Like CAA interruptions in HTT, CAT interruptions of the ATXN1 CAG repeat in four spinocerebellar ataxia 1 subjects supported better tracking of age at onset with the uninterrupted CAG repeat size, but, because CAT specifies histidine, this was interpreted as an effect of polyglutamine length (Menon et al., 2013). Here, HTT is linked to spinocerebellar ataxia type 1.