They include: myotonic dystrophy type 1 (DM1), caused by a CTG expansion in the DMPK1 gene, Huntingdon's disease (HD), caused by a CAG expansion in the huntingtin gene (HTT) and Friedreich's ataxia, caused by GAA expansion in frataxin (FXN). The gene discussed is FXN; the disease is Friedreich ataxia.