MECP2 and atypical Rett syndrome: Rett syndrome and ASD, which are progressive neurodevelopmental diseases marked by an increase in repetitive stereotyped behaviors and loss of social, cognitive, and language abilities, have a high prevalence of MECP2 gene mutations (Zappella et al., 2001; Heindel et al., 2006; Swanberg et al., 2009).