MTHFR and coronary artery disorder: Moreover, within different risk factors for CAD Methylenetetrahydrofolate reductase (MTHFR) is a rate-limiting enzyme in the methionine metabolism pathway that catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine.