Common Heritable Contributions to Low-Risk Trauma, High-Risk Trauma, Posttraumatic Stress Disorder, and Major Depression

Context: Understanding the relative contributions of genetic and environmental factors to trauma exposure, post-traumatic stress disorder (PTSD), and major depressive disorder (MDD) is critical to developing etiologic models of these conditions and their co-occurrence. Objectives: To quantify heritable influences on low-risk trauma, high-risk trauma, PTSD, and MDD and to estimate the degree of overlap between genetic and environmental sources of variance in these 4 phenotypes. Design: Adult twins and their siblings were ascertained from a large population-based sample of female and male twin pairs on the basis of screening items for childhood sexual abuse and physical abuse obtained in a previous assessment of this cohort. Setting: Structured psychiatric telephone interviews. Participants: Total sample size of 2591: 996 female and 536 male twins; 625 female and 434 male nontwin siblings. Main Outcome Measure: Lifetime low-and high-risk trauma exposure, PTSD, and MDD. Results: In the best-fitting genetic model, 47% of the variance in low-risk trauma exposure and 60% of the variance in high-risk trauma exposure was attributable to additive genetic factors. Heritable influences accounted for 46% of the variance in PTSD and 27% of the variance in MDD. An extremely high degree of genetic overlap was observed between high-risk trauma exposure and both PTSD (r = 0.89; 95% CI, 0.78-0.99) and MDD (r = 0.89; 95% CI, 0.77-0.98). Complete correlation of genetic factors contributing to PTSD and to MDD (r = 1.00) was observed. Conclusions: The evidence suggests that almost all the heritable influences on high-risk trauma exposure, PTSD, and MDD, can be traced to the same sources; that is, genetic risk is not disorder specific. Individuals with a positive family history of either PTSD or MDD are at elevated risk for both disorders and should be closely monitored after a traumatic experience for symptoms of PTSD and MDD.