Thrombocytopenia absent radius (TAR) syndrome is characterized by bilateral absence of the radii with the presence of both thumbs, and thrombocytopenia that is generally transient. Thrombocytopenia may be congenital or may develop within the first few weeks to months of life; in general, thrombocytopenic episodes decrease with age. Cow's milk allergy is common and can be associated with exacerbation of thrombocytopenia. Other anomalies of the skeleton (upper and lower limbs, ribs, and vertebrae), heart, and genitourinary system (renal anomalies and agenesis of uterus, cervix, and upper part of the vagina) can occur.

Troyer syndrome is characterized by progressive spastic paraparesis, dysarthria, pseudobulbar palsy, distal amyotrophy, short stature, and subtle skeletal abnormalities. Most affected children exhibit delays in walking and speech and difficulty in managing oral secretions, followed by increased lower-limb spasticity and slow deterioration in both gait and speech. Mild cerebellar signs are common. The most severely affected individuals have choreoathetosis. Emotional lability / difficulty in controlling emotions and affective disorders, such as inappropriate euphoria and/or crying, are frequently described. Life expectancy is normal.

Pseudoachondroplasia is characterized by normal length at birth and normal facies. Often the presenting feature is a waddling gait, recognized at the onset of walking. Typically, the growth rate falls below the standard growth curve by approximately age two years, leading to a moderately severe form of disproportionate short-limb short stature. Joint pain during childhood, particularly in the large joints of the lower extremities, is common. Degenerative joint disease is progressive; approximately 50% of individuals with pseudoachondroplasia eventually require hip replacement surgery.

Decreased fetal activity associated with multiple joint contractures, facial anomalies and pulmonary hypoplasia. Ultrasound examination may reveal polyhydramnios, ankylosis, scalp edema, and decreased chest movements (reflecting pulmonary hypoplasia).

The Verloes-David-Pfeiffer mesomelia-synostoses syndrome is an autosomal dominant form of mesomelic dysplasia comprising typical acral synostoses combined with ptosis, hypertelorism, palatal abnormality, congenital heart disease, and ureteral anomalies (summary by Isidor et al., 2009). Mesomelia and synostoses are also cardinal features of the Kantaputra type of mesomelic dysplasia (156232).

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).

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).

Craniofacial-deafness-hand syndrome (CDHS) is an autosomal dominant disorder characterized by dysmorphic facial features, hand abnormalities, absent or hypoplastic nasal and wrist bones, and severe sensorineural hearing impairment (summary by Gad et al., 2008).

Multicentric carpotarsal osteolysis syndrome is a rare skeletal disorder, usually presenting in early childhood with a clinical picture mimicking juvenile rheumatoid arthritis. Progressive destruction of the carpal and tarsal bone usually occurs and other bones may also be involved. Chronic renal failure is a frequent component of the syndrome. Mental retardation and minor facial anomalies have been noted in some patients. Autosomal dominant inheritance has been documented in many families (Pai and Macpherson, 1988). See also Torg-Winchester syndrome (259600), an autosomal recessive multicentric osteolysis syndrome.

Endocrine-cerebro-osteodysplasia (ECO) syndrome is characterized by various anomalies of the endocrine, cerebral, and skeletal systems resulting in neonatal mortality.

Alopecia, neurologic defects, and endocrinopathy syndrome (ANES) is an autosomal recessive disorder characterized by alopecia with skin involvement including multiple facial nevi and flexural hyperpigmentation; moderately to severely impaired intellectual development; progressive motor decline; and endocrine deficiency (summary by Spiegel et al., 2010).

Greenberg dysplasia (GRBGD), also known as hydrops-ectopic calcification-moth-eaten (HEM) skeletal dysplasia, is a rare autosomal recessive osteochondrodysplasia characterized by gross fetal hydrops, severe shortening of all long bones with a moth-eaten radiographic appearance, platyspondyly, disorganization of chondroosseous calcification, and ectopic ossification centers. It is lethal in utero. Patient fibroblasts show increased levels of cholesta-8,14-dien-3-beta-ol, suggesting a defect of sterol metabolism (summary by Konstantinidou et al., 2008). Herman (2003) reviewed the cholesterol biosynthetic pathway and 6 disorders involving enzyme defects in postsqualene cholesterol biosynthesis: Smith-Lemli-Opitz syndrome (SLOS; 270400), desmosterolosis (602398), X-linked dominant chondrodysplasia punctata (CDPX2; 302960), CHILD syndrome (308050), lathosterolosis (607330), and HEM skeletal dysplasia.

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

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.

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

Any lethal congenital contracture syndrome in which the cause of the disease is a mutation in the ADGRG6 gene.

Frontometaphyseal dysplasia (FMD) is a progressive sclerosing skeletal dysplasia characterized by supraorbital hyperostosis, undermodeling of the small bones, and small and large joint contractures, as well as extraskeletal developmental abnormalities, primarily of the cardiorespiratory system and genitourinary tract. Patients with FMD2 appear to have a propensity for keloid formation (summary by Wade et al., 2016). For a discussion of genetic heterogeneity of frontometaphyseal dysplasia, see FMD1 (305620).

Zellweger spectrum disorder (ZSD) is a phenotypic continuum ranging from severe to mild. While individual phenotypes (e.g., Zellweger syndrome [ZS], neonatal adrenoleukodystrophy [NALD], and infantile Refsum disease [IRD]) were described in the past before the biochemical and molecular bases of this spectrum were fully determined, the term "ZSD" is now used to refer to all individuals with a defect in one of the ZSD-PEX genes regardless of phenotype. Individuals with ZSD usually come to clinical attention in the newborn period or later in childhood. Affected newborns are hypotonic and feed poorly. They have distinctive facies, congenital malformations (neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling [chondrodysplasia punctata] of the patella[e] and the long bones), and liver disease that can be severe. Infants with severe ZSD are significantly impaired and typically die during the first year of life, usually having made no developmental progress. Individuals with intermediate/milder ZSD do not have congenital malformations, but rather progressive peroxisome dysfunction variably manifest as sensory loss (secondary to retinal dystrophy and sensorineural hearing loss), neurologic involvement (ataxia, polyneuropathy, and leukodystrophy), liver dysfunction, adrenal insufficiency, and renal oxalate stones. While hypotonia and developmental delays are typical, intellect can be normal. Some have osteopenia; almost all have ameleogenesis imperfecta in the secondary teeth.

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

ASXL3-related disorder is characterized by developmental delay or intellectual disability, typically in the moderate to severe range, with speech and language delay and/or absent speech. Affected individuals may also display autistic features. There may be issues with feeding. While dysmorphic facial features have been described, they are typically nonspecific. Affected individuals may also have hypotonia that can transition to spasticity resulting in unusual posture with flexion contractions of the elbows, wrists, and fingers. Other findings may include poor postnatal growth, strabismus, seizures, sleep disturbance, and dental anomalies.

Distal arthrogryposis type 2B3 (DA2B3) is characterized by facial dysmorphism and congenital joint contractures with predominantly distal involvement. Some patients exhibit muscle weakness (Tajsharghi et al., 2008). Considerable inter- and intrafamilial variability has been reported (Xu et al., 2018).

Ritscher-Schinzel syndrome-4 (RTSC4) is characterized by a constellation of congenital anomalies, including dysmorphic craniofacial features and structural brain anomalies, such as Dandy-Walker malformation (220200), hindbrain malformations, or agenesis of the corpus callosum, associated with global developmental delay and impaired intellectual development. Congenital cardiac defects have been reported in 1 family (summary by Ritscher et al., 1987 and Jeanne et al., 2021). For a discussion of genetic heterogeneity of Ritscher-Schinzel syndrome, see RTSC1 (220210).

This syndrome is an isolated upper limb mesomelic dysplasia. It has been described in four patients from two unrelated families (a man and his daughter, and a Lebanese man and his son). Patients present with ulnar hypoplasia with severe radial bowing, but normal stature. The mode of transmission is likely to be autosomal dominant with variable expressivity.

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

Bent bone dysplasia syndrome-2 (BBDS2) is characterized by defects in both the axial and appendicular skeleton, with radiographic findings of undermineralized bone and a distinct angulation of the mid femoral shaft. Extraskeletal features include facial dysmorphisms, abnormally formed ears with tags, widely spaced nipples, and atrial septal defects. Abnormalities of muscle function are suggested by the presence of elbow fusions, ulnar flexion contractions at the wrist, and bilateral talipes equinovarus, as well as failure to mount a respiratory effort at birth (Barad et al., 2020). For a general phenotypic description and discussion of genetic heterogeneity of bent bone dysplasia syndrome, see BBDS1 (614592).

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).

Congenital myopathy-20 (CMYP20) is an autosomal recessive neuromuscular disorder that shows wide phenotypic variability. Some patients present in early childhood with proximal muscle weakness affecting the lower and upper limbs resulting in difficulties running and climbing, whereas others present soon after birth with congenital limb or distal contractures. Additional features may include dysmorphic facial features and global developmental delay. Skeletal muscle biopsy may show nemaline rods (Nilipour et al., 2018; Pehlivan et al., 2019). For a discussion of genetic heterogeneity of congenital myopathy, see CMYP1A (117000).