C9orf72 and amyotrophic lateral sclerosis: Although the pathogenic mechanisms of ALS are not fully clear, a number of gene mutations linked to ALS were discovered over past 20 years, such as superoxide dismutase 1 (SOD1), TAR DNA-binding protein (TARDBP), fused in sarcoma (FUS), optinurin (OPTN), valosin-containing protein (VCP), sequestosome-1 (SQSTM1), ubiquilin-2 (UBQLN2), C9ORF72, heterogeneous nuclear ribonucleoproteins A1 and A2/B1 (HNRNPA1 and HNRNPA2B1)[9–18].