Parkinsonism is observed as a symptom of some REDs, such as Spinocerebellar ataxia 2 (SCA2), which is caused by REs greater than the pathogenic threshold of 33 pure CAG repeats in ATXN2, without any interruptions with alternative base pairs in the CAG motif sequence (schematic of interrupted alleles illustrated in Fig. 1A)3. The gene discussed is ATXN2; the disease is Parkinson disease.