MECP2 and atypical Rett syndrome: Rett syndrome (RTT) is a complex neurological disorder caused by loss-of-function mutations in the gene encoding methyl-CpG-binding protein 2 (MeCP2) (Amir et al., 1999; Shahbazian and Zoghbi, 2002), a transcriptional regulatory protein (Klose and Bird, 2006).