C9orf72 and juvenile Huntington disease: Examples of repeat expansions diseases include Huntington’s disease (HD), C9orf72-frontotemporal dementia (FTD)/amyotrophic lateral sclerosis (ALS), myotonic dystrophy types 1 (DM1) (Figure 1) and 2 (DM2), fragile X syndrome, spinal and bulbar muscular atrophy, Friedreich ataxia, spinocerebellar ataxias and progressive myoclonic epilepsy type 1, among others (Figure 1).