Cohen syndrome is characterized by failure to thrive in infancy and childhood; truncal obesity in the teen years; early-onset hypotonia and developmental delays; microcephaly developing during the first year of life; moderate to profound psychomotor retardation; progressive retinochoroidal dystrophy and high myopia; neutropenia in many with recurrent infections and aphthous ulcers in some; a cheerful disposition; joint hypermobility; and characteristic facial features.

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.

RNU4atac-opathy encompasses the phenotypic spectrum of biallelic RNU4ATAC pathogenic variants, including the three historically designated clinical phenotypes microcephalic osteodysplastic primordial dwarfism type I/III (MOPDI), Roifman syndrome, and Lowry-Wood syndrome, as well as varying combinations of the disease features / system involvement that do not match specific defined phenotypes. Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment. Less common but variable findings include brain anomalies, seizures, strokes, immunodeficiency, and cardiac anomalies, as well as ophthalmologic, skin, renal, gastrointestinal, hearing, and endocrine involvement.

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.

Autosomal dominant primary microcephaly-26 (MCPH26) is characterized by progressive microcephaly beginning at birth and associated with global developmental delay with variably impaired intellectual development. Some patients may have only mild learning difficulties or speech delay, whereas other are more severely affected with the inability to walk or speak. Additional features may include short stature, spasticity, feeding difficulties requiring tube feeding, and nonspecific dysmorphic facial features. Brain imaging in some patients shows a simplified gyral pattern or dysgenesis of the corpus callosum, suggesting abnormal neuronal migration (summary by Cristofoli et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of primary microcephaly, see MCPH1 (251200).

X-linked syndromic intellectual developmental disorder-37 (MRXS37) is a developmental disorder showing phenotypic variability and variable severity. Male mutation carriers tend to be more severely affected than female mutation carriers, some of whom may even be asymptomatic. In general, the disorder is characterized by global developmental delay with delayed walking, speech delay, impaired intellectual development that ranges from borderline low to moderate, and behavioral abnormalities, such as autism and sleeping difficulties. Many patients are able to attend mainstream schools with assistance and work under supervision. Additional more variable features include sensorineural hearing loss, ocular anomalies, feeding difficulties, dysmorphic facial features, inguinal and umbilical hernia, genitourinary defects, congenital heart defects, musculoskeletal anomalies, and endocrine dysfunction, such as hypogonadism or hyperparathyroidism (Shepherdson et al., 2024).