CHD8-related neurodevelopmental disorder with overgrowth (CHD8-NDD) is characterized by generalized overgrowth, developmental delay / intellectual disability (DD/ID), autism spectrum disorder (ASD), neuropsychiatric issues, neurologic problems, sleep disturbance, and gastrointestinal issues The most common findings are the development of macrocephaly (most often during infancy) and tall stature (most typically during puberty), which is often accompanied by ASD and/or DD/ID. Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays. When present, ID is most often in the mild-to-moderate range. Sleep disturbance is characterized by difficulty with both initiation (delayed sleep onset) and maintenance (frequent night awakenings) of sleep. The most common gastrointestinal issue is constipation with or without periods of diarrhea. Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare).

Intellectual disability and myopathy syndrome (IDMYS) is an autosomal recessive developmental disorder characterized by global developmental delay with mildly impaired intellectual development, hypotonia, muscle weakness and fatigue, and white matter abnormalities on brain imaging. Variable additional features may include sensorineural hearing loss, dysmorphic facies, and progressive heart disease (summary by Smeland et al., 2019).