MECP2 and X-linked syndromic intellectual disability: Anyway, MECP2 is not only associated with RTT, but is also related to severe neonatal encephalopathy (OMIM #300673), autism susceptibility (OMIM #300496), X-linked mental retardation syndrome (OMIM #300055), and MECP2 duplication syndrome (MDS) (OMIM #300260).