Overview of the human folate metabolic pathway. SAM indicates S-adenosylmethionine; SAH, S-adenosylhomocysteine; DHF, dihydrofolate; DHFR, dihydrofolate reductase; THF, tetrahydrofolate; SHMT, serine hydroxymethyltransferase; 5,10-methyleneTHF, 5,10-methylenetetrahydrofolate; MTHFR, 5,10-methylenetetrahydrofolate reductase; 5-methylTHF, 5-methyltetrahydrofolate; 10-formylTHF, 10-formyltetrahydrofolate; MTR, methionine synthase; TYMS, thymidylate synthase; dTMP, deoxythymidine monophosphate; B12, vitamin B12; and dUMP, deoxyuridine monophosphate.