C9orf72 and amyotrophic lateral sclerosis: The most common genetic mutations causing ALS are mutations in the ‘superoxide dismutase 1’ (SOD1), ‘fused in sarcoma’ (FUS), ‘TAR DNA binding protein’ (TARDBP) genes, or a hexanucleotide repeat expansion in the ‘chromosome 9 open reading frame 72’ (C9orf72) gene [92].