Rett syndrome (RTT) is a postnatal neurological disorder caused by loss-of-function mutations in the X-linked gene methyl-CpG binding protein 2 (MECP2), with an approximate prevalence of one in 10,000 births (Amir et al. 1999; Laurvick et al. 2006). This evidence concerns the gene MECP2 and atypical Rett syndrome.