This repeat expansion was also found in one third of familial ALS cases of outbred European decent, and it was more than twice as common as mutations in the SOD gene as a cause of familial ALS, and more than three times as common as TDP-43, fused in sarcoma (FUS), or optineurin (OPTN) mutations combined. Here, FUS is linked to amyotrophic lateral sclerosis.