PACS2 and developmental and epileptic encephalopathy, 66: Recent studies have shown that missense mutations in the middle region of the PACS2 gene are related to a genetic disease named developmental and epileptic encephalopathy-66 (DEE66) characterized by epilepsy, global developmental delay (with or without autism), common cerebellar dysgenesis, and facial dysmorphism (19, 20, 45).