AR and fragile X syndrome: The first genetic expansions (identified in 1991) consisted of CGG repeats in the 5′untranslated region of the fragile X messenger ribonucleoprotein 1 (FMR1) gene, associated with fragile X syndrome (FXS), and CAG repeats in the first exon of the androgen receptor (AR) gene, linked to spinal and bulbar muscular atrophy (SBMA).