C9orf72 and amyotrophic lateral sclerosis: To date, more than 40 genes have been implicated in ALS, with the most frequently mutated genes including chromosome 9 open reading frame 72 (C9orf72), superoxide dismutase 1 (SOD1), TAR DNA binding protein 43 (TARDBP) and fused in sarcoma (FUS) [9, 10].