40 APOE x BDNF Genetic Interaction is Associated with Poorer Cognitive Outcomes in Veterans with Histories of mTBI

Abstract

Objective:

Many Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) Veterans have sustained a mild traumatic brain injury (mTBI) during their military service and a substantial “miserable minority” frequently report significant cognitive complaints long after injury. Although existing studies have shown associations between genetic factors (e.g., apolipoprotein E [APOE] and brain-derived neurotrophic factor [BDNF]) and cognitive performance in this vulnerable population, the TBI-genetics literature has generally been varied and inconsistent. Although past findings suggest that individuals who possess APOE £4 and BDNF Met alleles have worse cognitive outcomes after mTBI, this has not been consistently reported. Additionally, the influence of any gene-by-gene interactions on cognition has not been sufficiently explored and therefore remains a critical area of interest. Thus, we examined relationships between APOE and BDNF genotypes on neuropsychological function in a well-characterized sample of younger Veterans with mTBI histories.

Participants and Methods:

Participants included Veterans with a history of mTBI who adequately completed performance validity testing. In total, 78 Veterans (84.6% male; age: M=32.95, SD=7.00; race/ethnicity: 51.3% White, 28.2% Hispanic/Latino, and 20.5% Another Race/Ethnicity) completed a structured clinical interview to collect detailed information on TBI history and underwent a comprehensive neuropsychological exam. A buccal swab was also collected to determine APOE and BDNF allele status for each participant. Three cognitive composite scores were computed reflecting memory (8 items), attention/processing speed (7 items), and executive functioning (10 items). Two-way analyses of covariance (ANCOVAs) adjusting for age, sex, and race/ethnicity were used to assess the effects of APOE (ε4+ vs. ε4-) and BDNF (Met+ vs. Met-) on cognitive functioning (ε4+/Met-: n=12, ε4+/Met+: n=8, £4-/Met-: n=35, and ε4-/Met+: n=23).

Results:

ANCOVAs revealed no significant main effects for APOE or BDNF genotypes on cognitive functioning; however, there was a significant APOE x BDNF genotype interaction for all three cognitive composites (memory: p=.026, np2=.068; attention/processing speed: p=.045, np2=.055; and executive functioning: p=.031, np2=.064). Specifically, the interaction was such that Veterans in the ε4+/Met+ group demonstrated the poorest cognitive functioning relative to all other allele group combinations (ε4+/Met-, ε4-/Met+, ε4-/Met-).

Conclusions:

The results of this preliminary study demonstrate that, compared to the other genetic subgroups in the TBI sample, Veterans with APOE £4 and BDNF Met alleles demonstrated the poorest cognitive functioning across several domains known to be negatively affected in the context of head injury (i.e., memory, attention/processing speed, and executive functioning). These findings are the first to show an APOE x BDNF interaction in Veterans with histories of mTBI. Further

research is necessary to replicate and extend this study in larger samples. Moreover, future work should incorporate neuroimaging variables to better interrogate structural and functional correlates of these observed genetic polymorphism associations in Veterans with mTBI histories.