Since Elden and colleagues reported that a 27–33 CAG repeat expansion in the ATXN2 gene was associated with sporadic ALS in 2010 [43], [47], about two dozen studies have sought to verify this association [46], [48]–[60], investigate the mechanisms by which ALS may develop [61], [62], or investigate different clinical manifestations in ALS patients carrying CAG repeat expansions in the ATXN2 gene [61]–[64]. This evidence concerns the gene ATXN2 and amyotrophic lateral sclerosis.