SUNDAY, July 12 (HealthDay News) -- A gene that may offer a highly accurate prediction of the risk of developing Alzheimer's disease and the age at which people will begin to show symptoms has been identified by U.S. researchers.

The TOMM40 gene may be the most highly predictive Alzheimer's gene discovered so far, said the Duke University Medical Center research team, who found that the gene could predict the age of Alzheimer's disease onset within a five- to seven-year window among people over 60.

The study was scheduled to be presented July 12 at the Alzheimer's Association 2009 International Conference on Alzheimer's Disease, held in Vienna, Austria.

"If borne out through additional research, a doctor could evaluate a patient based on age, especially among those over age 60, their APOE genotype and their TOMM40 status, to calculate an estimated disease risk and age of onset," lead author Dr. Allen Roses, director of the Deane Drug Discovery Institute at Duke, said in a university news release.

In previous research, Roses found that apolipoprotein E (APOE) genotypes, particularly APOE4, are associated with increased risk and younger age of development of Alzheimer's disease. APOE4 accounts for about 50 percent of late-onset cases of Alzheimer's, but the cause of the remainder of cases hasn't been known.

"It now looks fairly clear that there are two major genes -- APOE4 and TOMM40 -- and together they account for an estimated 85 to 90 percent of the genetic effect," Roses said.

The Duke team is planning a five-year study of APOE genotypes and TOMM40, along with a drug trial to assess prevention or delay of Alzheimer's disease onset.

More information

The U.S. National Institute on Aging has more about Alzheimer's disease.