People living in Scotland who also have a Scottish name are more than twice as likely to develop multiple sclerosis (MS) - a disease caused by the body's immune defences attacking the central nervous system - than the English.
In a study of 1,613 patients living in the southern region of Scotland, scientists at the Radcliffe Infirmary in Oxford found that the prevalence of MS was about two cases in every thousand members of the public. This compared with one case in a thousand in England and Wales.
The research supports the view that MS is caused by an unidentified factor in the environment, striking only thosewith a genetic predisposition which appears to be particularly prevalent among Scots.
The scientists also found that those Scottish residents with a surname beginning Mac or Mc were 24 per cent more likely to develop MS than those without this sign of a Celtic origin.
Dr Peter Rothwell, a clinical lecturer in neurology at the infirmary, said: "[The research] shows an underlying genetic distinction between the Scots and the English. It also confirms that Scotland has the highest rate of [MS] in the world."
The findings, published today in the Journal of Neurology, Neurosurgery and Psychiatry, reaffirm that the sharp increase in incidence occurs across the English-Scottish border.
Previous research showed that Orkney and the Shetlands had the highest rates of MS.
A higher incidence of Scottish genes could also explain why the disease tends to be more common in areas of the world, such as New Zealand, where there is a history of Scottish migration, Dr Rothwell said.