Nance-Horan syndrome (NHS) is an X-linked disorder characterized by congenital cataracts, dental anomalies, dysmorphic features, and, in some cases, mental retardation (summary by Burdon et al., 2003).

The Osebold-Remondini syndrome is a bone dysplasia with mesomelic shortness of limbs and, hence, shortness of stature, absence or hypoplasia of second phalanges with synostosis of the remaining phalanges, carpal and tarsal coalitions, and apparently no other anomalies (summary by Opitz and Gilbert, 1985). See 602875 for a discussion of genetic heterogeneity of autosomal recessive acromesomelic dysplasia.

The acromesomelic dysplasias are disorders in which there is disproportionate shortening of skeletal elements, predominantly affecting the middle segments (forearms and forelegs) and distal segments (hands and feet) of the appendicular skeleton. Acromesomelic dysplasia-1 (AMD1) is characterized by severe dwarfism (height below 120 cm) with shortening of the middle and distal segments of the limbs. This condition is usually diagnosed at birth and becomes more obvious in the first 2 years of life. X-rays show short broad fingers, square flat feet, and shortening of the long bones (particularly the forearms). The radius is bowed; the ulna is shorter than the radius, and its distal end is occasionally hypoplastic. The skull is dolichocephalic and a shortness of the trunk, with decreased vertebral height and narrowing of the lumbar interpedicular distances, is consistently observed. Facial appearance and intelligence are normal (summary by Faivre et al., 2000). Genetic Heterogeneity of Acromesomelic Dysplasia Additional autosomal recessive forms of acromesomelic dysplasia include acromesomelic dysplasia-2A (200700), -2B (228900), and -2C (201250), all caused by mutation in the GDF5 gene (601146) on chromosome 20q11; AMD3 (200700), caused by mutation in the BMPR1B gene (603248) on chromosome 4q22; and AMD4 (619636), caused by mutation in the PRKG2 gene (601591) on chromosome 4q21. An autosomal dominant form of acromesomelic dysplasia has also been reported (see 112910).

This multisystem disorder is characterized by moyamoya disease, short stature, hypergonadotropic hypogonadism, and facial dysmorphism. Other variable features include dilated cardiomyopathy, premature graying of the hair, and early-onset cataracts. Moyamoya disease is a progressive cerebrovascular disorder characterized by stenosis or occlusion of the internal carotid arteries and the main branches, leading to the development of small collateral vessels (moyamoya vessels) at the base of the brain. Affected individuals can develop acute neurologic events due to stroke-like episodes (summary by Miskinyte et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of moyamoya disease, see MYMY1 (252350).

CTNNB1 neurodevelopmental disorder (CTNNB1-NDD) is characterized in all individuals by mild-to-profound cognitive impairment and in up to 39% of reported individuals by exudative vitreoretinopathy, an ophthalmologic finding consistent with familial exudative vitreoretinopathy (FEVR). Other common findings include truncal hypotonia, peripheral spasticity, dystonia, behavior problems, microcephaly, and refractive errors and strabismus. Less common features include intrauterine growth restriction, feeding difficulties, and scoliosis.

White-Sutton syndrome is a neurodevelopmental disorder characterized by a wide spectrum of cognitive dysfunction, developmental delays (particularly in speech and language acquisition), hypotonia, autism spectrum disorder, and other behavioral problems. Additional features commonly reported include seizures, refractive errors and strabismus, hearing loss, sleep disturbance (particularly sleep apnea), feeding and gastrointestinal problems, mild genital abnormalities in males, and urinary tract involvement in both males and females.

Neurodevelopmental disorder with midbrain and hindbrain malformations (NEDMHM) is an autosomal recessive disorder comprising impaired intellectual development, speech delay, mild microcephaly, and midbrain-hindbrain malformation (Ravindran et al., 2017).

Acromesomelic dysplasia-4 (AMD4) is characterized by disproportionate short stature due to mesomelic shortening of the limbs. Radiographic hallmarks include mild to moderate platyspondyly, moderate brachydactyly, iliac flaring, and metaphyseal alterations of the long bones that progressively increase with age (Diaz-Gonzalez et al., 2022). For a discussion of genetic heterogeneity of acromesomelic dysplasia, see AMD1 (602875).

TBCK-related neurodevelopmental disorder (TBCK-NDD) is typically a progressive condition in which individuals have significant developmental and respiratory issues. A majority of affected individuals do not achieve independent ambulation or spoken language. Most affected individuals also have congenital and severe hypotonia, which can also lead to feeding issues and dysphagia, with many affected individuals requiring gastrostomy tube placement. Neuromuscular weakness usually affects the distal muscles first, leading to distal muscle wasting, and then the proximal muscles become involved. Electrophysiologic studies suggest that weakness is secondary to a motor neuronopathy. Respiratory issues are also progressive, with most affected individuals requiring noninvasive nocturnal respiratory support by age five years and about 75% of teenagers requiring a tracheostomy. Seizures are also common, and brain MRI imaging may show white matter lesions and progressive cortical atrophy over time. Most affected individuals exhibit some degree of developmental regression and/or neurologic decompensation in the setting of illness, which often raises clinical concerns for mitochondrial disorders. Other features include vision issues (including optic atrophy), the development of contractures and neuromuscular scoliosis, coarsening of facial features over time, recurrent nephrolithiasis and/or urinary tract infections, dyslipidemia without clear adverse cardiovascular events, and the development of left ventricular hypertrophy.

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).