C9orf72 and amyotrophic lateral sclerosis: Mutations in several genes have been demonstrated to be linked to ALS, Cu/Zn superoxide dismutase (SOD1), TAR DNA-binding protein (TARDBP), the gene encoding the TAR DNA-binding protein 43—TDP-43, the fused in sarcoma/translocated in liposarcoma (FUS/TLS) protein, and chromosome 9 open reading frame 72 gene (C9ORF72) being the most important [20].