The name FXS was derived from the folate-sensitive fragile site FRAXA (fragile site, X chromosome, A site) on the long arm of chromosome X (Xq27.3-Xq28) in affected males [5], corresponding to the locus of the causative gene of the syndrome, FMR1, which contains in its 5′ untranslated region (UTR) a polymorphic CGG triplet repeat [6]. Here, FMR1 is linked to fragile X syndrome.