Alleles are different variants of a gene. Everyone has the APOE gene, but what differs across people is which variant they happen to have: epsilon 2, epsilon 3 or epsilon 4. In addition, each person has two alleles of the gene -- one from the mother and one from the father. Having at least one APOE epsilon 4 allele is a risk factor for Alzheimer's, but not everyone who has it will develop the disease, Sachs-Ericsson said. And some people who develop Alzheimer's do not have the allele.
"While having the APOE epsilon 4 allele increases the risk of developing Alzheimer's disease, APOE genotype alone is not enough to predict the disease," she said. "We don't understand why the allele predicts Alzheimer's in some but not others. There may be other biological or genetic causes or even environmental factors, such as diet, that determine whether the allele will lead to Alzheimer's. We need a better understanding of what these factors are and whether they affect African Americans and Caucasians equally."
The researchers used data from the Duke Established Populations for Epidemiologic Studies of the Elderly. To determine genotype, DNA samples were collected through blood or cheek swabs from 2,076 people 65 or older.
In the study, participants were divided into two groups: those who had at least one APOE epsilon 4 allele and those who had no epsilon 4 allele. Cognitive errors on a standardized test were measured in four in-person interviews over a 10-year period ending in 1997. Those with the gene -- both blacks and whites -- made increasingly more cognitive errors over time on a questionnaire that assessed knowledge of items such as the day, date and current president than those without the gene.
|Contact: Natalie Sachs-Ericsson|
Florida State University