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

Dyggve-Melchior-Clausen disease (DMC) is an autosomal recessive disorder characterized by progressive spondyloepimetaphyseal dysplasia and impaired intellectual development. Short-trunk dwarfism and microcephaly are present, and specific radiologic appearances most likely reflect abnormalities of the growth plates, including platyspondyly with notched end plates, metaphyseal irregularities, laterally displaced capital femoral epiphyses, and small iliac wings with lacy iliac crests (summary by El Ghouzzi et al., 2003).

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).

A rare disorder of histidine metabolism characterized by histidinuria without histidinemia due to impaired intestinal and renal tubular absorption of histidine. Developmental delay, intellectual disability, seizures, and mild dysmorphic features have been reported in association. There have been no further descriptions in the literature since 1992.

Sialuria is a rare inborn error of metabolism in which excessive free sialic acid is synthesized. Clinical features include hepatosplenomegaly, coarse facial features, and varying degrees of developmental delay (summary by Enns et al., 2001).

Wiedemann-Rautenstrauch syndrome (WDRTS) is a rare autosomal recessive neonatal progeroid disorder characterized by intrauterine growth retardation, failure to thrive, short stature, a progeroid appearance, hypotonia, and variable mental impairment (summary by Toriello, 1990). Average survival in WDRTS is 7 months, although survival into the third decade of life has been reported (Akawi et al., 2013).

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

Pseudodiastrophic dysplasia (PDD) is an extremely rare and severe skeletal dysplasia associated with prenatal manifestation and early lethality. Phenotypic features include short-limbed short stature at birth, facial dysmorphism, and distinctive skeletal abnormalities including short ribs, mild to moderate platyspondyly, shortened long bones with metaphyseal flaring, elongation of the proximal and middle phalanges with subluxation of the proximal interphalangeal joints, subluxation of the elbow, and talipes equinovarus (summary by Byrne et al., 2020). Based on genetic analysis of patients with a clinical diagnosis of PDD, Byrne et al. (2020) proposed that PDD is likely not a separate genetic disorder, but rather the most severe phenotypic manifestation of skeletal dysplasia arising from defects in proteoglycan (PG) biosynthesis (see MOLECULAR GENETICS).

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

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

A rare multiple congenital malformation syndrome with characteristics of blepharophimosis, ptosis, dental hypoplasia, hearing impairment and intellectual disability. Abnormal ears, microcephaly, and growth retardation have been reported occasionally. Male patients may show cryptorchidism and scrotal hypoplasia. Most reported cases are sporadic, except the original cases of Ohdo who described two affected sisters and a first cousin, suggesting autosomal recessive inheritance. Autosomal dominant, X-linked- and mitochondrial inheritance have also been suggested.

Classic Joubert syndrome (JS) is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. Additional findings can include retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen.

Snyder-Robinson syndrome (SRS) is an X-linked intellectual disability syndrome characterized by asthenic build, facial dysmorphism with a prominent lower lip, kyphoscoliosis, osteoporosis, speech abnormalities, and seizures. Developmental delay usually presents as failure to meet early developmental milestones and then evolves to moderate to profound intellectual disability (which appears to remain stable over time) and variable motor disability. Asthenic habitus and low muscle mass usually develop during the first year, even in males who are ambulatory. During the first decade, males with SRS develop osteoporosis, resulting in fractures in the absence of trauma.

Wieacker-Wolff syndrome (WRWF) is a severe X-linked recessive neurodevelopmental disorder affecting the central and peripheral nervous systems. It is characterized by onset of muscle weakness in utero (fetal akinesia), which results in arthrogryposis multiplex congenita (AMC) apparent at birth. Affected boys are born with severe contractures, show delayed motor development, facial and bulbar weakness, characteristic dysmorphic facial features, and skeletal abnormalities, such as hip dislocation, scoliosis, and foot deformities. Additional features include global developmental delay with poor or absent speech and impaired intellectual development, feeding difficulties and poor growth, hypotonia, hypogenitalism, and spasticity. Carrier females may be unaffected or have mild features of the disorder (summary by Hirata et al., 2013 and Frints et al., 2019).

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

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

Aymé-Gripp syndrome is classically defined as the triad of bilateral early cataracts, sensorineural hearing loss, and characteristic facial features in combination with neurodevelopmental abnormalities. The facial features are often described as "Down syndrome-like" and include brachycephaly, flat facial appearance, short nose, long philtrum, narrow mouth, and low-set and posteriorly rotated ears. Hearing loss is often congenital. Other features may include postnatal short stature, seizure disorder, nonspecific brain abnormalities on head imaging, skeletal abnormalities, and joint limitations. A subset of individuals have been found to have pericarditis or pericardial effusion during the neonatal or infantile period. All affected individuals have had developmental delay, but the degree of cognitive impairment is extremely variable. Other features including gastrointestinal and endocrine abnormalities, ectodermal dysplasia (i.e., nail dystrophy and mammary gland hypoplasia), dental anomalies, and chronic glomerulopathy with proteinuria have been reported in rare affected individuals.

A very rare genetic overgrowth/obesity syndrome with characteristics of macrocephaly, obesity, mental (intellectual) disability and ocular abnormalities. Other frequent clinical signs include macrosomia, downslanting palpebral fissures, hypertelorism, broad nasal root, high and broad forehead and delay in bone maturation, in association with normal thyroid function and karyotype.

Congenital disorders of glycosylation (CDGs) are metabolic deficiencies in glycoprotein biosynthesis that usually cause severe mental and psychomotor retardation. Different forms of CDGs can be recognized by altered isoelectric focusing (IEF) patterns of serum transferrin. For a general discussion of CDGs, see CDG Ia (212065) and CDG Ib (602579).

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.

Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, a bleeding diathesis, and, in some individuals, pulmonary fibrosis, granulomatous colitis, or immunodeficiency. Ocular findings include reduced iris pigment with iris transillumination, reduced retinal pigment, foveal hypoplasia with significant reduction in visual acuity (usually in the range of 20/50 to 20/400), nystagmus, and increased crossing of the optic nerve fibers. Hair color ranges from white to brown; skin color ranges from white to olive and is usually a shade lighter than that of other family members. The bleeding diathesis can result in variable bruising, epistaxis, gingival bleeding, postpartum hemorrhage, colonic bleeding, and prolonged bleeding with menses or after tooth extraction, circumcision, and other surgeries. Pulmonary fibrosis, a restrictive lung disease, typically causes symptoms in the early thirties and can progress to death within a decade. Granulomatous colitis is severe in about 15% of affected individuals. Neutropenia and/or immune defects occur primarily in individuals with pathogenic variants in AP3B1 and AP3D1.

Nablus mask-like facial syndrome (NMLFS) is a rare entity defined by distinctive facial features, including blepharophimosis, tight-appearing glistening facial skin, an abnormal hair pattern with an upswept frontal hairline, sparse arched eyebrows, flat and broad nose, long philtrum, distinctive ears, and a happy demeanor (summary by Jain et al., 2010).

Craniolenticulosutural dysplasia is characterized by facial dysmorphism, late-closing fontanels, cataract, and skeletal defects (summary by Boyadjiev et al., 2011).

Claes-Jensen type of X-linked syndromic intellectual developmental disorder (MRXSCJ) is characterized by impaired intellectual development with substantial clinical heterogeneity in affected males. However, males are usually reported to have short stature, microcephaly, hyperreflexia, and aggressive behavior. In rare cases, female carriers exhibit mildly impaired intellectual development or learning difficulties (summary by Guerra et al., 2020).

Waardenburg syndrome type I (WS1) is an auditory-pigmentary disorder comprising congenital sensorineural hearing loss and pigmentary disturbances of the iris, hair, and skin along with dystopia canthorum (lateral displacement of the inner canthi). The hearing loss in WS1, observed in approximately 60% of affected individuals, is congenital, typically non-progressive, either unilateral or bilateral, and sensorineural. Most commonly, hearing loss in WS1 is bilateral and profound (>100 dB). The majority of individuals with WS1 have either a white forelock or early graying of the scalp hair before age 30 years. The classic white forelock observed in approximately 45% of individuals is the most common hair pigmentation anomaly seen in WS1. Affected individuals may have complete heterochromia iridium, partial/segmental heterochromia, or hypoplastic or brilliant blue irides. Congenital leukoderma is frequently seen on the face, trunk, or limbs.

Disorders of intracellular cobalamin metabolism have a variable phenotype and age of onset that are influenced by the severity and location within the pathway of the defect. The prototype and best understood phenotype is cblC; it is also the most common of these disorders. The age of initial presentation of cblC spans a wide range: In utero with fetal presentation of nonimmune hydrops, cardiomyopathy, and intrauterine growth restriction. Newborns, who can have microcephaly, poor feeding, and encephalopathy. Infants, who can have poor feeding and slow growth, neurologic abnormality, and, rarely, hemolytic uremic syndrome (HUS). Toddlers, who can have poor growth, progressive microcephaly, cytopenias (including megaloblastic anemia), global developmental delay, encephalopathy, and neurologic signs such as hypotonia and seizures. Adolescents and adults, who can have neuropsychiatric symptoms, progressive cognitive decline, thromboembolic complications, and/or subacute combined degeneration of the spinal cord.

Teebi-Shaltout syndrome is characterized by slow hair growth, scaphocephaly with prominent forehead, bitemporal depression, absence of primary teeth, camptodactyly, and caudal appendage with sacral dimple (summary by Aldemir et al., 2013).

Patients with mutations in the receptor for insulin-like growth factor I show intrauterine growth retardation and postnatal growth failure, resulting in short stature and microcephaly. Other features may include delayed bone age, developmental delay, and dysmorphic features.

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).

Gillessen-Kaesbach-Nishimura syndrome is an autosomal recessive multiple congenital anomaly disorder characterized by skeletal dysplasia, dysmorphic facial features, and variable visceral abnormalities, including polycystic kidneys, diaphragmatic hernia, lung hypoplasia, and congenital heart defects. It may be lethal in utero or early in life. The disorder is at the severe end of the phenotypic spectrum of congenital disorders of glycosylation (summary by Tham et al., 2016).

NOTCH3-related lateral meningocele syndrome (LMS) is characterized by multiple lateral spinal meningoceles (protrusions of the arachnoid and dura through spinal foramina), distinctive facial features, joint hyperextensibility, hypotonia, and skeletal, cardiac, and urogenital anomalies. Neurologic sequelæ of the meningoceles depend on size and location and can include neurogenic bladder, paresthesia, back pain, and/or paraparesis. Other neurologic findings can include Chiari I malformation, syringomyelia, and rarely, hydrocephalus. Additional findings of LMS include developmental delay, mixed or conductive hearing loss, and cleft palate. Skeletal abnormalities may include scoliosis, vertebral fusion, scalloping of vertebrae, and wormian bones. Infants may demonstrate feeding difficulties with poor weight gain.

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

Kaufman oculocerebrofacial syndrome (KOS) is characterized by developmental delay, severe intellectual disability, and distinctive craniofacial features. Most affected children have prenatal-onset microcephaly, hypotonia, and growth deficiency. Feeding issues, ocular abnormalities, hearing impairment, and respiratory tract abnormalities are common. Ocular abnormalities can include structural abnormalities (microcornea or microphthalmia, coloboma, optic nerve hypoplasia), refractive errors (myopia ± astigmatism, hyperopia), strabismus, and entropion. Both conductive and sensorineural hearing loss have been reported as well as mixed conductive-sensorineural hearing loss of variable severity. Breathing problems can lead to prolonged hospitalization after birth in more than half of individuals. Less common findings include ectodermal abnormalities, cardiac manifestations, urogenital abnormalities, seizures, and skeletal abnormalities.

A rare genetic disease characterized by the presence of Müllerian duct derivatives (rudimentary uterus, fallopian tubes, and atretic vagina) and other genital anomalies (cryptorchidism, micropenis) in male newborns, intestinal and pulmonary lymphangiectasia, protein-losing enteropathy, hepatomegaly, and renal anomalies. Postaxial polydactyly, facial dysmorphism (including broad nasal bridge, bulbous nasal tip, long and prominent upper lip with smooth philtrum, hypertrophic alveolar ridges, and mild retrognathia, among other features), and short limbs have also been described. The syndrome is fatal in infancy.

Blepharophimosis-intellectual disability syndrome, Verloes type is a rare, genetic multiple congenital anomalies/dysmorphic syndrome characterized by congenital microcephaly, severe epilepsy with hypsarrhythmia, adducted thumbs, abnormal genitalia, and normal thyroid function. Hypotonia, moderate to severe psychomotor delay, and characteristic facial dysmorphism (including round face with prominent cheeks, blepharophimosis, large, bulbous nose with wide alae nasi, posteriorly rotated ears with dysplastic conchae, narrow mouth, cleft palate, and mild micrognathia) are additional characteristic features.

Trichorhinophalangeal syndrome (TRPS) is characterized by craniofacial and skeletal abnormalities. Craniofacial features include sparse, slowly growing scalp hair, laterally sparse eyebrows, a bulbous tip of the nose, protruding ears, long flat philtrum, and thin upper vermillion border. The most typical radiographic findings in TRPS are cone-shaped epiphyses, predominantly at the middle phalanges. Hip malformations such as coxa plana, coxa magna, or coxa vara are present in over 70% of patients. In older patients, the hip abnormalities resemble degenerative arthrosis. TRPS3 differs from TRPS1 by the presence of severe brachydactyly, due to short metacarpals, and severe short stature (summary by Ludecke et al., 2001).

Mandibulofacial dysostosis-macroblepharon-macrostomia syndrome is a rare developmental defect during embryogenesis disorder characterized by macroblepharon, ectropion, and facial dysmorphism which includes severe hypertelorism, downslanting palpebral fissures, posteriorly rotated ears, broad nasal bridge, long and smooth philtrum, and macrostomia with thin upper lip vermilion border. Other features may include large fontanelles, prominent metopic ridge, thick eyebrows, mild synophrys, increased density of upper eyelashes, anterverted nares, abnormal dentition and capillary hemangioma.

PIK3CA-related overgrowth spectrum (PROS) encompasses a range of clinical findings in which the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia. Prior to the identification of PIK3CA as the causative gene, PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved (e.g., MCAP [megalencephaly-capillary malformation] syndrome and CLOVES [congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies] syndrome). The predominant areas of overgrowth include the brain, limbs (including fingers and toes), trunk (including abdomen and chest), and face, all usually in an asymmetric distribution. Generalized brain overgrowth may be accompanied by secondary overgrowth of specific brain structures resulting in ventriculomegaly, a markedly thick corpus callosum, and cerebellar tonsillar ectopia with crowding of the posterior fossa. Vascular malformations may include capillary, venous, and less frequently, arterial or mixed (capillary-lymphatic-venous or arteriovenous) malformations. Lymphatic malformations may be in various locations (internal and/or external) and can cause various clinical issues, including swelling, pain, and occasionally localized bleeding secondary to trauma. Lipomatous overgrowth may occur ipsilateral or contralateral to a vascular malformation, if present. The degree of intellectual disability appears to be mostly related to the presence and severity of seizures, cortical dysplasia (e.g., polymicrogyria), and hydrocephalus. Many children have feeding difficulties that are often multifactorial in nature. Endocrine issues affect a small number of individuals and most commonly include hypoglycemia (largely hypoinsulinemic hypoketotic hypoglycemia), hypothyroidism, and growth hormone deficiency.

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

A rare genetic developmental defect during embryogenesis disorder with characteristics of craniofacial dysmorphism (including brachycephaly, prominent forehead, sparse lateral eyebrows, severe hypertelorism, upslanting palpebral fissures, epicanthal folds, protruding ears, broad nasal bridge, pointed nasal tip, flat philtrum, anteverted nostrils, large mouth, thin upper vermilion border, highly arched palate and mild micrognathia) associated with osteopenia leading to repeated long bone fractures, severe myopia, mild to moderate sensorineural or mixed hearing loss, enamel hypoplasia, sloping shoulders and mild intellectual disability. There is evidence the disease can be caused by homozygous mutation in the IRX5 gene on chromosome 16q11.2.

Any autosomal recessive non-syndromic intellectual disability in which the cause of the disease is a mutation in the NSUN2 gene.

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.

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.

SATB2-associated syndrome (SAS) is a multisystem disorder characterized by significant neurodevelopmental compromise with limited to absent speech, behavioral issues, and craniofacial anomalies. All individuals described to date have manifest developmental delay / intellectual disability, with severe speech delay. Affected individuals often have hypotonia and feeding difficulties in infancy. Behavioral issues may include autistic features, hyperactivity, and aggressiveness. Craniofacial anomalies may include palatal abnormalities (cleft palate, high-arched palate, and bifid uvula), micrognathia, and abnormal shape or size of the upper central incisors. Less common features include skeletal anomalies (osteopenia, pectus deformities, kyphosis/lordosis, and scoliosis), growth restriction, strabismus/refractive errors, congenital heart defects, genitourinary anomalies, and epilepsy. While dysmorphic features have been described in individuals with this condition, these features are not typically distinctive enough to allow for a clinical diagnosis of SAS.

SLC25A24 Fontaine progeroid syndrome is a multisystem connective tissue disorder characterized by poor growth, abnormal skeletal features, and distinctive craniofacial features with sagging, thin skin, and decreased subcutaneous fat suggesting an aged appearance that is most pronounced in infancy and improves with time. Characteristic radiographic features include turribrachycephaly with widely open anterior fontanelle, craniosynostosis, and anomalies of the terminal phalanges. Cardiovascular, genitourinary, ocular, and gastrointestinal abnormalities may also occur. To date, 13 individuals with a molecularly confirmed diagnosis of SLC25A24 Fontaine progeroid syndrome have been described.

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

A rare chromosomal anomaly syndrome, resulting from the partial deletion of the long arm of chromosome 22, outside the DiGeorge critical region. The phenotype is characterized by prematurity, pre- and post-natal growth retardation, developmental delay (particularly speech), mild intellectual disability, variable cardiac defects, and minor skeletal anomalies (such as clinodactyly). Dysmorphic features present in half of the individuals include microcephaly, arched eyebrows, deep set eyes, narrow upslanting palpebral fissures, ear abnormalities (low-set ears, tags and pits), hypoplastic alae nasi, smooth philtrum, down-turned mouth, thin upper lip, retro/micrognatia and pointed chin. For certain very distal deletions including the <i>SMARCB1</i> gene, there is a risk of developing malignant rhabdoid tumours. Most deletions are <i>de novo </i>.

FLNA deficiency is associated with a phenotypic spectrum that includes FLNA-related periventricular nodular heterotopia (Huttenlocher syndrome), congenital heart disease (patent ductus arteriosus, atrial and ventricular septal defects), valvular dystrophy, dilation and rupture of the thoracic aortic, pulmonary disease (pulmonary hypertension, alveolar hypoplasia, emphysema, asthma, chronic bronchitis), gastrointestinal dysmotility and obstruction, joint hypermobility, and macrothrombocytopenia.

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

Any autosomal recessive non-syndromic intellectual disability in which the cause of the disease is a mutation in the TRAPPC9 gene.

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

An extremely rare form of carbohydrate deficient glycoprotein syndrome with, in the few cases reported to date, variable signs including microcephaly, growth retardation, psychomotor retardation and facial dysmorphism.

A rare genetic multiple congenital anomalies/dysmorphic syndrome characterized by intellectual disability, obesity, macrocephaly, behavioral abnormalities (such as aggressive tantrums and autistic-like behavior), and delayed speech development. Dysmorphic facial features include large, square forehead, prominent supraorbital ridges, broad nasal tip, large ears, prominent lower lip, and minor dental anomalies such as small upper lateral incisors and central incisor gap.

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.

BBS2 is an autosomal recessive ciliopathy characterized by retinal degeneration, polydactyly, renal disease, hypogonadism, obesity, dysmorphic features, and variable degrees of cognitive impairment (Innes et al., 2010). Mutation in the BBS2 gene is the third most frequent cause of BBS, accounting for approximately 8% of cases (Zaghloul and Katsanis, 2009). For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).

X-linked Opitz G/BBB syndrome (X-OS) is a multiple-congenital-anomaly disorder characterized by facial anomalies (hypertelorism, prominent forehead, widow's peak, broad nasal bridge, anteverted nares), genitourinary abnormalities (hypospadias, cryptorchidism, and hypoplastic/bifid scrotum), and laryngotracheoesophageal defects. Developmental delay and intellectual disability are observed in about 50% of affected males. Cleft lip and/or palate are present in approximately 50% of affected individuals. Other malformations (present in <50% of individuals) include congenital heart defects, imperforate or ectopic anus, and midline brain defects (Dandy-Walker malformation and agenesis or hypoplasia of the corpus callosum and/or cerebellar vermis). Wide clinical variability occurs even among members of the same family. Female heterozygotes usually manifest hypertelorism only.

6q25 microdeletion syndrome is a recently described syndrome characterized by developmental delay, facial dysmorphism and hearing loss.

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).

Cranioectodermal dysplasia (CED) is a ciliopathy with skeletal involvement (narrow thorax, shortened proximal limbs, syndactyly, polydactyly, brachydactyly), ectodermal features (widely spaced hypoplastic teeth, hypodontia, sparse hair, skin laxity, abnormal nails), joint laxity, growth deficiency, and characteristic facial features (frontal bossing, low-set simple ears, high forehead, telecanthus, epicanthal folds, full cheeks, everted lower lip). Most affected children develop nephronophthisis that often leads to end-stage kidney disease in infancy or childhood, a major cause of morbidity and mortality. Hepatic fibrosis and retinal dystrophy are also observed. Dolichocephaly, often secondary to sagittal craniosynostosis, is a primary manifestation that distinguishes CED from most other ciliopathies. Brain malformations and developmental delay may also occur.

Meier-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\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\nMost 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\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).\n\nAdditional features of Meier-Gorlin syndrome can include difficulty feeding and a lung condition known as pulmonary emphysema or other breathing problems.

A heterozygous deletion of chromosome 15q11.2 may increase the susceptibility to neuropsychiatric or neurodevelopmental problems, including delayed psychomotor development, speech delay, autism spectrum disorder, attention deficit-hyperactivity disorder, obsessive-compulsive disorder, and possibly seizures (summary by Doornbos et al., 2009 and Burnside et al., 2011). See also chromosome 15q11.2 duplication syndrome (608636).

Geleophysic dysplasia, a progressive condition resembling a lysosomal storage disorder, is characterized by short stature, short hands and feet, progressive joint limitation and contractures, distinctive facial features, progressive cardiac valvular disease, and thickened skin. Intellect is normal. Major findings are likely to be present in the first year of life. Cardiac, respiratory, and lung involvement result in death before age five years in approximately 33% of individuals with ADAMTSL2-related geleophysic dysplasia.

Geleophysic dysplasia, a progressive condition resembling a lysosomal storage disorder, is characterized by short stature, short hands and feet, progressive joint limitation and contractures, distinctive facial features, progressive cardiac valvular disease, and thickened skin. Intellect is normal. Major findings are likely to be present in the first year of life. Cardiac, respiratory, and lung involvement result in death before age five years in approximately 33% of individuals with ADAMTSL2-related geleophysic dysplasia.

Rafiq syndrome (RAFQS) is an autosomal recessive disorder characterized by variably impaired intellectual and motor development, a characteristic facial dysmorphism, truncal obesity, and hypotonia. The facial dysmorphism comprises prominent eyebrows with lateral thinning, downward-slanting palpebral fissures, bulbous tip of the nose, large ears, and a thin upper lip. Behavioral problems, including overeating, verbal and physical aggression, have been reported in some cases. Serum transferrin isoelectric focusing shows a type 2 pattern (summary by Balasubramanian et al., 2019).

Cranioectodermal dysplasia (CED) is a ciliopathy with skeletal involvement (narrow thorax, shortened proximal limbs, syndactyly, polydactyly, brachydactyly), ectodermal features (widely spaced hypoplastic teeth, hypodontia, sparse hair, skin laxity, abnormal nails), joint laxity, growth deficiency, and characteristic facial features (frontal bossing, low-set simple ears, high forehead, telecanthus, epicanthal folds, full cheeks, everted lower lip). Most affected children develop nephronophthisis that often leads to end-stage kidney disease in infancy or childhood, a major cause of morbidity and mortality. Hepatic fibrosis and retinal dystrophy are also observed. Dolichocephaly, often secondary to sagittal craniosynostosis, is a primary manifestation that distinguishes CED from most other ciliopathies. Brain malformations and developmental delay may also occur.

The 17q12 recurrent duplication is characterized by intellectual abilities ranging from normal to severe disability and other variable clinical manifestations. Speech delay is common, and most affected individuals have some degree of hypotonia and gross motor delay. Behavioral and psychiatric conditions reported in some affected individuals include autism spectrum disorder, schizophrenia, and behavioral abnormalities (aggression and self-injury). Seizures are present in 75%. Additional common findings include microcephaly, ocular abnormalities, and endocrine abnormalities. Short stature and renal and cardiac abnormalities are also reported in some individuals. Penetrance is incomplete and clinical findings are variable.

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

HCFP3 is an autosomal recessive congenital cranial dysinnervation disorder characterized by isolated dysfunction of the seventh cranial nerve resulting in facial palsy. Additional features may include orofacial anomalies, such as smooth philtrum, lagophthalmos, swallowing difficulties, and dysarthria, as well as hearing loss. There is some phenotypic overlap with Moebius syndrome (see, e.g., 157900), but patients with HCFP usually retain full eye motility or have esotropia without paralysis of the sixth cranial nerve (summary by Vogel et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of hereditary congenital facial paresis, see 601471.

PACS1 neurodevelopmental disorder (PACS1-NDD) is characterized by mild-to-severe neurodevelopmental delays. Language skills are more severely affected than motor skills. Hypotonia is reported in about a third of individuals and is noted to improve over time. Approximately 60% of individuals are ambulatory. Feeding difficulty is common, with 25% requiring gastrostomy tube to maintain appropriate caloric intake. Other common features include constipation, seizures, behavioral issues, congenital heart anomalies, short stature, and microcephaly. Common facial features include hypertelorism, downslanting palpebral fissures, bulbous nasal tip, low-set and simple ears, smooth philtrum, wide mouth with downturned corners, thin upper vermilion, and wide-spaced teeth. To date approximately 35 individuals with PACS1-NDD have been reported.

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.

Meckel syndrome, also known as Meckel-Gruber syndrome, is a severe pleiotropic autosomal recessive developmental disorder caused by dysfunction of primary cilia during early embryogenesis. There is extensive clinical variability and controversy as to the minimum diagnostic criteria. Early reports, including that of Opitz and Howe (1969) and Wright et al. (1994), stated that the classic triad of Meckel syndrome comprises (1) cystic renal disease; (2) a central nervous system malformation, most commonly occipital encephalocele; and (3) polydactyly, most often postaxial. However, based on a study of 67 patients, Salonen (1984) concluded that the minimum diagnostic criteria are (1) cystic renal disease; (2) CNS malformation, and (3) hepatic abnormalities, including portal fibrosis or ductal proliferation. In a review of Meckel syndrome, Logan et al. (2011) stated that the classic triad first described by Meckel (1822) included occipital encephalocele, cystic kidneys, and fibrotic changes to the liver. Genetic Heterogeneity of Meckel Syndrome See also MKS2 (603194), caused by mutation in the TMEM216 gene (613277) on chromosome 11q12; MKS3 (607361), caused by mutation in the TMEM67 gene (609884) on chromosome 8q; MKS4 (611134), caused by mutation in the CEP290 gene (610142) on chromosome 12q; MKS5 (611561), caused by mutation in the RPGRIP1L gene (610937) on chromosome 16q12; MKS6 (612284), caused by mutation in the CC2D2A gene (612013) on chromosome 4p15; MKS7 (267010), caused by mutation in the NPHP3 (608002) gene on chromosome 3q22; MKS8 (613885), caused by mutation in the TCTN2 gene (613846) on chromosome 12q24; MKS9 (614209), caused by mutation in the B9D1 gene (614144) on chromosome 17p11; MKS10 (614175), caused by mutation in the B9D2 gene (611951) on chromosome 19q13; MKS11 (615397), caused by mutation in the TMEM231 gene (614949) on chromosome 16q23; MKS12 (616258), caused by mutation in the KIF14 gene (611279) on chromosome 1q32; MKS13 (617562), caused by mutation in the TMEM107 gene (616183) on chromosome 17p13; and MKS14 (619879), caused by mutation in the TXNDC15 gene (617778) on chromosome 5q31.

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

Loeys-Dietz syndrome (LDS) is characterized by vascular findings (cerebral, thoracic, and abdominal arterial aneurysms and/or dissections), skeletal manifestations (pectus excavatum or pectus carinatum, scoliosis, joint laxity, arachnodactyly, talipes equinovarus, cervical spine malformation and/or instability), craniofacial features (widely spaced eyes, strabismus, bifid uvula / cleft palate, and craniosynostosis that can involve any sutures), and cutaneous findings (velvety and translucent skin, easy bruising, and dystrophic scars). Individuals with LDS are predisposed to widespread and aggressive arterial aneurysms and pregnancy-related complications including uterine rupture and death. Individuals with LDS can show a strong predisposition for allergic/inflammatory disease including asthma, eczema, and reactions to food or environmental allergens. There is also an increased incidence of gastrointestinal inflammation including eosinophilic esophagitis and gastritis or inflammatory bowel disease. Wide variation in the distribution and severity of clinical features can be seen in individuals with LDS, even among affected individuals within a family who have the same pathogenic variant.

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.

Hennekam lymphangiectasia-lymphedema syndrome (HKLLS1) is an autosomal recessive disorder characterized by generalized lymphatic dysplasia affecting various organs, including the intestinal tract, pericardium, and limbs. Additional features of the disorder include facial dysmorphism and cognitive impairment (summary by Alders et al., 2014). Genetic Heterogeneity of Hennekam Lymphangiectasia-Lymphedema Syndrome See also HKLLS2 (616006), caused by mutation in the FAT4 gene (612411) on chromosome 4q28, and HKLLS3 (618154), caused by mutation in the ADAMTS3 gene (605011) on chromosome 4q13.

Desbuquois dysplasia (DBQD) is an autosomal recessive chondrodysplasia belonging to the multiple dislocation group and characterized by severe prenatal and postnatal growth retardation (stature less than -5 SD), joint laxity, short extremities, and progressive scoliosis. The main radiologic features are short long bones with metaphyseal splay, a 'Swedish key' appearance of the proximal femur (exaggerated trochanter), and advanced carpal and tarsal bone age with a delta phalanx (summary by Huber et al., 2009). Desbuquois dysplasia is clinically and radiographically heterogeneous, and had been classified into 2 types based on the presence (type 1) or absence (type 2) of characteristic hand anomalies, including an extra ossification center distal to the second metacarpal, delta phalanx, bifid distal thumb phalanx, and dislocation of the interphalangeal joints (Faivre et al., 2004). However, patients with and without these additional hand anomalies have been reported to have mutations in the same gene (see, e.g., CANT1); thus, these features are not distinctive criteria to predict the molecular basis of DBQD (Furuichi et al., 2011). In addition, Kim et al. (2010) described another milder variant of DBQD with almost normal outwardly appearing hands, but significant radiographic changes, including short metacarpals, elongated phalanges, and remarkably advanced carpal bone age. However, there is no accessory ossification center distal to the second metacarpal, and patients do not have thumb anomalies. Similar changes occur in the feet. These patients also tend to develop precocious osteoarthritis of the hand and spine with age. This phenotype is sometimes referred to as the 'Kim variant' of DBQD (Furuichi et al., 2011). Genetic Heterogeneity of Desbuquois Dysplasia DBQD2 (615777) is caused by mutation in the XYLT1 gene (608124) on chromosome 16p12. Two unrelated patients with immunodeficiency-23 (IMD23; 615816), due to mutation in the PGM3 gene (172100), were reported to have skeletal features reminiscent of DBQD.

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

Congenital aplastic deformities of the breast include amastia (total absence of breasts and nipple), athelia (absence of the nipple), and amazia (absence of the mammary gland). Most common is amastia. Bilateral absence of the breasts may occur as an isolated anomaly or may be associated with a syndrome or a cluster of other anomalies, including anhidrotic ectodermal dysplasia (305100) or Poland syndrome (173800) (summary by Papadimitriou et al., 2009). For a discussion of genetic heterogeneity of aplasia or hypoplasia of the breasts and/or nipples, see 113700.

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).

Any autosomal dominant non-syndromic intellectual disability in which the cause of the disease is a mutation in the COL4A3BP gene.

UNC80 deficiency is characterized by hypotonia, strabismus, oral motor dysfunction, postnatal growth deficiency, and developmental delay. The majority of individuals do not learn to walk. All individuals lack expressive language; however, many have expressive body language, and a few have used signs to communicate. Seizures may develop during infancy or childhood. Additional features can include nystagmus, extremity hypertonia, a high-pitched cry, repetitive and self-stimulatory behaviors, constipation, clubfeet, joint contractures, and scoliosis. For most individuals the UNC80 deficiency syndrome is not progressive. Individuals have slow acquisition of skills and do not have a loss of skills suggestive of neurodegeneration.

Takenouchi-Kosaki syndrome is a highly heterogeneous autosomal dominant complex congenital developmental disorder affecting multiple organ systems. The core phenotype includes delayed psychomotor development with variable intellectual disability, dysmorphic facial features, and cardiac, genitourinary, and hematologic or lymphatic defects, including thrombocytopenia and lymphedema. Additional features may include abnormalities on brain imaging, skeletal anomalies, and recurrent infections. Some patients have a milder disease course reminiscent of Noonan syndrome (see, e.g., NS1, 163950) (summary by Martinelli et al., 2018).

Nephrotic syndrome type 11 (NPHS11) is an autosomal recessive disorder of the kidney with onset in the first decade of life. The disorder is progressive and usually results in end-stage renal disease necessitating renal transplantation, although some patients may have a slightly milder phenotype (Miyake et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of nephrotic syndrome, see NPHS1 (256300).

Yuan-Harel-Lupski syndrome (YUHAL) is a complex neurodevelopmental disorder characterized by global developmental delay and early-onset peripheral neuropathy. The disorder comprises features of both demyelinating Charcot-Marie-Tooth disease type 1A (CMT1A; 118220), which results from duplication of the PMP22 gene on 17p12, and Potocki-Lupski syndrome (PTLS; 610883), which results from duplication of a slightly proximal region on 17p11.2 that includes the RAI1 gene. These 2 loci are about 2.5 Mb apart. The resultant YUHAL phenotype may be more severe in comparison to the individual contributions of each gene, with particularly early onset of peripheral neuropathy and features of both central and peripheral nervous system involvement (summary by Yuan et al., 2015).

Smith-Kingsmore syndrome (SKS) is a rare autosomal dominant syndromic intellectual disability syndrome characterized by macrocephaly, seizures, umbilical hernia, and facial dysmorphic features including frontal bossing, midface hypoplasia, small chin, hypertelorism with downslanting palpebral fissures, depressed nasal bridge, smooth philtrum, and thin upper lip (Smith et al., 2013; Baynam et al., 2015).

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

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).

Singleton-Merten syndrome (SGMRT) is an uncommon autosomal dominant disorder characterized by abnormalities of blood vessels, teeth, and bone. Calcifications of the aorta and aortic and mitral valves occur in childhood or puberty and can lead to early death. Dental findings include delayed primary tooth exfoliation and permanent tooth eruption, truncated tooth root formation, early-onset periodontal disease, and severe root and alveolar bone resorption associated with dysregulated mineralization, leading to tooth loss. Osseous features consist of osteoporosis, either generalized or limited to distal extremities, distal limb osteolysis, widened medullary cavities, and easy tearing of tendons from bone. Less common features are mild facial dysmorphism (high anterior hair line, broad forehead, smooth philtrum, thin upper vermilion border), generalized muscle weakness, psoriasis, early-onset glaucoma, and recurrent infections. The disorder manifests with variable inter- and intrafamilial phenotypes (summary by Rutsch et al., 2015). Genetic Heterogeneity of Singleton-Merten Syndrome An atypical form of Singleton-Merten syndrome (SGMRT2; 616298) is caused by mutation in the DDX58 gene (609631) on chromosome 9p21.

The 10q22.3-q23.2 region is characterized by a complex set of low-copy repeats (LCRs), which can give rise to various genomic changes mediated by nonallelic homologous recombination (NAHR). Recurrent deletions of chromosome 10q22.3-q23.2, including the BMPR1A gene (601299) have been associated with dysmorphic facies, developmental delay, and multiple congenital anomalies. Some patients with deletions that extend distally to include the PTEN gene (601728) have a more severe phenotype with infantile/juvenile polyposis, macrocephaly, dysmorphic facial features, and developmental delay (summary by van Bon et al., 2011).

EBF3 neurodevelopmental disorder (EBF3-NDD) is associated with developmental delay (DD) / intellectual disability (ID), speech delay, gait or truncal ataxia, hypotonia, behavioral problems, and facial dysmorphism. Variability between individuals with EBF3-NDD is significant. Although all affected children have DD noted in early infancy, intellect generally ranges from mild to severe ID, with two individuals functioning in the low normal range. Less common issues can include genitourinary abnormalities and gastrointestinal and/or musculoskeletal involvement. To date, 42 symptomatic individuals from 39 families have been reported.

GDACCF is an intellectual disability syndrome apparent soon after birth with neonatal hypotonia, poor feeding, and respiratory insufficiency followed by delayed psychomotor development and intellectual disability with poor speech. Brain imaging shows aplasia or hypoplasia of the corpus callosum. Affected individuals have variable dysmorphic facial features, and some may have dysplastic, cystic kidneys or mild cardiac defects (summary by Stevens et al., 2016).

Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, a bleeding diathesis, and, in some individuals, pulmonary fibrosis, granulomatous colitis, or immunodeficiency. Ocular findings include reduced iris pigment with iris transillumination, reduced retinal pigment, foveal hypoplasia with significant reduction in visual acuity (usually in the range of 20/50 to 20/400), nystagmus, and increased crossing of the optic nerve fibers. Hair color ranges from white to brown; skin color ranges from white to olive and is usually a shade lighter than that of other family members. The bleeding diathesis can result in variable bruising, epistaxis, gingival bleeding, postpartum hemorrhage, colonic bleeding, and prolonged bleeding with menses or after tooth extraction, circumcision, and other surgeries. Pulmonary fibrosis, a restrictive lung disease, typically causes symptoms in the early thirties and can progress to death within a decade. Granulomatous colitis is severe in about 15% of affected individuals. Neutropenia and/or immune defects occur primarily in individuals with pathogenic variants in AP3B1 and AP3D1.

RERE-related disorders are characterized by neurodevelopmental problems with or without structural anomalies of the eyes, heart, kidneys, and genitourinary tract and mild sensorineural hearing loss. Hypotonia and feeding problems are common among affected individuals. Developmental delay and intellectual disability range from mild to profound. Behavior problems may include attention-deficit/hyperactivity disorder, self-injurious behavior, and autism spectrum disorder. A variety of eye anomalies (coloboma, optic nerve anomalies, microphthalmia, and/or Peter's anomaly) and vision issues (myopia, anisometropia, astigmatism, exotropia, esotropia) have been reported. Congenital heart defects, most commonly septal defects, have also been described. Genitourinary abnormalities include vesicoureteral reflux, and cryptorchidism and hypospadias in males. Sensorineural hearing loss can be unilateral or bilateral.

Witteveen-Kolk syndrome (WITKOS) is an autosomal dominant disorder with characteristic distinctive facial features, microcephaly, short stature, and mildly impaired intellectual development with delayed cognitive and motor development and subtle anomalies on MRI-brain imaging (summary by Balasubramanian et al., 2021).

CDK13-related disorder, reported in 43 individuals to date, is characterized in all individuals by developmental delay / intellectual disability (DD/ID); nearly all individuals older than age one year display impaired verbal language skills (either absent or restricted speech). Other common findings are recognizable facial features in some individuals, behavioral problems (autism spectrum disorder or autistic traits/stereotypies, attention-deficit/hyperactivity disorder), feeding difficulties in infancy, structural cardiac defects, and seizures.

An inherited condition caused by autosomal dominant mutation(s) in the PPP1CB gene, encoding serine/threonine-protein phosphatase PP1-beta catalytic subunit. The condition is characterized by facial features similar to those seen in Noonan syndrome but may also include short stature, cognitive deficits, relative macrocephaly, small posterior fossa resulting in Chiari I malformation, hypernasal voice, cardiac defects, and ectodermal abnormalities, which typically presents as slow-growing, sparse, and/or unruly hair.

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

Intellectual developmental disorder with neuropsychiatric features is an autosomal recessive disorder characterized by moderate intellectual disability, relatively mild seizures, and neuropsychiatric abnormalities, such as anxiety, obsessive-compulsive behavior, and autistic features. Mild facial dysmorphic features may also be present (summary by Srour et al., 2017).

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

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).

A rare genetic disorder with characteristics of infantile onset of stagnation and regression of motor and language development resulting in complete lack of communication and purposeful movement. Further neurological manifestations include truncal hypotonia, appendicular spasticity, dystonia, optic disc pallor, peripheral neuropathy and neurogenic bladder. Patients also present multiple contractures, late-onset relative macrocephaly, short stature and facial dysmorphism (including coarse facial features, sloping forehead, thick eyebrows, low-set ears, prominent nose, flat philtrum, and prominent lower lip). Brain imaging at advanced stages shows diffuse abnormal white matter signal and severe atrophy. Sural nerve biopsy reveals decreased myelination.

NEDMIAL is a neurodevelopmental disorder characterized by delayed psychomotor development and hypotonia apparent from early infancy, resulting in feeding difficulties, ataxic gait or inability to walk, delayed or absent speech development, and impaired intellectual development, sometimes with behavioral abnormalities, such as hand-flapping. Additional common features may include sleep disorder, nonspecific dysmorphic facial features, and joint hyperlaxity (summary by Lessel et al., 2017 and Mannucci et al., 2021).

Rubinstein-Taybi syndrome (RSTS) is characterized by distinctive facial features, broad and often angulated thumbs and halluces, short stature, and moderate-to-severe intellectual disability. The characteristic craniofacial features are downslanted palpebral fissures, low-hanging columella, high palate, grimacing smile, and talon cusps. Prenatal growth is often normal, then height, weight, and head circumference percentiles rapidly drop in the first few months of life. Short stature is typical in adulthood. Obesity may develop in childhood or adolescence. Average IQ ranges between 35 and 50; however, developmental outcome varies considerably. Some individuals with EP300-RSTS have normal intellect. Additional features include ocular abnormalities, hearing loss, respiratory difficulties, congenital heart defects, renal abnormalities, cryptorchidism, feeding problems, recurrent infections, and severe constipation.

Ververi-Brady syndrome (VEBRAS) is characterized by mild developmental delay, mildly impaired intellectual development and speech delay, and mild dysmorphic facial features. Affected individuals can usually attend mainstream schools with support, and may also show autistic features (summary by Ververi et al., 2018).

Developmental and epileptic encephalopathy-64 (DEE64) is a neurodevelopmental disorder characterized by onset of seizures usually in the first year of life and associated with intellectual disability, poor motor development, and poor or absent speech. Additional features include hypotonia, abnormal movements, and nonspecific dysmorphic features. The severity is variable: some patients are unable to speak, walk, or interact with others as late as the teenage years, whereas others may have some comprehension (summary by Straub et al., 2018). For a general phenotypic description and 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).

Mullegama-Klein-Martinez syndrome (MKMS) is an X-linked recessive disorder with features of microcephaly, microtia, hearing loss, developmental delay, dysmorphic features, congenital heart defect, and digit abnormalities. Females are generally affected more severely than males (Mullegama et al., 2019).

IDDCDF is an autosomal recessive syndromic neurodevelopmental disorder characterized by globally impaired development with intellectual disability and speech delay, congenital cardiac malformations, and dysmorphic facial features. Additional features, such as distal skeletal anomalies, may also be observed (Stephen et al., 2018).

Polymicrogyria with or without vascular-type Ehlers-Danlos syndrome is an autosomal recessive disorder with a highly variable phenotype. Although all patients have polymicrogyria and other variable structural brain anomalies on imaging, only some show developmental delay and/or seizures. Similarly, only some patients have connective tissue defects that particularly affect the vascular system and can result in early death (summary by Vandervore et al., 2017).

Galloway-Mowat syndrome-7 (GAMOS7) is an autosomal recessive disorder characterized by developmental delay, microcephaly, and early-onset nephrotic syndrome (summary by Rosti et al., 2017). For a general phenotypic description and a discussion of genetic heterogeneity of GAMOS, see GAMOS1 (251300).

Myoectodermal gonadal dysgenesis syndrome (MEGD) is characterized by 46,XY complete or partial gonadal dysgenesis, or 46,XX gonadal dysgenesis, in association with extragonadal anomalies, including low birth weight, typical facies, rod and cone dystrophy, sensorineural hearing loss, omphalocele, anal atresia, renal agenesis, skeletal abnormalities, dry and scaly skin, severe myopathy, and neuromotor delay. Dysmorphic facial features along with muscular habitus are the hallmarks of the syndrome. Abnormal hair patterning with frontal upsweep and additional whorls, eyebrow abnormalities comprising broad, arched, and sparse or thick eyebrows, underdeveloped alae nasi, smooth philtrum, and low-set ears with overfolded helices facilitate a gestalt diagnosis. (Guran et al., 2019; Altunoglu et al., 2022).

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).

Cerebellar, ocular, craniofacial, and genital syndrome (COFG) is characterized by moderate to severe developmental delay and impaired intellectual development, severe cerebellar hypoplasia, a noticeably short forehead, medially sparse/flared and laterally extended eyebrows, corneal dystrophy, underdeveloped labioscrotal folds, and tufts of hair extruding from the lactiferous ducts with breast and nipple underdevelopment. Additional features such as pontine involvement, retinal degeneration, anteverted nares, and low-set ears have been variably observed (Rad 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).

Basilicata-Akhtar syndrome (MRXSBA) is characterized by global developmental delay apparent from infancy, feeding difficulties, hypotonia, and poor or absent speech. Most patients are able to walk, although they may have an unsteady gait or spasticity. Additional findings include dysmorphic facial features and mild distal skeletal anomalies. Males and females are similarly affected (summary by Basilicata et al., 2018).

Autosomal dominant intellectual developmental disorder-61 (MRD61) is characterized by global developmental delay apparent in infancy with mildly impaired intellectual development, expressive speech delay, and behavioral abnormalities, including autism spectrum disorder and attention deficit-hyperactivity disorder (ADHD). Most affected individuals learn to walk on time or with some mild delay. Additional features are highly variable and may include nonspecific dysmorphic features, obstipation, ocular anomalies, and poor overall growth (Snijders Blok et al., 2018).

Multiple congenital anomalies-hypotonia-seizures syndrome-4 (MCAHS4) is an autosomal recessive neurologic disorder characterized by onset of refractory seizures in the first months of life. Patients have severe global developmental delay, and may have additional variable features, including dysmorphic or coarse facial features, visual defects, and mild skeletal or renal anomalies. At the cellular level, the disorder is caused by a defect in the synthesis of glycosylphosphatidylinositol (GPI), and thus affects the expression of GPI-anchored proteins at the cell surface (summary by Starr et al., 2019). For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Developmental and epileptic encephalopathy-80 (DEE80) is an autosomal recessive neurologic disorder characterized by the onset of refractory seizures in the first year of life. Patients have severe global developmental delay and may have additional variable features, including dysmorphic or coarse facial features, distal skeletal abnormalities, and impaired hearing or vision. At the cellular level, the disorder is caused by a defect in the synthesis of glycosylphosphatidylinositol (GPI), and thus affects the expression of GPI-anchored proteins at the cell surface (summary by Murakami et al., 2019). For a discussion of genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Neurodevelopmental disorder with brain anomalies, seizures, and scoliosis (NEDBSS) is an autosomal recessive disorder characterized by severely impaired psychomotor development, hypotonia, seizures, and structural brain anomalies, including thin corpus callosum and cerebellar atrophy. Other features include scoliosis, dysmorphic facies, and visual impairment. Affected individuals are usually unable to walk or speak and may require tube feeding in severe cases. The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis (summary by Knaus et al., 2019). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Neurodevelopmental disorder with microcephaly, arthrogryposis, and structural brain anomalies (NEDMABA) is an autosomal recessive disorder characterized by severe global developmental delay, usually with hypotonia and absence of spontaneous movements other than head control, impaired intellectual development with absent speech, distal contractures, progressive microcephaly, dysmorphic features, and distal skeletal abnormalities, such as rocker-bottom feet and clenched hands with camptodactyly. Brain imaging tends to show a simplified gyral pattern of the cerebral cortex, delayed myelination, thin corpus callosum, and hypoplasia of the brainstem and cerebellum. The disorder may be complicated by feeding and/or breathing difficulties, often resulting in death in infancy (summary by Magini et al., 2019).

Neurooculocardiogenitourinary syndrome (NOCGUS) is a multisystem disorder characterized by poor growth and anomalies of the ocular, craniofacial, neurologic, cardiovascular, genitourinary, skeletal, and gastrointestinal systems. Lethality before 2 years of age has been observed (Reis et al., 2019).

Intellectual developmental disorder with impaired language and dysmorphic facies (IDDILF) is an autosomal dominant disorder characterized by global developmental delay apparent from infancy, impaired language development, and dysmorphic facial features, including hypertelorism, epicanthal folds, and abnormal palpebral fissures. Some patients may have additional findings, including feeding difficulties, mild cardiac or genitourinary defects, and distal skeletal anomalies (summary by Balak et al., 2019).

Neurodevelopmental disorder with dysmorphic facies and distal skeletal anomalies (NEDDFSA) is a global neurodevelopmental disorder with highly variable features. Patients often show poor feeding, poor overall growth, and hypotonia from early infancy, followed by mildly delayed motor development, poor language acquisition, and behavioral abnormalities. Intellectual development varies from severe with absent speech to mild with the ability to attend special schools. Common features include dysmorphic facial features with notable eye anomalies, joint hypermobility, and mild skeletal anomalies of the hands and feet (summary by Carapito et al., 2019).

Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is a neurologic disorder characterized in most cases by early-onset seizures and variably impaired intellectual development (ID). The severity of neurologic impairment is highly variable: some patients may have refractory seizures and be bedridden with no meaningful speech, whereas others may have treatment-responsive seizures and achieve normal psychomotor development (summary by Li et al., 2019).

Complex cortical dysplasia with other brain malformations-15 (CDCBM15) is an autosomal recessive neurologic disorder characterized by progressive microcephaly associated with abnormal facial features, hypotonia, and variable global developmental delay with impaired intellectual development. Brain imaging shows variable malformation of cortical development on the lissencephaly spectrum, mainly pachygyria and thin corpus callosum (summary by Mitani et al., 2019). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039).

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

Developmental and epileptic encephalopathy-84 (DEE84) is an autosomal recessive neurologic disorder characterized by onset of refractory seizures in the first months or years of life. Affected individuals have severely impaired global development with impaired intellectual development, absent speech, and inability to walk. Other features include axial hypotonia, peripheral spasticity, feeding difficulties that sometimes necessitate tube feeding, and mild dysmorphic facial features. Brain imaging may show nonspecific findings such as cerebral/cerebellar atrophy and/or hypomyelination. The severity of the disorder is variable (summary by Hengel et al., 2020). For a discussion of genetic heterogeneity of DEE, see 308350.

Rhizomelic limb shortening with dysmorphic features (RLSDF) is characterized by rhizomelic shortening of the extremities, predominantly of the upper limbs, and variable dysmorphic features, including macrocephaly, prominent forehead, hypertelorism, depressed or broad nasal bridge, and micrognathia. Hearing loss has also been observed (Sajan et al., 2019; Pagnamenta et al., 2023).

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).

Agenesis of corpus callosum, cardiac, ocular, and genital syndrome (ACOGS) is a syndromic neurodevelopmental disorder characterized by global developmental delay and/or intellectual disability, corpus callosum agenesis or hypoplasia, craniofacial dysmorphisms, and ocular, cardiac, and genital anomalies (Accogli et al., 2019).

Suleiman-El-Hattab syndrome (SULEHS) is an autosomal recessive multisystem developmental disorder characterized by hypotonia and feeding difficulties soon after birth, global developmental delay with impaired intellectual development and poor expressive speech, and a general happy demeanor. There is a distinctive facial appearance with microcephaly, thick arched eyebrows with synophrys, hypertelorism, epicanthal folds, low-set ears, broad nasal bridge, and thin upper lip. Additional more variable features include recurrent respiratory infections, cardiovascular malformations, cryptorchidism, seizures, and distal anomalies of the hands and feet (summary by Suleiman et al., 2019).

Congenital myopathy-17 (CMYO17) is an autosomal recessive muscle disorder. Affected individuals present at birth with hypotonia and respiratory insufficiency associated with high diaphragmatic dome on imaging. Other features include poor overall growth, pectus excavatum, dysmorphic facies, and renal anomalies in some. The severity of the disorder is highly variable: some patients may have delayed motor development with mildly decreased endurance, whereas others have more severe hypotonia associated with distal arthrogryposis and lung hypoplasia, resulting in early death (summary by Watson et al., 2016 and Lopes et al., 2018). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Developmental and epileptic encephalopathy-89 (DEE89) is a severe autosomal recessive disorder characterized by profound global developmental delay with impaired intellectual development, absent speech, inability to sit or walk due to axial hypotonia and spastic quadriparesis, and onset of seizures in the first days or months of life. EEG shows suppression-burst pattern or hypsarrhythmia, consistent with DEE or a clinical diagnosis of West syndrome. More variable features include joint contractures with foot deformities, dysmorphic facial features with cleft palate, and omphalocele. Affected individuals have poor motor skills, poor eye contact, and lack of language development; some die in infancy or early childhood. Brain imaging may be normal or show nonspecific abnormalities (summary by Chatron et al., 2020).

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).

Den Hoed-de Boer-Voisin syndrome (DHDBV) is characterized by global developmental delay with moderately to severely impaired intellectual development, poor or absent speech, and delayed motor skills. Although the severity of the disorder varies, many patients are nonverbal and have hypotonia with inability to sit or walk. Early-onset epilepsy is common and may be refractory to treatment, leading to epileptic encephalopathy and further interruption of developmental progress. Most patients have feeding difficulties with poor overall growth and dysmorphic facial features, as well as significant dental anomalies resembling amelogenesis imperfecta. The phenotype is reminiscent of Kohlschutter-Tonz syndrome (KTZS; 226750). More variable features of DHDBV include visual defects, behavioral abnormalities, and nonspecific involvement of other organ systems (summary by den Hoed et al., 2021).

SOFM is characterized by marked short stature, oligodontia, mild facial dysmorphism, and motor delay. Endosteal hyperostosis has also been observed, and patients may exhibit some features of progeria (Terhal et al., 2020; Beauregard-Lacroix et al., 2020).

Alzahrani-Kuwahara syndrome (ALKUS) is an autosomal recessive neurodevelopmental syndrome characterized by global developmental delay with severely impaired intellectual function and poor or absent speech. Patients have poor overall growth and dysmorphic facial features. More variable findings include early-onset cataracts, hypotonia, congenital heart defects, lower limb spasticity, and hypospadias (summary by Alzahrani et al., 2020).

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).

Pontocerebellar hypoplasia type 1F (PCH1F) is an autosomal recessive neurologic disorder characterized by hypotonia, global developmental delay, poor overall growth, and dysmorphic facial features. Brain imaging shows pontocerebellar hypoplasia, thin corpus callosum, cerebral atrophy, and delayed myelination (summary by Somashekar et al., 2021). For a phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

Neurodevelopmental disorder with dysmorphic facies and cerebellar hypoplasia (NEDFACH) is an autosomal recessive disorder characterized by global developmental delay and intellectual disability. The phenotype is variable: more severely affected individuals have poor overall growth with microcephaly, delayed walking, spasticity, and poor or absent speech, whereas others may achieve more significant developmental milestones and even attend special schooling. Brain imaging shows abnormalities of the cerebellum, most commonly cerebellar hypoplasia, although other features, such as thin corpus callosum and delayed myelination, may also be present. Dysmorphic facial features include sloping forehead, upslanting palpebral fissures, and hypertelorism. Additional more variable manifestations may include cardiac ventricular septal defect, spasticity, cataracts, optic nerve hypoplasia, seizures, and joint contractures (summary by Van Bergen et al., 2020).

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

Marbach-Rustad progeroid syndrome (MARUPS) is characterized by progeroid appearance with little subcutaneous fat and triangular facies, growth retardation with short stature, hypoplastic mandible crowded with unerupted supernumerary teeth, and cerebellar intention tremor. Psychomotor development is normal. Although features are reminiscent of Hutchinson-Gilford progeria syndrome (HGPS; 176670), MARUPS is less severe, with a relatively good prognosis. Two patients have been reported (Marbach et al., 2019).

Autosomal recessive spinocerebellar ataxia-31 (SCAR31) is a complex neurodevelopmental disorder characterized by global developmental delay with hypotonia and variably impaired intellectual and language development. Affected individuals have an ataxic gait, tremor, and dysarthria; more severely affected patients also have spasticity with inability to walk. Most have optic atrophy. Brain imaging shows cerebellar hypoplasia, enlarged ventricles, and atrophy of the posterior corpus callosum. Additional features may include retinitis pigmentosa, sensorineural deafness, dysmorphic facial features, and possibly endocrine dysfunction (summary by Collier et al., 2021).

Focal segmental glomerulosclerosis and neurodevelopmental syndrome (FSGSNEDS) is characterized by global developmental delay and renal dysfunction manifest as proteinuria and nephrotic syndrome apparent from infancy or early childhood. Some patients present with renal disease, whereas others present with developmental delay and develop renal disease later in childhood. Renal biopsy shows focal segmental glomerulosclerosis (FSGS), but the course of the disease is variable: some patients have transient proteinuria and others require renal transplant. Neurodevelopmental features are also variable, with some patients having only mildly impaired intellectual development, and others having a severe developmental disorder associated with early-onset refractory seizures or epileptic encephalopathy. Additional features, including feeding difficulties, poor overall growth, and nonspecific dysmorphic facial features, are commonly observed (summary by Assoum et al., 2018 and Weng et al., 2021).

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

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

Chopra-Amiel-Gordon syndrome (CAGS) is an autosomal dominant disorder characterized by developmental delay and/or impaired intellectual development, speech delay, facial dysmorphism, and variable other features, including recurrent bacterial infections, ophthalmologic abnormalities, and nonspecific brain abnormalities (Chopra et al., 2021).

A rare mitochondrial oxidative phosphorylation disorder with decreased respiratory complex I and IV enzyme activity. Characteristics of this disease hypotonia, global developmental delay, neonatal onset of progressive pectus carinatum without other skeletal abnormalities, poor growth, sensorineural hearing loss, dysmorphic features and brain abnormalities such as cerebral atrophy, quadriventricular dilatation and thin corpus callosum posteriorly.

DYRK1A syndrome is characterized by intellectual disability including impaired speech development, autism spectrum disorder including anxious and/or stereotypic behavior problems, and microcephaly. Affected individuals often have a clinically recognizable phenotype including a typical facial gestalt, feeding problems, seizures, hypertonia, gait disturbances, and foot anomalies. The majority of affected individuals function in the moderate-to-severe range of intellectual disability; however, individuals with mild intellectual disability have also been reported. Other medical concerns relate to febrile seizures in infancy; the development of epilepsy with seizures of the atonic, absence, and generalized myoclonic types; short stature; and gastrointestinal problems. Ophthalmologic, urogenital, cardiac, and/or dental anomalies have been reported.

Bryant-Li-Bhoj neurodevelopmental syndrome-1 (BRYLIB1) 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 abnormal head shape, 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). Genetic Heterogeneity of Bryant-Li-Bhoj Neurodevelopmental Syndrome See also BRYLIB2 (619721), caused by heterozygous mutation in the H3F3B gene (601058).

Chilton-Okur-Chung neurodevelopmental syndrome (CHOCNS) is characterized mainly by global developmental delay with variably impaired intellectual development and occasional speech delay. Most patients have behavioral abnormalities, including autism spectrum disorder, ADHD, and aggression. About half of patients have dysmorphic facial features, and about half have nonspecific brain abnormalities, including thin corpus callosum. Rare involvement of other organ systems may be present. At least 1 child with normal development at age 2.5 years has been reported (Chilton et al., 2020).

Neurodevelopmental disorder with speech delay and variable ocular anomalies (NEDSOA) is an autosomal recessive disorder characterized by global developmental delay with impaired intellectual development and poor speech acquisition apparent from infancy. Most affected individuals have dysmorphic facial features with notable ocular anomalies, including exotropia, strabismus, hypo- or hypertropia, and refraction problems. Additional features may include febrile seizures, sensorineural hearing loss, and behavioral abnormalities. Brain imaging is usually normal, but abnormalities of the corpus callosum have been reported (Broly et al., 2022).

Primordial dwarfism-immunodeficiency-lipodystrophy syndrome (PDIL) is characterized by pre- and postnatal growth restriction, with extreme microcephaly, short stature, and absence of subcutaneous fat. There is also significant hematologic/immune dysfunction, with hypo- or agammaglobulinemia, as well as lymphopenia, anemia, and thrombocytopenia, and most affected individuals succumb to infection in early childhood (Parry et al., 2020).

Neurodevelopmental disorder with facial dysmorphism, absent language, and pseudo-Pelger-Huet anomaly (NEDFLPH) is an autosomal recessive disorder characterized by global developmental delay with severely impaired intellectual development. Affected individuals often have behavioral abnormalities and may have variable findings on brain imaging, such as thin corpus callosum. Laboratory studies show nuclear lobulation defects in a subset of neutrophils, indicating a pseudo-Pelger-Huet anomaly (see 169400) and suggesting defects in the integrity of the nuclear envelope, where TMEM147 localizes (Thomas et al., 2022).

Developmental delay with variable intellectual disability and dysmorphic facies (DIDDF) is a clinically heterogeneous disorder characterized by neurologic deficits and characteristic dysmorphic facial features apparent from infancy or early childhood. Affected individuals usually show impaired intellectual development, speech delay, learning difficulties, and/or behavioral problems. Additional features may include hypotonia, hand or foot deformities, and palatal defects (Verberne et al., 2021; Verberne et al., 2022).

Neurodevelopmental disorder with growth retardation, dysmorphic facies, and corpus callosum abnormalities (NEDGFC) is an autosomal recessive disorder characterized by these cardinal features apparent from infancy. There is phenotypic variability both in disease manifestations and severity. More severely affected individuals are unable to walk independently, are nonverbal, and may have other anomalies, including congenital heart defects, feeding difficulties, or skeletal defects, whereas others show mildly delayed motor and speech acquisition with mild or borderline intellectual disability (summary by von Elsner et al., 2022).

Complex cortical dysplasia with other brain malformations-11 (CDCBM11) is an autosomal recessive disorder characterized by dilated ventricles and reduced white matter and associated with axonal developmental defects (Qian et al., 2022). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039).

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).

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).

Developmental delay with hypotonia, myopathy, and brain abnormalities (DEDHMB) is an autosomal recessive disorder characterized by global developmental delay and muscle weakness apparent in infancy. Affected individuals show severe motor delay and may not achieve independent walking due to central hypotonia and skeletal muscle myopathy. Some have poor overall growth with microcephaly, subtle dysmorphic features, and delayed language acquisition. Brain imaging shows cerebral atrophy, thinning of the corpus callosum, and delayed myelination (Shamseldin et al., 2016; Kotecha 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).

Lymphatic malformation-13 (LMPHM13) is characterized by the presence of nonimmune hydrops fetalis which often resolves with age. Capillary or cavernous hemangiomas are present in most patients, as are cardiac defects, often mild (Abdelrahman et al., 2018). For a discussion of genetic heterogeneity of lymphatic malformation, see 153100.

RECON progeroid syndrome (RECON) is a chromosomal instability disorder characterized by postnatal growth retardation, progeroid facial appearance, hypoplastic nose, prominent premaxilla, skin photosensitivity and xeroderma, muscle wasting with reduced subcutaneous fat, and slender elongated thumbs (Abu-Libdeh et al., 2022).

Neurodevelopmental disorder with intracranial hemorrhage, seizures, and spasticity (NEDIHSS) is an autosomal recessive disorder characterized by prenatal or neonatal onset of intracranial hemorrhage, usually with ventriculomegaly and calcifications, resulting in parenchymal brain damage. Some affected individuals have symptoms incompatible with life and die in utero. Those that survive show profound global developmental delay with almost no motor or cognitive skills, hypotonia, spasticity, and seizures. Other features may include facial dysmorphism, retinal vascular abnormalities, and poor overall growth. The pathogenesis of the disease likely results from dysfunction of vascular endothelial cells in the brain (Lecca et al., 2023).

Autosomal recessive intellectual developmental disorder-79 (MRT79) is characterized by global developmental delay apparent from infancy. Affected individuals have mildly delayed walking with an ataxic gait and severely impaired intellectual development with poor or absent speech. Additional features may include postnatal microcephaly and dysmorphic features (Van Bergen et al., 2022).

Autosomal dominant intellectual developmental disorder-72 (MRD72) is characterized by developmental delay, predominant speech delay, autistic or attention-deficit/hyperactivity disorder features, overfriendliness, generalized hypotonia, overweight/obesity, and dysmorphic features (Cuinat et al., 2022).

Neurodevelopmental disorder with microcephaly and movement abnormalities (NEDMIM) is an autosomal recessive disorder characterized by global developmental delay, impaired intellectual development with poor or absent speech, and delayed walking with an abnormal gait. Affected individuals may show hypotonia or hypertonia with spasticity, ataxia, and choreoathetoid movements. Most patients have microcephaly and short stature. Ophthalmic features, behavioral abnormalities, and nonspecific dysmorphic features are commonly observed. Additional more variable features include seizures, brain imaging abnormalities, and skeletal defects (Serey-Gaut et al., 2023).

Autosomal dominant intellectual developmental disorder-73 (MRD73) is a highly variable neurodevelopmental disorder characterized by impaired intellectual development that ranges from mild to severe, speech delay, behavioral abnormalities, and nonspecific dysmorphic facial features (Janssen et al., 2022).

Thrombocytopenia-11 with multiple congenital anomalies and dysmorphic facies (THC11) is a syndromic disorder characterized by dysmorphic facial features, multiple congenital anomalies that may involve the heart, brain, genitourinary, endocrine, and/or skeletal systems, chronic and persistent thrombocytopenia, sometimes with leukopenia or anemia, poor growth with microcephaly, hypotonia, and mildly impaired intellectual development or learning disabilities. The disorder results from constitutive activation of the RAS signaling pathway and can be considered a RASopathy (Niemann et al., 2020; Miller et al., 2022). For a discussion of genetic heterogeneity of thrombocytopenia, see 313900.

Alfadhel syndrome (AFDL) is an autosomal recessive neurodevelopmental disorder with features of global developmental delay, hypotonia, and facial dysmorphism (Asiri et al., 2020, Bertoli-Avella et al., 2021).

Autosomal dominant intellectual developmental disorder-74 (MRD74) is characterized by global developmental delay, including delay of gross and fine motor skills and speech delay, and variable subtle dysmorphic facial features (Niggl et al., 2023).