DHFR and neural tube defect: One important gene that is involved in this metabolism is DHFR, which encodes the enzyme responsible for reducing folic acid in THF.9 A common polymorphism in this gene, 19-bp deletion polymorphism in intron-1, has been correlated with modulation of the maternal risk of neural tube defects (NTDs),10,11 and of the concentrations of the metabolites involved in the folate pathway.9,13,25