Rett syndrome (RTT), an X-linked postnatal neurodevelopmental disorder associated with intellectual disabilities, is primarily caused by mutations in methyl-CpG-binding protein 2 (MECP2), the gene encoding MeCP2, a transcriptional modulator that binds to methylated CpG sites in promoter regions of DNA (Nan et al., 1997; Amir et al., 1999; Percy and Lane, 2005). The gene discussed is MECP2; the disease is Rett syndrome.