Mota NP, et al. - The relationship between apolipoprotein E (APOE) genotype and posttraumatic stress disorder (PTSD) symptoms were examined in 2 nationally representative samples of U.S. military veterans. In addition, the authors aimed to assess the potential effect of cumulative trauma burden and social support in moderating this association. Compared to ε4 noncarriers, U.S. military veterans who were APOE ε4 allele carriers and exposed to a high number of traumas could be at increased risk for developing PTSD symptoms. Greater social support could moderate this association. Thereby, findings underscored the potential importance of social support promoting interventions in mitigating the effect of ε4 × cumulative trauma burden on PTSD risk.