SOD1 and amyotrophic lateral sclerosis type 4: Among the more than 40 genes associated with ALS, repeat expansions of chromosome 9 open reading frame 72 (C9orf72), and variants in superoxide dismutase 1 (SOD1), fused in sarcoma (FUS), and TAR DNA-binding protein 43 (TARDBP), are the most frequent genes identified in ALS4,6.