MECP2 and Intellectual disability: In addition to RTT, patients can also exhibit duplication or triplication of the MECP2 gene, resulting in MECP2 duplication syndrome (MDS), a disorder characterized by numerous abnormal symptoms such as hypotonia, seizures, intellectual disability, and recurrent infections (Ramocki, Peters et al. 2009, Ramocki, Tavyev et al. 2010, Collins and Neul 2022).