APOE and post-traumatic stress disorder: They reported that circulating levels of plasma ApoE levels were positively associated with APOE methylation at CpG −775 and negatively associated with methylation at CpG-877; however, there were no conclusive differences in circulating plasma ApoE between TBI + PTSD and TBI-only participants among ε4 carriers (d = −0.25, 95% CI: −1.37, 0.88) or non-carriers (d = 0.43, 95% CI: −0.25, 1.11).