Apolipoprotein e (APOE) ε4 genotype influences memory performance following remote traumatic brain injury in US military service members and veterans

The purpose of this study was to examine the association between the apolipoprotein E (APOE) epsilon 4 allele and neurocognitive functioning following traumatic brain injury (TBI) in military service members and veterans (SMVs). Participants included 176 SMVs with a history of remote TBI (>= 1 year post-injury), categorized into mild (n = 100), moderate (n = 40), and severe (n = 36) TBI groups. Participants completed a neuropsychological assessment and APOE genotyping (n = 46 epsilon 4+, n = 130 epsilon 4-). Neurocognitive composite scores representing memory, executive functioning, and visual processing speed were computed. ANCOVAs adjusting for race, education, combat exposure, and PTSD symptom severity showed a significant main effect of epsilon 4 on the memory composite, such that epsilon 4+ SMVs exhibited poorer memory performance than epsilon 4- SMVs. When epsilon 2 allele carriers were removed from the analyses, associations with memory were strengthened, demonstrating a possible protective effect of the epsilon 2 allele. No main effect of TBI group was identified on any cognitive composite, nor were there any significant TBI group x epsilon 4 status interactions for any cognitive composite. Future studies with larger samples are needed to verify these findings, but our results suggest an important relationship between epsilon 4 status and memory functioning following remote TBI of all severities.