Isolating the Genetic Component of Mania in Bipolar Disorder

Bipolar disorder typically features episodes of mania and depression, frequently accompanied by psychosis. While progress has been made in understanding the genetics of depression and psychosis, mania remains underexplored, limiting opportunities for targeted interventions and a fuller understanding of bipolar disorder's heterogeneity.

We used genomic structural equation modeling to subtract the genetic effects of major depressive disorder (MDD) from bipolar disorder, allowing us to isolate a genetic component specific to mania. This approach used genome-wide association study (GWAS) summary statistics from large-scale studies of European ancestry, including 576,327 effective samples for MDD and 27,196 cases with 43,792 controls for bipolar disorder.

The structural equation model revealed significant loadings for "mania" (0.90, p < .001) and "depression" (0.43, p < .001) factors, with mania and MDD explaining 81.5% and 18.5% of the variance in bipolar disorder, respectively. Seventy-one independent significant single nucleotide polymorphisms associated with mania were identified, spread in 37 genomic loci. Mania exhibited distinct genetic correlations compared with bipolar disorder, including significantly different correlations with psychiatric phenotypes, tiredness (r_g = -0.13 vs. -0.17), subjective well-being (r_g = 0.08 vs. -0.13), and educational attainment (r_g = 0.26 vs. 0.14). Pathway analysis highlighted a significant enrichment in the voltage-gated calcium channel activity pathway.

These findings enhance understanding of bipolar disorder's genetic architecture, offering a more bipolar disorder-specific GWAS. Identifying mania-specific loci may inform earlier diagnosis, personalized treatment approaches, and the development of targeted therapies.