July 31 (HealthDay News) -- Scientists say they've spotted a gene that may lessen the risk of migraines with aura.

However, the risk is still there, and if the person goes on to develop migraines with aura, this migraine-protective gene actually boosts their risk for stroke.

"There is a reduced association of migraine with aura with this gene, but if you have migraine with aura, the risk of stroke is magnified," said study senior author, Dr. Tobias Kurth, an assistant professor of medicine at Harvard Medical School and an associate epidemiologist at Brigham and Women's Hospital in Boston.

Using data from just over 25,000 white women who participated in the Women's Health Study, Tobias and his team found that almost 4,600 -- or about 18 percent -- of the women reported a history of migraine.

From that group, nearly 40 percent said they had migraines accompanied by an aura. An aura is a visual disturbance, such as seeing flashing lights.

During nearly 12 years of follow-up, 625 women had a cardiovascular event, such as a stroke, according to the study, which appears in the July 30 online issue of Neurology.

The researchers reviewed the data to see which women carried a particular form of the gene MTHFR 677C -- a gene that had been suggested by prior research as a possible link between migraine with aura and stroke. They found that 11 percent of the study population carried this gene variant.

Alone, the MTHFR 677C variant doesn't appear to raise the risk of cardiovascular disease. However, in women with the gene and a history of migraine with aura, the researchers found more than three times the risk of cardiovascular disease.

Kurth said it's too soon to start recommending that anyone have genetic testing done, even if they do have migraines with auras.

"At the moment, we're not suggesting genotyping for women with migraines with aura. The consequences [of having this gene] are completely unclear right now," said Kurth.

Kurth also noted that researchers can't know from this study what the effect of this gene might be for men.

Another expert agreed.

"The problem here is they're trying to find the exact gene, and they're getting into the ballpark, but to isolate the exact gene is so complicated. This might be more of an association rather than a direct cause, so until more research is done, screening isn't justified," said Dr. Keith Siller, medical director of the Comprehensive Stroke Care Center at New York University's Langone Medical Center in New York City.

There may still be ways women with migraine can cut their stroke risk, however. Both Kurth and Siller said that while no one should smoke, it's especially important that women who have migraines with aura forgo cigarettes. Additionally, since birth control pills can increase the risk of vascular problems, women who smoke or have migraines with auras might want to discuss other birth control options with their doctors, Kurth said.

"The take-home message here is that if you have migraine with aura, you're likely have an increased stroke risk and you may want to be more careful," said Siller.

SOURCES: Tobias Kurth, M.D., Sc.D., assistant professor, medicine, Harvard Medical School, and associate epidemiologist, Brigham and Women's Hospital, Boston, Mass.; Keith Siller, M.D., medical director, Comprehensive Stroke Care Center, NYU Langone Medical Center, and assistant professor, New York University School of Medicine; July 30, 2008 online edition Neurology