A recent analysis from the Brisbane Longitudinal Twin Study indicates that the heritability of suicidal behaviors is significantly higher than that of major depressive disorder (MDD). The findings were published in Behavior Genetics and reveal moderate genetic associations between suicide-related outcomes and MDD, while also highlighting distinct environmental factors influencing these conditions.
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Suicidal thoughts and behaviors, which include suicidal ideation, planning, attempts, and completed suicides, pose a major public health challenge. Although MDD is a strong risk factor for suicide, it does not fully account for the risk.
Previous twin and family studies suggest that genetics play a role in suicidal behaviors, leading researchers to utilize polygenic risk scores. These scores aggregate genetic variants to assess an individual’s vulnerability to suicidal outcomes. Past research has shown modest correlations between these scores for both MDD and suicidal behavior, indicating a shared genetic component in multiple psychiatric disorders.
Study co-author Nathan A. Gillespie and his team evaluated the impact of polygenic risk scores for MDD and suicide attempts on specific suicidal behaviors, aiming to understand their contributions to suicidal ideation, planning, and attempts. Analyzed data came from a subset of 2,876 participants within the broader Brisbane Longitudinal Twin Study, which started in 1992 with over 7,000 individuals of European descent. Participants were assessed at ages 12, 14, 16, 21, and 25.
The researchers generated two polygenic risk scores based on data from previous studies. Their results indicated that the heritability of suicidal behaviors ranges from 51% to 80%, compared to an estimated 39% to 41% heritability for MDD. The polygenic risk score for MDD demonstrated more consistent associations with diagnosed cases of depression, while both scores showed modest correlations with suicidal behaviors. Notably, the study found that environmental factors influencing MDD were largely distinct from those affecting suicidal thoughts and behaviors.
The study concluded that there is a significant shared genetic architecture between MDD and suicidal behaviors, and while the polygenic risk score for MDD was a better predictor of its diagnosis, both scores remained relevant to suicide outcomes. The authors acknowledged that their analysis pooled data from both genders, which may overlook specific genetic differences between sexes.
The research paper is titled “Genetic Overlap Between DSM-IV Major Depressive Disorder and Suicidal Behaviors: Evidence from Polygenic Risk Scores in Young Adult Twins” and includes contributions from authors Nathan A. Gillespie, Mei-Hsin Su, Séverine Lannoy, Mallory Stephenson, Miguel E. Rentería, Zuriel Ceja, Ian B. Hickie, Nicholas G. Martin, and Alexis C. Edwards.