A British study finds a family history of cardiovascular events such as strokes or heart attacks is a significant risk factor for specific kinds of stroke in other members of the family, particularly among younger people.
"Only about half of all strokes can be explained by the traditional risk factors -- high blood pressure, smoking, diabetes, cholesterol," says Dr. Paula Jerrard-Dunne, a clinical research fellow at St. George's Hospital Medical School in London and lead author of the study in the April 25 online issue of Stroke. "Not all people have these risk factors, and it is hard to explain why some people with risk factors go on to develop a stroke while others do not. This means that other factors, such as a genetic predisposition, may also be important."
"What this study says from a practical standpoint is that if you have a family member who has had a stroke under age 65, you should speak to your own physician about modifiable risk factors and try to be careful about them," says Dr. Larry B. Goldstein, a professor of medicine at Duke University School of Medicine and a spokesman for the American Heart Association.
A number of studies have hinted strongly at a genetic factor in stroke risk, Goldstein says, but this one is valuable because of its careful focus on two specific types of ischemic stroke, which are the kind that happen when a clot blocks a blood vessel. That clot can block a large vessel, causing severe brain damage that can be fatal, or a small blood vessel, causing loss of mental function.
The British researchers selected 1,000 people who had suffered ischemic strokes. Their average age was 65. They were given thorough neurological examinations to distinguish between small-vessel and large-vessel stroke, and then they were compared with 800 stroke-free persons matched for age and sex. The presence of risk factors such as smoking and diabetes and family histories of heart attack and stroke were also factored into the equation.
The large-vessel stroke patients were more than twice as likely to have an immediate family member who had suffered a stroke or heart attack at 65 or younger. For small-vessel stroke patients, the risk was slightly lower but still significant; they were 1.93 times more likely to have the same kind of family history.
When the researchers looked only at stroke patients aged 65 and younger, things got worse.
Those with large-vessel strokes were almost three times as likelyto have a close relative who had suffered stroke at age 65 or younger or a family member who had a heart attack. Those with small-vessel stroke were more than three times as likely to have this family history.
Family history is much more important in young people because "in older people, the effects of blood pressure, smoking, poor diet, etc. have had a longer time to cause damage to the blood vessels," Jerrard-Dunne says. For people who have strokes when they are relatively young, "we suspect that there might be an underlying genetic susceptibility which makes them much more sensitive to the effects of risk factors."
While the researchers looked just at stroke, "there is evidence from a number of studies to suggest that a family history of heart disease is an important risk factor for heart attacks," she says.
Goldstein says another reason why the study is valuable is that "it helps direct future research that can lead to a better understanding of the genetic basis for stroke."
That research can be more effective if it focuses on specific types of stroke and on younger patients, Jerrard-Dunne says.