ATXN2 and Parkinson disease: Significant expansion of this tract (greater than 34 CAG repeats) is the genetic cause of spinocerebellar ataxia 2 (SCA2), intermediate expansions of the ATXN2 polyQ tract have been associated with parkinsonism, and some ATXN2 polyQ expansions have been associated with ALS [7,9,11,12,13,14,15,16,17].