Longitudinal Differences in White Matter Integrity Between APOE ε4 Carriers Versus Noncarriers

Abstract

Alzheimer's disease (AD) is a neurodegenerative disorder that causes atrophy in gray and white matter (WM) as well as cognitive declines. Even though recent literature suggests that the apolipoprotein E (APOE) ε4 allele increases cognitive deficiencies in older adults, especially through increasing risk for the late-onset form of AD, relatively little is known about longitudinal differences in brain white matter integrity changes between APOE ε4 carriers and noncarriers. Data was obtained from 53 individuals (ages 55-91) which included 34 APOE ε4 noncarriers and 19 APOE ε4 carriers. From diffusion weighted images (DWI) fractional anisotropy (FA) maps were calculated at two time points 2.7 years apart, on average, in order to measure differences in the change in white matter integrity over time between the APOE ε4 groups. Regions of interest (ROI) were selected based on significant regions of difference at the first scan. No significant decreases in WM integrity were observed over time for the ROIs selected. However, in the left superior temporal white matter there was a significant increase in FA over time for the ε4 non-carriers but not the carriers. A similar, trending pattern was found in the left middle frontal white matter. Interestingly, these were two ROIs in which ε4 carriers had greater volumes at initial scan, suggesting that the regions of advantage with regard to white matter efficiency that ε4 carriers had compared to noncarriers disappear over time. Further analysis into associations between changes in white matter and changes in cognition over time should be undertaken.