MECP2 and fragile X syndrome: Besides the FMR1 gene responsible for the fragile X mental retardation syndrome, the chromosomal region Xq27.3-qter harbours several genes that have been shown to be responsible for syndromic and non-syndromic forms of XLMR (e.g. IDS, ABCD1, L1CAM, MECP2, FLNA, IKBKG, DKC,1 FMR2, GDI1, SLC6A8, and MECP2) [14].