MECP2 and Rett syndrome: The majority of individuals with RTT carry loss-of-function mutations in the gene that encodes methyl-CpG-binding protein 2 (MeCP2), a transcriptional regulator that binds to methylated DNA sites and recruits transcriptional repressors and modulates chromatin compaction and its accessibility (Amir et al., 1999; Chahrour et al., 2008; Lyst and Bird, 2015; Nan et al., 1997; Percy and Lane, 2005).