People with a common form of genetic defect are two to three times more likely to have a stroke than those without, according to a study of more than 9,000 people in Denmark.

The finding adds to a collection of genetic and lifestyle factors that have been linked with strokes and may help researchers develop a genetic test for risk of attacks.

The researchers followed the health of 9,178 people over 24 years. Of the sample 393 had a stroke during that time. Those with a particular mutation to the HFE gene (also known as the haemochromatosis gene) were two to three times more likely to develop the condition.

"This type of gene has previously been associated with brain diseases such as Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis or ALS, multiple sclerosis and cerebrovascular disease, but this is the first time we've been able to determine this gene predicts such a significant increased risk of stroke," said Borge Nordestgaard, at Herlev University Hospital in Copenhagen, who led the study, which is published in the journal Neurology.

The most common form of stroke, ischaemic stroke, happens when a clot in one of the arteries supplying the brain prevents blood flow, leading to damage to that brain region.

The researchers do not know how the genetic defect, which is carried by about a quarter of people in northern Europe, might cause a stroke. Its involvement may give researchers new leads for understanding and preventing strokes as well as the potential for genetic tests to predict who is most at risk. The gene is involved in iron metabolism.

Strokes are the leading cause of disability in the UK and the third most common cause of death after cancer and heart disease. Smoking, obesity, excessive alcohol intake, lack of exercise, diabetes, high blood cholesterol and high blood pressure all increase the risk.