While more than 230 different ALS-associated SOD1 mutations have been identified to date, p.D91A (SOD1D91A; c.272A>C) takes a unique position distinct from other SOD1 mutations: ALS caused by SOD1D91A is most frequently inherited as a recessive trait, while all other mutations in SOD1 are dominantly inherited5. This evidence concerns the gene SOD1 and amyotrophic lateral sclerosis.