Genetic Overlap Between DSM-IV Major Depressive Disorder and Suicidal Behaviors: Evidence from Polygenic Risk Scores in Young Adult Twins.

Suicidal thoughts and behaviors (STBs) represent a significant public health concern. This study aimed to examine the extent to which polygenic risk scores (PRSs) for suicide attempt and major depression (MD) explain variance in suicidal ideation, plans, and attempts among young adult twins. Data from 2876 participants of European ancestry in the Brisbane Longitudinal Twin Study were analyzed. PRSs for MD and suicidal behavior (SB PRS) were calculated. Multivariate twin modeling was used to estimate genetic and environmental influences on DSM-IV Major Depressive Disorder (MDD) diagnosis and STBs, as well as their associations with PRSs. Heritability estimates were higher for STB phenotypes (51-80%) compared to DSM-IV MDD (39-41%). The MD PRS showed more consistent genetic correlations with DSM-IV MDD, while both PRSs showed modest correlations with suicide outcomes. Multivariate analyses revealed remarkably high genetic correlations among STBs (rA = 0.85-0.99) and moderate genetic correlations with MDD (rA = 0.48-0.65). Environmental factors contributing to DSM-IV MDD risk were largely distinct from those influencing suicide-related phenotypes. This study provided compelling evidence for shared genetic architecture between DSM-IV MDD and STBs. The MD PRS demonstrated more consistent prediction of MDD compared to the SB PRS, though both showed modest correlations with suicide outcomes. These results have important implications for risk assessment strategies, though the substantial unique environmental influences highlight the need to address modifiable environmental risk factors. Future research should focus on replication in larger, more diverse samples and exploring the interactions between genetic risk factors and environmental influences across the lifespan.