[P1–406]: EFFECT OF AGE AND <i>APOE</i> GENOTYPES ON BRAIN MICROSTRUCTURE IN COGNITIVELY HEALTHY SUBJECTS AS MEASURED BY DIFFUSION‐WEIGHTED IMAGING

Age and ApoE status are among the most established non-modifiable risk factors to developing Alzheimer's disease (AD). It is also well known that human brain structure changes at both macro and microscopical level with healthy aging. The ApoE-ε4 allele is thought to impact with aging-related mechanisms and carriers are at increased risk of developing AD. AD patients carrying the e4 allele show increased pathological hallmarks and earlier age of onset. We present here results on microstructural differences found between cognitively healthy subjects with increased risk for AD as a function of their ApoE genotype using diffusion-weighted (DW) imaging. T1 and DW images were acquired from 514 subjects. ApoE genotyping was performed in all participants. We first applied denoising on both T1 and DWI using adaptive non-local means algorithm, then correction for eddy currents and of gradient directions. Diffusion models were estimated and mean diffusivity (MD) maps generated. DW B0 maps were warped to T1 space by coregistering white matter masks from both image types. We finally normalized MD maps from T1 space the MNI space. A multiple regression analysis was performed over MD maps to determine effects of genotype, age, and the interaction between both factors after accounting for gender and educational attainment. Images were also analyzed with Voxel-Based Morphometry (VBM). Our dataset included 245 non-carriers, 204 heterozygotes and 65 homozygotes for the ApoE-ε4 allele. We detected significant bilateral effects of genotype in the basal forebrain, in the pons as well as in orbitofrontal cortex. We also find some significant differences in posterior bilateral periventricular areas and in left corona radiata. In these regions carriers of the ApoE-ε4 allele showed decreased MD compared to non-carriers. These regions were not found in the VBM results.