ATXN2 and Machado-Joseph disease: In particular, ATXN2, with an intermediate CAG repeat length, was previously described as a modifying factor for an earlier AAO in amyotrophic lateral sclerosis (ALS) patients, ATXN2 is associated with autosomal-dominant Parkinson’s disease and has been described as a potential modifying factor for an earlier onset in SCA3 patients [7, 17, 28–31].