C9orf72 and amyotrophic lateral sclerosis: Familial ALS has been associated with mutations in over 30 genes, but mutations in 4 genes, C9orf72, SOD1 (encoding superoxide dismutase), TARDBP (encoding TAR DNA-binding protein 43, TDP43), and FUS (encoding fused in sarcoma RNA-binding protein), account for more than 70% of cases [3,4,5,6].