ATXN2 and Parkinson disease: More than 90% of the human population carry a repeat size of 22–23 triplets in the Ataxin-2 (ATXN2) gene [3], while alleles between 27 and 33 are considered intermediate size expansions and were recently shown to result in a higher risk for related neurodegenerative diseases such as ALS and Parkinsonism [5]–[7].