FMR1 and fragile X syndrome: Fragile X syndrome (FXS) is the leading known genetic cause of autism (Reddy, 2005; Hagerman et al., 2010), caused by a trinucleotide repeat expansion mutation in the 5′-untranslated region of the fragile X messenger ribonucleoprotein 1 (FMR1) gene located on the X-chromosome (Verkerk et al., 1991).