SOD1 and amyotrophic lateral sclerosis: As an example, we show a gold standard variant Ala5Val in the superoxide dismutase 1 (SOD1) gene (Fig. 6), located on Chromosome 21, which is the most common ALS-causing mutation in the United States (Rosen et al. 1994; Cudkowicz et al. 1997; Valentine and Hart 2003).