Alzheimer's disease, genes, and environment: the value of international studies.

OBJECTIVE To describe the construction of a disease model incorporating both genetic an environmental factors in the etiology of Alzheimer's disease (AD), using data generated from the Indianapolis-Ibadan dementia project (I-IDP). METHOD The I-IDP is a longitudinal comparative study of the prevalence and incidence o dementia in 2 communities: elderly African Americans living in Indianapolis, Indiana, an Yoruba living in Ibadan, Nigeria. RESULTS African Americans are more than twice as likely as Yoruba to develop AD. Possible explanations for this finding include genetic factors: the possession of the apolipoprotein E epsilon4 allele does not increase risk for AD among Yoruba but confers a sligh increase in AD risk for African Americans. As well, environmental factors may play a role: African Americans have a higher risk of vascular risk factors than do Yoruba. CONCLUSIONS International comparative studies, particularly those involving population from developing and developed countries, offer a unique opportunity for applying new in formation regarding population genetics to traditional AD risk factor research.