Alzheimer's Disease, Genes, and Environment: The Value of International Studies

Objective: To describe the construction of a disease model incorporating both genetic and 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 of dementia in 2 communities: elderly African Americans living in Indianapolis, Indiana, and 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 ɛ4 allele does not increase risk for AD among Yoruba but confers a slight 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 populations from developing and developed countries, offer a unique opportunity for applying new information regarding population genetics to traditional AD risk factor research.