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This is the VOA Special English Health Report.

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Scientists in Iceland say they have identified the first gene linked to common forms of stroke. These strokes are caused by a blockage in the flow of blood to the brain. They are known as ischemic (eh-SKEE-mic) strokes. Ischemic strokes often result in death or severe disability.

Researchers at the Decode Genetics company say differences in the gene can increase the chance of a stroke by three to five times. They believe that a protein produced by the gene influences the movement and growth of muscle cells. They believe this influence causes the cells to grow inside arteries and restrict the flow of blood.

All people have this gene. But the risk of stroke appears higher in those with a version that produces low levels of the protein. Work has begun on a genetic test to identify those at risk.

The researchers say other genes are probably also involved in a stroke. But they believe this one is among the strongest. They say treatments are possible in the future to reduce the risk of stroke. Such drugs could target the protein produced by the gene. The Swiss drug company Hoffman-La Roche is already doing tests on rats.

The scientists mapped the genes of almost one-thousand-eight-hundred people. Half had suffered a stroke.

The discovery is part of a larger genetic study of the Icelandic people. Their family histories have been unusually well documented. Vikings from Norway settled in Iceland in the ninth and tenth century. The population of three-hundred-thousand is a mix of Norwegian and Celtic. Celtic means Scottish and Irish.

The researchers say they expect to find that the gene has a similar effect in people outside Iceland. The discovery appears in the publication Nature Genetics. The work is part of the effort by Decode to identify the genetic causes of more than fifty common diseases.

At least eighty percent of all strokes are from blockages. The others happen when a blood vessel breaks and causes bleeding in the brain.

The new finding may help explain why strokes happen in some people who do not seem at high risk. Doctors say high blood pressure, heart disease, smoking, diabetes and high cholesterol all increase the risk of stroke.

This VOA Special English Health Report was written by Nancy Steinbach.