PCDH19 and developmental and epileptic encephalopathy, 9: Mutations in the human gene PCDH19 result in an epileptic syndrome known as EIEE9 (epileptic encephalopathy, early infantile, 9; OMIM # 300088), characterized by early-onset seizures, cognitive impairment, and autistic features, in addition to a variety of behavioral problems and sleep dysregulation [1–3].