FMR1 and fragile X syndrome: Fragile X Syndrome (FXS) is the leading single gene cause of inherited intellectual disability and autism spectrum disorder (ASD) (Turner et al., 1996), and is caused by a cytosine-guanine-guanine (CGG) trinucleotide repeat expansion in the promoter region of the fragile X messenger ribonucleoprotein 1 (FMR1) gene (Fu et al., 1991).