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African-Americans with a particular gene are twice as likely to develop Alzheimer's disease in old age as those without it, however there is no major genetic difference that could account for the slight excess risk, a new study said Tuesday.

Researchers identified the same gene variants in older African-Americans that they had found in older people of European ancestry. But they found that African-Americans with Alzheimer's disease were slightly more likely to have one gene, ABCA7, that is thought to confer risk for the disease, according to a new study published in the Journal of the American Medical Association.

This finding is a result of the largest database search for Alzheimer's genes among 6,000 African-Americans.

"Until now, data on the genetics of Alzheimer's in this patient population have been extremely limited," said Dr. Richard Mayeux, chair of neurology at Columbia University Medical Center and senior author of the study.

Since the ABCA7 gene is involved with the production of cholesterol in the body, it suggests that Alzheimer's in African-Americans may be more affected by cholesterol levels than whites. It is also associated with the production of amyloid, a protein that makes up most of the plaques found in the brains of those with Alzheimer's.

However, the experts caution that widespread genetic testing for Alzheimer's is still a long way to come. "We are not yet at the point where we can take what we know about Alzheimer's genes and come up with an accurate risk assessment," Mayeux said.

John Hardy, an Alzheimer's researcher at University College London and a discoverer of the first gene mutation found to cause Alzheimer's, said the data confirmed what was already known among those of European descent, "I don't think they tell us much new."