White Matter Integrity in Individuals at Risk for Alzheimer's Disease: A Diffusion Tensor Imaging Study
Diffusion Tensor Imaging (DTI) studies have confirmed changes in white matter integrity in normal aging which appear more pronounced in both Mild Cognitive Impairment (MCI) and Alzheimer's Disease (AD). Few DTI studies have examined asymptomatic individuals at risk for AD, and most have focused solely on changes in fractional anisotropy (FA). In this study, we compared three other DTI indices, mean diffusivity (MD), axial diffusivity (DA), and radial diffusivity (DR) in addition to FA, in cognitively intact older participants who differed on AD risk factors (APOE 4 allele and family history). The At-Risk group had a positive family history of AD and one or both Apolipoprotein (APOE) ϵ4 alleles (n = 29) and the No-Risk group had neither risk factor (n = 29). There were no group differences on age, education, sex, or cognitive status. Groups were compared on four DTI indices, using both tract-based spatial statistics (TBSS) and region of interest (ROI) approaches. The At-Risk group showed widespread, bilateral increase in DA, and to a lesser extent in DR and MD, relative to the No-Risk group. In contrast, no group differences were observed in FA. Good correspondence was observed between the ROI and TBSS analyses. FA was most correlated with measures of memory, while radial diffusivity and especially axial diffusivity showed less relation to cognitive variables. These findings suggest that DTI indices of diffusivity, especially in the axial direction, may be a useful biomarker in identifying older persons at risk for AD. Longitudinal studies are needed to determine if these DTI indices can play a role in the prediction of future cognitive decline in asymptomatic individuals.
0622: Clinical psychology