The most common mutation affecting SOD1 and causing ALS is the substitution of alanine for aspartate at position 91 of exon 4, called p.D91A (also known as p.D90A; dbSNP155 ID rs80265967; NM_000454.5, c.272A>C) [4]. The gene discussed is SOD1; the disease is amyotrophic lateral sclerosis.