Methylenetetrahydrofolate reductase (MTFHR) is an enzyme involved in the processing of amino acids using folic acid, specifically the conversion of homocysteine to methionine. Patients with C677T polymorphism may see increased levels of blood homocysteine when folate levels are low, which may lead to a need for folate supplementation. Various mutations to the MTFHR enzyme may result in altered need and response to folate supplementation.

L-Methylfolate is the centrally active derivative of the vitamin folate and is used for both neurotransmitter synthesis, and vital methylation reactions in all cells. It regulates BH4 (or tetrahydrobiopterin) a critical enzyme cofactor required for serotonin, dopamine and norepinephrine synthesis. Some forms of depression resistant to antidepressant treatment may respond to folate or l-methylfolate. Synthesis of the monoamine neurotransmitters serotonin, dopamine, and norepinephrine is regulated by L-methylfolate, a derivate of the vitamin folate. Copyright 2008 Physicians Postgraduate Press, Inc.