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Abstract
Objective: To comprehensively assess neurobiological effects of the protective APOE2 allele in the aged brain using a cross-sectional multimodal neuroimaging approach.
Methods: Multimodal neuroimaging data were obtained from a total of 572 older individuals without dementia (cognitively normal and mild cognitive impairment) enrolled in the Alzheimer's Disease Neuroimaging Initiative and included assessments of regional amyloid load with AV45-PET, glucose metabolism with fluorodeoxyglucose-PET, and gray matter volume with structural MRI. Imaging indexes of APOE2 carriers were contrasted to risk-neutral APOE3 homozygotes, and analyses were controlled for age, sex, education, and clinical diagnosis. Additional models examined genotype-specific effects of age on the imaging markers.
Results: In region-of-interest–based analyses, APOE2 carriers had significantly less precuneal amyloid pathology and did not show the typical age-related increase in amyloid load, although the age × genotype interaction was only trend-level significant. In contrast, parietal metabolism and hippocampal volume did not differ between APOE2 and APOE3 genotypes, and both groups showed comparable negative effects of age on these markers. The amyloid specificity of APOE2-related brain changes was corroborated in 2 complementary analyses: spatially unbiased voxel-wise analyses showing widespread reductions in amyloid deposition but no differences in gray matter volume or metabolism and an analysis of CSF-based biomarkers showing a significant effect on amyloid but not on tau pathology.
Conclusions: Regarding the range of Alzheimer disease biomarkers considered in the present study, the APOE2 allele appears to have a relatively selective effect on reduced accumulation of amyloid pathology in the aged brain.
GLOSSARY
- Aβ=
- β-amyloid;
- AD=
- Alzheimer disease;
- ADNI=
- Alzheimer's Disease Neuroimaging Initiative;
- ANCOVA=
- analysis of covariance;
- CN=
- cognitively normal;
- FDG=
- fluorodeoxyglucose;
- GM=
- gray matter;
- MCI=
- mild cognitive impairment;
- PiB=
- Pittsburgh compound B;
- p-tau=
- phosphorylated tau;
- ROI=
- region of interest;
- t-tau=
- total tau
Footnotes
Data used in preparation of this article were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database (adni.loni.usc.edu/). As such, the investigators within the ADNI contributed to the design and implementation of ADNI and/or provided data but did not participate in analysis or writing of this report. A complete listing of ADNI investigators can be found in the coinvestigators list at Neurology.org.
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Supplemental data at Neurology.org
- Received April 30, 2016.
- Accepted in final form November 16, 2016.
- © 2017 American Academy of Neurology
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