MECP2 and Intellectual disability: MECP2 mutations are responsible for Rett syndrome (RTT; OMIM 312750), a severe and progressive postnatal neurodevelopmental disorder that affects 1/10000-15000 female live births [9,10,11], considered one of the leading causes of intellectual disability in girls [12,13] and characterized by the presence of motor dysfunction and autistic-like features [14,15].