Anti-methylenetetrahydrofolate reductase antibodies are used in the immunodetection of the protein encoded by the MTHFR gene. In humans, the canonical protein has a reported length of 656 amino acid residues and a mass of 74.6 kDa. Alternative splicing is reported to yield 2 different isoforms for this protein. A member of the Methylenetetrahydrofolate reductase protein family, it is known to catalyze the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine. Post-translational modifications have been described, including phosphorylation. Other names for this target antigen include 5,10-methylenetetrahydrofolate reductase (NADPH), methylenetetrahydrofolate reductase (NAD(P)H), and methylenetetrahydrofolate reductase (NADPH).