Sodium valproate's ability to inhibit GABA transaminase (GABA-T) results in increased synaptic GABA. However, its teratogenicity (neural tube defects) is mechanistically linked to:

• A Inhibition of histone deacetylase (HDAC), altering epigenetic regulation of neural tube closure genes such as Pax3 ✓
• B Depletion of free folate by competitive inhibition of dihydrofolate reductase
• C Excessive GABA-mediated inhibition during neurulation causing failure of cranial neural tube closure
• D Direct teratogenic metabolite (valproate-4-en, Δ4-VPA) that alkylates folate receptors on the yolk sac

Explanation

Valproate is a class I and II HDAC inhibitor. During neurulation (weeks 3–4 of gestation), HDAC inhibition alters histone acetylation patterns, dysregulating expression of Pax3 and other genes critical for neural tube closure. This epigenetic mechanism accounts for the ~1–2% risk of open neural tube defects (myelomeningocele). Valproate also depletes folate indirectly (by increasing folate utilisation), but the HDAC inhibition mechanism is the primary epigenetic driver of its teratogenicity. This distinguishes valproate from other AEDs whose teratogenicity is folate-mediated.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.