C9orf72 and amyotrophic lateral sclerosis: ALS could be then triggered not solely by a powerful mutation in a single gene such as C9ORF72, but would rather commence through a concerted action of the latter and the affected genes from Group I. Once triggered, the respective fALS clinical phenotype will be formed in a manner similar to that suggested for sALS [8] by the mutated genes from Groups II and III.