Future longitudinal cohort studies will be important in elucidating the association between CI in PTSD and specific biomarkers by investigating multiple mediating factors including APOE ε4 (Averill et al., 2019, Elias et al., 2020), psychiatric morbidity (Qassem et al., 2021), such as depression and intake of antidepressants, or other medical comorbidities such as cardiovascular disorders that could contribute to risk of dementia (Jacob et al., 2018). This evidence concerns the gene APOE and major depressive disorder.