary by Altunhan et al., 2011). Genetic Heterogeneity of Carpenter Syndrome Carpenter syndrome-2 (CRPT2; 614976), in which the features of Carpenter syndrome are sometimes associated with defective lateralization, is caused by mutation in the MEGF8 gene (604267).

Immunodeficiency, centromeric instability, and facial dysmorphism (ICF) syndrome is a rare autosomal recessive disease characterized by facial dysmorphism, immunoglobulin deficiency, and branching of chromosomes 1, 9, and 16 after phytohemagglutinin (PHA) stimulation of lymphocytes. Hypomethylation of DNA of a small fraction of the genome is an unusual feature of ICF patients that is explained by mutations in the DNMT3B gene in some, but not all, ICF patients (Hagleitner et al., 2008). Genetic Heterogeneity of Immunodeficiency-Centromeric Instability-Facial Anomalies Syndrome See also ICF2 (614069), caused by mutation in the ZBTB24 gene (614064) on chromosome 6q21; ICF3 (616910), caused by mutation in the CDCA7 gene (609937) on chromosome 2q31; and ICF4 (616911), caused by mutation in the HELLS gene (603946) on chromosome 10q23.

Knobloch syndrome-1 (KNO1) is an autosomal recessive developmental disorder primarily characterized by typical eye abnormalities, including high myopia, cataracts, dislocated lens, vitreoretinal degeneration, and retinal detachment, with occipital skull defects, which can range from occipital encephalocele to occult cutis aplasia (summary by Aldahmesh et al., 2011). Genetic Heterogeneity of Knobloch Syndrome KNO2 (618458) is caused by mutation in the PAK2 gene (605022) on chromosome 3q29.

Ritscher-Schinzel syndrome (RSS) is a clinically recognizable condition that includes the cardinal findings of craniofacial features, cerebellar defects, and cardiovascular malformations resulting in the alternate diagnostic name of 3C syndrome. Dysmorphic facial features may include brachycephaly, hypotonic face with protruding tongue, flat appearance of the face on profile view, short midface, widely spaced eyes, downslanted palpebral fissures, low-set ears with overfolding of the upper helix, smooth or short philtrum, and high or cleft palate. Affected individuals also typically have a characteristic metacarpal phalangeal profile showing a consistent wavy pattern on hand radiographs. RSS is associated with variable degrees of developmental delay and intellectual disability. Eye anomalies and hypercholesterolemia may be variably present.

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

Weill-Marchesani syndrome (WMS) is a connective tissue disorder characterized by abnormalities of the lens of the eye, short stature, brachydactyly, joint stiffness, and cardiovascular defects. The ocular problems, typically recognized in childhood, include microspherophakia (small spherical lens), myopia secondary to the abnormal shape of the lens, ectopia lentis (abnormal position of the lens), and glaucoma, which can lead to blindness. Height of adult males is 142-169 cm; height of adult females is 130-157 cm. Autosomal recessive WMS cannot be distinguished from autosomal dominant WMS by clinical findings alone.

ALKKUCS is an autosomal recessive severe neurodevelopmental disorder characterized by arthrogryposis, brain abnormalities associated with cerebral parenchymal underdevelopment, and global developmental delay. Most affected individuals die in utero or soon after birth. Additional abnormalities may include hypotonia, dysmorphic facial features, and involvement of other organ systems, such as cardiac or renal. The few patients who survive have variable intellectual disability and may have seizures (summary by Gueneau et al., 2018).

Neurodevelopmental disorder with movement abnormalities, abnormal gait, and autistic features (NEDMAGA) is characterized by infantile-onset global developmental delay with severe to profound intellectual disability, mildly delayed walking with broad-based and unsteady gait, and absence of meaningful language. Patients have features of autism, with repetitive behaviors and poor communication, but usually are socially reactive and have a happy demeanor. More variable neurologic features include mild seizures, spasticity, and peripheral neuropathy (summary by Palmer et al., 2017).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia with or without polydactyly, see SRTD1 (208500).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330).

JABELS is an autosomal recessive neurodevelopmental disorder characterized by developmental delay and intellectual disability with additional variable features. Patients have onset of symptoms in infancy, but the severity is highly variable. Some patients have social interaction and learn to walk but have an ataxic gait and abnormal movements, such as tremor or dystonia, whereas others do not achieve any motor control and are unable to speak. Additional features may include retinal anomalies, visual impairment, microcephaly, abnormal foot or hand posturing, and kyphoscoliosis; some patients have dysmorphic facial features or seizures. Brain imaging typically shows cerebellar atrophy and hypoplasia of the corpus callosum (summary by et al., 2016 and Bertoli-Avella et al., 2018).

Developmental and epileptic encephalopathy-64 (DEE64) is a neurodevelopmental disorder characterized by onset of seizures usually in the first year of life and associated with intellectual disability, poor motor development, and poor or absent speech. Additional features include hypotonia, abnormal movements, and nonspecific dysmorphic features. The severity is variable: some patients are unable to speak, walk, or interact with others as late as the teenage years, whereas others may have some comprehension (summary by Straub et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Characteristic features of the distal 3p- syndrome include low birth weight, microcephaly, trigonocephaly, hypotonia, psychomotor and growth retardation, ptosis, telecanthus, downslanting palpebral fissures, and micrognathia. Postaxial polydactyly, renal anomalies, cleft palate, congenital heart defects (especially atrioventricular septal defects), preauricular pits, sacral dimple, and gastrointestinal anomalies are variable features. Although intellectual deficits are almost invariably associated with cytogenetically visible 3p deletions, rare patients with a 3p26-p25 deletion and normal intelligence or only mild abnormalities have been described (summary by Shuib et al., 2009).

Rhizomelic skeletal dysplasia with or without Pelger-Huet anomaly (SKPHA) is an autosomal recessive disorder characterized by rhizomelic skeletal dysplasia of variable severity with or without abnormal nuclear shape and chromatin organization in blood granulocytes (Hoffmann et al., 2002; Borovik et al., 2013; Collins et al., 2020). Initial skeletal features may improve with age (Sobreira et al., 2014).

Coffin-Siris syndrome (CSS) is classically characterized by aplasia or hypoplasia of the distal phalanx or nail of the fifth and additional digits, developmental or cognitive delay of varying degree, distinctive facial features, hypotonia, hirsutism/hypertrichosis, and sparse scalp hair. Congenital anomalies can include malformations of the cardiac, gastrointestinal, genitourinary, and/or central nervous systems. Other findings commonly include feeding difficulties, slow growth, ophthalmologic abnormalities, and hearing impairment.

MFRG is an autosomal recessive syndrome in which microcephaly, unilateral renal agenesis, ambiguous genitalia, and facial dysmorphisms, including severe micrognathia, are observed in most patients. Variable brain, cardiac, and skeletal anomalies are present, including corpus callosum agenesis or dysgenesis, lissencephaly, atrial and ventricular septal defects, patent ductus arteriosus, hypoplastic right ventricle, and joint contractures (Shaheen et al., 2016).

Squalene synthase deficiency (SQSD) is a rare inborn error of cholesterol biosynthesis with multisystem clinical manifestations similar to Smith-Lemli-Optiz syndrome. Key clinical features include facial dysmorphism, a generalized seizure disorder presenting in the neonatal period, nonspecific structural brain malformations, cortical visual impairment, optic nerve hypoplasia, profound developmental delay / intellectual disability, dry skin with photosensitivity, and genital malformations in males.

Joubert syndrome-35 (JBTS35) is an autosomal recessive disorder characterized by brain malformations that result in developmental delay, oculomotor apraxia, and hypotonia. Some patients have renal and retinal involvement (Alkanderi et al., 2018). For a discussion of genetic heterogeneity of Joubert syndrome, see JBTS1 (213300).

Vertebral anomalies and variable endocrine and T-cell dysfunction is a syndrome characterized by an overlapping spectrum of features. Skeletal malformations primarily involve the vertebrae, and endocrine abnormalities involving parathyroid hormone (PTH; 168450), growth hormone (GH1; 139250), and the thyroid gland have been reported. T-cell abnormalities have been observed, with some patients showing thymus gland aplasia or hypoplasia. Patients have mild craniofacial dysmorphism, and some show developmental delay or behavioral problems. Cardiac defects may be present (Liu et al., 2018).

A rare genetic overgrowth syndrome characterised by global developmental delay, macrosomia with subsequent somatic overgrowth, bilateral cystic lung lesions, congenital nephromegaly and bilateral Wilms tumour. Craniofacial dysmorphism includes macrocephaly, frontal bossing, large anterior fontanelle, mild hypertelorism, ear pit, flat nasal bridge, anteverted nares and mild micrognathia. Additional features may include brain and skeletal anomalies, enlarged protuberant abdomen, fat pads on dorsum of feet and toes, and rugated soles with skin folds, as well as umbilical/inguinal hernia and autistic behaviour.

ASXL3-related disorder is characterized by developmental delay or intellectual disability, typically in the moderate to severe range, with speech and language delay and/or absent speech. Affected individuals may also display autistic features. There may be issues with feeding. While dysmorphic facial features have been described, they are typically nonspecific. Affected individuals may also have hypotonia that can transition to spasticity resulting in unusual posture with flexion contractions of the elbows, wrists, and fingers. Other findings may include poor postnatal growth, strabismus, seizures, sleep disturbance, and dental anomalies.

Neurodevelopmental disorder with brain abnormalities, poor growth, and dysmorphic facies (NEDBGF) is an autosomal recessive disorder characterized by global developmental delay with delayed walking, impaired intellectual development, and speech delay apparent from infancy or early childhood. Most patients have dysmorphic facial features, often with microcephaly and strabismus, and white matter abnormalities on brain imaging. More variable features may include teeth anomalies, distal joint contractures, spasticity, peripheral neuropathy, and behavioral problems (summary by Sharkia et al., 2019).

Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is characterized by distinctive craniofacial features, genital anomalies, hypotonia, and mild-to-profound developmental delay / intellectual disability (DD/ID). Craniofacial abnormalities include small head circumference, telecanthus or widely spaced eyes, short triangular nose, tented upper lip, and thick or everted lower lip with coarsening of the facial features over time. While all affected individuals have a normal 46,XY karyotype, genital anomalies comprise a range from hypospadias and undescended testicles, to severe hypospadias and ambiguous genitalia, to normal-appearing female external genitalia. Alpha-thalassemia, observed in about 75% of affected individuals, is mild and typically does not require treatment. Osteosarcoma has been reported in a few males with germline pathogenic variants.

Calvarial hyperostosis is a benign X-linked disorder that affects only the skull. Symptoms are prominent frontoparietal bones, flat nasal root, short upturned nose, high forehead with ridging of the metopic and sagittal sutures, and lateral frontal prominences. Radiographs of the skull show increased bone thickness at the sagittal suture line and prominent lateral frontal horns. Increased intracranial pressure and cranial nerve entrapment do not occur (summary by Borra et al., 2014).

Mullegama-Klein-Martinez syndrome (MKMS) is an X-linked recessive disorder with features of microcephaly, microtia, hearing loss, developmental delay, dysmorphic features, congenital heart defect, and digit abnormalities. Females are generally affected more severely than males (Mullegama et al., 2019).

IDDCDF is an autosomal recessive syndromic neurodevelopmental disorder characterized by globally impaired development with intellectual disability and speech delay, congenital cardiac malformations, and dysmorphic facial features. Additional features, such as distal skeletal anomalies, may also be observed (Stephen et al., 2018).

Lissencephaly-9 with complex brainstem malformation (LIS9) is an autosomal dominant neurologic disorder characterized by global developmental delay apparent since infancy, impaired intellectual development with poor or absent speech, and sometimes abnormal or involuntary movements associated with abnormal brain imaging that typically shows pachygyria, lissencephaly, and malformation of the brainstem consistent with a neuronal migration defect (summary by Dobyns et al., 2018). For a general description and a discussion of genetic heterogeneity of lissencephaly, see LIS1 (607432).

Menke-Hennekam syndrome-1 (MKHK1) is a congenital disorder characterized by variable impairment of intellectual development and facial dysmorphisms. Feeding difficulties, autistic behavior, recurrent upper airway infections, hearing impairment, short stature, and microcephaly are also frequently seen. Although mutations in the same gene cause Rubinstein-Taybi syndrome-1 (RSTS1; 180849), patients with MKHK1 do not resemble the striking phenotype of RSTS1. Genetic Heterogeneity of Menke-Hennekam Syndrome Menke-Hennekam syndrome-2 (MKHK2; 618333) is caused by heterozygous mutation in exons 30 or 31 of the EP300 gene (602700). Mutation elsewhere in that gene results in RSTS2 (613684).

Menke-Hennekam syndrome-2 (MKHK2) is a congenital disorder characterized by variable impairment of intellectual development and facial dysmorphisms. Feeding difficulties, autistic behavior, recurrent upper airway infections, and hearing impairment are also frequently seen. Although mutations in the same gene cause Rubinstein-Taybi syndrome-2 (RSTS2; 613684), patients with MKHK1 do not resemble the striking phenotype of RSTS2. For a discussion of genetic heterogeneity of Menke-Hennekam syndrome, see MKHK1 (618332).

Microcephaly, growth deficiency, seizures, and brain malformations (MIGSB) is a severe autosomal recessive disorder characterized by intrauterine growth retardation, postnatal growth deficiency with severe microcephaly, and poor or absent psychomotor development. Additional features include optic atrophy, early-onset seizures, dysmorphic facial features, and brain malformations, such as partial agenesis of the corpus callosum and simplified gyration (summary by Shaheen et al., 2015).

Developmental delay with variable intellectual impairment and behavioral abnormalities (DDVIBA) is an autosomal dominant neurodevelopmental disorder. Most patients have impaired intellectual development with speech difficulties, and many have behavioral abnormalities, most commonly autism spectrum disorder (ASD), defects in attention, and/or hyperactivity. Many patients have dysmorphic features, although there is not a consistent gestalt. Additional more variable features may include hypotonia, somatic overgrowth with macrocephaly, mild distal skeletal anomalies, sleep disturbances, movement disorders, and gastrointestinal issues, such as constipation. The phenotype is highly variable (summary by Vetrini et al., 2019 and Torti et al., 2019).

Developmental delay with or without dysmorphic facies and autism (DEDDFA) is a complex neurodevelopmental disorder apparent from infancy or early childhood and associated with variably impaired intellectual development. Some patients may be severely affected with no speech and inability to walk, whereas others may be able to attend special schools or have normal intellectual function associated with autism spectrum disorder and mild speech delay. Genetic analysis has suggested that the phenotype can be broadly categorized into 2 main groups. Patients with TRRAP mutations affecting residues 1031-1159 have a more severe disorder, often with multisystem involvement, including renal, cardiac, and genitourinary systems, as well as structural brain abnormalities. Patients with mutations outside of that region tend to have a less severe phenotype with a higher incidence of autism and usually no systemic involvement. Patients in both groups usually have somewhat similar dysmorphic facial features, such as upslanting palpebral fissures, hypertelorism, low-set ears, and broad or depressed nasal bridge, although these features are highly variable (summary by Cogne et al., 2019).

Hypotonia, hypoventilation, impaired intellectual development, dysautonomia, epilepsy, and eye abnormalities (HIDEA) is an autosomal recessive neurodevelopmental syndrome characterized by global developmental delay, poor or absent speech, hypotonia, variable ocular movement and visual abnormalities, and respiratory difficulties, including hypoventilation, and sleep apnea. Patients may have significant breathing problems during respiratory infections that may lead to early death (summary by Rahikkala et al., 2019).

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Holoprosencephaly-12 with or without pancreatic agenesis (HPE12) is a developmental disorder characterized by abnormal separation of the embryonic forebrain (HPE) resulting in dysmorphic facial features and often, but not always, impaired neurologic development. Most patients with this form of HPE also have congenital absence of the pancreas, resulting in early-onset type 1 diabetes mellitus and requiring pancreatic enzyme replacement. Other features may include hearing loss and absence of the gallbladder (summary by De Franco et al., 2019 and Kruszka et al., 2019). For a phenotypic description and a discussion of genetic heterogeneity of holoprosencephaly, see HPE1 (236100).

Stolerman neurodevelopmental syndrome (NEDSST) is a highly variable disorder characterized by developmental delay, often with motor and speech delay, mildly impaired intellectual development (in most patients), learning difficulties, and behavioral abnormalities, including autism spectrum disorder. Psychosis is observed in a small percentage of individuals over the age of 12 years. Most individuals have nonspecific and mild dysmorphic facial features without a common gestalt. A subset of patients may have involvement of other organ systems, including gastrointestinal with poor early feeding or gastroesophageal reflux, distal skeletal anomalies, and congenital heart defects. Most mutations occur de novo, but rare autosomal dominant inheritance with incomplete penetrance has been observed (Stolerman et al., 2019; Rots et al., 2023).

Rothmund-Thomson syndrome (RTS) is characterized by a rash that progresses to poikiloderma; sparse hair, eyelashes, and/or eyebrows; small size; skeletal and dental abnormalities; juvenile cataracts; and an increased risk for cancer, especially osteosarcoma. A variety of benign and malignant hematologic abnormalities have been reported in affected individuals. The rash of RTS typically develops between ages three and six months (occasionally as late as age two years) as erythema, swelling, and blistering on the face, subsequently spreading to the buttocks and extremities. The rash evolves over months to years into the chronic pattern of reticulated hypo- and hyperpigmentation, telangiectasias, and punctate atrophy (collectively known as poikiloderma) that persist throughout life. Hyperkeratotic lesions occur in approximately one third of individuals. Skeletal abnormalities can include radial ray defects, ulnar defects, absent or hypoplastic patella, and osteopenia.

Neurodevelopmental disorder with brain anomalies, seizures, and scoliosis (NEDBSS) is an autosomal recessive disorder characterized by severely impaired psychomotor development, hypotonia, seizures, and structural brain anomalies, including thin corpus callosum and cerebellar atrophy. Other features include scoliosis, dysmorphic facies, and visual impairment. Affected individuals are usually unable to walk or speak and may require tube feeding in severe cases. The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis (summary by Knaus et al., 2019). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Neurodevelopmental disorder with microcephaly, arthrogryposis, and structural brain anomalies (NEDMABA) is an autosomal recessive disorder characterized by severe global developmental delay, usually with hypotonia and absence of spontaneous movements other than head control, impaired intellectual development with absent speech, distal contractures, progressive microcephaly, dysmorphic features, and distal skeletal abnormalities, such as rocker-bottom feet and clenched hands with camptodactyly. Brain imaging tends to show a simplified gyral pattern of the cerebral cortex, delayed myelination, thin corpus callosum, and hypoplasia of the brainstem and cerebellum. The disorder may be complicated by feeding and/or breathing difficulties, often resulting in death in infancy (summary by Magini et al., 2019).

Developmental and epileptic encephalopathy-83 (DEE83) is a severe autosomal recessive neurodevelopmental disorder characterized by onset of frequent seizures in the first days to months of life that are usually refractory to medical treatment and are associated with significant EEG abnormalities. Affected individuals have profoundly impaired development, with no motor or language skill acquisition, poor or absent visual tracking, and poor oromotor function necessitating tube feeding. Many patients die in the first years of life (summary by Perenthaler et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Neurogenic arthrogryposis multiplex congenita-4 with agenesis of the corpus callosum (AMC4) is a severe neurologic disorder with onset in utero. Affected individuals show little or no fetal movements and are born with significant contractures affecting the upper and lower limbs, as well as dysmorphic facial features. Other abnormalities include globally impaired development, optic atrophy, agenesis of the corpus callosum, seizures, and peripheral neuropathy. Many patients die in early childhood (summary by Seidahmed et al., 2020).

Coffin-Siris syndrome-11 (CSS11) is a syndromic neurodevelopmental disorder characterized by global developmental delay and impaired intellectual development associated with hypotonia, feeding difficulties, and variable dysmorphic features. Most patients have distal anomalies, such as small hands and feet and hypoplastic fifth toenails (summary by Nixon et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Individuals with MN1 C-terminal truncation (MCTT) syndrome have mild-to-moderate intellectual disability, severe expressive language delay, dysmorphic facial features (midface hypoplasia, downslanting palpebral fissures, hypertelorism, exophthalmia, short upturned nose, and small low-set ears), and distinctive findings on brain imaging (including perisylvian polymicrogyria and atypical rhombencephalosynapsis). Mild-to-moderate prelingual hearing loss (usually bilateral, conductive, and/or sensorineural) is common. Generalized seizures (observed in the minority of individuals) are responsive to anti-seizure medication. There is an increased risk for craniosynostosis and, thus, increased intracranial pressure. To date, 25 individuals with MCTT syndrome have been identified.

Neurodevelopmental disorder with hypotonia, neonatal respiratory insufficiency, and thermodysregulation (NEDHRIT) is a severe autosomal recessive disorder characterized by neonatal respiratory distress, poor feeding, and impaired global development. Affected individuals are unable to walk or speak and have poor or absent eye contact. Some patients may develop seizures (summary by Wagner et al., 2020).

Nabais Sa-de Vries syndrome type 1 (NSDVS1) is characterized by global developmental delay apparent from infancy, variable behavioral abnormalities, microcephaly, and dysmorphic facial features, including round face, small palpebral fissures, highly arched eyebrows, and short nose. The severity is variable (summary by Nabais Sa et al., 2020).

Nabais Sa-de Vries syndrome type 2 (NSDVS2) is characterized by global developmental delay apparent from birth and distinctive dysmorphic facial features. Most patients have additional anomalies, including congenital heart defects, sleep disturbances, hypotonia, and variable endocrine abnormalities, such as hypothyroidism (summary by Nabais Sa et al., 2020).

Anauxetic dysplasia-3 (ANXD3) is characterized by severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations. Radiographs show short metacarpals, broad middle phalanges, and metaphyseal irregularities. Most patients also exhibit motor and cognitive delays (Narayanan et al., 2019). For a discussion of genetic heterogeneity of anauxetic dysplasia, see ANXD1 (607095).

CSGALNACT1 deficiency is characterized by mild skeletal dysplasia, joint hypermobility, and advanced bone age. Shortness of long bones is evident prenatally, and patients exhibit short stature and relative macrocephaly. Advanced carpotarsal bone age and monkey-wrench appearance of the femur observed in infancy may disappear with age (Mizumoto et al., 2020).

Nizon-Isidor syndrome (NIZIDS) is a neurodevelopmental disorder characterized by global developmental delay, mildly delayed walking, poor speech and language, variably impaired intellectual development, and behavioral abnormalities, such as autistic features or attention deficit-hyperactivity disorder (ADHD). Some patients may have additional features, including nonspecific facial dysmorphism, gastrointestinal difficulties, distal hand anomalies, and thin corpus callosum on brain imaging (summary by Nizon et al., 2019).

Agenesis of corpus callosum, cardiac, ocular, and genital syndrome (ACOGS) is a syndromic neurodevelopmental disorder characterized by global developmental delay and/or intellectual disability, corpus callosum agenesis or hypoplasia, craniofacial dysmorphisms, and ocular, cardiac, and genital anomalies (Accogli et al., 2019).

Developmental and epileptic encephalopathy-88 (DEE88) is an autosomal recessive severe neurologic disorder characterized by global developmental delay, early-onset epilepsy, and progressive microcephaly. Brain MRI findings may include corpus callosum abnormalities, prominent ventricles, and mild hypoplasia of the inferior vermis and pons (Broeks et al., 2019). For a discussion of genetic heterogeneity of developmental and epileptic encephalopathy, see 308350.

Spondylometaphyseal dysplasia with corneal dystrophy (SMDCD) is characterized by short stature due to short proximal and distal long bones. Affected individuals also exhibit narrow thorax with pulmonary hypoplasia and respiratory failure, as well as corneal dystrophy. Severe developmental delay has been observed (Ben-Salem et al., 2018).

ROR2-related Robinow syndrome is characterized by distinctive craniofacial features, skeletal abnormalities, and other anomalies. Craniofacial features include macrocephaly, broad prominent forehead, low-set ears, ocular hypertelorism, prominent eyes, midface hypoplasia, short upturned nose with depressed nasal bridge and flared nostrils, large and triangular mouth with exposed incisors and upper gums, gum hypertrophy, misaligned teeth, ankyloglossia, and micrognathia. Skeletal abnormalities include short stature, mesomelic or acromesomelic limb shortening, hemivertebrae with fusion of thoracic vertebrae, and brachydactyly. Other common features include micropenis with or without cryptorchidism in males and reduced clitoral size and hypoplasia of the labia majora in females, renal tract abnormalities, and nail hypoplasia or dystrophy. The disorder is recognizable at birth or in early childhood.

Mitochondrial complex IV deficiency nuclear type 2 (MC4DN2) is an autosomal recessive multisystem metabolic disorder characterized by the onset of symptoms at birth or in the first weeks or months of life. Affected individuals have severe hypotonia, often associated with feeding difficulties and respiratory insufficiency necessitating tube feeding and mechanical ventilation. The vast majority of patients develop hypertrophic cardiomyopathy in the first days or weeks of life, which usually leads to death in infancy or early childhood. Patients also show neurologic abnormalities, including developmental delay, nystagmus, fasciculations, dystonia, EEG changes, and brain imaging abnormalities compatible with a diagnosis of Leigh syndrome (see 256000). There may also be evidence of systemic involvement with hepatomegaly and myopathy, although neurogenic muscle atrophy is more common and may resemble spinal muscular atrophy type I (SMA1; 253300). Serum lactate is increased, and laboratory studies show decreased mitochondrial complex IV protein and activity levels in various tissues, including heart and skeletal muscle. Most patients die in infancy of cardiorespiratory failure (summary by Papadopoulou et al., 1999). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Li-Ghorbani-Weisz-Hubshman syndrome (LIGOWS) is a neurodevelopmental disorder characterized by global developmental delay, mild to moderately impaired intellectual development with language delay, and mild dysmorphic features. Affected individuals may have behavioral abnormalities and difficulties with numbers and understanding certain concepts, such as money. Some patients have seizures. Brain imaging often shows enlarged ventricles, thin corpus callosum, and gray matter nodular heterotopia, suggesting abnormal cortical brain development. More variable additional features may be present (summary by Li et al., 2020).

Neurodevelopmental disorder with dysmorphic facies, impaired speech, and hypotonia (NEDDISH) is an autosomal recessive disorder characterized by global developmental delay and mildly to severely impaired intellectual development with poor speech and language acquisition. Some patients may have early normal development with onset of the disorder in the first years of life. More variable neurologic abnormalities include hypotonia, seizures, apnea, mild signs of autonomic or peripheral neuropathy, and autism. Aside from dysmorphic facial features and occasional findings such as scoliosis or undescended testes, other organ systems are not involved (summary by Schneeberger et al., 2020).

Neurodevelopmental disorder with dysmorphic facies, sleep disturbance, and brain abnormalities (NEDFASB) is a syndromic disorder with multisystemic involvement. Affected individuals have severe global developmental delay with severely impaired intellectual development, poor or absent language, behavioral abnormalities, seizures, and sleep disturbances. Craniofacial dysmorphisms, while variable, include round face, prognathism, depressed nasal bridge, and cleft or high-arched palate. Brain imaging shows dysgenesis of the corpus callosum and progressive cerebellar atrophy. Additional features may include genitourinary tract anomalies, hearing loss, and mild distal skeletal defects (summary by Humbert et al., 2020).

Developmental and epileptic encephalopathy-89 (DEE89) is a severe autosomal recessive disorder characterized by profound global developmental delay with impaired intellectual development, absent speech, inability to sit or walk due to axial hypotonia and spastic quadriparesis, and onset of seizures in the first days or months of life. EEG shows suppression-burst pattern or hypsarrhythmia, consistent with DEE or a clinical diagnosis of West syndrome. More variable features include joint contractures with foot deformities, dysmorphic facial features with cleft palate, and omphalocele. Affected individuals have poor motor skills, poor eye contact, and lack of language development; some die in infancy or early childhood. Brain imaging may be normal or show nonspecific abnormalities (summary by Chatron et al., 2020).

Mandibuloacral dysplasia progeroid syndrome (MDPS) is an autosomal recessive severe laminopathy-like disorder characterized by growth retardation, bone resorption, arterial calcification, renal glomerulosclerosis, and hypertension (Elouej et al., 2020).

Coffin-Siris syndrome-12 (CSS12) is a neurodevelopmental disorder characterized by global developmental delay with variably impaired intellectual development, speech and language delay, and behavioral abnormalities, such as autism or hyperactivity. Affected individuals may have hypotonia and poor feeding in infancy. There are variable dysmorphic facial features, although most patients do not have the classic hypoplastic fifth digit/nail abnormalities that are often observed in other forms of CSS (Barish et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

RAB18 deficiency is the molecular deficit underlying both Warburg micro syndrome (characterized by eye, nervous system, and endocrine abnormalities) and Martsolf syndrome (characterized by similar – but milder – findings). To date Warburg micro syndrome comprises >96% of reported individuals with genetically defined RAB18 deficiency. The hallmark ophthalmologic findings are bilateral congenital cataracts, usually accompanied by microphthalmia, microcornea (diameter <10), and small atonic pupils. Poor vision despite early cataract surgery likely results from progressive optic atrophy and cortical visual impairment. Individuals with Warburg micro syndrome have severe to profound intellectual disability (ID); those with Martsolf syndrome have mild to moderate ID. Some individuals with RAB18 deficiency also have epilepsy. In Warburg micro syndrome, a progressive ascending spastic paraplegia typically begins with spastic diplegia and contractures during the first year, followed by upper-limb involvement leading to spastic quadriplegia after about age five years, often eventually causing breathing difficulties. In Martsolf syndrome infantile hypotonia is followed primarily by slowly progressive lower-limb spasticity. Hypogonadism – when present – manifests in both syndromes, in males as micropenis and/or cryptorchidism and in females as hypoplastic labia minora, clitoral hypoplasia, and small introitus.

Autosomal dominant intellectual developmental disorder-64 (MRD64) is characterized by mildly to severely impaired intellectual development (ID) with speech delays. Most patients also have autism spectrum disorder (ASD). Additional features are highly variable but may include motor delay, attention deficit-hyperactivity disorder (ADHD), and nonspecific dysmorphic features (summary by Mirzaa et al., 2020).

SHILCA is characterized by early-onset retinal degeneration in association with sensorineural hearing loss, short stature, vertebral anomalies, and epiphyseal dysplasia, as well as motor and intellectual delay. Delayed myelination, leukoencephalopathy, and hypoplasia of the corpus callosum and cerebellum have been observed on brain MRI (Bedoni et al., 2020).

Neurodevelopmental disorder with spasticity, cataracts, and cerebellar hypoplasia (NEDSCAC) is an autosomal recessive disorder characterized by global developmental delay with variably impaired intellectual development. More severely affected individuals are nonverbal and do not achieve independent ambulation, whereas others develop some speech and can walk, or show regression later in childhood. Common features include axial hypotonia, peripheral spasticity, dystonia, cataracts, and seizures. Brain imaging usually shows cerebellar hypoplasia with variable additional abnormalities, such as thin corpus callosum, cerebral atrophy, and hypomyelination (summary by Meng et al., 2021).

Pontocerebellar hypoplasia type 1F (PCH1F) is an autosomal recessive neurologic disorder characterized by hypotonia, global developmental delay, poor overall growth, and dysmorphic facial features. Brain imaging shows pontocerebellar hypoplasia, thin corpus callosum, cerebral atrophy, and delayed myelination (summary by Somashekar et al., 2021). For a phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

Radio-Tartaglia syndrome (RATARS) is a neurodevelopmental disorder characterized by global developmental delay with impaired intellectual development, speech delay, and variable behavioral abnormalities. Affected individuals show hypotonia, mild motor difficulties, and craniofacial dysmorphism. Brain imaging may show nonspecific defects; rare patients have seizures or pyramidal signs. A subset of individuals may have congenital heart defects, precocious puberty, and obesity in females. Some of the features are similar to those observed in patients with chromosome 1p36 deletion syndrome (607872) (summary by Radio et al., 2021).

Infantile-onset multisystem neurologic, endocrine, and pancreatic disease-2 (IMNEPD2) is an autosomal recessive multisystemic disorder characterized by cholestatic hepatitis, poor feeding associated with poor overall growth, and hypoglycemia apparent from infancy. Most, but not all, patients have variable global developmental delay. Additional common features include sensorineural deafness, retinal abnormalities with visual defects, and hypotonia. Some patients have endocrine abnormalities, including hyperinsulinemic hypoglycemia, pancreatic dysfunction, hypothyroidism, and primary amenorrhea. Additional features may include hypertriglyceridemia, anemia, proteinuria, increased lactate, and recurrent infections. Brain imaging often shows dysmyelination, thin corpus callosum, cerebral atrophy, and white matter abnormalities. Although the clinical manifestations and severity of the disorder are highly variable, death in early childhood may occur (summary by Williams et al., 2019 and Zeiad et al., 2021). For a discussion of genetic heterogeneity of IMNEPD, see IMNEPD1 (616263).

White-Kernohan syndrome (WHIKERS) is a neurodevelopmental disorder characterized by global developmental delay with variably impaired intellectual development, hypotonia, and characteristic facial features. Some patients may have abnormalities of other systems, including genitourinary and skeletal (summary by White et al., 2021).

Otospondylomegaepiphyseal dysplasia (OSMED) is characterized by sensorineural hearing loss, enlarged epiphyses, disproportionate shortness of the limbs, abnormalities in vertebral bodies, and typical facial features (summary by Harel et al., 2005).

X-linked syndromic intellectual developmental disorder with pigmentary mosaicism and coarse facies (MRXSPF) is characterized by a phenotypic triad of severe developmental delay, coarse facial dysmorphisms, and Blaschkoid pigmentary mosaicism. Additional clinical features may include epilepsy, orthopedic abnormalities, hypotonia, and growth abnormalities. The disorder affects both males and females (Villegas et al., 2019; Diaz et al., 2020).

Luo-Schoch-Yamamoto syndrome (LUSYAM) is a neurodevelopmental disorder characterized by global developmental delay and impaired intellectual development apparent from infancy. Affected individuals have delayed walking, early-onset seizures, hypotonia, dysmorphic facial features, and white matter abnormalities on brain imaging (Luo et al., 2021).

VISS syndrome is a generalized connective tissue disorder characterized by early-onset thoracic aortic aneurysm and other connective tissue findings, such as aneurysm and tortuosity of other arteries, joint hypermobility, skin laxity, and hernias, as well as craniofacial dysmorphic features, structural cardiac defects, skeletal anomalies, and motor developmental delay (Van Gucht et al., 2021). Immune dysregulation has been observed in some patients (Ziegler et al., 2021).

Short-rib thoracic dysplasia-21 (SRTD21) is characterized by rhizomelic limb shortening with bowing of long bones and metaphyseal abnormalities, narrow chest with short broad ribs, and trident pelvis. Other features include hypotonia and global developmental delay, with corpus callosum hypoplasia and cerebellar vermis abnormalities on brain imaging, which may show the 'molar tooth' sign (Hammarsjo et al., 2017). For a general phenotypic description and discussion of genetic heterogeneity of SRTD, see SRTD1 (208500). Mutation in the KIAA0753 gene also causes orofaciodigital syndrome (OFD15; 617127) and Joubert syndrome (JBTS28; 619476), phenotypes with features overlapping those of SRTD21.

Neurodevelopmental disorder with hypotonia and dysmorphic facies (NEDHYDF) is characterized by global developmental delay and hypotonia apparent from birth. Affected individuals have variably impaired intellectual development, often with speech delay and delayed walking. Seizures are generally not observed, although some patients may have single seizures or late-onset epilepsy. Most patients have prominent dysmorphic facial features. Additional features may include congenital cardiac defects (without arrhythmia), nonspecific renal anomalies, joint contractures or joint hyperextensibility, dry skin, and cryptorchidism. There is significant phenotypic variability in both the neurologic and extraneurologic manifestations (summary by Tan et al., 2022).

Biliary, renal, neurologic, and skeletal syndrome (BRENS) is an autosomal recessive complex ciliopathy with multisystemic manifestations. The most common presentation is severe neonatal cholestasis that progresses to liver fibrosis and cirrhosis. Most patients have additional clinical features suggestive of a ciliopathy, including postaxial polydactyly, hydrocephalus, retinal abnormalities, and situs inversus. Additional features of the syndrome may include congenital cardiac defects, echogenic kidneys with renal failure, ocular abnormalities, joint hyperextensibility, and dysmorphic facial features. Some patients have global developmental delay. Brain imaging typically shows dilated ventricles, hypomyelination, and white matter abnormalities, although some patients have been described with abnormal pituitary development (summary by Shaheen et al., 2020 and David et al., 2020).

Developmental delay with or without intellectual impairment or behavioral abnormalities (DDIB) is an autosomal dominant disorder with a nonspecific phenotype of developmental delay. Additional features may include neonatal feeding problems, hypotonia, and dysmorphic facial features (Dulovic-Mahlow et al., 2019; van Woerden et al., 2021).

Joubert syndrome-40 (JBTS40) is an autosomal recessive neurodevelopmental disorder characterized by developmental delay, postaxial polydactyly, subtle midline notching or clefting of the upper lip, hypotonia, and the 'molar tooth sign' on brain imaging. Affected individuals do not exhibit retinal or renal anomalies, or significant obesity (Zhongling et al., 2021). For a discussion of genetic heterogeneity of Joubert syndrome, see JBTS1 (213300).

Neurodevelopmental disorder with hearing loss and spasticity (NEDHLS) is characterized by hearing loss, global developmental delay/impaired intellectual development, spastic-dystonic cerebral palsy, focal or generalized epilepsy, and microcephaly. Some children present with hypotonia (Richard et al., 2021).

Marbach-Schaaf neurodevelopmental syndrom (MASNS) is characterized by global developmental delay with speech delay and behavioral abnormalities, including autism spectrum disorder and ADHD. Affected individuals also show movement disorders, such as dyspraxia and apraxia. More variable features include high pain tolerance, sleep disturbances, and variable nonspecific dysmorphic features (summary by Marbach et al., 2021).

Rauch-Steindl syndrome (RAUST) is characterized by poor pre- and postnatal growth, sometimes with short stature and small head circumference, characteristic dysmorphic facial features, and variable developmental delay with delayed motor and speech acquisition and impaired intellectual function that can be mild. Other features may include hypotonia and behavioral abnormalities. The phenotype represents a mild form of Wolf-Hirschhorn syndrome (WHS; 194190), which is a contiguous gene deletion syndrome caused by heterozygous deletion of several genes on chromosome 4p16. The clinical features of RAUST are similar to but milder than those of WHS, with less severe dysmorphic facial features, less severe developmental disabilities in general, and absence of a seizure disorder. The phenotype and expressivity of RAUST is highly variable (summary by Rauch et al., 2001; Zanoni et al., 2021).

A rare mitochondrial oxidative phosphorylation disorder with decreased respiratory complex I and IV enzyme activity. Characteristics of this disease hypotonia, global developmental delay, neonatal onset of progressive pectus carinatum without other skeletal abnormalities, poor growth, sensorineural hearing loss, dysmorphic features and brain abnormalities such as cerebral atrophy, quadriventricular dilatation and thin corpus callosum posteriorly.

A rare genetic multiple congenital anomalies/dysmorphic syndrome with characteristics of global developmental delay and intellectual disability, progressive spondyloepimetaphyseal dysplasia, short stature, short fourth metatarsals and dysmorphic craniofacial features (including microcephaly, hypertelorism, epicanthal folds, mild ptosis, strabismus, malar hypoplasia, short nose, depressed nasal bridge, full lips, small, low-set ears and short neck). Craniosynostosis, generalized hypotonia, as well as asymmetry of the cerebral hemispheres and mild thinning of the corpus callosum on brain imaging have also been described.

Carey-Fineman-Ziter syndrome-1 (CFZS1) is a multisystem congenital disorder characterized by hypotonia, Moebius sequence (bilateral congenital facial palsy with impairment of ocular abduction), Pierre Robin complex (micrognathia, glossoptosis, and high-arched or cleft palate), delayed motor milestones, and failure to thrive. More variable features include dysmorphic facial features, brain abnormalities, and intellectual disability. It has been postulated that many clinical features in CFZS1 may be secondary effects of muscle weakness during development or brainstem anomalies (summary by Pasetti et al., 2016). Di Gioia et al. (2017) determined that CFZS1 represents a slowly progressive congenital myopathy resulting from a defect in myoblast fusion. Genetic Heterogeneity of Carey-Fineman-Ziter Syndrome Carey-Fineman-Ziter syndrome-2 (CFZS2) is caused by mutation in the MYMX gene (619912) on chromosome 6p21.

A restrictive dermopathy that has material basis in homozygous or compound heterozygous mutation in the ZMPSTE24 gene on chromosome 1p34.

Bryant-Li-Bhoj neurodevelopmental syndrome-1 (BRYLIB1) is a highly variable phenotype characterized predominantly by moderate to severe global developmental delay with impaired intellectual development, poor or absent speech, and delayed motor milestones. Most patients have hypotonia, although some have peripheral hypertonia. Common features include abnormal head shape, variable dysmorphic facial features, oculomotor abnormalities, feeding problems, and nonspecific brain imaging abnormalities. Additional features may include hearing loss, seizures, short stature, and mild skeletal defects (summary by Bryant et al., 2020). Genetic Heterogeneity of Bryant-Li-Bhoj Neurodevelopmental Syndrome See also BRYLIB2 (619721), caused by heterozygous mutation in the H3F3B gene (601058).

Teebi hypertelorism syndrome-2 (TBHS2) is characterized primarily by hypertelorism, prominent forehead, thick and broad eyebrows, and short nose with depressed nasal root and broad nasal tip. Other features include thin upper lip, small chin with horizontal crease, and high or cleft palate. Developmental delay and/or impaired intellectual development have been observed in some patients (Li et al., 2021). For a general phenotypic description and a discussion of genetic heterogeneity of Teebi hypertelorism syndrome, see TBHS1 (145420).

Combined oxidative phosphorylation deficiency-55 (COXPD55) is characterized by global developmental delay, hypotonia, short stature, and impaired intellectual development with speech disabilities in childhood. Indolent progressive external ophthalmoplegia phenotype has been described in 1 patient (summary by Olahova et al., 2021). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Immunodeficiency-94 with autoinflammation and dysmorphic facies (IMD94) is a systemic immunologic disorder with onset in early infancy. Primary features include lymphadenopathy, autoinflammation, immunodeficiency with hypogammaglobulinemia, and dysmorphic facial features. Intellectual development is normal and serum IgE is not elevated. The disease results from constitutive activation of the IL6 signaling cascade, resulting in immune dysregulation and a hyperinflammatory state (summary by Materna-Kiryluk et al., 2021).

Tessadori-Bicknell-van Haaften neurodevelopmental syndrome-2 (TEBIVANED2) is characterized by poor overall growth, profound global developmental delay with absent speech, and characteristic dysmorphic facial features, including hypertelorism, abnormal nose, and wide mouth (Tessadori et al., 2020). For a discussion of genetic heterogeneity of Tessadori-Bicknell-van Haaften neurodevelopmental syndrome, see TEBIVANED1 (619758).

Developmental and epileptic encephalopathy-100 (DEE100) is a severe neurologic disorder characterized by global developmental delay and onset of variable types of seizures in the first months or years of life. Most patients have refractory seizures and show developmental regression after seizure onset. Affected individuals have ataxic gait or inability to walk and severe to profoundly impaired intellectual development, often with absent speech. Additional more variable features may include axial hypotonia, hyperkinetic movements, dysmorphic facial features, and brain imaging abnormalities (summary by Schneider et al., 2021). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Autosomal recessive agammaglobulinemia-8B (AGM8B) is characterized by onset of recurrent infections in early childhood. Laboratory studies of affected individuals show decreased circulating immunoglobulins and decreased peripheral B cells. More variable features may include dysmorphic facies and subtle abnormalities of other immune cells, such as T cells. One patient who developed childhood B-cell acute lymphocytic leukemia (B-ALL) has been described (summary by Ben-Ali et al., 2017).

Neurodevelopmental disorder with neuromuscular and skeletal abnormalities (NEDNMS) is an autosomal recessive disorder characterized by global developmental delay apparent from infancy or early childhood. The severity of the disorder is highly variable. Affected individuals show impaired intellectual development and motor delay associated with either severe hypotonia or hypertonia and spasticity. Most affected individuals have skeletal defects and dysmorphic facial features. Some may have ocular or auditory problems, peripheral neuropathy, behavioral abnormalities, and nonspecific findings on brain imaging (Kurolap et al., 2022).

Tessadori-Bicknell-van Haaften neurodevelopmental syndrome-4 (TEBIVANED4) is characterized by global developmental delay with poor overall growth, variably impaired intellectual development, learning difficulties, distal skeletal anomalies, and dysmorphic facies. Some patients have visual or hearing deficits. The severity and manifestations of the disorder are highly variable (Tessadori et al., 2022). For a discussion of genetic heterogeneity of TEBIVANED, see TEBIVANED1 (619758).

Dworschak-Punetha neurodevelopmental syndrome (DWOPNED) is an autosomal recessive disorder characterized mainly by global developmental delay and mildly impaired intellectual development (IQ range 77 to 85), often with behavioral abnormalities, including autism spectrum disorder and hyperactivity. Some affected individuals may have only speech delay or behavioral manifestations. More variable additional features include optic disc hypoplasia, ptosis, hypo- or hyperpigmented skin lesions, nonspecific dysmorphic facial features, and brain imaging abnormalities of the ventricles or corpus callosum. Of note, not all patients exhibit all features, and there is significant inter- and intrafamilial phenotypic variability (Dworschak et al., 2021).

Chilton-Okur-Chung neurodevelopmental syndrome (CHOCNS) is characterized mainly by global developmental delay with variably impaired intellectual development and occasional speech delay. Most patients have behavioral abnormalities, including autism spectrum disorder, ADHD, and aggression. About half of patients have dysmorphic facial features, and about half have nonspecific brain abnormalities, including thin corpus callosum. Rare involvement of other organ systems may be present. At least 1 child with normal development at age 2.5 years has been reported (Chilton et al., 2020).