Mutations in the X-linked Mecp2 gene, which encodes the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2), cause the majority of Rett syndrome cases [76–78] which is characterized by an apparently normal early development followed by loss of language skill, motor abnormalities, cognitive deficits, stereotyped behavior, respiratory dysrhythmias, and seizures leading sometimes to premature death. Here, MECP2 is linked to atypical Rett syndrome.