GSTP1 and amyotrophic lateral sclerosis: To the best of our knowledge, this is the first study showing the relationship between DNA methylation of specific biomarkers of oxidative stress, neuroprotection, cognitive behavior (fundamentally the D-loop, but also GSTP1 and the CpG1 site of LINE-1), and nutritional status in accordance with disease progression at diagnosis and mortality in patients with ALS.