Pharmacogenomics of Antiepileptic Drug Mood Stabilizer Treatment Response in Bipolar Disorder: A MoStGen Consortium Study

Why It Matters

These findings pinpoint the first genome‑wide markers for lamotrigine efficacy, paving the way for genetically informed, personalized treatment strategies in bipolar disorder.

Key Takeaways

• ROBO2 variants linked to lamotrigine response
• POLR1E gene associated with lamotrigine efficacy
• No genome-wide hits for overall AMS or valproate
• Polygenic scores predict medication-specific response
• Epilepsy genetic risk modestly improves AMS response prediction

Pulse Analysis

Bipolar disorder remains a therapeutic challenge because response to mood‑stabilizing drugs varies widely among patients. While lithium genetics have been explored extensively, antiepileptic mood stabilizers—particularly valproic acid and lamotrigine—have lacked large‑scale pharmacogenomic scrutiny. The MoStGen Consortium’s pooled cohort of nearly a thousand individuals, phenotyped with the validated Alda scale, provides the statistical power needed to detect genome‑wide signals that were previously out of reach, offering a new layer of biological insight into treatment heterogeneity.

The study’s most striking result is the identification of ROBO2 as a lamotrigine‑response locus, reaching genome‑wide significance (p = 1.9 × 10⁻¹⁰). ROBO2 encodes a receptor involved in axon guidance and synaptic plasticity, pathways plausibly linked to mood regulation. A secondary gene‑level hit implicates POLR1E, though its neuropsychiatric role is less clear. Notably, valproic acid showed no significant associations, underscoring that pharmacogenomic predictors may be drug‑specific rather than class‑wide. These discoveries expand the catalog of actionable genetic markers beyond the lithium‑focused literature and suggest that future trials should stratify participants by medication type when searching for genetic predictors.

Polygenic score (PGS) analyses further demonstrate that AMS response is polygenic, with medication‑specific PGS explaining modest variance in treatment outcomes. The nominal association between epilepsy PGS and better AMS response hints at shared neurobiological mechanisms between epilepsy and bipolar disorder, reflecting the overlapping sodium‑channel targets of these drugs. Although effect sizes are small, integrating PGS with clinical variables could eventually refine decision‑making tools. Limitations include a predominance of European ancestry and the aggregation of diverse AMS agents in the combined analysis. Expanding the consortium to non‑European cohorts and deepening phenotype granularity will be essential steps toward translating these genomic insights into routine, precision‑psychiatry practice.