C9orf72 and juvenile Huntington disease: These typically late-onset diseases include myotonic dystrophy type 1 (DM1) and 2 (DM2), fragile X syndrome (FXS), fragile X-associated tremor ataxia syndrome (FXTAS), C9orf72 amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD), Friedreich’s ataxia (FRDA) and nine polyglutamine diseases, such as Huntington’s disease (HD) and a number of spinocerebellar ataxias (SCA).