C9orf72 and amyotrophic lateral sclerosis: Chromosome 9 open reading frame 72 (C9orf72), Cu/Zn superoxide dismutase 1 (SOD1), transactive response DNA binding protein (TARDBP) and fused in sarcoma (FUS), in that order, are ranked as the four most common genes causing familial ALS and mutations in these genes are increasingly detected in sporadic cases9,10.