Objective: The authors examined the interaction between apolipoprotein E (APOE) ε4 and brain-derived neurotrophic factor (BDNF) Val66Met alleles on neuropsychological functioning among veterans with histories of mild traumatic brain injury (mTBI).
Methods: Participants were 78 veterans with mTBI (85% males; mean±SD age=32.95±7.00 years; mean time since injury=67.97±34.98 months) who completed a structured clinical interview and underwent a comprehensive neuropsychological assessment. Participants also provided a buccal swab for determination of their APOE and BDNF genotypes. Three cognitive composite scores were calculated from the neuropsychological assessment, reflecting visuospatial speed (seven variables), executive functioning (10 variables), and memory (eight variables). Two-way analyses of covariance (ANCOVAs) adjusted 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.
Results: ANCOVAs revealed no significant main effects of APOE or BDNF genotypes on cognitive functioning; however, there was a significant APOE-by-BDNF genotype interaction for all three cognitive composite measures (visuospatial speed: ηp2=0.055; executive functioning: ηp2=0.064; and memory: ηp2=0.068). Specifically, the ε4+/Met+ (N=8) subgroup demonstrated the poorest cognitive functioning relative to all other allele subgroups (ε4+/Met-: N=12, ε4-/Met+: N=23, and ε4-/Met-: N=35).
Conclusions: This exploratory study is the first to show that, compared with other allele subgroups assessed, veterans with both ε4 and Met alleles demonstrated the poorest cognitive functioning across several cognitive domains known to be negatively affected in the context of mTBI. Further research with larger sample sizes is needed to replicate these findings.
Keywords: APOE; BDNF; Cognition; Genetics; Military Veterans; Traumatic Brain Injury.