WASHINGTON (AP) — For the first time, researchers have identified a genetic form of late-in-life Alzheimer’s disease — in people who inherit two copies of a worrisome gene.

Scientists have long known a gene called APOE4 is one of many things that can increase people’s risk for Alzheimer’s, including simply getting older. The vast majority of Alzheimer’s cases occur after age 65. But research published Monday suggests that for people who carry not one but two copies of the gene, it’s more than a risk factor, it’s an underlying cause of the mind-robbing disease.

The findings mark a distinction with “profound implications,” said Dr. Juan Fortea, who led the study the Sant Pau Research Institute in Barcelona, Spain.

Among them: Symptoms can begin seven to 10 years sooner than in other older adults who develop Alzheimer’s.

An estimated 15% of Alzheimer’s patients carry two copies of APOE4, meaning those cases “can be tracked back to a cause and the cause is in the genes,” Fortea said. Until now, genetic forms of Alzheimer’s were thought to be only types that strike at much younger ages and account for less than 1% of all cases.