Sodium valproate's teratogenicity (causing neural tube defects) is best attributed to which molecular mechanism?

• A Inhibition of histone deacetylase (HDAC) altering expression of folate transport genes and disrupting neural tube closure through epigenetic mechanisms ✓
• B Direct competitive inhibition of MTHFR enzyme, depleting methylenetetrahydrofolate
• C Blockade of SLC19A1 folate transporter at the placental level
• D Formation of valproyl-CoA that competes with acetyl-CoA in neural tube lipid synthesis

Explanation

Valproate is a potent HDAC inhibitor that causes epigenetic dysregulation of gene expression critical for neural tube closure, including folate receptor genes (FOLR1) and homeobox (HOX) genes. This mechanism is distinct from direct folate antagonism and explains why high-dose folate supplementation (5 mg/day) reduces but does not fully prevent valproate-related neural tube defects. The epigenetic mechanism also underlies valproate's effects on cognitive development (valproate embryopathy). Understanding the HDAC mechanism is important for counselling women of reproductive age.

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

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