Predictive Utility of Apolipoprotein E Genotype for Alzheimer Disease in Outpatients With Mild Cognitive Impairment

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Abstract
The gene for apolipoprotein E (APOE) is on the long arm of chromosome 19 and exists in 3 allelic forms (ε2, ε3, and ε4). APOE ε4 is associated with an increased risk of Alzheimer disease (AD).1 In studies that compared patients who had AD with healthy controls, the mean odds ratio for heterozygotes was approximately 4 in clinical samples and approximately 2 in community samples, with considerable variability across studies.2,3 The APOE ε4 allele’s association with AD is not influenced by sex, diminishes after the ninth decade of life,4,5 and may not hold in all ethnic groups.2,6