Amongst these genes, the major established causal ALS genes are SOD1 (Cu-Zn superoxide dismutase 1), TARDBP (transactive response DNA Binding protein 43kDa), FUS (fused in sarcoma) and hexanucleotide expansion repeat in Chromosome 9 Open Reading Frame 72 (C9ORF72). Here, SOD1 is linked to amyotrophic lateral sclerosis.