A 28-year-old woman in her first trimester presents with megaloblastic anemia and a previous child with a neural tube defect (NTD). Which biochemical function of folic acid is most directly related to NTD prevention?

• A Synthesis of pyridine nucleotides
• B Methylation of homocysteine to methionine
• C Hydroxylation of procollagen
• D Provision of one-carbon units for nucleotide synthesis, specifically thymidylate synthesis ✓

Explanation

Folate, as 5,10-methylenetetrahydrofolate, donates a methylene group to deoxyuridylate (dUMP) via thymidylate synthase to produce deoxythymidylate (dTMP), essential for DNA synthesis. Rapidly proliferating neural tube cells during days 21-28 of gestation have extremely high thymidylate requirements; folate deficiency impairs de novo dTMP synthesis, causing replication stress and defective neural tube closure. Periconceptional folic acid supplementation reduces NTD risk by approximately 70% by ensuring adequate dTMP production.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.