By Jamie Eske Reviewed by Shilpa Amin MD, CAQ, FAAFP Methylenetetrahydrofolate reductase, or MTHFR, is an enzyme that breaks down the amino acids homocysteine and folate. The MTHFR gene that codes for this enzyme has the potential to mutate, which can either interfere with the enzyme’s ability to function normally or completely inactivate it. People have...