1). Normal RAI1 CAG repeats range from 10 to 19 in the general population, with 13 or 14 repeats being most common (Refs 22, 82, 83). Indeed, expansion of CAG repeats is associated not only with SCA and Huntington’s disease but also with other neurodegenerative conditions (Ref. 84). The finding that CAG repeat length in RAI1 modifies the age of onset in SCA patients aligns with the broader theory that (CAG)n repeat expansions influence disease onset (Ref. 66). This evidence concerns the gene RAI1 and juvenile Huntington disease.