Among the most common repeat expansion diseases (REDs) are fragile X syndrome (GCC repeat in 5′ untranslated regions (UTR) of the FMR1 gene), myotonic dystrophy (CTG repeat in 3′ UTR of the DMPK gene), spinocerebellar ataxias (many caused by exonic CAG repeats in their respective genes) and cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS; AAGGG repeat expansion in the intron of RFC1). Here, FMR1 is linked to cerebellar ataxia.