An international team of scientists has discovered a genetic mutation that increases the risk of stroke by 30 percent. Stroke is caused by a blood clot or other loss of blood supply to the brain, and it's a leading cause of paralysis and death.

Scientists long have understood the environmental risk factors that contribute to stroke, such as smoking and high-fat diets, but they have struggled to find the genes that underlie the heritable component of the disease - until now.

In a study examining the genetic material of 23,000 people, U.S. and Dutch researchers found that stroke victims were about one-third more likely to have a mutation in a gene called NINJ2.

Researcher Eric Boerwinkle says the mutated gene is not a death sentence for those who carry it. 

"I think what's important is if a person is now known to have this particular gene variation or gene mutations, that doesn't necessarily mean they are predestined to have a stroke. That's not true," he said.

Boerwinkle is a researcher at the University of Texas in Houston, and co-author of the study which appears in this week's New England Journal of Medicine. He stresses that other factors contribute to stroke, including high blood pressure and a build-up of cholesterol that can choke off the blood supply, killing brain tissue.

Boerwinkle adds that, as with other diseases, no single gene is involved in stroke. 

"This discovery shows and documents that the science we have in place can identify the genes - the several genes - that are contributing to stroke risk. When those genes are found and combined into a diagnostic test, then individuals can have that test and use it to guide their lifestyle choices," he said.

But sophisticated genetic testing may not be necessary, says David Goldstein, a professor of molecular genetics at Duke University. He wrote an editorial in the New England Journal suggesting that large population studies like Boerwinkle's that pinpoint the location and distribution of abnormal genes don't offer much information on the cause of a disease or how to cure it.

"Most of the genetic findings are of such small effect that you would do as well or better just using family history, for example," he said.

But Goldstein says population studies such as the one identifying the stroke mutation may be of more help to researchers than to patients, since they point to regions of the human genome where scientists can narrow their search for the heritable causes of disease.