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

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).

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

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

Schilbach-Rott syndrome (SBRS) is an autosomal dominant disorder characterized by hypotelorism, epicanthal folds, cleft palate, dysmorphic facies, and hypospadias in males. The phenotype is variable, and mildly impaired intellectual development has been reported (summary by Shkalim et al., 2009).

A rare non-syndromic syndactyly characterized by unilateral or bilateral fusion of the 4th and 5th metacarpals with no other associated abnormalities. Patients present shortened 4th and 5th metacarpals with excessive separation between their distal ends, resulting in marked ulnar deviation of the little finger and an inability to bring the 5th finger in parallel with the other fingers.

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

Oculofaciocardiodental (OFCD) syndrome is a condition that affects the development of the eyes (oculo-), facial features (facio-), heart (cardio-) and teeth (dental). This condition occurs only in females.\n\nThe eye abnormalities associated with OFCD syndrome can affect one or both eyes. Many people with this condition are born with eyeballs that are abnormally small (microphthalmia). Other eye problems can include clouding of the lens (cataract) and a higher risk of glaucoma, an eye disease that increases the pressure in the eye. These abnormalities can lead to vision loss or blindness.\n\nPeople with OFCD syndrome often have a long, narrow face with distinctive facial features, including deep-set eyes and a broad nasal tip that is divided by a cleft. Some affected people have an opening in the roof of the mouth called a cleft palate.\n\nHeart defects are another common feature of OFCD syndrome. Babies with this condition may be born with a hole between two chambers of the heart (an atrial or ventricular septal defect) or a leak in one of the valves that controls blood flow through the heart (mitral valve prolapse).\n\nTeeth with very large roots (radiculomegaly) are characteristic of OFCD syndrome. Additional dental abnormalities can include delayed loss of primary (baby) teeth, missing or abnormally small teeth, misaligned teeth, and defective tooth enamel.

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).

10q26 deletion syndrome is a condition that results from the loss (deletion) of a small piece of chromosome 10 in each cell. The deletion occurs on the long (q) arm of the chromosome at a position designated 10q26.\n\nThe signs and symptoms of 10q26 deletion syndrome vary widely, even among affected members of the same family. Among the more common features associated with this chromosomal change are distinctive facial features, mild to moderate intellectual disability, growth problems, and developmental delay. People with 10q26 deletion syndrome often have delayed development of speech and of motor skills such as sitting, crawling, and walking. Some have limited speech throughout life. Affected individuals may experience seizures, attention-deficit/hyperactivity disorder (ADHD), poor impulse control (impulsivity), or exhibit autistic behaviors that affect communication and social interaction.\n\nA range of facial features is seen in people with 10q26 deletion syndrome, but not all affected individuals have these features. Facial features of people with 10q26 deletion syndrome may include a prominent or beaked nose, a broad nasal bridge, a small jaw (micrognathia), malformed ears that are low set, a thin upper lip, and an unusually small head size (microcephaly). Many affected individuals have widely spaced eyes (hypertelorism) that do not look in the same direction (strabismus). Some people with this condition have a short neck with extra folds of skin (webbed neck).\n\nLess common signs and symptoms can occur in 10q26 deletion syndrome. Skeletal problems include a spine that curves to the side (scoliosis), limited movement in the elbows or other joints, or curved fifth fingers and toes (clinodactyly). Slow growth before and after birth can also occur in affected individuals. Males with this condition may have genital abnormalities, such as a small penis (micropenis), undescended testes (cryptorchidism), or the urethra opening on the underside of the penis (hypospadias). Some people with 10q26 deletion syndrome have kidney abnormalities, heart defects, breathing problems, recurrent infections, or hearing or vision problems.

Familial and <i>de novo</i> recurrent Xp11.22-p11.23 microduplication has been recently identified in males and females.

Ectodermal dysplasia-syndactyly syndrome (EDSS) is characterized by sparse to absent scalp hair, eyebrows, and eyelashes, hypoplastic nails, tooth enamel hypoplasia, conical-shaped teeth, palmoplantar keratoderma, and partial cutaneous syndactyly (summary by Raza et al., 2015). Genetic Heterogeneity of Ectodermal Dysplasia-Syndactyly Syndrome Ectodermal dysplasia-syndactyly syndrome-2 (EDSS2; 613576) maps to chromosome 7p21-p14.

Cerebellar dysfunction with variable cognitive and behavioral abnormalities (CECBA) is an autosomal dominant neurologic disorder with significant phenotypic heterogeneity, even within families. The disorder is most often diagnosed through genetic analysis with retrospective clinical phenotyping. Symptom onset is usually in early childhood, although later onset, even in adulthood, has been reported. Most affected individuals show global developmental delay from early childhood, particularly of motor and language skills. Many have mild intellectual disability; behavioral and psychiatric abnormalities such as autism and obsessive-compulsive disorder are also often observed. The movement disorder is prominent and may include cerebellar signs such as ataxia, tremor, dysmetria, poor coordination, and dysarthria. Other abnormal movements including spasticity, myoclonus, and dystonia have been reported, thus widening the phenotypic spectrum. Brain imaging is usually normal, but may show cerebellar atrophy or nonspecific white matter lesions. Variable dysmorphic facial features may also be present (summary by Thevenon et al., 2012; Jacobs et al., 2021; Wijnen et al., 2020).

Vulto-van Silfout-de Vries syndrome (VSVS) is an intellectual developmental disorder characterized by delayed psychomotor development, poor expressive speech, and behavioral abnormalities, including autistic features and poor eye contact. Most patients have additional nonspecific features, including hypotonia and gait abnormalities, seizures, which may be refractory, high pain threshold, and sleep disturbances (summary by Nabais Sa et al., 2019).

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

Postaxial polydactyly type A7 (PAPA7) is an autosomal recessive disorder characterized by postaxial polydactyly and brachydactyly of the hands and/or feet. Features reported in some patients include syndactyly of the second and third digits of the feet, learning disabilities, and increased body weight (Umair et al., 2017; Estrada-Cuzcano et al., 2020). For a discussion of genetic heterogeneity of postaxial polydactyly, see 174200.

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).

X-linked epilepsy-2 with or without impaired intellectual development and dysmorphic features (EPILX2) is a neurologic disorder characterized by the onset of seizures usually in the first years of life, although later onset may also occur. Most individuals also have developmental delay, speech delay, and intellectual disability or learning difficulties. Some patients have dysmorphic facial features or mild skeletal anomalies. The severity of the disorder and accompanying features are highly variable, even within the same family. In general, males are more severely affected than females, although there is evidence for incomplete penetrance in both sexes (Niturad et al., 2017).

Neurodevelopmental disorder with hypotonia, language delay, and skeletal defects with or without seizures (NEDHLSS) is characterized by global developmental delay apparent from infancy. Affected individuals show severe hypotonia with delayed walking or inability to walk, poor or absent speech, and impaired intellectual development with behavioral abnormalities. Most patients have early-onset seizures, mild skeletal defects that are usually distal, and nonspecific dysmorphic features. More severely affected individuals have additional congenital abnormalities; however, cardiac involvement is rare (summary by Rodan et al., 2021).

Neurodevelopmental disorder with poor growth and behavioral abnormalities (NEDGBA) is an autosomal recessive disorder characterized by global developmental delay, moderately to severely impaired intellectual development, often with absent speech, and behavioral abnormalities, including hyperactivity, short attention span, and ADHD. Affected individuals show failure to thrive with poor overall growth; some have microcephaly. Additional features may include nonspecific facial dysmorphism, hypotonia, and feeding difficulties (Vogt et al., 2022; Meng et al., 2023).