Neural tube defects are the second most common type of birth defect after congenital heart defects. The 2 most common NTDs are open spina bifida, also known as spina bifida cystica (SBC) or myelomeningocele, and anencephaly (see 206500) (Detrait et al., 2005). Spina bifida occulta (SBO), a bony defect of the spine covered by normal skin, is a mild form of spina bifida that is often asymptomatic. The term 'spinal dysraphia' refers to both SBC and SBO (Botto et al., 1999; Fineman et al., 1982). The most severe neural tube defect, craniorachischisis (CRN), leaves the neural tube open from the midbrain or rostral hindbrain to the base of the spine (summary by Robinson et al., 2012). Neural tube defects represent a complex trait with multifactorial etiology encompassing both genetic and environmental components (summary by Bartsch et al., 2012 and Lei et al., 2014). An X-linked form of spina bifida has been suggested; see 301410. See also folate-sensitive neural tube defects (601634), which are caused by genes involved in folate metabolism.

Dubowitz syndrome (DS) is a rare multiple congenital syndrome characterized primarly by growth retardation, microcephaly, distinctive facial dysmorphism, cutaneous eczema, a mild to severe intellectual deficit and genital abnormalities.

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.

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.

Holt-Oram syndrome (HOS) is characterized by upper-limb defects, congenital heart malformation, and cardiac conduction disease. Upper-limb malformations may be unilateral, bilateral/symmetric, or bilateral/asymmetric and can range from triphalangeal or absent thumb(s) to phocomelia. Other upper-limb malformations can include unequal arm length caused by aplasia or hypoplasia of the radius, fusion or anomalous development of the carpal and thenar bones, abnormal forearm pronation and supination, abnormal opposition of the thumb, sloping shoulders, and restriction of shoulder joint movement. An abnormal carpal bone is present in all affected individuals and may be the only evidence of disease. A congenital heart malformation is present in 75% of individuals with HOS and most commonly involves the septum. Atrial septal defect and ventricular septal defect can vary in number, size, and location. Complex congenital heart malformations can also occur in individuals with HOS. Individuals with HOS with or without a congenital heart malformation are at risk for cardiac conduction disease. While individuals may present at birth with sinus bradycardia and first-degree atrioventricular (AV) block, AV block can progress unpredictably to a higher grade including complete heart block with and without atrial fibrillation.

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).

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 term '3MC syndrome' encompasses 4 rare autosomal recessive disorders that were previously designated the Carnevale, Mingarelli, Malpuech, and Michels syndromes, respectively. The main features of these syndromes are facial dysmorphism that includes hypertelorism, blepharophimosis, blepharoptosis, and highly arched eyebrows, which are present in 70 to 95% of cases. Cleft lip and palate, postnatal growth deficiency, cognitive impairment, and hearing loss are also consistent findings, occurring in 40 to 68% of cases. Craniosynostosis, radioulnar synostosis, and genital and vesicorenal anomalies occur in 20 to 30% of cases. Rare features include anterior chamber defects, cardiac anomalies, caudal appendage, umbilical hernia (omphalocele), and diastasis recti (summary by Rooryck et al., 2011). For a discussion of genetic heterogeneity of 3MC syndrome, see 3MC1 (257920).

The term '3MC syndrome' encompasses 4 rare autosomal recessive disorders that were previously designated the Carnevale, Mingarelli, Malpuech, and Michels syndromes, respectively. The main features of these syndromes are facial dysmorphism that includes hypertelorism, blepharophimosis, blepharoptosis, and highly arched eyebrows, which are present in 70 to 95% of cases. Cleft lip and palate, postnatal growth deficiency, cognitive impairment, and hearing loss are also consistent findings, occurring in 40 to 68% of cases. Craniosynostosis, radioulnar synostosis, and genital and vesicorenal anomalies occur in 20 to 30% of cases. Rare features include anterior chamber defects, cardiac anomalies, caudal appendage, umbilical hernia (omphalocele), and diastasis recti (summary by Rooryck et al., 2011). Genetic Heterogeneity of 3MC Syndrome Also see 3MC syndrome-2 (3MC2; 265050), caused by mutation in the COLEC11 gene (612502), and 3MC syndrome-3 (3MC3; 248340), caused by mutation in the COLEC1 gene (607620).

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

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).

Emanuel syndrome is characterized by pre- and postnatal growth deficiency, microcephaly, hypotonia, severe developmental delays, ear anomalies, preauricular tags or pits, cleft or high-arched palate, congenital heart defects, kidney abnormalities, and genital abnormalities in males.

Cataract-congenital heart disease-neural tube defect syndrome is a multiple congenital anomaly syndrome characterized by sacral neural tube defects resulting in tethered cord, atrial and/or ventricular septal heart defects (that are detected in infancy), bilateral, symmetrical hyperopia, rapidly progressive early childhood cataracts, bilateral aphakic glaucoma, and abnormal facial features (low frontal hairline, small ears, short philtrum, prominent, widely spaced central incisors, and micrognathia). Hypotonia, growth and developmental delay, seizures, and joint limitation are also reported.

Phelan-McDermid syndrome is characterized by neonatal hypotonia, absent to severely delayed speech, developmental delay, and minor dysmorphic facial features. Most affected individuals have moderate to profound intellectual disability. Other features include large fleshy hands, dysplastic toenails, and decreased perspiration that results in a tendency to overheat. Normal stature and normal head size distinguishes Phelan-McDermid syndrome from other autosomal chromosome disorders. Behavior characteristics include mouthing or chewing non-food items, decreased perception of pain, and autism spectrum disorder or autistic-like affect and behavior.

Wiedemann-Steiner syndrome (WSS) is characterized by developmental delay, intellectual disability, and characteristic facial features, with or without additional congenital anomalies. The facial features include thick eyebrows with lateral flare, vertically narrow and downslanted palpebral fissures, widely spaced eyes, long eyelashes, wide nasal bridge, broad nasal tip, thin vermilion of the upper lip, and thick scalp hair. About 60% of affected individuals have hypertrichosis cubiti ("hairy elbows"), which was once thought to be pathognomic for the syndrome, with a majority having hypertrichosis of other body parts. Other clinical features include feeding difficulties, prenatal and postnatal growth restriction, epilepsy, ophthalmologic anomalies, congenital heart defects, hand anomalies (such as brachydactyly and clinodactyly), hypotonia, vertebral anomalies (especially fusion anomalies of the cervical spine), renal and uterine anomalies, immune dysfunction, brain malformations, and dental anomalies.

A very rare syndrome associating an acro-fronto-facio-nasal dysostosis with genitourinary anomalies. It has been described in three families. Craniofacial manifestations include wide anterior fontanelle, flat occiput, hypertelorism, ptosis, proptosis, broad nasal bridge and nasal tip, long philtrum and posteriorly rotated or low set ears. Hypospadias and shawl scrotum are present in all males. Acral manifestations include syndactyly of fingers, broad thumbs or halluces or preaxial polydactyly. The affected patients have no intellectual deficit. The condition seems to be hereditary, and transmitted as an autosomal recessive trait.

Koolen-de Vries syndrome (KdVS) is characterized by developmental delay / intellectual disability, neonatal/childhood hypotonia, dysmorphisms, congenital malformations, and behavioral features. Psychomotor developmental delay is noted in all individuals from an early age. The majority of individuals with KdVS function in the mild-to-moderate range of intellectual disability. Other findings include speech and language delay (100%), epilepsy (~33%), congenital heart defects (25%-50%), renal and urologic anomalies (25%-50%), and cryptorchidism (71% of males). Behavior in most is described as friendly, amiable, and cooperative.

Wolf-Hirschhorn syndrome is a congenital malformation syndrome characterized by pre- and postnatal growth deficiency, developmental disability of variable degree, characteristic craniofacial features ('Greek warrior helmet' appearance of the nose, high forehead, prominent glabella, hypertelorism, high-arched eyebrows, protruding eyes, epicanthal folds, short philtrum, distinct mouth with downturned corners, and micrognathia), and a seizure disorder (Battaglia et al., 2008).

Pitt-Hopkins syndrome (PTHS) is characterized by significant developmental delays with moderate-to-severe intellectual disability and behavioral differences, characteristic facial features, and episodic hyperventilation and/or breath-holding while awake. Speech is significantly delayed and most individuals are nonverbal with receptive language often stronger than expressive language. Other common findings are autism spectrum disorder symptoms, sleep disturbance, stereotypic hand movements, seizures, constipation, and severe myopia.

KCNK9 imprinting syndrome is characterized by congenital central hypotonia (manifest as decreased movement, lethargy, and weak cry), severe feeding difficulties (resulting from facial weakness and poor suck), delayed development/intellectual disability, and dysmorphic manifestations. Poor feeding can cause failure to thrive during infancy unless managed appropriately. Significant dysphagia of solid foods typically persists until puberty. Intellectual disability can be severe. To date 19 individuals with a molecularly confirmed diagnosis have been reported.

VACTERL is an acronym for vertebral anomalies (similar to those of spondylocostal dysplasia), anal atresia, cardiac malformations, tracheoesophageal fistula, renal anomalies (urethral atresia with hydronephrosis), and limb anomalies (hexadactyly, humeral hypoplasia, radial aplasia, and proximally placed thumb; see 192350). Some patients may have hydrocephalus, which is referred to as VACTERL-H (Briard et al., 1984).

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).

Meckel syndrome is a disorder with severe signs and symptoms that affect many parts of the body. The most common features are enlarged kidneys with numerous fluid-filled cysts; an occipital encephalocele, which is a sac-like protrusion of the brain through an opening at the back of the skull; and the presence of extra fingers and toes (polydactyly). Most affected individuals also have a buildup of scar tissue (fibrosis) in the liver.\n\nOther signs and symptoms of Meckel syndrome vary widely among affected individuals. Numerous abnormalities of the brain and spinal cord (central nervous system) have been reported in people with Meckel syndrome, including a group of birth defects known as neural tube defects. These defects occur when a structure called the neural tube, a layer of cells that ultimately develops into the brain and spinal cord, fails to close completely during the first few weeks of embryonic development. Meckel syndrome can also cause problems with development of the eyes and other facial features, heart, bones, urinary system, and genitalia.\n\nBecause of their serious health problems, most individuals with Meckel syndrome die before or shortly after birth. Most often, affected infants die of respiratory problems or kidney failure.

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.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

A rare, genetic, neurodevelopmental disorder characterized by global developmental delay, borderline to severe intellectual disability, feeding difficulties, behavioral anomalies, vision anomalies and mild facial dysmorphism. Other associated features may include microcephaly, short stature, urogenital or palatal anomalies (e.g. cleft palate), minor cardiac defects, recurrent infections or hearing loss.

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

PDE4D haploinsufficiency syndrome is a rare syndromic intellectual disability characterized by developmental delay, intellectual disability, low body mass index, long arms, fingers and toes, prominent nose and small chin.

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

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).

Male EBP disorder with neurologic defects (MEND) is an X-linked recessive disorder representing a continuous phenotypic spectrum with variable manifestations associated with a defect in sterol biosynthesis. Features include intellectual disability, short stature, scoliosis, digital abnormalities, cataracts, and dermatologic abnormalities. Not all patients show all features, and the severity is highly variable. Molecular studies indicate that affected males are hemizygous for a nonmosaic hypomorphic EBP allele. Carrier females are generally clinically asymptomatic, but may show biochemical abnormalities (summary by Arnold et al., 2012 and Barboza-Cerda et al., 2014).

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

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.

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

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

X-linked syndromic intellectual developmental disorder-33 (MRXS33) is an X-linked recessive neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, and characteristic facial features (summary by O'Rawe et al., 2015).

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).

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.

IDDFSDA is an autosomal recessive severe multisystem disorder characterized by poor overall growth, developmental delay, early-onset seizures, intellectual disability, and dysmorphic features. There is phenotypic variability. The most severely affected patients have a neurodevelopmental disorder with microcephaly, absent speech, and inability to walk, and they require feeding tubes. Some patients have congenital heart defects or nonspecific abnormalities on brain imaging. Less severely affected individuals have mild to moderate intellectual disability with normal speech and motor development (summary by Santiago-Sim et al., 2017).

Stankiewicz-Isidor syndrome (STISS) is a neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, behavioral disorders, mild craniofacial anomalies, and variable congenital defects of the cardiac and/or urogenital systems (summary by Kury et al., 2017).

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

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.

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

Van Maldergem syndrome is an autosomal recessive disorder characterized by intellectual disability, typical craniofacial features, auditory malformations resulting in hearing loss, and skeletal and limb malformations. Some patients have renal hypoplasia. Brain MRI typically shows periventricular nodular heterotopia (summary by Cappello et al., 2013). Genetic Heterogeneity of Van Maldergem Syndrome See also VMLDS2 (615546), caused by mutation in the FAT4 gene (612411) on chromosome 4q28.

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

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

SMALED2B is a severe neuromuscular disorder with onset in utero. Affected individuals show decreased fetal movements and are usually born with congenital contractures consistent with arthrogryposis multiplex congenita (AMC). After birth, they have severe hypotonia and muscle atrophy as well as respiratory insufficiency due to muscle weakness. Some patients may have dysmorphic facial features and/or abnormalities on brain imaging. Many patients die in early childhood (summary by Storbeck et al., 2017) For discussion of genetic heterogeneity of lower extremity-predominant spinal muscular atrophy, see SMALED1 (158600).

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).

Neurodevelopmental disorder with seizures and speech and walking impairment (NEDSSWI) is an autosomal recessive disorder with onset in infancy. Patients show global developmental delay, particularly of speech acquisition, as well as walking difficulties due to hypotonia, hypertonia, spasticity, or poor coordination. Other features include seizures, mild dysmorphic features, and variable short stature. The pregnancies tend to be complicated by hyper- or hypotension (summary by Ganapathi et al., 2019).

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).

Vertebral, cardiac, renal, and limb defects syndrome-3 (VCRL3) is an autosomal recessive disorder characterized by severe cardiac and renal anomalies that are lethal in infancy, including hypoplastic or absent left ventricle, transposition of the great arteries, absent pulmonary trunk, and hypoplastic or absent kidneys. Patients also exhibit vertebral segmentation defects and shortening of the proximal long bones or micromelia (Szot et al., 2020). For a discussion of genetic heterogeneity of VCRL, see VCRL1 (617660).

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

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.

KINSSHIP syndrome (KINS) is an autosomal dominant disorder characterized by a recognizable pattern of anomalies including developmental delay, impaired intellectual development, seizures, mesomelic dysplasia, dysmorphic facial features, horseshoe or hypoplastic kidney, and failure to thrive (summary by Voisin et al., 2021).

Oculogastrointestinal neurodevelopmental syndrome (OGIN) is characterized by microphthalmia and/or coloboma in association with other congenital anomalies, including imperforate anus, horseshoe kidney, and structural cardiac defects. Hearing loss and severe developmental delay are also observed in most patients (Zha et al., 2020; Mor-Shaked 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).

Zaki syndrome (ZKS) is characterized by developmental delay, progressive microcephaly, and short stature, as well as dysmorphic features including sparse scalp hair, cupped ears, wide nose and mouth, short philtrum, and high-arched palate. Other variable features have been observed, including ocular, skeletal, cardiac, and renal anomalies (Chai et al., 2021).

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

Kury-Isidor syndrome (KURIS) is a neurodevelopmental disorder with a highly variable phenotype. It is characterized mainly by mild global developmental delay apparent from infancy or early childhood with walking delayed by a few years and speech delay, often with language deficits. Intellectual development may be mildly delayed, borderline, or even normal; most patients have behavioral problems, including autism. Additional variable systemic features may include poor overall growth, hypotonia, distal skeletal anomalies, seizures, and nonspecific dysmorphic facial features (summary by Kury et al., 2022).

Congenital disorder of deglycosylation-2 (CDDG2) is an autosomal recessive disorder with variable associated features such as dysmorphic facies, impaired intellectual development, and brain anomalies, including polymicrogyria, interhemispheric cysts, hypothalamic hamartoma, callosal anomalies, and hypoplasia of brainstem and cerebellar vermis (Maia et al., 2022). For a discussion of genetic heterogeneity of congenital disorder of deglycosylation, see CDGG1 (615273).

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 intention tremor, pyramidal signs, dyspraxia, and ocular anomalies (NEDITPO) is an autosomal recessive multiple congenital anomaly syndrome characterized by mild to moderate intellectual disability, dysmorphic facial features, intention tremor, dyspraxia, and vertical strabismus (Rahikkala et al., 2022).

Atelis syndrome-2 (ATELS2) is an autosomal recessive disorder characterized by poor overall growth with microcephaly and short stature, dysmorphic facial features, and congenital cardiac defects. Additional more variable features may include hematologic abnormalities, variable ocular abnormalities, motor delay, and anxiety. Patient cells exhibit a unique chromosomal instability phenotype consisting of segmented and dicentric chromosomes with mosaic variegated hyperploidy (Grange et al., 2022). See also ATELS1 (620184), caused by mutation in the SLF2 gene (610348). For a discussion of genetic heterogeneity of MVA, see MVA1 (257300).

Tessadori-Bicknell-van Haaften neurodevelopmental syndrome-3 (TEBIVANED3) is characterized by global developmental delay with poor overall growth, impaired intellectual development, and speech difficulties. More variable features include hypotonia, microcephaly, and dysmorphic facies. The severity and manifestations of the disorder are highly variable (Tessadori et al., 2022). For a discussion of genetic heterogeneity of Tessadori-Bicknell-van Haaften neurodevelopmental disorder, see TEBIVANED1 (619758).