Rett syndrome (RTT) is a severe progressive neurodevelopmental disorder, mainly caused by mutations in the X-linked gene encoding methyl-CpG binding protein 2 (MeCP2), a protein involved in transcriptional regulation (Amir et al., 1999; Wan et al., 1999; Xiang et al., 2000). Here, MECP2 is linked to atypical Rett syndrome.