Association of apolipoprotein E genotype and Alzheimer disease in African Americans

Background: Alzheimer disease (AD) is the most frequent cause of dementia. Even though the incidence of AD in the African American population is similar to or higher than that in persons of European descent, AD in African Americans is understudied. Identification of genetic risk factors in African Americans is essential for understanding the etiology of AD. Objective: To determine the effect of apolipoprotein E (APOE) genotype on the risk of AD in elderly African Americans. Design: Population-based longitudinal study of AD. Setting: Indianapolis, Ind. Participants: African Americans 65 years and older. Main Outcome Measures: APOE genotype and diagnosis of AD. Results: The APOE genotype was determined in 1822 samples. Of these, 690 were clinically evaluated: 31.8 were normal, and 162 had a diagnosis of AD. The presence of APOE epsilon 4 was significantly associated with increased risk of AD (epsilon 3/epsilon 4: OR, 2.32; 951,16 confidence interval [C1], 1.41-3.82; and epsilon 4/epsilon 4: OR, 7.19; 95% Cl, 3.00-17.29, compared with the epsilon 3/epsilon 3 genotype). There was also a significant protective effect with APOE epsilon 2 (epsilon 2/epsilon 2 and epsilon 2/epsilon 3: OR, 0.42; 95% Cl, 0.20-0.89). Conclusions: These findings are in marked contrast to the lack of association between APOE and AD in the Ibadan, Nigeria, sample of this project. These results suggest that other genetic factors and different environmental influences may play a role in the risk for AD in individuals of African ancestry.