It describes the assumption that amyotrophic lateral sclerosis, similar to cancer, is triggered by the accumulation of multiple triggering risk factors.26 According to the model, in sporadic forms, six of such steps are necessary, whereas a mutation in the C9orf72 gene requires only three steps, and a mutation in the SOD1 gene only two.27 Since C9orf72 mutation carriers require more environmental risk factors28-30 than SOD1 mutation carriers, but less compared to non-mutation carriers, the disease might occur later compared to SOD1 and earlier compared to sporadic patients. Here, SOD1 is linked to amyotrophic lateral sclerosis.