At one end of the spectrum, mutations in PGRN (encoding the secretory protein progranulin) and MAPT (encoding the microtubule binding protein tau) almost only ever cause FTD, whereas mutations in the antioxidant enzyme SOD1 only cause ALS.11 However, the majority of genetic mutations can lead to both disorders. The gene discussed is SOD1; the disease is amyotrophic lateral sclerosis.