NDevDs are associated with abnormal development of the nervous system, leading to defects in neural connections or brain architecture, which often entail intellectual disability, seizures, behavioral abnormalities, etc. Diseases of this group include, for example, Rett syndrome (RTT), most often caused by mutations in the MECP2 gene [168], and autism spectrum disorders (ASD), associated with mutations in more than 800 genes (such as CHD8, PTEN, SHANK3, etc.)[169]. Here, MECP2 is linked to Rett syndrome.