Researchers have identified a gene that may put people at greater risk of strokes and heart attacks.
Writing in PLOS ONE they say the gene fault may encourage the formation of blood clots - the ultimate cause of most heart attacks and strokes.
Scientists hope gene tests may help doctors one day to pinpoint individuals more likely to suffer these conditions.
But experts say lifestyle factors such as smoking and exercise have the greatest influence on risk.
Around one in 10 people in the Caucasian population carries this variation of the gene, named PIA2.
And researchers from King's College London reviewed more than 80 studies involving about 50,000 people - the largest analysis of this genetic fault to date.
Threat to under-45s
They found individuals with PIA2 were more likely to have a
stroke - caused by a blood clot blocking blood supply to the brain -
than those without the gene.
Scientists calculate the gene increases a person's risk of having a stroke by 10-15%.
But how significant this increase is depends on an
individual's baseline risk - influenced by factors such as smoking,
diet, weight and exercise, the scientists say.
More than 100,000 heart attacks are recorded in the UK each year
And for people with two copies of the gene the risk rises by up to 70% from this baseline.
In a second study published in the same journal, the
scientists show PIA2 is also linked to an increased risk of heart
attacks in people under 45.
More research is needed to see whether this holds true for the whole population, they say.
About 150,000 people have a stroke in the UK each year and more than 100,000 heart attacks are recorded annually.
Both thrombotic strokes (the most common kind) and heart
attacks are caused by blockage of blood vessels in the heart and brain -
ultimately through the formation of clots.
'Devastating condition'
The faulty gene appears to affect a protein called
glycoprotein IIIa - present on platelets, natural clotting cells in the
blood.
Platelets help trigger the formation of clots to stop
bleeding after injury. But scientists say carrying the gene may render
them overactive.
They caution that overall the genes play a smaller role in
risk than more established factors, such as high blood pressure and
obesity.
But developing a genetic test could help predict people at
highest risk, allowing doctors to suggest more potent medication or
lifestyle changes, they say.
Prof Albert Ferro, of King's College London, who led the research,
told the BBC: "We would now need to validate this test and see how
useful it is in the clinical world."
Dr Shamim Quadir, of the Stroke Association, said: "These latest results are an important step forward in stroke research.
"We hope the findings from this study could lead to many more
people who are most at risk of this devastating condition being
identified.
'High cholesterol'
"However, if you have a family history
of stroke or have any other risk factors, this does not mean the
condition is inevitable. Regular exercise, eating a balanced diet and
stopping smoking can be important steps to significantly reduce your
stroke risk."
Prof Jeremy Pearson, of the British Heart Foundation,
said: "It is as yet uncertain whether a genetic test to detect a
variation in this protein would be beneficial for patients in everyday
practice.
"All patients who are at risk should be monitored to see
whether or not lifestyle changes or medication have a positive impact on
the more standard major risk factors such as high blood pressure and
high cholesterol."
