title: White matter alterations in cognitively normal apoE ε2 carriers: insight into Alzheimer resistance?
abstract: OBJECTIVE
  The basis for decreased vulnerability to AD among apoE ε2 carriers is unknown. The purpose of this study was to use diffusion tensor imaging to detect possible differences in white matter integrity between cognitively normal elderly apoE ε2 carriers and apoE ε3/ε3 controls.
  
  
  METHODS
  Thirty-nine cognitively normal elderly individuals (19 heterozygous carriers of the apoE ε2 allele, 20 apoE ε3/ε3 subjects as controls) underwent diffusion tensor MR imaging on a 4T scanner. Fractional anisotropy, MD, and axial and radial diffusivity were compared using a ROI approach. In addition, an exploratory whole-brain analysis of fractional anisotropy between the 2 groups was undertaken using TBSS.
  
  
  RESULTS
  apoE ε2 carriers had higher FA in the posterior cingulate white matter (P = .01) and anterior corpus callosum (P = .005) than apoE ε3/ε3 controls, secondary to lower radial diffusivity. No significant differences in the FA of the posterior corpus callosum, anterior cingulate white matter, or parahippocampal white matter were seen. Whole-brain TBSS analysis detected regions of higher FA in the apoE ε2 group in the superior longitudinal fasciculus, right thalamus, and the bilateral anterior limbs of the internal capsule, in addition to the posterior cingulum and corpus callosum (P < .005). There were no regions in which the apoE ε3/ε3 group had higher FA.
  
  
  CONCLUSIONS
  apoE ε2 carriers harbor more robust white matter integrity that may be associated with decreased vulnerability to developing AD. This provides further evidence that regional DTI metrics may serve as early imaging biomarkers of AD risk.
authors.affiliation: Center for Imaging of Neurodegenerative Diseases, Department of Veteran Affairs Medical Center, San Francisco, California, USA. gloria.chiang@ucsf.edu
authors.forename: G C
authors.initials: GC
authors.lastname: Chiang
authors.forename: W
authors.initials: W
authors.lastname: Zhan
authors.forename: N
authors.initials: N
authors.lastname: Schuff
authors.forename: M W
authors.initials: MW
authors.lastname: Weiner
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000235:genetics* / Q000473:pathology*; D053329:Apolipoprotein E2 / Q000235:genetics*; D001921:Brain / Q000473:pathology* / Q000503:physiopathology*; D003072:Cognition Disorders / Q000235:genetics / Q000473:pathology; D056324:Diffusion Tensor Imaging / Q000379:methods; D060467:Disease Resistance / Q000235:genetics; D005260:Female; D006579:Heterozygote; D006801:Humans; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D053329:Apolipoprotein E2