Despite of many extensive studies held on an inielieciual disability, it still reimains one of the most mysterious neuropsychiatric disorders. The prevalence of an intellectual disability (2-3% of the population) and its variability induce active research of the etiology of this disorder. Frequently, such research directs to genetic causes of an intellectual disability. The epidemiology of an intellectual disability is quite astonishing - there are more males, affected by inteliectual disability, than there are females.
Phelan-McDermid syndrome or 22q13.3 deletion syndrome is a neurodevelopmental disorder caused by deletion of chromosome 22q13.3 or pathogenic variant in SHANK3 gene. Phelan-McDermid syndrome is characterized by global developmental delay, intellectual disability, autism spectrum disorder, hypotonia, seizures, severely delayed or absentspeech, and minor facial anomalies. To date, about 1300 individuals with Phelan-McDermid syndrome are reported worldwide according to Phelan-McDermid Syndrome Foundation. It is believed that the prevalence is considerably greater.
