Waardenburg syndrome type 3 is an auditory-pigmentary syndrome characterized by pigmentary abnormalities of the hair, skin, and eyes; congenital sensorineural hearing loss; presence of 'dystopia canthorum,' the lateral displacement of the ocular inner canthi; and upper limb abnormalities (reviews by Read and Newton, 1997 and Pingault et al., 2010). WS type 3 is also referred to as 'Klein-Waardenburg syndrome' (Gorlin et al., 1976). Clinical Variability of Waardenburg Syndrome Types 1-4 Waardenburg syndrome has been classified into 4 main phenotypes. Type I Waardenburg syndrome (WS1; 193500) is characterized by pigmentary abnormalities of the hair, including a white forelock and premature graying; pigmentary changes of the iris, such as heterochromia iridis and brilliant blue eyes; congenital sensorineural hearing loss; and 'dystopia canthorum.' WS type II (WS2) is distinguished from type I by the absence of dystopia canthorum. WS type III has dystopia canthorum and is distinguished by the presence of upper limb abnormalities. WS type IV (WS4; 277580), also known as Waardenburg-Shah syndrome, has the additional feature of Hirschsprung disease (reviews by Read and Newton, 1997 and Pingault et al., 2010).

Lathosterolosis is characterized by global developmental delays, intellectual disability, microcephaly, characteristic facial features (bitemporal narrowing, sloping forehead, epicanthal folds, ptosis, downslanting palpebral fissures, anteverted nares, broad nasal tip, long philtrum, high-arched palate, and micrognathia), cataracts, digit anomalies (postaxial polydactyly, toe syndactyly), and liver disease. The severity of liver disease can range from asymptomatic elevation of liver enzymes to cirrhosis and liver failure.

Mowat-Wilson syndrome (MWS) is characterized by distinctive facial features (widely spaced eyes, broad eyebrows with a medial flare, low-hanging columella, prominent or pointed chin, open-mouth expression, and uplifted earlobes with a central depression), congenital heart defects with predilection for abnormalities of the pulmonary arteries and/or valves, Hirschsprung disease or chronic constipation, genitourinary anomalies (particularly hypospadias in males), and hypogenesis or agenesis of the corpus callosum. Most affected individuals have moderate-to-severe intellectual disability. Speech is typically limited to a few words or is absent, with relative preservation of receptive language skills. Growth restriction with microcephaly and seizure disorder are also common. Most affected people have a happy demeanor and a wide-based gait that can sometimes be confused with Angelman syndrome.

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

3-M syndrome is characterized by severe pre- and postnatal growth deficiency (final height five standard deviations below the mean), characteristic facies (relative macrocephaly, dolichocephaly, triangular face, midface retrusion, thick eyebrows, fleshy nasal tip, long philtrum, thick vermilion of the upper and low lips, and pointed chin), and normal intelligence. Additional features of 3-M syndrome include short, broad neck, prominent trapezii, pectus carinatum/excavatum, short thorax, square shoulders, winged scapulae, thoracic kyphoscoliosis, hyperlordosis, spina bifida occulta, clinodactyly of the fifth fingers, generalized or distal joint hypermobility, dislocated hips, prominent heels, and pes planus. Males with 3-M syndrome can have hypogonadism and occasionally hypospadias.

Potocki-Lupski syndrome (PTLS) is characterized by cognitive, behavioral, and medical manifestations. Cognitively, most individuals present with developmental delay, later meeting criteria for moderate intellectual disability. Behaviorally, issues with attention, hyperactivity, withdrawal, and anxiety may be seen. Some individuals meet criteria for autism spectrum disorder. Medically, hypotonia, oropharyngeal dysphagia leading to failure to thrive, congenital heart disease, hypoglycemia associated with growth hormone deficiency, and mildly dysmorphic facial features are observed. Medical manifestations typically lead to identification of PTLS in infancy; however, those with only behavioral and cognitive manifestations may be identified in later childhood.

3-M syndrome is characterized by severe pre- and postnatal growth deficiency (final height five standard deviations below the mean), characteristic facies (relative macrocephaly, dolichocephaly, triangular face, midface retrusion, thick eyebrows, fleshy nasal tip, long philtrum, thick vermilion of the upper and low lips, and pointed chin), and normal intelligence. Additional features of 3-M syndrome include short, broad neck, prominent trapezii, pectus carinatum/excavatum, short thorax, square shoulders, winged scapulae, thoracic kyphoscoliosis, hyperlordosis, spina bifida occulta, clinodactyly of the fifth fingers, generalized or distal joint hypermobility, dislocated hips, prominent heels, and pes planus. Males with 3-M syndrome can have hypogonadism and occasionally hypospadias.

Asparagine synthetase deficiency (ASD) mainly presents as a triad of congenital microcephaly, severe developmental delay, and axial hypotonia followed by spastic quadriplegia. Low cerebrospinal fluid (CSF) asparagine level can help the clinician in differentiating this disorder from others. In most cases age of onset of apnea, excessive irritability, and seizures is soon after birth. Affected individuals typically do not acquire any developmental milestones. Spastic quadriplegia can lead to severe contractures of the limbs and neurogenic scoliosis. Feeding difficulties (gastroesophageal reflux disease, frequent vomiting, swallowing dysfunction, and gastroesophageal incoordination) are a significant problem in most affected individuals. A majority have cortical blindness. MRI findings are nonspecific but may include generalized atrophy and simplified gyral pattern.

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

BCL11A-related intellectual disability (BCL11A-ID) is characterized by developmental delay / intellectual disability of variable degree, neonatal hypotonia, microcephaly, distinctive but variable facial characteristics, behavior problems, and asymptomatic persistence of fetal hemoglobin. Growth delay, seizures, and autism spectrum disorder have also been reported in some affected individuals.

Developmental and epileptic encephalopathy-91 (DEE91) is characterized by delayed psychomotor development apparent in infancy and resulting in severely to profoundly impaired intellectual development with poor or absent speech. Most patients never achieve independent walking. Patients typically have onset of refractory multifocal seizures between the first weeks and years of life, and some may show developmental regression. Additional features, such as hypotonia and cortical visual impairment, are more variable (summary by Myers et al., 2017). For a discussion of genetic heterogeneity of DEE, see 308350.

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).

Turnpenny-Fry syndrome (TPFS) is characterized by developmental delay, impaired intellectual development, impaired growth, and recognizable facial features that include frontal bossing, sparse hair, malar hypoplasia, small palpebral fissures and oral stoma, and dysplastic 'satyr' ears. Other common findings include feeding problems, constipation, and a range of brain, cardiac, vascular, and skeletal malformations (Turnpenny et al., 2018).

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

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).

Cardioacrofacial dysplasia-2 (CAFD2) is characterized by congenital cardiac defects, primarily common atrium or atrioventricular septal defect; limb anomalies, including short limbs, brachydactyly, and postaxial polydactyly; and dysmorphic facial features. Developmental delay of variable severity has also been observed (Palencia-Campos et al., 2020). For a discussion of genetic heterogeneity of CAFD, see CAFD1 (619142).

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

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

Parenti-Mignot neurodevelopmental syndrome (PMNDS) is an autosomal dominant neurodevelopmental disorder frequently characterized by impaired intellectual development, speech delay, motor delay, behavioral problems, and epilepsy (Parenti et al., 2021).

Neurodevelopmental disorder with hypotonia, dysmorphic facies, and skin abnormalities (NEDHFS) is an autosomal recessive disorder characterized by severe global developmental delay with impaired intellectual development and poor or absent speech. Affected individuals have dysmorphic facies, including large abnormally shaped ears and strabismus, hypotonia, and dry skin with keratosis pilaris. Some patients develop seizures. Metabolic studies are unremarkable (Morava et al., 2021).

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).

Autosomal recessive intellectual developmental disorder-80 with variant lissencephaly (MRT80) is characterized by global developmental delay with mildly to moderately impaired intellectual development and behavioral abnormalities. Speech delay and motor abnormalities, such as hypotonia, may also be present. Brain imaging shows lissencephaly with pachygyria and mild cortical thickening in the frontotemporal lobes (Uctepe et al., 2024).