A gene which may increase the risk of stroke has been uncovered by Iceland-based researchers.
Impotence drug Viagra works by blocking a similar protein
The discovery could prompt the discovery of drug treatments to help those at highest risk.
This protein it produces plays a role in the growth of blood vessels. but too much of it may increase stroke risk.
Writing in the journal Nature Genetics, the scientists said people with certain forms of a gene called PDE4D may be most at risk.
Proteins from a similar "family", called phosphodiesterase (PDE), are linked to other illnesses, such as asthma, inflammation and even erectile dysfunction.
This suggests that it may be possible to develop a drug to block the effects of the gene - the breakthrough impotence drug Viagra already works by targeting another member of the PDE family.
Solveig Gretarsdottir and colleagues at a company called deCode Genetics in Reykjavik believe this gene is associated with an increased risk of stroke.
They carried out DNA tests on over 1,700 people in Iceland, half of whom had suffered strokes.
The Icelandic population is generally regarded as the best testing ground for geneticists.
This is because the gene pool is relatively pure. Unlike most other countries, there has been little immigration since the first Vikings arrived almost 1,000 years ago.
Scientists working on this latest study say they have identified genetic differences between those people who have had strokes and those who have not.
These differences centre on the gene PDE4D, located on chromosome 5.
They have found that three different isoforms of the gene were expressed at lower levels in people who had strokes.
Isoforms are groups of proteins that are produced by a gene.
They also found different combinations of genes in regions of chromosome 5 flanking the PDE4D gene in people who had strokes.
It is already known that this gene provides the coding which enables a protein called a phosphodiesterase to work.
But the Icelandic scientists believe that too much of it may increase the risks of atherosclerosis - furring up of the arteries.
This causes the arteries to narrow, which can trigger a stroke.
"We propose that PDE4D is involved in the pathogenesis of stroke, possibly through atherosclerosis, which is the primary pathological process underlying ischemic stroke," the scientists said.
They believe that blocking the protein in people with these potentially problematic forms of the PDE4D gene could protect them against stroke.
There are already drugs available to do this. These so-called phosphodiesterase inhibitors are used to treat asthma, inflammation and erectile dysfunction, with Viagra probably the best known.
However, much further study is needed before these drugs could be used to treat people who may have a high risk of having a stroke.
Viagra, for one, has potentially serious side effects if taken by men with underlying health problems.