African-Americans with a particular gene are twice as likely to develop Alzheimer’s disease in old age as those without it, says 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 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.

Alzheimer’s disease is the most common cause of dementia — a brain disease that affects memory, personality and the ability to reason. At age 65, only one percent of people have Alzheimer’s, yet over 80 years of age, it increases to 30 percent.