MMUT and amyotrophic lateral sclerosis: We hypothesized that genetic mutations alter the function of enzymes responsible for the metabolism of estrone-3-sulphate and isoleucine, namely 17β-Hydroxysteroid dehydrogenase 1 (17β-HSD1) and methylmalonyl-CoA mutase, might have a significant impact on ALS risk if they interfere with downstream toxic or protective compounds.