Senior author Dr. Erik Ingelsson, a professor of cardiovascular epidemiology at the Karolinska Institutet in Stockholm, Sweden, said the findings were the first large study to examine the combined influence of age, gender and sibling history on stroke risk.
The study focused on ischemic strokes, which are caused by blood vessel blockage that cuts off blood flow to part of the brain. Ischemic strokes are by far the most common type, striking almost 700,000 U.S. adults annually.
The study, published in the journal Circulation: Cardiovascular Genetics, found if a sibling was age 55 or younger at the time of a stroke, the risk of a sibling at age 55 or younger was almost doubled, Ingelsson said.
"Health professionals should pay as much attention to a family history of stroke in siblings as in parents, and make patients aware that a genetic predisposition exists," Ingelsson said in a statement. "The gender of either sibling did not influence the stroke risk."
The researchers studied national health records in Sweden from 1987 to 2007. For each stroke diagnosed, they tracked whether a sibling had a stroke during the remainder of the study period.
The investigators found ischemic strokes were 94 percent more likely to occur at age 55 or younger in siblings of affected patients whose stroke occurred at 55 or younger.