The gene MTHFR (Methylenetetrahydofolate Reductase) encodes the protein MTHFR. Its job is to convert one
form of folate (5,10-Methylenetetrahydofolate) to another
form of folate (5-Methyltetrahydrofolate). 5-Methyltetrahydrofolate is used to convert Homocysteine (a "bad" amino acid) to Methionine (a "good" amino acid). Therefore, if MTHFR is not doing its job as well, homocysteine will not be converted to Methionine and will be elevated in plasma.