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.

Aarskog-Scott syndrome is a genetic disorder that affects the development of many parts of the body, most commonly the head and face, the hands and feet, and the genitals and urinary system (genitourinary tract). This condition mainly affects males, although females may have mild features of the syndrome.\n\nPeople with Aarskog-Scott syndrome often have distinctive facial features, such as widely spaced eyes (hypertelorism), a small nose, a long area between the nose and mouth (philtrum), and a widow's peak hairline. They frequently have mild to moderate short stature during childhood, but their growth usually catches up with that of their peers during puberty. Hand abnormalities are common in this syndrome and include short fingers (brachydactyly), curved pinky fingers (fifth finger clinodactyly), webbing of the skin between some fingers (cutaneous syndactyly), and a single crease across the palm. Affected individuals can also have wide, flat feet with broad, rounded toes. Other abnormalities in people with Aarskog-Scott syndrome include heart defects and a split in the upper lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate).\n\nMost males with Aarskog-Scott syndrome have a shawl scrotum, in which the scrotum surrounds the penis instead of hanging below. Less often, they have undescended testes (cryptorchidism) or a soft out-pouching around the belly-button (umbilical hernia) or in the lower abdomen (inguinal hernia).\n\nThe intellectual development of people with Aarskog-Scott syndrome varies widely. Most individuals with Aarskog-Scott syndrome have normal intelligence; however, some may have mild learning and behavior problems, and in rare cases, severe intellectual disability has been reported.

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.

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.

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 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).

PAFAH1B1-related lissencephaly/subcortical band heterotopia (SBH) comprises a spectrum of severity. Affected newborns typically have mild-to-moderate hypotonia, feeding difficulties, and poor head control. During the first years, neurologic examination typically demonstrates poor visual tracking and response to sounds, axial hypotonia, and mild distal spasticity that can transition over time to more severe spasticity. Seizures occur in more than 90% of individuals with lissencephaly and often include infantile spasms. Seizures are often drug resistant, but even with good seizure control, the best developmental level achieved (excluding the few individuals with partial lissencephaly) is the equivalent of about age three to five months. In individuals with PAFAH1B1-related lissencephaly/SBH, developmental delay ranges from mild to severe. Other findings in PAFAH1B1-related lissencephaly/SBH include feeding issues and aspiration (which may result in need for gastrostomy tube placement), progressive microcephaly, and occasional developmental regression.

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.

Freeman-Sheldon syndrome (FSS), or DA2A, is phenotypically similar to DA1. In addition to contractures of the hands and feet, FSS is characterized by oropharyngeal abnormalities, scoliosis, and a distinctive face that includes a very small oral orifice (often only a few millimeters in diameter at birth), puckered lips, and an H-shaped dimple of the chin; hence, FSS has been called 'whistling face syndrome.' The limb phenotypes of DA1 and FSS may be so similar that they can only be distinguished by the differences in facial morphology (summary by Bamshad et al., 2009). For a general phenotypic description and a discussion of genetic heterogeneity of distal arthrogryposis, see DA1 (108120).

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 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.

Coffin-Lowry syndrome (CLS) is usually characterized by severe-to-profound intellectual disability in males; less severely impaired individuals have been reported. Neuropsychiatric concerns can include behavioral problems, loss of strength, progressive spasticity or paraplegia, sleep apnea, or stroke. Stimulus-induced drop attacks (SIDAs) in which unexpected tactile or auditory stimuli or excitement triggers a brief collapse but no loss of consciousness are present in approximately 20% of affected individuals. Typically SIDAs begin between mid-childhood and the teens. Characteristic facial features may be more apparent with age. Upper-extremity differences may be subtle and include short, soft, fleshy hands with tapered fingers as well as fleshy forearms. Progressive kyphoscoliosis is one of the most difficult aspects of long-term care. Affected females tend to have intellectual disability in the mild-to-moderate range and may also have the typical facial, hand, and skeletal findings noted in males.

Femoral-facial syndrome (FFS), also known as femoral hypoplasia-unusual facies syndrome (FHUFS), is a rare and sporadic multiple congenital anomaly syndrome comprising bilateral femoral hypoplasia and characteristic facial features, such as long philtrum, thin upper lip, micrognathia with or without cleft palate, upward-slanting palpebral fissures, and a short nose with broad tip. Other features, such as renal anomalies, are more variable (summary by Nowaczyk et al., 2010).

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).

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).

Adenylosuccinase deficiency is an autosomal recessive inborn error of metabolism caused by an enzymatic defect in de novo purine synthesis (DNPS) pathway. ADSL deficiency leads to the accumulation of toxic intermediates, including succinyladenosine (S-Ado) and succinylaminoimidazole carboxamide riboside (SAICAr) in body fluids. There are 3 major phenotypic forms of the disorder that correlate with different values of the S-Ado and SAICAr concentration ratios (S-Ado/SAICAr) in the cerebrospinal fluid. These include the most severe fatal neonatal encephalopathy (S-Ado/SAICAr ratio less than 1); childhood form (type I) with severe psychomotor retardation (S-Ado/SAICAr ratio close to 1), and a milder form (type II) with psychomotor retardation or hypotonia (S-Ado/SAICAr ratio greater than 2) (summary by Baresova et al., 2012).

ATP6V0A2-related cutis laxa is characterized by generalized cutis laxa, findings associated with generalized connective tissue disorder, developmental delays, and a variety of neurologic findings including abnormality on brain MRI. At birth, hypotonia, overfolded skin, and distinctive facial features are present and enlarged fontanelles are often observed. During childhood, the characteristic facial features and thick or coarse hair may become quite pronounced. The skin findings decrease with age, although easy bruising and Ehlers-Danlos-like scars have been described in some. In most (not all) affected individuals, cortical and cerebellar malformations are observed on brain MRI. Nearly all affected individuals have developmental delays, seizures, and neurologic regression.

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.

PLA2G6-associated neurodegeneration (PLAN) comprises a continuum of three phenotypes with overlapping clinical and radiologic features: Infantile neuroaxonal dystrophy (INAD). Atypical neuroaxonal dystrophy (atypical NAD). PLA2G6-related dystonia-parkinsonism. INAD usually begins between ages six months and three years with psychomotor regression or delay, hypotonia, and progressive spastic tetraparesis. Many affected children never learn to walk or lose the ability shortly after attaining it. Strabismus, nystagmus, and optic atrophy are common. Disease progression is rapid, resulting in severe spasticity, progressive cognitive decline, and visual impairment. Many affected children do not survive beyond their first decade. Atypical NAD shows more phenotypic variability than INAD. In general, onset is in early childhood but can be as late as the end of the second decade. The presenting signs may be gait instability, ataxia, or speech delay and autistic features, which are sometimes the only evidence of disease for a year or more. Strabismus, nystagmus, and optic atrophy are common. Neuropsychiatric disturbances including impulsivity, poor attention span, hyperactivity, and emotional lability are also common. The course is fairly stable during early childhood and resembles static encephalopathy but is followed by neurologic deterioration between ages seven and 12 years. PLA2G6-related dystonia-parkinsonism has a variable age of onset, but most individuals present in early adulthood with gait disturbance or neuropsychiatric changes. Affected individuals consistently develop dystonia and parkinsonism (which may be accompanied by rapid cognitive decline) in their late teens to early twenties. Dystonia is most common in the hands and feet but may be more generalized. The most common features of parkinsonism in these individuals are bradykinesia, resting tremor, rigidity, and postural instability.

GRIN2A-related speech disorders and epilepsy are characterized by speech disorders in all affected individuals and a range of epilepsy syndromes present in about 90%. Severe speech disorders observed can include dysarthria and speech dyspraxia, and both receptive and expressive language delay/regression; more mildly affected individuals may display subtly impaired intelligibility of conversational speech. Epilepsy features include seizure onset usually between ages three and six years, focal epilepsy with language and/or global developmental regression, and electroencephalogram (EEG) showing continuous spike-and-wave discharges in sleep or very active centrotemporal discharges. Seizure types include seizures associated with aura of perioral paresthesia, focal or focal motor seizures (often evolving to generalized tonic-clonic), and atypical absence seizures. Epilepsy syndromes can include: Landau-Kleffner syndrome (LKS), epileptic encephalopathy with continuous spike-and-wave during sleep (ECSWS), childhood epilepsy with centrotemporal spikes (CECTS), atypical childhood epilepsy with centrotemporal spikes (ACECTS), autosomal dominant rolandic epilepsy with speech dyspraxia (ADRESD), and infantile-onset epileptic encephalopathy.

Neurohypophyseal diabetes insipidus is an autosomal dominant disorder of free water conservation characterized by childhood onset of polyuria and polydipsia. Affected individuals are apparently normal at birth, but characteristically develop symptoms of vasopressin deficiency during childhood (summary by Wahlstrom et al., 2004).

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).

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.

Individuals with trigonocephaly have a keel-shaped forehead with wide biparietal diameter, resulting in a triangular shape of the head. Trigonocephaly results from premature closure of the metopic sutures and usually occurs sporadically (summary by Frydman et al., 1984). Genetic Heterogeneity of Isolated Trigonocephaly Also see trigonocephaly-2 (TRIGNO2; 614485), caused by mutation in the FREM1 gene (608944) on chromosome 9p22.

Schneckenbecken dysplasia (SHNKND) is a perinatally lethal skeletal dysplasia. The German term 'Schneckenbecken' refers to the distinctive, snail-like appearance of the ilia that results from a medial bone projection from the inner iliac margin. Other hallmarks of the disorder include thoracic hypoplasia, severe flattening of the vertebral bodies, and short, thick long bones (summary by Hiraoka et al., 2007).

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).

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).

Microphthalmia with limb anomalies (MLA), also known as Waardenburg anophthalmia syndrome or ophthalmoacromelic syndrome (OAS), is a rare autosomal recessive developmental disorder characterized by unilateral or bilateral microphthalmia, clinical anophthalmia, syndactyly, polydactyly, synostosis, or oligodactyly. Long-bone hypoplasia and renal, venous, and vertebral anomalies may also be present. Impaired intellectual development is present in about half of affected individuals (summary by Tekin et al., 2000, Abouzeid et al., 2011).

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).

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.

Hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC), a neurodevelopmental and neurodegenerative disorder, is characterized by severe progressive sensorimotor neuropathy with resulting hypotonia, areflexia, and amyotrophy, and by variable degrees of dysgenesis of the corpus callosum. Mild-to-severe intellectual disability and "psychotic episodes" during adolescence are observed. Sensory modalities are moderately to severely affected beginning in infancy. The average age of onset of walking is 3.8 years; the average age of loss of walking is 13.8 years; the average age of death is 33 years.

Gomez-Lopez-Hernandez syndrome (GLHS), also known as cerebellotrigeminal dermal dysplasia, is a rare neurocutaneous syndrome classically characterized by the triad of rhombencephalosynapsis, trigeminal anesthesia, often giving rise to corneal opacities, and bilateral parietal or parietooccipital alopecia. However, trigeminal anesthesia is an inconsistent finding (summary by Sukhudyan et al., 2010).

Kabuki syndrome (KS) is characterized by typical facial features (long palpebral fissures with eversion of the lateral third of the lower eyelid; arched and broad eyebrows; short columella with depressed nasal tip; large, prominent, or cupped ears), minor skeletal anomalies, persistence of fetal fingertip pads, mild-to-moderate intellectual disability, and postnatal growth deficiency. Other findings may include: congenital heart defects, genitourinary anomalies, cleft lip and/or palate, gastrointestinal anomalies including anal atresia, ptosis and strabismus, and widely spaced teeth and hypodontia. Functional differences can include: increased susceptibility to infections and autoimmune disorders, seizures, endocrinologic abnormalities (including isolated premature thelarche in females), feeding problems, and hearing loss.

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.

The C syndrome, also known as Opitz trigonocephaly syndrome, is a malformation syndrome characterized by trigonocephaly, severe mental retardation, hypotonia, variable cardiac defects, redundant skin, and dysmorphic facial features, including upslanted palpebral fissures, epicanthal folds, depressed nasal bridge, and low-set, posteriorly rotated ears (summary by Kaname et al., 2007). C syndrome shows phenotypic overlap with Bohring-Opitz syndrome, or C-like syndrome (605039), a disorder with more severe features than C syndrome, caused by heterozygous mutation in the ASXL1 gene (612990) on chromosome 20q11.

Syndrome with characteristics of intellectual deficit associated with progressive spastic quadriplegia, microcephaly, and glaucoma, absence of the eyebrows and eyelashes, and a malformation of the nose. It has been described in two brothers.

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.

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.

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.

Any non-syndromic X-linked intellectual disability in which the cause of the disease is a mutation in the PAK3 gene.

Oculodentodigital dysplasia (ODDD) is characterized by a typical facial appearance and variable involvement of the eyes, dentition, and fingers. Characteristic facial features include a narrow, pinched nose with hypoplastic alae nasi, prominent columella and thin anteverted nares together with a narrow nasal bridge, and prominent epicanthic folds giving the impression of hypertelorism. The teeth are usually small and carious. Typical eye findings include microphthalmia and microcornea. The characteristic digital malformation is complete syndactyly of the fourth and fifth fingers (syndactyly type III) but the third finger may be involved and associated camptodactyly is a common finding (summary by Judisch et al., 1979). Neurologic abnormalities are sometimes associated (Gutmann et al., 1991), and lymphedema has been reported in some patients with ODDD (Brice et al., 2013). See review by De Bock et al. (2013). Genetic Heterogeneity of Oculodentodigital Syndrome An autosomal recessive form of ODDD (257850) is also caused by mutation in the GJA1 gene, but the majority of cases are autosomal dominant.

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.

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).

Nicolaides-Baraitser syndrome (NCBRS) is characterized by sparse scalp hair, prominence of the inter-phalangeal joints and distal phalanges due to decreased subcutaneous fat, characteristic coarse facial features, microcephaly, seizures, and developmental delay / intellectual disability. Seizures are of various types and can be difficult to manage. Developmental delay / intellectual disability (ID) is severe in nearly a half, moderate in a third, and mild in the remainder. Nearly a third never develop speech or language skills.

Trichothiodystrophy is a rare autosomal recessive disorder in which patients have brittle, sulfur-deficient hair that displays a diagnostic alternating light and dark banding pattern, called 'tiger tail banding,' under polarizing microscopy. TTD patients display a wide variety of clinical features, including cutaneous, neurologic, and growth abnormalities. Common additional clinical features are ichthyosis, intellectual/developmental disabilities, decreased fertility, abnormal characteristics at birth, ocular abnormalities, short stature, and infections. There are both photosensitive and nonphotosensitive forms of the disorder (summary by Faghri et al., 2008). Sabinas brittle hair syndrome (211390) is another form of nonphotosensitive TTD. For a discussion of genetic heterogeneity of trichothiodystrophy, see 601675.

Potocki-Shaffer syndrome is a rare contiguous gene deletion syndrome due to haploinsufficiency of the 11p12-p11.2 region and is characterized by craniofacial abnormalities, developmental delay, intellectual disability, multiple exostoses (168500), and biparietal foramina (609597) (summary by Swarr et al., 2010).

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.

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).

Holoprosencephaly (HPE) is the most commonly occurring congenital structural forebrain anomaly in humans. HPE is associated with mental retardation and craniofacial malformations. Considerable heterogeneity in the genetic causes of HPE has been demonstrated (Ming et al., 2002). For general phenotypic information and a discussion of genetic heterogeneity of holoprosencephaly, see HPE1 (236100).

Mandibuloacral dysplasia with type B lipodystrophy (MADB) is a rare autosomal recessive disorder characterized by postnatal growth retardation, craniofacial anomalies such as mandibular hypoplasia, skeletal anomalies such as progressive osteolysis of the terminal phalanges and clavicles, and skin changes such as mottled hyperpigmentation and atrophy. The lipodystrophy is characterized by generalized loss of subcutaneous fat involving the face, trunk, and extremities. Some patients have a progeroid appearance. Metabolic complications associated with insulin resistance have been reported (Schrander-Stumpel et al., 1992; summary by Simha et al., 2003). For a general phenotypic description of lipodystrophy associated with mandibuloacral dysplasia, see MADA (248370).

Congenital melanocytic nevus syndrome is characterized by pigmentary skin defects apparent at birth. Most individuals have 1 or more large or giant lesions greater than 20 cm and up to over 60 cm in diameter, which may cover up to 80% of total body area. These lesions may or may not be hairy. Smaller 'satellite' pigmented lesions numbering in the hundreds may also be present all over the body. Congenital melanocytic nevi (CMN) can be associated with malignant melanoma (see CMM1, 155600), but the risk appears to be low, ranging from 1 to 2% for all individuals, but rising to 10 to 15% in those with very large nevi (greater than 40 cm). A small subset of patients with CMNS have abnormalities of the central nervous system, known as 'neurocutaneous melanosis' or 'neuromelanosis' (249400), which may be symptomatic. Patients with CMNS also tend to have a characteristic facial appearance, including wide or prominent forehead, periorbital fullness, small short nose with narrow nasal bridge, round face, full cheeks, prominent premaxilla, and everted lower lip (summary by Kinsler et al., 2008; Kinsler et al., 2012). Spitz nevi are benign melanocytic melanomas composed of epithelioid or spindle cell melanocytes. They usually present as solitary skin tumors but can occur in multiple patterns, having agminated, dermatomal, and disseminated forms (summary by Sarin et al., 2013). Nevus spilus, also known as speckled lentiginous nevus, is a congenital hyperpigmented patch that progressively evolves, with affected individuals developing dark macules and papules during childhood and adolescence. Over time, nevus spilus may give rise to common lentigines, melanocytic nevi, Spitz nevi, and melanomas (summary by Sarin et al., 2014).

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).

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.

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.

The 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\nAdditional 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\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.

Any non-syndromic X-linked intellectual disability in which the cause of the disease is a mutation in the ZDHHC15 gene.

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.

Lathosterolosis (LATHOS) is an autosomal recessive disorder characterized by a recognizable pattern of multiple congenital anomalies involving axial and appendicular skeleton, liver, central nervous and urogenital systems, and lysosomal storage. It is caused by a defect of cholesterol biosynthesis due to sterol C5-desaturase deficiency (summary by Rossi et al., 2007).

Deficiency of all vitamin K-dependent clotting factors leads to a bleeding tendency that is usually reversed by oral administration of vitamin K. Acquired forms of the disorder can be caused by intestinal malabsorption of vitamin K. Familial multiple coagulation factor deficiency is rare. Clinical symptoms of the disease include episodes of intracranial hemorrhage in the first weeks of life, sometimes leading to a fatal outcome. The pathomechanism is based on a reduced hepatic gamma-carboxylation of glutamic acid residues of all vitamin K-dependent blood coagulation factors, as well as the anticoagulant factors protein C (612283) and protein S (176880). Posttranslational gamma-carboxylation of proteins enables the calcium-dependent attachment of the proteins to the phospholipid bilayer of membranes, an essential prerequisite for blood coagulation. Vitamin K1 acts as a cofactor for the vitamin K-dependent carboxylase in liver microsomes, GGCX. Genetic Heterogeneity of Combined Deficiency of Vitamin K-Dependent Clotting Factors Combined deficiency of vitamin K-dependent clotting factors-2 (VKFCD2; 607473) is caused by mutation in the gene encoding vitamin K epoxide reductase (VKORC1; 608547) on chromosome 16p11.

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.

Spondylometaepiphyseal dysplasia, short limb-hand type is an autosomal recessive disorder with clinical and radiologic features of disproportionate short stature, platyspondyly, abnormal epiphyses and metaphyses, shortening of the lower and upper limbs, short and broad fingers, and premature calcifications. The disorder is progressive with respect to the severity of the bowing of the lower limbs and the appearance of calcifications, with some patients being wheelchair-bound from age 11 years (Bargal et al., 2009).

Bartsocas-Papas syndrome-1 (BPS1) is an autosomal recessive disorder characterized by multiple popliteal pterygia, ankyloblepharon, filiform bands between the jaws, cleft lip and palate, and syndactyly. Early lethality is common, although survival into childhood and beyond has been reported (summary by Mitchell et al., 2012). Genetic Heterogeneity of Bartsocas-Papas Syndrome Bartsocas-Papas syndrome-2 (BPS2) is caused by mutation in the CHUK gene (600664). A less severe form of popliteal pterygium syndrome (PPS; 119500) is caused by mutation in the IRF6 gene (607199).

PEHO is a severe autosomal recessive neurodevelopmental disorder characterized by extreme cerebellar atrophy due to almost total loss of granule neurons. Affected individuals present in early infancy with hypotonia, profoundly delayed psychomotor development, optic atrophy, progressive atrophy of the cerebellum and brainstem, and dysmyelination. Most patients also develop infantile seizures that are often associated with hypsarrhythmia on EEG, and many have peripheral edema (summary by Anttonen et al., 2017).

A rare genetic neurological disease characterized by progressive encephalopathy, early-onset seizures with a hypsarrhythmic pattern, facial and limb edema, severe hypotonia, early arrest of psychomotor development and craniofacial dysmorphism (evolving microcephaly, narrow forehead, short nose, prominent auricles, open mouth, micrognathia), in the absence of neuro-ophthalmic or neuroradiologic findings. Poor visual responsiveness, growth failure and tapering fingers are also associated. There is evidence the disease is caused by homozygous mutation in the CCDC88A gene on chromosome 2p16.

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.

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).

A multisystem malformation syndrome that has been reported in about 10 patients. The clinical features include bilateral anophthalmia, abnormal nares, central nervous system anomalies, and neurodevelopmental delay. Additional features include brachycephaly and other facial anomalies. Non-facial anomalies have also been reported: postaxial polydactyly, genital hypoplasia. All cases reported so far have been sporadic, suggesting that the syndrome may be due to a new dominant mutation.

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).

Molybdenum cofactor deficiency (MoCD) represents a spectrum, with some individuals experiencing significant signs and symptoms in the neonatal period and early infancy (termed early-onset or severe MoCD) and others developing signs and symptoms in childhood or adulthood (termed late-onset or mild MoCD). Individuals with early-onset MoCD typically present in the first days of life with severe encephalopathy, including refractory seizures, opisthotonos, axial and appendicular hypotonia, feeding difficulties, and apnea. Head imaging may demonstrate loss of gray and white matter differentiation, gyral swelling, sulci injury (typically assessed by evaluating the depth of focal lesional injury within the sulci), diffusely elevated T2-weighted signal, and panlobar diffusion restriction throughout the forebrain and midbrain with relative sparring of the brain stem. Prognosis for early-onset MoCD is poor, with about 75% succumbing in infancy to secondary complications of their neurologic disability (i.e., pneumonia). Late-onset MoCD is typically characterized by milder symptoms, such as acute neurologic decompensation in the setting of infection. Episodes vary in nature but commonly consist of altered mental status, dystonia, choreoathetosis, ataxia, nystagmus, and fluctuating hypotonia and hypertonia. These features may improve after resolution of the inciting infection or progress in a gradual or stochastic manner over the lifetime. Brain imaging may be normal or may demonstrate T2-weighted hyperintense or cystic lesions in the globus pallidus, thinning of the corpus callosum, and cerebellar atrophy.

Molybdenum cofactor deficiency (MoCD) represents a spectrum, with some individuals experiencing significant signs and symptoms in the neonatal period and early infancy (termed early-onset or severe MoCD) and others developing signs and symptoms in childhood or adulthood (termed late-onset or mild MoCD). Individuals with early-onset MoCD typically present in the first days of life with severe encephalopathy, including refractory seizures, opisthotonos, axial and appendicular hypotonia, feeding difficulties, and apnea. Head imaging may demonstrate loss of gray and white matter differentiation, gyral swelling, sulci injury (typically assessed by evaluating the depth of focal lesional injury within the sulci), diffusely elevated T2-weighted signal, and panlobar diffusion restriction throughout the forebrain and midbrain with relative sparring of the brain stem. Prognosis for early-onset MoCD is poor, with about 75% succumbing in infancy to secondary complications of their neurologic disability (i.e., pneumonia). Late-onset MoCD is typically characterized by milder symptoms, such as acute neurologic decompensation in the setting of infection. Episodes vary in nature but commonly consist of altered mental status, dystonia, choreoathetosis, ataxia, nystagmus, and fluctuating hypotonia and hypertonia. These features may improve after resolution of the inciting infection or progress in a gradual or stochastic manner over the lifetime. Brain imaging may be normal or may demonstrate T2-weighted hyperintense or cystic lesions in the globus pallidus, thinning of the corpus callosum, and cerebellar atrophy.

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.

Baraitser-Winter cerebrofrontofacial (BWCFF) syndrome is a multiple congenital anomaly syndrome characterized by typical craniofacial features and intellectual disability. Many (but not all) affected individuals have pachygyria that is predominantly frontal, wasting of the shoulder girdle muscles, and sensory impairment due to iris or retinal coloboma and/or sensorineural deafness. Intellectual disability, which is common but variable, is related to the severity of the brain malformations. Seizures, congenital heart defects, renal malformations, and gastrointestinal dysfunction are also common.

A very rare syndrome including short stature, facial dysmorphism, hand abnormalities and shawl scrotum. It has been observed in 16 subjects from five distantly related sibships of a large Kuwaiti Bedouin tribe. The affected patients had no intellectual deficit. Transmitted as an autosomal recessive trait.

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.

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.

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.

The acromesomelic dysplasias are disorders in which there is disproportionate shortening of skeletal elements, predominantly affecting the middle segments (forearms and forelegs) and distal segments (hands and feet) of the appendicular skeleton. Acromesomelic dysplasia-1 (AMD1) is characterized by severe dwarfism (height below 120 cm) with shortening of the middle and distal segments of the limbs. This condition is usually diagnosed at birth and becomes more obvious in the first 2 years of life. X-rays show short broad fingers, square flat feet, and shortening of the long bones (particularly the forearms). The radius is bowed; the ulna is shorter than the radius, and its distal end is occasionally hypoplastic. The skull is dolichocephalic and a shortness of the trunk, with decreased vertebral height and narrowing of the lumbar interpedicular distances, is consistently observed. Facial appearance and intelligence are normal (summary by Faivre et al., 2000). Genetic Heterogeneity of Acromesomelic Dysplasia Additional autosomal recessive forms of acromesomelic dysplasia include acromesomelic dysplasia-2A (200700), -2B (228900), and -2C (201250), all caused by mutation in the GDF5 gene (601146) on chromosome 20q11; AMD3 (200700), caused by mutation in the BMPR1B gene (603248) on chromosome 4q22; and AMD4 (619636), caused by mutation in the PRKG2 gene (601591) on chromosome 4q21. An autosomal dominant form of acromesomelic dysplasia has also been reported (see 112910).

Mandibulofacial dysostosis with microcephaly (MFDM) is characterized by malar and mandibular hypoplasia, microcephaly (congenital or postnatal onset), intellectual disability (mild, moderate, or severe), malformations of the external ear, and hearing loss that is typically conductive. Associated craniofacial malformations may include cleft palate, choanal atresia, zygomatic arch cleft (identified on cranial CT scan), and facial asymmetry. Other relatively common findings (present in 25%-35% of individuals) can include cardiac anomalies, thumb anomalies, esophageal atresia/tracheoesophageal fistula, short stature, spine anomalies, and epilepsy.

Congenital glutamine deficiency (GLND) 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).

Desmosterolosis is a rare autosomal recessive disorder characterized by multiple congenital anomalies and elevated levels of the cholesterol precursor desmosterol in plasma, tissue, and cultured cells (summary by Waterham et al., 2001).

Pierpont syndrome (PRPTS) is a multiple congenital anomaly syndrome associated with learning disability. Key features include distinctive facial characteristics, especially when smiling, plantar fat pads, and other limb anomalies (summary by Burkitt Wright et al., 2011).

Penttinen syndrome (PENTT) is characterized by a prematurely aged appearance involving lipoatrophy and epidermal and dermal atrophy, as well as hypertrophic lesions that resemble scars, thin hair, proptosis, underdeveloped cheekbones, and marked acroosteolysis (Johnston et al., 2015).

Bleeding problems are common in the vascular type of Ehlers-Danlos syndrome and are caused by unpredictable tearing (rupture) of blood vessels and organs. These complications can lead to easy bruising, internal bleeding, a hole in the wall of the intestine (intestinal perforation), or stroke. During pregnancy, women with vascular Ehlers-Danlos syndrome may experience rupture of the uterus. Additional forms of Ehlers-Danlos syndrome that involve rupture of the blood vessels include the kyphoscoliotic, classical, and classical-like types.\n\nOther types of Ehlers-Danlos syndrome have additional signs and symptoms. The cardiac-valvular type causes severe problems with the valves that control the movement of blood through the heart. People with the kyphoscoliotic type experience severe curvature of the spine that worsens over time and can interfere with breathing by restricting lung expansion. A type of Ehlers-Danlos syndrome called brittle cornea syndrome is characterized by thinness of the clear covering of the eye (the cornea) and other eye abnormalities. The spondylodysplastic type features short stature and skeletal abnormalities such as abnormally curved (bowed) limbs. Abnormalities of muscles, including hypotonia and permanently bent joints (contractures), are among the characteristic signs of the musculocontractural and myopathic forms of Ehlers-Danlos syndrome. The periodontal type causes abnormalities of the teeth and gums.\n\nMany people with the Ehlers-Danlos syndromes have soft, velvety skin that is highly stretchy (elastic) and fragile. Affected individuals tend to bruise easily, and some types of the condition also cause abnormal scarring. People with the classical form of Ehlers-Danlos syndrome experience wounds that split open with little bleeding and leave scars that widen over time to create characteristic "cigarette paper" scars. The dermatosparaxis type of the disorder is characterized by loose skin that sags and wrinkles, and extra (redundant) folds of skin may be present.\n\nAn unusually large range of joint movement (hypermobility) occurs in most forms of Ehlers-Danlos syndrome, and it is a hallmark feature of the hypermobile type. Infants and children with hypermobility often have weak muscle tone (hypotonia), which can delay the development of motor skills such as sitting, standing, and walking. The loose joints are unstable and prone to dislocation and chronic pain. In the arthrochalasia type of Ehlers-Danlos syndrome, infants have hypermobility and dislocations of both hips at birth.\n\nThe various forms of Ehlers-Danlos syndrome have been classified in several different ways. Originally, 11 forms of Ehlers-Danlos syndrome were named using Roman numerals to indicate the types (type I, type II, and so on). In 1997, researchers proposed a simpler classification (the Villefranche nomenclature) that reduced the number of types to six and gave them descriptive names based on their major features. In 2017, the classification was updated to include rare forms of Ehlers-Danlos syndrome that were identified more recently. The 2017 classification describes 13 types of Ehlers-Danlos syndrome.\n\nEhlers-Danlos syndrome is a group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Defects in connective tissues cause the signs and symptoms of these conditions, which range from mildly loose joints to life-threatening complications.

About half of all people with trichothiodystrophy have a photosensitive form of the disorder, which causes them to be extremely sensitive to ultraviolet (UV) rays from sunlight. They develop a severe sunburn after spending just a few minutes in the sun. However, for reasons that are unclear, they do not develop other sun-related problems such as excessive freckling of the skin or an increased risk of skin cancer. Many people with trichothiodystrophy report that they do not sweat.\n\nIntellectual disability and delayed development are common in people with trichothiodystrophy, although most affected individuals are highly social with an outgoing and engaging personality. Some people with trichothiodystrophy have brain abnormalities that can be seen with imaging tests. A common neurological feature of this disorder is impaired myelin production (dysmyelination). Myelin is a fatty substance that insulates nerve cells and promotes the rapid transmission of nerve impulses.\n\nTrichothiodystrophy is also associated with recurrent infections, particularly respiratory infections, which can be life-threatening. People with trichothiodystrophy may have abnormal red blood cells, including red blood cells that are smaller than normal. They may also have elevated levels of a type of hemoglobin called A2, which is a protein found in red blood cells. Other features of trichothiodystrophy can include dry, scaly skin (ichthyosis); abnormalities of the fingernails and toenails; clouding of the lens in both eyes from birth (congenital cataracts); poor coordination; and skeletal abnormalities including degeneration of both hips at an early age.\n\nMothers of children with trichothiodystrophy may experience problems during pregnancy including pregnancy-induced high blood pressure (preeclampsia) and a related condition called HELLP syndrome that can damage the liver. Babies with trichothiodystrophy are at increased risk of premature birth, low birth weight, and slow growth. Most children with trichothiodystrophy have short stature compared to others their age. \n\nThe signs and symptoms of trichothiodystrophy vary widely. Mild cases may involve only the hair. More severe cases also cause delayed development, significant intellectual disability, and recurrent infections; severely affected individuals may survive only into infancy or early childhood.\n\nIn people with trichothiodystrophy, tests show that the hair is lacking sulfur-containing proteins that normally gives hair its strength. A cross section of a cut hair shows alternating light and dark banding that has been described as a "tiger tail."\n\nTrichothiodystrophy, commonly called TTD, is a rare inherited condition that affects many parts of the body. The hallmark of this condition is hair that is sparse and easily broken. 

MBD5 haploinsufficiency is a neurodevelopmental disorder characterized by developmental delay, intellectual disability, severe speech impairment, seizures, sleep disturbances, and abnormal behaviors. Most children lack speech entirely or have single words, short phrases, or short sentences. Seizures are present in more than 80% of children; onset is usually around age two years. Sleep disturbances, present in about 90%, can result in excessive daytime drowsiness. Abnormal behaviors can include autistic-like behaviors (80%) and self-injury and aggression (>60%).

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.

Diamond-Blackfan anemia (DBA) is characterized by a profound normochromic and usually macrocytic anemia with normal leukocytes and platelets, congenital malformations in up to 50%, and growth deficiency in 30% of affected individuals. The hematologic complications occur in 90% of affected individuals during the first year of life. The phenotypic spectrum ranges from a mild form (e.g., mild anemia or no anemia with only subtle erythroid abnormalities, physical malformations without anemia) to a severe form of fetal anemia resulting in nonimmune hydrops fetalis. DBA is associated with an increased risk for acute myelogenous leukemia (AML), myelodysplastic syndrome (MDS), and solid tumors including osteogenic sarcoma.

BCARD syndrome is an autosomal recessive connective tissue disorder characterized by bone abnormalities, including low bone mineral density, scoliosis, contractures of the fingers and other joints, prominent knees, and rare pathologic fractures; cataract and other ocular abnormalities, including high myopia, optically empty vitreous, and risk for retinal detachment; risk of arterial rupture due to vascular aneurysm or dissection; and sensorineural deafness. Affected individuals also exhibit recognizable craniofacial dysmorphisms, and variable skin features have been observed, including reduced palmar creases, soft skin with easy bruising, and blistering. Developmental delay, which is present in most patients, may be attributable to sensory deficits or medical complications (Ewans et al., 2019).

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.

CASK disorders include a spectrum of phenotypes in both females and males. Two main types of clinical presentation are seen: Microcephaly with pontine and cerebellar hypoplasia (MICPCH), generally associated with pathogenic loss-of-function variants in CASK. X-linked intellectual disability (XLID) with or without nystagmus, generally associated with hypomorphic CASK pathogenic variants. MICPCH is typically seen in females with moderate-to-severe intellectual disability, progressive microcephaly with or without ophthalmologic anomalies, and sensorineural hearing loss. Most are able to sit independently; 20%-25% attain the ability to walk; language is nearly absent in most. Neurologic features may include axial hypotonia, hypertonia/spasticity of the extremities, and dystonia or other movement disorders. Nearly 40% have seizures by age ten years. Behaviors may include sleep disturbances, hand stereotypies, and self biting. MICPCH in males may occur with or without severe epileptic encephalopathy in addition to severe-to-profound developmental delay. When seizures are present they occur early and may be intractable. In individuals and families with milder (i.e., hypomorphic) pathogenic variants, the clinical phenotype is usually that of XLID with or without nystagmus and additional clinical features. Males have mild-to-severe intellectual disability, with or without nystagmus and other ocular features. Females typically have normal intelligence with some displaying mild-to-severe intellectual disability with or without ocular features.

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).

3q29 microduplication syndrome (also known as 3q29 duplication syndrome) is a condition that results from the copying (duplication) of a small piece of chromosome 3 in each cell. The duplication occurs on the long (q) arm of the chromosome at a position designated q29.\n\nThe features associated with 3q29 microduplication syndrome vary widely. Some individuals with this chromosomal change have very mild or no related signs and symptoms, and the duplication is discovered because they undergo genetic testing only after a family member is diagnosed. Other people with a 3q29 microduplication have delayed development (particularly speech delay) and intellectual disability or learning difficulties. Although most affected individuals have no major birth defects, eye abnormalities, heart defects, and an unusually small head (microcephaly) can occur. 3q29 microduplication syndrome may increase the likelihood of being overweight or having obesity, although it is hard to determine whether these weight issues are caused by the duplication.

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.

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). CPHD8 (620303) is caused by mutation in the ROBO1 gene (602430).

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).

CDG IIe is caused by a mutation that impairs the integrity of the conserved oligomeric Golgi (COG) complex and alters Golgi trafficking, resulting in the disruption of multiple glycosylation pathways. For a general discussion of CDGs, see CDG1A (212065).

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.

The features of frontofacionasal dysplasia include blepharophimosis, lower lid lagophthalmos, primary telecanthus, S-shaped palpebral fissures, facial hypoplasia, eyelid coloboma, widow's peak, cranium bifidum occultum, frontal lipoma, nasal hypoplasia, deformed nostrils, bifid nose, and cleft of lip, premaxilla, palate, and uvula (White et al., 1991). Also see frontonasal dysplasia (136760).

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).

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.

The cardinal features of chromosome 6q11-q14 interstitial deletions include hypotonia, short stature, skeletal/limb anomalies, umbilical hernia, and urinary tract anomalies, as well as characteristic facial features including upslanting palpebral fissures, low-set and/or dysplastic ears, and high-arched palate (summary by Wang et al., 2009).

The chromosome 16p12.2-p11.2 deletion syndrome is characterized phenotypically by dysmorphic facial features, feeding difficulties, recurrent ear infections, developmental delay, and cognitive impairment. Additional features, such as heart defects and short stature, are variable (Ballif et al., 2007; Battaglia et al., 2009). The pericentric region of chromosome 16, specifically involving 16p12-p11, is a structurally complex region enriched in repetitive sequence elements, rendering this region susceptible to deletion or rearrangement (Ballif et al., 2007). There are several phenotypes associated with variation in this region: see 611913 for a deletion or duplication at 16p11.2 associated with autism; see 136570 for discussion of a recurrent 520-kb deletion at 16p12.1 associated with developmental delay and craniofacial dysmorphism; and see 613444 for a 220-kb deletion at 16p11.2 associated with isolated severe early-onset obesity and obesity with developmental delay. Battaglia et al. (2009) emphasized that the region at chromosome 16p11.2 that confers susceptibility to autism (AUTS14; see 611913) is located more centromeric to and is distinct from the 16p12.2-p11.2 region involved in the multiple congenital anomalies and intellectual disability phenotype.

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).

X-linked dominant chondrodysplasia Chassaing-Lacombe type is a rare genetic bone disorder characterized by chondrodysplasia, intrauterine growth retardation (IUGR), hydrocephaly and facial dysmorphism in the affected males.

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.

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.

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).

The GPAPP-type of chondrodysplasia with joint dislocations is an autosomal recessive disorder characterized by short stature, chondrodysplasia with brachydactyly, congenital joint dislocations, cleft palate, and facial dysmorphism (Vissers et al., 2011).

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.

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.

Hyperphosphatasia with impaired intellectual development syndrome-3 (HPMRS3) is an autosomal recessive disorder characterized by severe intellectual disability, hypotonia with poor motor development, poor speech, and increased serum alkaline phosphatase (summary by Hansen et al., 2013). However, the severity of the disorder can also vary to include more mild intellectual impairment (Krawitz et al., 2013). 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).

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.

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.

The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth: microcephaly and generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet, early-onset intractable epilepsy, and profound developmental delay. Seizures, which can be focal, tonic, and complex partial and can include infantile spasms, appear to stabilize after age two years. Myoclonus of the limbs and eyelids is common; other abnormal movements (dyskinetic, choreiform) may be seen. To date, the diagnosis has been confirmed in 18 individuals from 15 families.

Fibrochondrogenesis is a severe skeletal dysplasia characterized by a flat midface, short long bones, short ribs with broad metaphyses, and vertebral bodies that show distinctive hypoplastic posterior ends and rounded anterior ends, giving the vertebral bodies a pinched appearance on lateral radiographic views. The chest is small, causing perinatal respiratory problems which usually, but not always, result in lethality. Affected individuals who survive the neonatal period have high myopia, mild to moderate hearing loss, and severe skeletal dysplasia (summary by Tompson et al., 2012). For a discussion of genetic heterogeneity of fibrochondrogenesis, see FBCG1 (228520).

Acrocephalopolydactylous dysplasia, or Elejalde syndrome, is a lethal multiple congenital disorder characterized by increased birth weight, globular body with thick skin, organomegaly, and fibrosis in multiple tissues (summary by Phadke et al., 2011).

Microphthalmia with linear skin defects (MLS) syndrome is characterized by unilateral or bilateral microphthalmia and/or anophthalmia and linear skin defects, usually involving the face and neck, which are present at birth and heal with age, leaving minimal residual scarring. Other findings can include a wide variety of other ocular abnormalities (e.g., corneal anomalies, orbital cysts, cataracts), central nervous system involvement (e.g., structural anomalies, developmental delay, infantile seizures), cardiac concerns (e.g., hypertrophic or oncocytic cardiomyopathy, atrial or ventricular septal defects, arrhythmias), short stature, diaphragmatic hernia, nail dystrophy, hearing impairment, and genitourinary malformations. Inter- and intrafamilial variability is described.

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).

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.

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.

Hyperphosphatasia with impaired intellectual development syndrome-2 (HPMRS2) is an autosomal recessive disorder characterized by moderately to severely delayed psychomotor development, facial dysmorphism, brachytelephalangy, and increased serum alkaline phosphatase (hyperphosphatasia). Some patients may have additional features, such as cardiac septal defects or seizures (summary by Krawitz et al., 2012). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of hyperphosphatasia with impaired intellectual development syndrome, see HPMRS1 (239300). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Malan syndrome (MALNS) is clinically characterized by overgrowth, advanced bone age, macrocephaly, and dysmorphic facial features. Patients develop marfanoid habitus, with long and slender body, very low body mass, long narrow face, and arachnodactyly, with age. Impaired intellectual development and behavior anomalies are present (summary by Martinez et al., 2015).

Peroxisome biogenesis disorder-4B (PBD4B) includes the overlapping phenotypes of neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD), which represent milder manifestations of the Zellweger syndrome spectrum (ZSS) of peroxisome biogenesis disorders (PBDs). The clinical course of patients with the NALD and IRD presentation is variable and may include developmental delay, hypotonia, liver dysfunction, sensorineural hearing loss, retinal dystrophy, and visual impairment. Children with the NALD presentation may reach their teens, and those with the IRD presentation may reach adulthood (summary by Waterham and Ebberink, 2012). For a complete phenotypic description and a discussion of genetic heterogeneity of PBD(NALD/IRD), see 601539. Individuals with mutations in the PEX6 gene have cells of complementation group 4 (CG4, equivalent to CG6 and CGC). For information on the history of PBD complementation groups, see 214100.

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.

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).

Lipodystrophies are rare disorders characterized by loss of body fat from various regions and predisposition to metabolic complications of insulin resistance and lipid abnormalities. FPLD7 is an autosomal dominant disorder with a highly variable phenotype. Additional features, including early-onset cataracts and later onset of spasticity of the lower limbs, have been noted in some patients (summary by Garg et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of familial partial lipodystrophy (FPLD), see 151660.

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).

Infantile hypotonia with psychomotor retardation and characteristic facies (IHPRF) is a severe autosomal recessive neurologic disorder with onset at birth or in early infancy. Affected individuals show very poor, if any, normal cognitive development. Some patients are never learn to sit or walk independently (summary by Al-Sayed et al., 2013). Genetic Heterogeneity of Infantile Hypotonia with Psychomotor Retardation and Characteristic Facies See also IHPRF2 (616801), caused by mutation in the UNC80 gene (612636) on chromosome 2q34; and IHPRF3 (616900), caused by mutation in the TBCK gene (616899) on chromosome 4q24.

The musculocontractural type of Ehlers-Danlos syndrome (EDSMC2) is characterized by progressive multisystem fragility-related manifestations, including joint dislocations and deformities; skin hyperextensibility, bruisability, and fragility, with recurrent large subcutaneous hematomas; cardiac valvular, respiratory, gastrointestinal, and ophthalmologic complications; and myopathy, featuring muscle hypoplasia, muscle weakness, and an abnormal muscle fiber pattern in histology in adulthood, resulting in gross motor developmental delay (summary by Muller et al., 2013). For a discussion of genetic heterogeneity of the musculocontractural type of Ehlers-Danlos syndrome, see EDSMC1 (601776).

Verheij syndrome is characterized by growth retardation, delayed psychomotor development, dysmorphic facial features, and skeletal, mainly vertebral, abnormalities. Additional variable features may include coloboma, renal defects, and cardiac defects (summary by Verheij et al., 2009 and Dauber et al., 2013).

Hyperphosphatasia with impaired intellectual development syndrome-4 (HPMRS4) is an autosomal recessive neurologic disorder characterized by severely delayed psychomotor development, impaired intellectual development, lack of speech acquisition, seizures, and dysmorphic facial features. Laboratory studies show increased serum alkaline phosphatase (summary by Howard et al., 2014). 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).

Meckel-Gruber syndrome is a severe autosomal recessive ciliopathy classically defined by the triad of encephalocele, polydactyly, and renal and biliary ductal dysplasia. Clinical heterogeneity exists even within families (summary by Shaheen et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of Meckel syndrome, see MKS1 (249000).

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.

Intellectual developmental disorder with language impairment and with or without autistic features (IDDLA) is a neurodevelopmental disorder characterized by global developmental delay with moderate to severe speech delay that particularly affects expressive speech. Most patients have articulation defects, but frank verbal dyspraxia is not observed. Common dysmorphic features include broad forehead, downslanting palpebral fissures, short nose with broad tip, relative macrocephaly, frontal hair upsweep, and prominent digit pads. Gross motor skills are also delayed. Some patients have autistic features and/or behavioral problems. All reported cases have occurred de novo (review by Le Fevre et al., 2013).

Pontocerebellar hypoplasia type 2E is an autosomal recessive neurodegenerative disorder characterized by profound mental retardation, progressive microcephaly, spasticity, and early-onset epilepsy (summary by Feinstein et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of pontocerebellar hypoplasia type 2, see PCH2A (277470).

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).

ADNP-related disorder is characterized by hypotonia, severe speech and motor delay, mild-to-severe intellectual disability, and characteristic facial features (prominent forehead, high anterior hairline, wide and depressed nasal bridge, and short nose with full, upturned nasal tip) based on a cohort of 78 individuals. Features of autism spectrum disorder are common (stereotypic behavior, impaired social interaction). Other common findings include additional behavioral problems, sleep disturbance, brain abnormalities, seizures, feeding issues, gastrointestinal problems, visual dysfunction (hypermetropia, strabismus, cortical visual impairment), musculoskeletal anomalies, endocrine issues including short stature and hormonal deficiencies, cardiac and urinary tract anomalies, and hearing loss.

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).

CHOPS syndrome is a disorder involving multiple abnormalities that are present from birth (congenital). The name "CHOPS" is an abbreviation for a list of features of the disorder including cognitive impairment, coarse facial features, heart defects, obesity, lung (pulmonary) involvement, short stature, and skeletal abnormalities.\n\nChildren with CHOPS syndrome have intellectual disability and delayed development of skills such as sitting and walking. Characteristic facial features include a round face; thick hair; thick eyebrows that grow together in the middle (synophrys); wide-set, bulging eyes with long eyelashes; a short nose; and down-turned corners of the mouth.\n\nMost affected individuals are born with a heart defect called patent ductus arteriosus (PDA). The ductus arteriosus is a connection between two major arteries, the aorta and the pulmonary artery. This connection is open during fetal development and normally closes shortly after birth. However, the ductus arteriosus remains open, or patent, in babies with PDA. If untreated, this heart defect causes infants to breathe rapidly, feed poorly, and gain weight slowly; in severe cases, it can lead to heart failure. Multiple heart abnormalities have sometimes been found in children with CHOPS syndrome. In addition to PDA, affected individuals may have ventricular septal defect, which is a defect in the muscular wall (septum) that separates the right and left sides of the heart's lower chamber.\n\nPeople with CHOPS syndrome have abnormalities of the throat and airways that cause momentary cessation of breathing while asleep (obstructive sleep apnea). These abnormalities can also cause affected individuals to breathe food or fluids into the lungs accidentally, which can lead to a potentially life-threatening bacterial lung infection (aspiration pneumonia) and chronic lung disease. Affected individuals are shorter than more than 97 percent of their peers and are overweight for their height. They also have skeletal differences including unusually short fingers and toes (brachydactyly) and abnormally-shaped spinal bones (vertebrae).\n\nOther features that can occur in CHOPS syndrome include a small head size (microcephaly); hearing loss; clouding of the lens of the eye (cataract); a single, horseshoe-shaped kidney; and, in affected males, undescended testes (cryptorchidism).

Complex lethal osteochondrodysplasia of the Symoens-Barnes-Gistelinck type is characterized by severe skeletal osteopenia, microcephaly, multiple fractures, and congenital anomalies including ascites, pleural effusion, and intracranial ventriculomegaly (Symoens et al., 2015).

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.

EVEN-plus syndrome (EVPLS) is characterized by prenatal-onset short stature, vertebral and epiphyseal changes, microtia, midface hypoplasia with flat nose and triangular nares, cardiac malformations, and other findings including anal atresia, hypodontia, and aplasia cutis. The features overlap those reported in patients with CODAS syndrome (600373; Royer-Bertrand et al., 2015).

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

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).

Au-Kline syndrome is characterized by developmental delay and hypotonia with moderate-to-severe intellectual disability, and typical facial features that include long palpebral fissures, ptosis, shallow orbits, large and deeply grooved tongue, broad nose with a wide nasal bridge, and downturned mouth. There is frequently variable autonomic dysfunction (gastrointestinal dysmotility, high pain threshold, heat intolerance, recurrent fevers, abnormal sweating). Congenital heart disease, hydronephrosis, palate abnormalities, and oligodontia are also reported in the majority of affected individuals. Additional complications can include craniosynostosis, feeding difficulty, vision issues, osteopenia, and other skeletal anomalies.

The Cincinnati type of acrofacial dysostosis is a ribosomopathy characterized by a spectrum of mandibulofacial dysostosis phenotypes, with or without extrafacial skeletal defects (Weaver et al., 2015). In addition, a significant number of neurologic abnormalities have been reported, ranging from mild delays to refractory epilepsy, as well as an increased incidence of congenital heart defects, primarily septal in nature (Smallwood et al., 2023).

Hypomyelinating leukodystrophy-10 (HLD10) is an autosomal recessive neurologic disorder characterized by postnatal progressive microcephaly, severely delayed psychomotor development, and hypomyelination on brain imaging (summary by Nakayama et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of HLD, see 312080.

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.

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).

The Nishimura type of spondyloepiphyseal dysplasia (SEDN) is characterized by disproportionate short stature with short limbs, small hands and feet, and midface hypoplasia with small nose. Radiologic hallmarks include mild spondylar dysplasia, delayed epiphyseal ossification of the hip and knee, and severe brachydactyly with cone-shaped phalangeal epiphyses (Grigelioniene et al., 2019).

Periventricular nodular heterotopia-7 (PVNH7) is a neurologic disorder characterized by abnormal neuronal migration during brain development resulting in delayed psychomotor development and intellectual disability; some patients develop seizures. Other features include cleft palate and 2-3 toe syndactyly (summary by Broix et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of periventricular heterotopia, see 300049.

Harel-Yoon syndrome is a syndromic neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, truncal hypotonia, spasticity, and peripheral neuropathy. Other more variable features such as optic atrophy may also occur. Laboratory studies in some patients show evidence of mitochondrial dysfunction (summary by Harel et al., 2016).

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).

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.

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).

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).

Distal chromosome 19q13.11 deletion syndrome is an autosomal dominant neurodevelopmental disorder characterized by poor overall growth, slender habitus, microcephaly, delayed development, intellectual disability with poor or absent speech, and feeding difficulties. Additional features include dysmorphic facies, signs of ectodermal dysplasia, hand and foot anomalies, and genitourinary anomalies, particularly in males (summary by Chowdhury et al., 2014).

A brain disorder caused by pathogenic variants in NFIA that is characterized by developmental delay, corpus callosum agenesis/hypoplasia and craniofacial dysmorphism, such as macrocephaly (caused by hydrocephalus or ventriculomegaly), low-set ears, anteverted nostrils and micrognathia. Urinary tract defects (e.g. vesicoureteral reflux, urinary incontinence) are also frequently associated. Other reported variable manifestations include hypotonia, tethered spinal cord, Chiari type I malformation and seizures.

Neurodevelopmental disorder with progressive microcephaly, spasticity, and brain anomalies (NDMSBA) is an autosomal recessive neurodevelopmental disorder characterized by infantile onset of progressive microcephaly and spasticity and severe global developmental delay resulting in profoundly impaired intellectual development and severely impaired or absent motor function. More variable features include seizures and optic atrophy. Brain imaging may show myelinating abnormalities and white matter lesions consistent with a leukoencephalopathy, as well as structural anomalies, including thin corpus callosum, gyral abnormalities, and cerebral or cerebellar atrophy. Some patients die in early childhood (summary by Falik Zaccai et al., 2017 and Hall et al., 2017).

Congenital heart defects and skeletal malformations syndrome (CHDSKM) is characterized by atrial and ventricular septal defects, with aortic root dilation in adulthood. Skeletal defects are variable and include pectus excavatum, scoliosis, and finger contractures, and some patients exhibit joint laxity. Failure to thrive is observed during infancy and early childhood (Wang et al., 2017).

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).

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.

Hyperphosphatasia with impaired intellectual development syndrome-1 (HPMRS1) is an autosomal recessive disorder characterized by impaired intellectual development, various neurologic abnormalities such as seizures and hypotonia, and hyperphosphatasia. Other features include facial dysmorphism and variable degrees of brachytelephalangy (summary by Krawitz et al., 2010). The disorder is caused by a defect in glycosylphosphatidylinositol biosynthesis; see GPIBD1 (610293). Genetic Heterogeneity of Hyperphosphatasia with Impaired Intellectual Development Syndrome See also HPMRS2 (614749), caused by mutation in the PIGO gene (614730) on chromosome 9p13; HPMRS3 (614207), caused by mutation in the PGAP2 gene (615187) on chromosome 11p15; HPMRS4 (615716), caused by mutation in the PGAP3 gene (611801) on chromosome 17q12; HPMRS5 (616025), caused by mutation in the PIGW gene (610275) on chromosome 17q12; and HPMRS6 (616809), caused by mutation in the PIGY gene (610662) on chromosome 4q22. Knaus et al. (2018) provided a review of the main clinical features of the different types of HPMRS, noting that some patients have a distinct pattern of facial anomalies that can be detected by computer-assisted comparison, particularly those with mutations in the PIGV and PGAP3 genes. Individuals with HPMRS have variable increased 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 HPMRS and MCAHS (see, e.g., 614080), 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 under the more encompassing term of 'GPI biosynthesis defects' (GPIBD).

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.

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).

Jaberi-Elahi syndrome (JABELS) is an autosomal recessive neurodevelopmental disorder characterized by developmental delay and impaired intellectual development 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). Neurodevelopmental disorder with characteristic facial and ectodermal features and tetraparesis-1 (NEDFET1; 620888) is a similar disorder caused by mutation in the GTPBP1 gene (602245) on chromosome 22q13.

Chung-Jansen syndrome (CHUJANS) is characterized by global developmental delay apparent from infancy, impaired intellectual development or learning difficulties, behavioral abnormalities, dysmorphic features, and obesity. The severity of the phenotype and additional features are variable (summary by Jansen et al., 2018).

Congenital disorder of glycosylation with defective fucosylation is an autosomal recessive multisystem disorder apparent from birth. Affected infants have poor growth, failure to thrive, hypotonia, skeletal anomalies, and delayed psychomotor development with intellectual disability. Additional highly variable congenital defects may be observed (summary by Ng et al., 2018). Genetic Heterogeneity of Congenital Disorders of Glycosylation with Defective Fucosylation See also CDGF2 (618323), caused by mutation in the FCSK gene (608675) on chromosome 16q22. For an overview of congenital disorders of glycosylation (CDG), see CDG1A (212065) and CDG2A (212066).

Baker-Gordon syndrome (BAGOS) is a neurodevelopmental disorder characterized by infantile hypotonia, ophthalmic abnormalities, moderate to profound global developmental delay, poor or absent speech, behavioral abnormalities, hyperkinetic movements, and EEG abnormalities in the absence of overt seizures (summary by Baker et al., 2018).

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.

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.

Pontocerebellar hypoplasia type 10 is an autosomal recessive neurodevelopmental and neurodegenerative disorder characterized by severely delayed psychomotor development, progressive microcephaly, spasticity, seizures, and brain abnormalities, including brain atrophy and delayed myelination. Some patients have dysmorphic features and an axonal sensorimotor neuropathy (summary by Karaca et al., 2014 and Schaffer et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1 (607596).

A rare fatal inborn error of metabolism disorder with characteristics of respiratory distress and severe hypotonia at birth, severe global developmental delay, early-onset intractable seizures, myopathic facies with craniofacial dysmorphism (trigonocephaly/progressive microcephaly, low anterior hairline, arched eyebrows, hypotelorism, strabismus, small nose, prominent philtrum, thin upper lip, high-arched palate, micrognathia, malocclusion), severe, congenital flexion joint contractures and elevated serum creatine kinase levels. Scoliosis, optic atrophy, mild hepatomegaly, and hypoplastic genitalia may also be associated. There is evidence the disease is caused by homozygous or compound heterozygous mutation in the DPM2 gene on chromosome 9q34.

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).

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).

Developmental and epileptic encephalopathy-73 (DEE73) is a neurologic disorder characterized by the onset of refractory seizures in the first months of life. Affected individuals meet almost no developmental milestones: they have hypotonia and are unable to walk, speak, or feed properly. They have poor overall growth with small head circumference and dysmorphic facial features. Additional manifestations include cortical visual impairment with roving eye movements and variable hearing loss (summary by Edvardson et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

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 and epileptic encephalopathy-75 (DEE75) is an autosomal recessive neurodevelopmental and neurodegenerative disorder characterized by onset of severe refractory seizures in the first months of life. Patients often have global developmental delay before the onset of seizures, and thereafter achieve few milestones. EEG usually shows multifocal spikes and hypsarrhythmia, consistent with a clinical diagnosis of West syndrome. They have severely impaired intellectual development with inability to walk, absent speech, and hypotonia with axial hyperreflexia. Brain imaging shows progressive cerebral atrophy, frontal lobe atrophy, white matter abnormalities, and delayed myelination. Since the disorder is due to mitochondrial dysfunction, some patients may develop other organ involvement, including cardiomyopathy or liver and renal dysfunction. Death may occur in childhood (summary by Yin et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

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).

Khan-Khan-Katsanis syndrome (3KS) is an autosomal recessive neurodevelopmental disorder with variable involvement of the ocular, renal, skeletal, and sometimes cardiac systems. Affected individuals present at birth with multiple congenital anomalies, defects in urogenital and limb morphogenesis, poor overall growth with microcephaly, and global developmental delay (summary by Khan et al., 2019).

Autosomal recessive Robinow syndrome-2 (RRS2) is a skeletal dysplasia characterized by postnatal mesomelic short stature and relative macrocephaly as well as dysmorphic facial features, including frontal bossing, hypertelorism, prominent eyes, wide short nose with anteverted nares, and triangular mouth. Variable other congenital anomalies may be present, including omphalocele, ventral hernia, and cardiac anomalies (White et al., 2018). For a discussion of genetic heterogeneity of autosomal recessive Robinow syndrome, see RRS1 (268310).

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 structural brain anomalies and dysmorphic facies (NEDBAF) is a complex syndromic disorder including features of moderate to severe psychomotor delay leading to impaired intellectual development, dysplastic corpus callosum, cortical malformations, hypotonia, dyspraxia, musculoskeletal abnormalities, and feeding difficulties. Seizures occur in about half of patients. Dysmorphic features include wide forehead with frontal bossing and high anterior hairline, prominent eyes with upslanted palpebral fissures, arched eyebrows, long eyelashes, midface hypoplasia, broad nasal bridge, and anteverted nares (summary by Scala et al., 2022).

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).

Weiss-Kruszka syndrome is characterized by metopic ridging or synostosis, ptosis, nonspecific dysmorphic features, developmental delay, and autistic features. Brain imaging may identify abnormalities of the corpus callosum. Developmental delay can present as global delay, motor delay, or speech delay. Affected individuals may also have ear anomalies, feeding difficulties (sometimes requiring placement of a gastrostomy tube), and congenital heart defects. There is significant variability in the clinical features, even between affected members of the same family.

Developmental and epileptic encephalopathy-85 with or without midline brain defects (DEE85) is an X-linked neurologic disorder characterized by onset of severe refractory seizures in the first year of life, global developmental delay with impaired intellectual development and poor or absent speech, and dysmorphic facial features. The seizures tend to show a cyclic pattern with clustering. Many patients have midline brain defects on brain imaging, including thin corpus callosum and/or variable forms of holoprosencephaly (HPE). The severity and clinical manifestations are variable. Almost all reported patients are females with de novo mutations predicted to result in a loss of function (LOF). However, some patients may show skewed X inactivation, and the pathogenic mechanism may be due to a dominant-negative effect. The SMC1A protein is part of the multiprotein cohesin complex involved in chromatid cohesion during DNA replication and transcriptional regulation; DEE85 can thus be classified as a 'cohesinopathy' (summary by Symonds et al., 2017 and Kruszka et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

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.

Individuals with PPP1R12A-related urogenital and/or brain malformation syndrome (UBMS) usually present with multiple congenital anomalies, commonly including brain and/or urogenital malformations. The brain abnormalities are variable, with the most severe belonging to the holoprosencephaly spectrum and associated with moderate-to-profound intellectual disability, seizures, and feeding difficulties. In individuals without brain involvement, variable degrees of developmental delay and/or intellectual disability may be present, although normal intelligence has been seen in a minority of affected individuals. Eye abnormalities and skeletal issues (kyphoscoliosis, joint contractures) can also be present in individuals of either sex. Regardless of the presence of a brain malformation, affected individuals with a 46,XY chromosome complement may have a disorder of sex development (DSD) with gonadal abnormalities (dysgenetic gonads or streak gonads). Individuals with a 46,XX chromosome complement may have varying degrees of virilization (clitoral hypertrophy, posterior labial fusion, urogenital sinus).

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).

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.

DEEAH syndrome is an autosomal recessive multisystemic disorder with onset in early infancy. Affected individuals usually present in the perinatal period with respiratory insufficiency, apneic episodes, and generalized hypotonia. The patients have failure to thrive and severely impaired global development with poor acquisition of motor, cognitive, and language skills. Other common features include endocrine, pancreatic exocrine, and autonomic dysfunction, as well as hematologic disturbances, mainly low hemoglobin. Patients also have dysmorphic and myopathic facial features. Additional more variable features include seizures, undescended testes, and distal skeletal anomalies. Death in early childhood may occur (summary by Schneeberger 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).

Autosomal dominant primary microcephaly-26 (MCPH26) is characterized by progressive microcephaly beginning at birth and associated with global developmental delay with variably impaired intellectual development. Some patients may have only mild learning difficulties or speech delay, whereas other are more severely affected with the inability to walk or speak. Additional features may include short stature, spasticity, feeding difficulties requiring tube feeding, and nonspecific dysmorphic facial features. Brain imaging in some patients shows a simplified gyral pattern or dysgenesis of the corpus callosum, suggesting abnormal neuronal migration (summary by Cristofoli et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of primary microcephaly, see MCPH1 (251200).

Growth restriction, hypoplastic kidneys, alopecia, and distinctive facies (GKAF) is characterized by microcephaly, congenital alopecia, distinctive craniofacial features, severe congenital sensorineural hearing loss, global developmental delay, hydrocephalus, hypoplastic kidneys with renal insufficiency, genital hypoplasia, and early mortality (Ito et al., 2018).

Onychodystrophy, osteodystrophy, impaired intellectual development, and seizures syndrome (OORS) is an autosomal recessive syndromic developmental disorder characterized by global developmental delay with impaired intellectual development, dysmorphic facial features, and hypoplastic terminal phalanges and nails. Patients have seizures or tonic posturing. The disorder is associated with a defect in GPI anchoring of membrane-bound proteins (summary by Salian et al., 2021). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293). See also DOORS syndrome (220500), which shows some overlapping clinical features.

Neurodevelopmental disorder with hypotonia, facial dysmorphism, and brain abnormalities (NEDHFBA) is an autosomal recessive neurologic syndrome characterized by global developmental delay with severely impaired intellectual development, hypotonia and muscle weakness, often resulting in the inability to walk or sit, and characteristic coarse facial features. Additional features include feeding difficulties, respiratory distress, scoliosis, poor visual function, and rotary nystagmus. Brain imaging shows variable abnormalities, including enlarged ventricles, decreased white matter volume, white matter changes, thin corpus callosum, and cerebellar hypoplasia (summary by Loddo et al., 2020).

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).

NR0B1-related adrenal hypoplasia congenita includes both X-linked adrenal hypoplasia congenita (X-linked AHC) and Xp21 deletion (previously called complex glycerol kinase deficiency). X-linked AHC is characterized by primary adrenal insufficiency and/or hypogonadotropic hypogonadism (HH). Adrenal insufficiency is acute infantile onset (average age 3 weeks) in approximately 60% of affected males and childhood onset (ages 1-9 years) in approximately 40%. HH typically manifests in a male with adrenal insufficiency as delayed puberty (i.e., onset age >14 years) and less commonly as arrested puberty at about Tanner Stage 3. Rarely, X-linked AHC manifests initially in early adulthood as delayed-onset adrenal insufficiency, partial HH, and/or infertility. Heterozygous females very occasionally have manifestations of adrenal insufficiency or hypogonadotropic hypogonadism. Xp21 deletion includes deletion of NR0B1 (causing X-linked AHC) and GK (causing glycerol kinase deficiency), and in some cases deletion of DMD (causing Duchenne muscular dystrophy). Developmental delay has been reported in males with Xp21 deletion when the deletion extends proximally to include DMD or when larger deletions extend distally to include IL1RAPL1 and DMD.

Developmental delay, impaired speech, and behavioral abnormalities (DDISBA) is characterized by global developmental delay apparent from early childhood. Intellectual disability can range from mild to severe. Additional variable features may include dysmorphic facial features, seizures, hypotonia, motor abnormalities such as Tourette syndrome or dystonia, and hearing loss (summary by Cousin et al., 2021).

DEGCAGS syndrome is an autosomal recessive syndromic neurodevelopmental disorder characterized by global developmental delay, coarse and dysmorphic facial features, and poor growth and feeding apparent from infancy. Affected individuals have variable systemic manifestations often with significant structural defects of the cardiovascular, genitourinary, gastrointestinal, and/or skeletal systems. Additional features may include sensorineural hearing loss, hypotonia, anemia or pancytopenia, and immunodeficiency with recurrent infections. Death in childhood may occur (summary by Bertoli-Avella et al., 2021).

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).

Neurodevelopmental-craniofacial syndrome with variable renal and cardiac abnormalities (NECRC) is an autosomal dominant disorder characterized by dysmorphic craniofacial features associated with mild developmental delay, mildly impaired intellectual development or learning difficulties, speech delay, and behavioral abnormalities. About half of patients have congenital anomalies of the kidney and urinary tract (CAKUT) and/or congenital cardiac defects, including septal defects (Connaughton et al., 2020).

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.

Stuve-Wiedemann syndrome is an autosomal recessive disorder characterized by bowing of the long bones and other skeletal anomalies, episodic hyperthermia, respiratory distress, and feeding difficulties usually resulting in early death (Dagoneau et al., 2004). See also 'classic' Schwartz-Jampel syndrome type 1 (SJS1; 255800), a phenotypically similar but genetically distinct disorder caused by mutation in the HSPG2 gene (142461) on chromosome 1p36. Genetic Heterogeneity of Stuve-Wiedemann Syndrome Stuve-Wiedemann syndrome-2 (STWS2; 619751) is caused by mutation in the IL6ST gene (600694) on chromosome 5q11.

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).

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).

Neurodevelopmental disorder with hypotonia, impaired speech, and behavioral abnormalities (NEDHISB) is characterized by global developmental delay apparent since infancy or early childhood, hypotonia with delayed motor development, impaired intellectual development with significant speech delay or absent speech, and variable behavioral abnormalities, such as autism, repetitive actions, or aggression. About two-thirds of patients have early-onset seizures that range from intractable to self-limiting. More variable features include nonspecific dysmorphic facial features, distal skeletal anomalies, and brain imaging abnormalities. The phenotypic manifestations and severity are highly variable (Muir et al., 2021).

Craniofacial dysmorphism, skeletal anomalies, and impaired intellectual development syndrome-1 (CFSMR1) is characterized by cranial involvement with macrocrania at birth, brachycephaly, anomalies of middle fossa structures including hypoplasia of corpus callosum, enlargement of septum pellucidum, and dilated lateral ventricles, as well as cortical atrophy and hypodensity of the gray matter. Facial dysmorphisms include flat face, hypertelorism, epicanthal folds, synophrys, broad nasal bridge, cleft lip and cleft palate, and low-set posteriorly rotated ears. Patients also exhibit short neck and multiple costal and vertebral anomalies. The face is rather characteristic, and various authors have consistently reported affable/friendly personality, despite intellectual delay (summary by Alanay et al., 2014). Genetic Heterogeneity of Craniofacial Dysmorphism, Skeletal Anomalies, and Impaired Intellectual Development Syndrome CFSMR2 (616994) is caused by mutation in the RAB5IF gene (619960) on chromosome 20q11.

Neurodevelopmental disorder with seizures, spasticity, and partial or complete agenesis of the corpus callosum (NEDSSCC) is an autosomal recessive disorder characterized by axial hypotonia and global developmental delay apparent from the first days or months of life. Affected individuals often have feeding difficulties and develop early-onset seizures that tend to be well-controlled. Other features include peripheral spasticity with hyperreflexia, variable dysmorphic features, impaired intellectual development, behavioral abnormalities, and hypoplasia or absence of the corpus callosum on brain imaging (Faqeih et al., 2023).

Neurodevelopmental disorder with language delay and behavioral abnormalities, with or without seizures (NEDLBAS), is characterized by global developmental delay with variably impaired intellectual development apparent from infancy or early childhood. Affected individuals have significant speech delay, and most demonstrate behavioral abnormalities, including autistic features. About half of patients develop seizures, which may be controlled or refractory. More variable features include hypotonia, feeding difficulties, and subtle facial dysmorphism (Schalk et al., 2022).

Autosomal dominant intellectual developmental disorder-71 with behavioral abnormalities (MRD71) is a neurodevelopmental disorder characterized by global developmental delay with hypotonia, speech delay, and variably impaired cognitive development. Almost all affected individuals show marked behavioral manifestations, including autism spectrum disorder (ASD), ADHD, hypersensitivity, and aggression. Many have dysmorphic features, although there is not a common gestalt (Harris et al., 2021).

Severe fetal congenital myopathy-22B (CMYO22B) is an autosomal recessive muscle disorder characterized by in utero onset of severe muscle weakness manifest as fetal akinesia. The pregnancies are often complicated by polyhydramnios, and affected individuals develop fetal hydrops with pulmonary hypoplasia, severe joint contractures, and generalized muscle hypoplasia. Those who are born have respiratory failure resulting in death. Dysmorphic facial features may be present. The features in these patients overlap with fetal akinesia deformation sequence (FADS; see 208150) and lethal congenital contractures syndrome (LCCS; see 253310) (Zaharieva et al., 2016). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Cornelia de Lange syndrome (CDLS) is a genetically heterogeneous developmental disorder characterized by malformations affecting multiple systems. Affected individuals have dysmorphic facial features, cleft palate, distal limb defects, growth retardation, and developmental delay. About 60% of patients have mutations in the NIPBL gene (608667) (summary by Musio et al., 2006 and Hoppman-Chaney et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of Cornelia de Lange syndrome, see CDLS1 (122470).

Teebi hypertelorism syndrome-1 (TBHS1) is an autosomal dominant disorder characterized by hypertelorism with upslanting palpebral fissures, prominent forehead, broad and depressed nasal bridge with short nose, thick eyebrows, and widow's peak. Additional features include small broad hands with mild interdigital webbing and shawl scrotum. Umbilical malformations, cardiac defects, natal teeth, cleft lip/palate, congenital diaphragmatic hernia, and malformations of the central nervous system (ventriculomegaly, abnormal corpus callosum) have also been reported. Development is typically normal, although some patients with developmental delays have been reported (summary by Bhoj et al., 2015). Genetic Heterogeneity of Teebi Hypertelorism Syndrome Teebi hypertelorism syndrome-2 (TBHS2; 619736) is caused by mutation in the CDH11 gene (600023) on chromosome 16q21.