C9orf72 and amyotrophic lateral sclerosis: Several studies in ALS patients and model systems have identified numerous genes in ALS pathogenesis, among which four major genes, chromosome 9 open reading frame 72 (C9ORF72), superoxide dismutase 1 (SOD1), TAR DNA-binding protein 43 (TARDBP) and mutations in fused in sarcoma protein (FUS), are largely responsible for genetic forms of ALS [7,8].