Less than 10 % of ALS cases are familial (fALS), of which most are caused by repeat expansions of the C9ORF72 gene or mutations in genes encoding copper–zinc superoxide dismutase (SOD1), TAR DNA binding protein 43 (TDP-43) and fused in sarcoma (FUS). The gene discussed is FUS; the disease is amyotrophic lateral sclerosis.