SOD1 and amyotrophic lateral sclerosis: Hexanucleotide GGGGCC intronic expansions in the newly identified C9ORF72 (chromosome 9 open reading frame 72) gene represents the most common cause of both familial and sporadic ALS,7, 8 responsible for up to 50% of familial ALS and ∼10% of sporadic ALS, but to date SOD1 mutations have been the genetic subtype most widely studied and utilized to model ALS.