This concentration can be achieved in vivo but only in certain disease states (eg, genetic polymorphisms in MTHFR—the gene encoding methylenetetrahydrofolate reductase, which is required for homocysteine synthesis) and in severe nutritional deficiency.110,111 However, a concentration of 10 μmol/L may be sufficient if the redox potential of the cell is influenced by other factors, for example, by the presence of certain cations such as Cu+, Cu2+, Fe2+, or Fe3+. The gene discussed is MTHFR; the disease is nutritional deficiency disease.