Averill LA, Abdallah CG, Levey DF, et al. - The ε4 allele of the apolipoprotein E (APOE) gene and posttraumatic stress disorder (PTSD)have been suggested to be related to cognitive dysfunction and dementia risk, so researchers assessed if they interact to predict cognitive dysfunction. From European-American (EA) veterans who participated in the National Health and Resilience in Veterans Study, data were analyzed, via a main sample (n = 1,386) and a primary replication sample (n = 509). The analysis revealed an independent correlation of APOE ε4 allele carrier status and PTSD with lower cognitive functioning. ε4 carriers with PTSD vs those without PTSD scored lower, with executive function and attention/concentration showing the most marked alterations. Substantially larger cognitive difficulties were seen in APOE ε4 allele carriers with PTSD vs ε4 carriers without PTSD.