Previous studies have indicated that genetic factors influence the risk of exposure to trauma, perhaps through personality differences (8). Although exposure to trauma (or perceived exposure to trauma) is essential to PTSD, in the primary GWAS analyses, we did not restrict the control subjects to trauma-exposed subjects. The significant genetic markers found by this method thus contribute to the risk of PTSD after trauma exposure and/or trauma exposure, which lead to PTSD. After restricting the control subjects to those who were trauma exposed, the significant genetic markers would appear to contribute to PTSD risk only. Although the p values were less significant, which was probably due to a smaller sample size, the two most significant genomic regions did not change when this restriction was imposed on the control group. Thus, the two regions identified are most likely to contribute to PTSD, rather than trauma exposure.
