MECP2 and atypical Rett syndrome: The common link between our study and previously published human GWAS studies is the role of epigenetics in regulating the expression of key genes/associated loci by MECP2, which is a DNA methylation protein implicated in Rett syndrome (Amir et al., 1999), autism (Loat et al., 2008), mental retardation (Shahbazian and Zoghbi, 2001), and mild learning disabilities (Shibayama et al., 2004).