Also, triplet expansion variants in ATXN2 (MIM*601517), responsible for autosomal dominant cerebellar ataxia type 2 (SCA2, MIM#183090), may cause a form of typical PD with onset after 40 years, good response to levodopa therapy without cognitive impairment, and cerebellar signs. This evidence concerns the gene ATXN2 and Parkinson disease.