Incidence of Alzheimer disease in a biracial urban community: relation to apolipoprotein E allele status.

CONTEXT Few studies compare Alzheimer disease (AD) incidence among black and white subjects. OBJECTIVE To estimate incidence and the effect of the apolipoprotein E (APOE) epsilon4 allele in these races. DESIGN Population-based study of disease incidence using a random, stratified sample. SETTING A geographically defined community of 3 adjacent neighborhoods in Chicago, Ill. PARTICIPANTS A total of 6158 persons (78.7% overall; 80.5% of the black subjects and 74.6% of the white subjects) participated; 4.1 years later, persons initially free of AD were sampled for clinical evaluation for disease incidence (overall 842 persons [74.8%] participated; 67.6% of the black subjects and 81.9% of the white subjects). INTERVENTIONS None. MAIN OUTCOME MEASURE Incident, clinically diagnosed AD. RESULTS The effect of the APOE epsilon4 allele on the risk of AD differed strongly for black and white subjects. Among white subjects, the presence of the APOE epsilon4 allele was associated with a 2.73-fold (95% confidence interval [CI], 1.40-5.32) increase in risk while among black subjects there was no increase in risk (odds ratio, 1.02; 95% confidence interval, 0.39-2.68). Black race was associated with a nonsignificantly increased risk of AD with an odds ratio of 1.84 (95% CI, 0.73-4.66) if APOE and its interaction with race are considered, and an odds ratio of 1.28 (95% CI, 0.54-2.98) if they are not. The incidence of AD was 1.45% (95% CI, 0.89%-2.01%) per year among persons 65 to 74 years old, 4.73% (95% CI, 3.83%-5.64%) among those 75 to 84 years old, and 9.11% (95% CI, 7.36%-10.9%) among those 85 years and older. CONCLUSION Apolipoprotein E epsilon4 led to increased risk of AD among white subjects but not black subjects.