SOD1 and amyotrophic lateral sclerosis: Studies of common SOD1-ALS mutations have suggested that a disease modifying factor located nearby SOD1 may influence the penetrance of SOD1 p.D91A (D90A) and p.A5V (AV4) mutations (historical names noted in brackets are not reflective of the amino acid position), thus contributing broadly to ALS risk [38, 39].