A stroke gene has been identified that could help scientists save lives and prevent disability.
People with a mutant form of the ABO gene that determines blood group are more likely to have certain types of stroke, researchers found.
The research highlights differences between various of types of stroke, paving the way to personalised therapies.
Scientists unscrambled the DNA of 2,100 healthy volunteers and identified 23 genetic variants linked to blood clotting, one of the chief causes of strokes.
Next, they focused on the 23 variants in 4,200 stroke patients and stroke-free individuals from centres across Europe.
The research showed that a particular variant of the ABO gene was significantly associated with stroke.
In the final stage of the study, the scientists scanned the DNA of almost 900 stroke victims from Europe, the US and Australia.
This linked the mutant ABO gene to two specific kinds of stroke known as "large vessel" and "cardioembolic". However, no association was found with "small vessel" strokes.
Lead researcher Dr Frances Williams, from King's College London, said: "The discovery of the association between this genetic variant and stroke identifies a new target for potential treatments which could help reduce the risk of stroke in the future.
"It is also significant that no association was found with small vessel disease, as this suggests that stroke sub-types involve different genetic mechanisms which emphasises the need for individualised treatments."
The findings are published today in the journal Annals of Neurology.
Each year, around 152,000 people in the UK have a stroke, costing the country more than £8.2 billion.
More than half of the estimated 1.2 million stroke survivors in the UK suffer from disabilities that affect their daily lives.
All strokes result in damage to the brain, either due to blocked arteries or bleeding from ruptured blood vessels.
Cardioembolic strokes involve a blood vessel blockage, usually a clot, that originates in the heart and travels to the brain. They are especially severe and account for up to 30% of strokes.
Large vessel strokes are the result of blood clots forming in the brain's larger arteries. Small vessel strokes are similar but affect small arterial vessels.
The Face-Arm-Speech-Time (FAST) test lists the main symptoms to look out for
Has the person's face fallen on one side? Can the person smile? Has their mouth or eye drooped?
Can the person raise both arms and keep them there?
Is their speech slurred?
It's time to call 999 if you see one or more of these signs.