A 28-year-old woman with bipolar disorder on valproate presents at 8 weeks gestation. Valproate's main teratogenic mechanism linked to neural tube defects involves:

• A Competitive antagonism at folic acid intestinal transporters, producing folate deficiency
• B Direct inhibition of dihydrofolate reductase in the embryo
• C Inhibition of histone deacetylase (HDAC) causing epigenetic disruption of folate-dependent neural tube closure genes ✓
• D Sodium channel blockade impairing neuroepithelial cell migration

Explanation

Valproate is a potent inhibitor of histone deacetylases (HDACs), leading to abnormal histone acetylation and dysregulation of genes required for neural tube closure. This epigenetic mechanism is responsible for the 1–2% risk of spina bifida and other NTDs; supplementation with high-dose folic acid reduces but does not eliminate the risk because the mechanism is not purely folate-deprivation. Valproate does not directly inhibit DHFR or intestinal folate transporters.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.