Of the numerous XLIDS arising from gene dosage alterations in the Xq28 region, MECP2 dosage alterations are probably the most known or heard of within the medical community, since deletions and duplications involving the MECP2 locus have been associated with two distinct forms of syndromic XLIDS having multiple overlapping features: Rett syndrome and MECP2 duplication syndrome, respectively [5,6,7]. This evidence concerns the gene MECP2 and atypical Rett syndrome.