There is evidence that the cognitive effects of Alzheimer's disease can be seen decades before disease diagnosis. If this is the case, then the apolipoprotein E (APOE) * E4 allele might be expected to have effects on cognitive functioning earlier in the life span. To assess such effects, the authors examined data on the * E4 allele and cognitive functioning from a population sample of 6,560 Caucasians covering the age groups of 20 -24, 40 -44, and 60 -64 years. Participants were assessed on

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... s of episodic memory, working memory, mental speed, reaction time, and reading vocabulary. Although performance on all tests except reading vocabulary declined across age groups, there was no effect of the APOE * E4 allele at any age. These results indicate that APOE * E4 does not have preclinical effects early in the life span on these cognitive functions. Cognitive aging effects between the ages of 20 and 64 years must not be due to preclinical Alzheimer's disease.