SOD1 and amyotrophic lateral sclerosis: Superoxide dismutase 1 (SOD1) is an antioxidant protein expressed abundantly and ubiquitously [3] and since the discovery in 1993 that mutations in SOD1 cause ALS [4], [5] a further 140 mutations have since been found scattered throughout the 153 amino acid Cu/Zn-homodimer.