Spatial Navigation and APOE in Amnestic Mild Cognitive Impairment

Background: The effect of APOE epsilon 4 allele (epsilon 4) on spatial navigation in amnestic mild cognitive impairment (aMCI) is unknown. Objective: Our purpose was to examine the characteristics of spatial navigation impairment in epsilon 4-positive (epsilon 4+) and epsilon 4-negative (epsilon 4-) aMCI subgroups. Methods: Blood samples were collected to determine the APOE genotype. A total of 34 aMCI patients were stratified into aMCI-epsilon 4- (n = 23) and aMCI-epsilon 4+ (n = 11) groups. Control (n = 28) and mild Alzheimer's disease (AD; n = 16) groups were also used. We used a human analogue of the Morris water maze (enclosed arena 2.9 m in diameter) to examine body-centered (egocentric) and world-centered (allocentric) spatial navigation. Results: The aMCI-epsilon 4+ group performed poorer on spatial navigation than the aMCI-epsilon 4-group in both egocentric and allocentric tasks even though these 2 groups did not differ in global cognitive functioning or neuropsychological tests. The aMCI-epsilon 4+ and mild AD groups performed similarly on all Morris Water Maze tasks and were outperformed by the aMCI-epsilon 4- group, which also resembled the control group in performance on the egocentric tasks. The aMCI groups showed poor spatial navigation learning regardless of their epsilon 4 positivity. Conclusion: We found more profound deficits in spatial navigation in aMCI-epsilon 4+ relative to aMCI-epsilon 4- patients. The aMCI-epsilon 4+ group resembled the mild AD group in spatial navigation performance. Although the epsilon 4 genotype was indicative of spatial navigation performance, it was not indicative of the aMCI patients' ability to learn the tasks. Spatial navigation testing represents a promising area with respect to identifying individuals at higher risk for AD among the heterogeneous MCI population. Copyright (C) 2010 S. Karger AG, Basel