THERE is not yet enough evidence to pinpoint whether any aspects of contact sport participation led to an increased risk of being diagnosed with motor neurone disease, according to the MND Association's head of research.

Former Leeds Rhinos player Rob Burrow, 37, announced on Thursday that he had been diagnosed with the condition, which affects the nerve cells in the brain and the spinal cord and for which there is currently no cure.

Scotland rugby union great Doddie Wear - who was honoured at the BBC Sports Personality of the Year awards on Sunday - is another high-profile sports figure to suffer from the disease.

Life expectancy for about half of those with the condition is three years from the start of symptoms.

Former Bantams captain Stephen Darby is suffering from the disease after being forced to retire from football in September 2018, while Keighley Cougars legend Phil Stephenson died at the age of 47 earlier this year after battling MND.

A study by academics at Glasgow University, supported by the Football Association and the Professional Footballers' Association, published results in October which found that footballers were at four times greater risk of developing motor neurone disease than the general population.

Lenny Johnrose, a former player and an MND sufferer, called for an immediate ban on heading in under-14s football.

However, Dr Nicholas Cole, head of research at the MND Association, has advised caution.

"While the studies carried out to date show a correlation between professional footballers and MND they don't demonstrate causation - so they recognise that professional footballers are more likely to develop MND but they don't suggest that playing football professionally, or any particular aspect of doing that, directly leads to a person developing MND," he said.

"At present there is not yet enough evidence to pinpoint that specific aspects of contact sport participation, such as heading the ball in football, is directly linked to an increased incidence of neurodegenerative disease. However, public attention regarding the risk is increasing.

"While there is a growing movement within sport to understand, recognise and, where necessary, mitigate against negative long-term effects, it is also clear that a lot more research is needed. We recognise this and are now working with researchers and institutions to facilitate research in this area."

Genetic factors can play a part in the development of the disease in around one in 10 sufferers, while previous studies have found possible links between MND and electrical or mechanical trauma, military service, high levels of exercise, exposure to agricultural chemicals and exposure to heavy metals.

However, the evidence gained in those studies has often been conflicting and there are no clear conclusions.

Dr Cole added: "We do know a combination of environmental and lifestyle factors act together with specific genes to predispose people to get MND.

"What we don't know is the exact recipe of these factors that triggers onset of the disease. Scientific research costs money and, sadly, there is a limit to the budgets available to us.

"We would urge organisations with an interest in this work to consider research funding to boost what's possible."