In the context of this comparison, the total proteome of fibroblasts from ALS patients carrying the C9ORF72 repeat expansion was analyzed against that of ALS patients who tested negative for the C9ORF72 repeat expansion, including patients also negative for the remaining three main ALS genes (SOD1, TARDBP and FUS) and patients carrying a mutation in SOD1. The gene discussed is SOD1; the disease is amyotrophic lateral sclerosis.