The prevalent forms of ALS are sporadic (90%), while familial forms (10%) are mostly caused by mutations in genes encoding superoxide dismutase-1 (SOD-1), TAR-DNA binding protein-43 (TDP-43), fused in sarcoma (FUS), and C9orf72, even though mutations in numerous other genes have been associated with the disease. Here, SOD1 is linked to amyotrophic lateral sclerosis.