MTR and neural tube defect: Mutations and polymorphisms in folate pathway genes such as methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), methionine synthase reductase (MTRR), and betaine-homocysteine methyltransferase (BHMT), have been intensively investigated and in some studies have shown an association with NTD risk [6-9].