Blacks and Hispanics may run a higher risk of Alzheimer's disease than whites for reasons that are not clear, according to a report published Tuesday.

"Our results suggest that as African Americans and Hispanics age, the frequency of Alzheimer's disease in those populations may increase disproportionately," said the study from the Columbia University College of Physicians and Surgeons in New York.The finding, published in this week's Journal of the American Medical Association, was based on a study of 1,079 elderly white, black and Hispanic Medicare recipients whose health histories were followed for six years.

The researchers said blacks and Hispanics with a previously identified gene mutation linked to Alzheimer's disease were as likely as whites with the same gene mutation to develop the debilitating disease.

But they said blacks who did not carry the gene were four times more likely than whites in general to develop the disease by age 90 and Hispanics without the gene were two times more likely than whites to develop the disease by age 90.

"These results suggest that other genes or risk factors may contribute to the increased risk of Alzheimer's disease in African-Americans and Hispanics," the study said.

In an editorial in the same issue commenting on the study, experts at the University of Washington in Seattle called the findings "provocative and exciting."

They said few other studies have addressed the question of Alzheimer's incidence in this way.