ARX and lissencephaly spectrum disorders: The ARX mutations encompass a nearly continuous spectrum of neurodevelopmental disorders (NDDs), including developmental and epileptic encephalopathy (DEE) 1 (MIM #308350), hydranencephaly with abnormal genitalia (MIM #300215), intellectual developmental disorder, X-linked 29 (MIM #300419), lissencephaly, X-linked 2 (MIM #300215), Partington syndrome (MIM #309510), and Proud syndrome (MIM #300004).