title: Exploring the effect of the apolipoprotein E (APOE) gene on executive function, working memory, and processing speed during the early recovery period following traumatic brain injury.
abstract: BACKGROUND
  There is evidence that the e4 allele of the apolipoprotein E (APOE) gene is detrimental to cognitive function, but results from traumatic brain injury (TBI) populations are mixed. A possible explanation is that APOEe2 carriers have routinely been incorporated into APOEe4 and non-e4 groups, despite APOEe2 being proposed to have an ameliorative effect. Our primary aim was to investigate the influence of APOEe4 on cognitive impairment during early recovery following TBI, excluding the potential confound of APOEe2 possession. A secondary objective was to explore whether APOEe4 displays more pronounced effects in moderate to severe TBI and to consider the potential postinjury protective influence of the APOEe2 allele.
  
  
  METHODS
  Participants who recently sustained a TBI (posttraumatic amnesia > 5 minutes) were assessed on measures of information processing speed, executive function, and working memory upon remission of posttraumatic amnesia. APOE genotype was determined by buccal saliva DNA extraction (APOEe4 n = 37, APOEe3 n = 92, APOEe2 n = 13).
  
  
  RESULTS
  Stepwise multiple regressions were performed to compare APOEe4 carriers to APOEe3 homozygotes, with injury severity, age, and estimated premorbid IQ included in the first step. This model was found to significantly predict performance on all tasks, accounting for 17.3-24.3% of the variance. When APOEe4 status was added for the second step, there were no significant changes on any tasks (additional variance <1%). The effect of APOEe4 in moderate to severe TBI and the effect of APOEe2 were explored by analysis of covariance (ANCOVA), with no significant effects revealed.
  
  
  CONCLUSIONS
  It is unlikely that APOE genotype influences cognitive function in the initial recovery period following TBI, regardless of injury severity. However, a more nuanced and long-term exploration of the effect of APOE genotype in the TBI population is warranted.
authors.affiliation: a School of Medicine , University of Tasmania , Launceston , TAS , Australia.|b Tasmanian Neurotrauma Register , Royal Hobart Hospital , Hobart , TAS , Australia.
authors.forename: Christine R
authors.initials: CR
authors.lastname: Padgett
authors.affiliation: c School of Social Sciences , University of the Sunshine Coast , Maroochydore , QLD , Australia.|d Wicking Dementia Research and Education Centre , University of Tasmania , Hobart , TAS , Australia.
authors.forename: Mathew J
authors.initials: MJ
authors.lastname: Summers
authors.affiliation: d Wicking Dementia Research and Education Centre , University of Tasmania , Hobart , TAS , Australia.
authors.forename: James C
authors.initials: JC
authors.lastname: Vickers
authors.affiliation: d Wicking Dementia Research and Education Centre , University of Tasmania , Hobart , TAS , Australia.
authors.forename: Graeme H
authors.initials: GH
authors.lastname: McCormack
authors.affiliation: a School of Medicine , University of Tasmania , Launceston , TAS , Australia.|b Tasmanian Neurotrauma Register , Royal Hobart Hospital , Hobart , TAS , Australia.
authors.forename: Clive E
authors.initials: CE
authors.lastname: Skilbeck
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D053318:Apolipoprotein E3 / Q000235:genetics; D053327:Apolipoprotein E4 / Q000235:genetics; D000070642:Brain Injuries, Traumatic / Q000150:complications* / Q000235:genetics; D016009:Chi-Square Distribution; D003072:Cognition Disorders / Q000209:etiology*; D056344:Executive Function / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000209:etiology*; D008570:Memory, Short-Term / Q000502:physiology*; D008875:Middle Aged; D009483:Neuropsychological Tests; D020127:Recovery of Function / Q000502:physiology*; D012044:Regression Analysis; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D053318:Apolipoprotein E3; D053327:Apolipoprotein E4
keywords: TBI; apolipoprotein E2; apolipoprotein E4; executive function; processing speed; traumatic brain injury; working memory