Beckwith-Wiedemann syndrome (BWS) is a growth disorder variably characterized by neonatal hypoglycemia, macrosomia, macroglossia, hemihyperplasia, omphalocele, embryonal tumors (e.g., Wilms tumor, hepatoblastoma, neuroblastoma, and rhabdomyosarcoma), visceromegaly, adrenocortical cytomegaly, renal abnormalities (e.g., medullary dysplasia, nephrocalcinosis, medullary sponge kidney, and nephromegaly), and ear creases/pits. BWS is considered a clinical spectrum, in which affected individuals may have many of these features or may have only one or two clinical features. Early death may occur from complications of prematurity, hypoglycemia, cardiomyopathy, macroglossia, or tumors. However, the previously reported mortality of 20% is likely an overestimate given better recognition of the disorder along with enhanced treatment options. Macroglossia and macrosomia are generally present at birth but may have postnatal onset. Growth rate slows around age seven to eight years. Hemihyperplasia may affect segmental regions of the body or selected organs and tissues.

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).

Floating-Harbor syndrome (FHS) is characterized by typical craniofacial features; low birth weight, normal head circumference, and short stature; bone age delay that normalizes between ages six and 12 years; skeletal anomalies (brachydactyly, clubbing, clinodactyly, short thumbs, prominent joints, clavicular abnormalities); severe receptive and expressive language impairment; hypernasality and high-pitched voice; and intellectual disability that is typically mild to moderate. Difficulties with temperament and behavior that are present in many children tend to improve in adulthood. Other features can include hyperopia and/or strabismus, conductive hearing loss, seizures, gastroesophageal reflux, renal anomalies (e.g., hydronephrosis / renal pelviectasis, cysts, and/or agenesis), and genital anomalies (e.g., hypospadias and/or undescended testes).

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.

AICA-ribosiduria is characterized by severe to profound global neurodevelopmental impairment, severe visual impairment due to chorioretinal atrophy, ante-postnatal growth impairment, and severe scoliosis. Dysmorphic features include coarse facies and upturned nose. Early-onset epilepsy may occur. Less common features may include aortic coarctation, chronic hepatic cytolysis, minor genital malformations, and nephrocalcinosis (Ramond et al., 2020).

Intellectual disability-brachydactyly-Pierre Robin syndrome is a rare developmental defect during embryogenesis syndrome characterized by mild to moderate intellectual disability and phsychomotor delay, Robin sequence (incl. severe micrognathia and soft palate cleft) and distinct dysmorphic facial features (e.g. synophris, short palpebral fissures, hypertelorism, small, low-set, and posteriorly angulated ears, bulbous nose, long/flat philtrum, and bow-shaped upper lip). Skeletal anomalies, such as brachydactyly, clinodactyly, small hands and feet, and oral manifestations (e.g. bifid, short tongue, oligodontia) are also associated. Additional features reported include microcephaly, capillary hemangiomas on face and scalp, ventricular septal defect, corneal clouding, nystagmus and profound sensorineural deafness.

This syndrome combines skeletal anomalies (short stature, ridging of the metopic suture, fusion of cervical vertebrae, thoracic hemivertebrae, scoliosis, sacral hypoplasia and short middle phalanges) and mild intellectual deficit. It has been described in four male cousins in three sibships. Glucose intolerance was present in three cases, and imperforated anus in one case. Carrier females had minor manifestations (fusion of cervical vertebrae and glucose intolerance). Transmission seems to be X-linked.

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

Microcephalic osteodysplastic primordial dwarfism type I (MOPD1) is a severe autosomal recessive skeletal dysplasia characterized by dwarfism, microcephaly, and neurologic abnormalities, including mental retardation, brain malformations, and ocular/auditory sensory deficits. Patients often die in early childhood (summary by Pierce and Morse, 2012).

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.

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

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

Most people with Meier-Gorlin syndrome have distinctive facial features. In addition to being abnormally small, the ears may be low-set or rotated backward. Additional features can include a small mouth (microstomia), an underdeveloped lower jaw (micrognathia), full lips, and a narrow nose with a high nasal bridge.\n\nAbnormalities in sexual development may also occur in Meier-Gorlin syndrome. In some males with this condition, the testes are small or undescended (cryptorchidism). Affected females may have unusually small external genital folds (hypoplasia of the labia majora) and small breasts. Both males and females with this condition can have sparse or absent underarm (axillary) hair.\n\nAdditional features of Meier-Gorlin syndrome can include difficulty feeding and a lung condition known as pulmonary emphysema or other breathing problems.\n\nMeier-Gorlin syndrome is a condition primarily characterized by short stature. It is considered a form of primordial dwarfism because the growth problems begin before birth (intrauterine growth retardation). After birth, affected individuals continue to grow at a slow rate. Other characteristic features of this condition are underdeveloped or missing kneecaps (patellae), small ears, and, often, an abnormally small head (microcephaly). Despite a small head size, most people with Meier-Gorlin syndrome have normal intellect.\n\nSome people with Meier-Gorlin syndrome have other skeletal abnormalities, such as unusually narrow long bones in the arms and legs, a deformity of the knee joint that allows the knee to bend backwards (genu recurvatum), and slowed mineralization of bones (delayed bone age).

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).

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

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

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.

PPP2R1A-related neurodevelopmental disorder (NDD) is characterized by: severe, persistent hypotonia; developmental delay with variable intellectual outcomes, typically in the moderate-to-severe intellectual disability range; seizures (more commonly seen in individuals with microcephaly and/or severe intellectual disability); attention-deficit/hyperactivity disorder and other behavioral problems (anxiousness, repetitive movements, self-injurious or destructive behavior, and autism spectrum disorder); feeding and swallowing issues; and dysmorphic features of the head and face. A minority of affected individuals have ear anomalies, hearing loss, ptosis, generalized joint hypermobility, and patent ductus arteriosus. Brain MRI findings are nonspecific but typically include complete or partial agenesis of the corpus callosum. Nonprogressive ventriculomegaly may be seen in a subset of affected individuals and is often associated with specific pathogenic variants in PPP2R1A: c.544C>T (p.Arg182Trp) and c.547C>T (p.Arg183Trp).

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

Sweeney-Cox syndrome (SWCOS) is characterized by striking facial dysostosis, including hypertelorism, deficiencies of the eyelids and facial bones, cleft palate/velopharyngeal insufficiency, and low-set cupped ears (Kim et al., 2017).

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).

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

Sandestig-Stefanova syndrome (SANDSTEF) is an autosomal recessive developmental syndrome characterized by pre- and postnatal microcephaly, trigonocephaly, congenital cataract, microphthalmia, facial gestalt, camptodactyly, loss of periventricular white matter, thin corpus callosum, delayed myelinization, and poor prognosis (Sandestig et al., 2019).

Permanent neonatal diabetes mellitus-2 (PNDM2) is characterized by onset of insulin-requiring hyperglycemia within the first months of life that requires insulin therapy throughout life. Some patients additionally have marked developmental delay, muscle weakness, and epilepsy (Gloyn et al., 2004). The triad of developmental delay, epilepsy, and neonatal diabetes is known as DEND (Shimomura et al., 2007). Proks et al. (2006) stated that heterozygous activating mutations in KCNJ11 are the most common cause of PNDM and account for 26 to 64% of cases, and that neurologic features are found in 20% of patients with KCNJ11 mutations. For a discussion of genetic heterogeneity of permanent neonatal diabetes mellitus, see PNDM1 (606176).

Neurodevelopmental disorder with hypotonia, microcephaly, and seizures (NEDHYMS) is an autosomal recessive disorder characterized by global developmental delay with axial hypotonia, inability to sit or walk, and severely impaired intellectual development with absent language. Most patients develop early-onset intractable seizures that prevent normal development. Additional features include feeding difficulties with poor overall growth and microcephaly. Some patients may have spastic quadriplegia, poor eye contact due to cortical blindness, variable dysmorphic features, and nonspecific abnormalities on brain imaging (summary by Tan et al., 2020).

Periventricular nodular heterotopia-9 (PVNH9) is an autosomal dominant neurologic disorder characterized as a malformation of cortical development. Anterior predominant PVNH, thin corpus callosum, and decreased white matter volume are found on brain imaging, but the clinical effects are variable. Most patients have impaired intellectual development and cognitive defects associated with low IQ (range 50 to 80), learning disabilities, and behavior abnormalities. Some patients develop seizures that tend to have a focal origin. However, some mutation carriers may be less severely affected with borderline or even normal IQ, suggesting incomplete penetrance of the phenotype (summary by Heinzen et al., 2018, Walters et al., 2018). For a discussion of genetic heterogeneity of periventricular nodular heterotopia, see 300049.

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.

Chromosome 13q33-q34 deletion syndrome is associated with developmental delay and/or impaired intellectual development, facial dysmorphism, and an increased risk for epilepsy, cardiac defects and additional anatomic anomalies (summary by Sagi-Dain et al., 2019).

Joubert syndrome-37 (JBTS37) is an autosomal recessive neurodevelopmental ciliopathy characterized classically by a distinctive hindbrain malformation affecting the midbrain and cerebellum, recognizable as the 'molar tooth sign' on brain imaging. Affected individuals have hypotonia, ataxia, and variably impaired intellectual development. Additional variable features, such as postaxial polydactyly, liver or kidney anomalies, retinal dystrophy, and coloboma, may also occur. In severe cases, affected fetuses with these malformations may be terminated (summary by Latour et al., 2020). For a phenotypic description and a discussion of genetic heterogeneity of Joubert syndrome, see JBTS1 (213300).

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

Autosomal dominant intellectual developmental disorder-65 (MRD65) is characterized by delayed motor and speech acquisition, variably impaired intellectual development, and behavioral abnormalities. Affected individuals also have dysmorphic facial features. Brain imaging may be normal or may show abnormalities, including cerebellar hypoplasia, poor development of the corpus callosum, dysmorphic hippocampus, and polymicrogyria. Feeding difficulties, hypotonia, and seizures may also be observed (Duncan et al., 2020).

Neurodevelopmental disorder with hypotonia and brain abnormalities (NEDHYBA) is characterized by impaired development of motor skills, cognitive function, and speech acquisition beginning in infancy or early childhood. Some affected individuals may have feeding difficulties, seizures, behavioral abnormalities, and nonspecific dysmorphic facial features. Brain imaging shows variable abnormalities, including corpus callosum defects, cerebellar defects, and decreased white matter volume. There is significant phenotypic variability (summary by Duncan et al., 2021).

A rare genetic multiple congenital anomalies/dysmorphic syndrome with variable intellectual disability and characteristics of abnormal head shape/metopic ridging and facial dysmorphism which may include arched eyebrows, ptosis, downslanting palpebral fissures, epicanthal folds and short upturned nose. Many patients present variable global developmental delay and/or autism spectrum disorder. Additional reported features are cardiac, skeletal or urogenital anomalies. Brain imaging may show agenesis of the corpus callosum.

Bryant-Li-Bhoj neurodevelopmental syndrome-2 (BRYLIB2) is a highly variable phenotype characterized predominantly by moderate to severe global developmental delay with impaired intellectual development, poor or absent speech, and delayed motor milestones. Most patients have hypotonia, although some have peripheral hypertonia. Common features include variable dysmorphic facial features, oculomotor abnormalities, feeding problems, and nonspecific brain imaging abnormalities. Additional features may include hearing loss, seizures, short stature, and mild skeletal defects (summary by Bryant et al., 2020). For a discussion of genetic heterogeneity of Bryant-Li-Bhoj neurodevelopmental syndrome, see BRYLIB1 (619720).

Neurodevelopmental disorder with spasticity, seizures, and brain abnormalities (NEDSSBA) is an autosomal recessive disorder characterized by global developmental delay apparent in infancy, axial hypotonia, peripheral spasticity, and early-onset seizures of various types and severity. Affected individuals have delayed walking or are unable to walk and show impaired intellectual development with poor or absent speech. Brain imaging may show developmental defects of the operculum, cerebellum, and corpus callosum. Death in early childhood may occur (Calame et al., 2021).

Complex cortical dysplasia with other brain malformations-12 (CDCBM12) is an autosomal recessive disorder of developmental neuronal migration characterized by severe to profound neurodevelopmental delay with absent speech, central hypotonia, peripheral spasticity, cortical visual impairment, and dysmorphic craniofacial features. Affected individuals usually have feeding difficulties and show minimal developmental progress of motor or cognitive skills. Most have microcephaly and develop early-onset refractory seizures. Brain imaging shows cortical abnormalities, such as lissencephaly and pachygyria, as well as other brain malformations, including thin or absent corpus callosum, dysplastic basal ganglia, and mild cerebellar hypoplasia. Due to the function of CAMSAP1 in microtubule stability and maintenance, this disorder can be classified as a 'tubulinopathy' (Khalaf-Nazzal et al., 2022). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039).

Thrombocytopenia-8 with dysmorphic features and developmental delay (THC8) is an autosomal dominant syndromic disorder characterized by early-childhood onset of chronic thrombocytopenia with anisotropy and immature enlarged platelets, usually without spontaneous bleeding episodes. Affected individuals have dysmorphic facial features and variable developmental delay with speech delay and mildly impaired intellectual development (Latham et al., 2018). For a discussion of genetic heterogeneity of thrombocytopenia, see 313900.

Neurodevelopmental disorder with hypotonia and characteristic brain abnormalities (NEDHBA) is an autosomal recessive disorder characterized by impaired intellectual development with striking radiologic abnormalities of the lateral ventricles (Fasham et al., 2023).

Jeffries-Lakhani neurodevelopmental syndrome (JELANS) is an autosomal recessive disorder characterized by hypotonia, early-onset seizures, and global developmental delay apparent from infancy. Affected individuals have motor delay, speech delay, and impaired intellectual development, and about half of patients are nonambulatory and/or nonverbal. Some patients have cardiac arrhythmia, but congenital cardiac septal defects are only rarely observed. Additional features may include feeding difficulties, recurrent infections, ocular defects, and nonspecific dysmorphic features. Premature death due to cardiac arrhythmia or epilepsy may occur (Jeffries et al., 2024).