Amongst genetically confirmed (or suspected) HCAs, Friedreich Ataxia (FRDA) (n = 178), spinocerebellar ataxias (SCA) (most often SCA2 [n = 463], SCA3 [n = 320] and SCA6 [n = 154]), Niemann-Pick type C (NPC) (n = 197), fragile-X tremor ataxia syndrome (FXTAS) (n = 157) and ataxia telangiectasia (A-T) (n = 96) were most frequently reported (see Table 1 for distribution of specific disorders). This evidence concerns the gene CACNA1A and autosomal dominant cerebellar ataxia.