FXN and fragile X syndrome: The TRED group also comprises fragile X syndrome (FXS) and fragile X-associated tremor/ataxia syndrome (FXTAS), both of which are caused by a CGG expansion in the 5’-untranslated region (5’UTR) of the FMR1 gene, as well as Friedreich ataxia (FRDA) caused by a GAA expansion in the first intron of the frataxin (FXN) gene.