ATXN3 and Spinocerebellar ataxia type 3: In addition, we identified a participant with an ATXN3 repeat expansion exceeding the pathogenic, high-penetrance threshold of >55 CAGs for spinocerebellar ataxia type 3 (Supplementary Fig. 7) with a diagnosis of cerebellar ataxia recorded in their EHR, supporting this genotype51.