These pathogenic CAG•CTG repeats showed lower levels of expansion in the cerebellum despite high expression levels of the ATXN1, ATXN2, ATXN3 and ATXN7 genes.14 The absence of significant somatic instability of the CAG•CTG repeat in the cerebellum, which is one of the most pathologically affected brain regions in these spinocerebellar ataxias,44 further supports the possibility that different alternative DNA structures and various repair pathways may differentially impact the stability of CAG•CTG repeats compared to GAA•TTC repeats in the cerebellum. This evidence concerns the gene ATXN2 and cerebellar ataxia.