April 24, 2003 -- It has long been believed that genes influence stroke risk, and now a large study from the U.K. offers some of the best evidence yet that this is so. Stroke patients in the study who were 65 or younger were almost three times as likely as non-stroke patients to have a parent or sibling who had an early stroke or heart attack.
The association between family history and stroke risk was stronger in this study than in previous ones because the researchers examined different stroke subtypes instead of lumping them all together. Strokes caused by large vessel disease -- in which the carotid arteries in the neck become blocked -- and small vessel disease -- in which the blockages occur in the vessels within the brain -- appeared to be strongly influenced by genetic predisposition. The familial association was less clear, however, for other types of stroke.
"Stroke is a complex disease, which is likely caused by a mixture of genetic and environmental risk factors," lead researcher Paula Jerrard-Dunne, MRCPI, tells WebMD. "By focusing genetic research on these high-risk stroke groups, we may be able to improve our chances of identifying the genes that create stroke risk."
Approximately 80% of strokes are caused by blood clots that obstruct the blood vessel supplying blood to the brain. In addition to large- and small-vessel disease, these so-called "ischemic" strokes can result from clots that travel from the heart through the blood vessels.
In this study, Jerrard-Dunne and colleagues from London's St. George's Hospital Medical School compared 1,000 ischemic stroke patients with 800 people matched for age and sex with no history of stroke or vascular disease. All participants were interviewed to determine their family history of stroke and heart attack, and other stroke risk factors were also recorded.
Compared with non-stoke patients, stroke patients with large-vessel disease were more than twice as likely to have a parent or sibling who had suffered a stroke or heart attack before age 66. The association was slightly smaller for stroke patients with small-vessel disease.
When the researchers included only patients who were 65 or younger at the time of their stroke, the significance of family history increased. Those with large-vessel strokes were almost three times as likely to have a first-degree relative who suffered early stroke or heart attack. The association was slightly greater for the small-vessel stroke patients. The findings are to be published in the May issue of the American Heart Association journal Stroke.
Jerrard-Dunne says her research team is currently collecting and analyzing DNA from people with large- and small-vessel disease to try and identify the specific genes associated with stroke.
"Genes that increase an individual's susceptibility to large-vessel disease or small-vessel disease may be inherited within families, and this could explain why we found that a positive family history of stroke was a risk factor for stroke in these subjects," she says.
The American Heart Association (AHA) lists family history as an important non-modifiable stroke risk factor, along with advancing age, male sex, and prior history of heart attack or stroke. Modifiable risk factors include obesity, inactivity, excessive alcohol consumption, drug abuse, and tobacco use. Cigarette smoking is the No. 1 preventable stroke risk factor.
Stroke expert and AHA spokesman Larry Goldstein, MD, tells WebMD that although almost all stroke patients have some risk factors, a specific cause is identified in just 60%. Goldstein is director of the Duke University Center for Cerebral Medicine, and he leads the advisory committee of the American Stroke Association.
"Having a positive family history of stroke in a first-degree relative under the age of 65 should alert someone that they are probably at increased risk," Goldstein says. "For these people it is particularly important to make lifestyle changes that can decrease this risk."