C9orf72 and amyotrophic lateral sclerosis: ALS can be generally classified into both familial and sporadic ALS, the familial ALS accounts for about 5%–10% of ALS and involves the genetic mutations in genes such as superoxide dismutase 1 (SOD1), chromosome 9 open reading frame 72 (C9orf72), fused in sarcoma (FUS), TAR DNA-binding protein (TDP-43/TARDBP), and others.