Loss of function or deletion mutations of MECP2 cause Rett syndrome (RTT, MIM# 312750),3 a severe neurodevelopmental disorder (NDD) characterized by developmental delay/intellectual disability (DD/ID), dysautonomia, epilepsy, gastrointestinal problems, sleep disturbances, and hand stereotypies.4 This evidence concerns the gene MECP2 and atypical Rett syndrome.