A NEW study by Scottish researchers shows evidence that the neurological disease multiple sclerosis (MS) could be linked to a viral infection.

While Scotland has the highest prevalence of MS in the world, the exact factors which lead to its development still remain a mystery. A combination of hereditary and environmental factors are thought to be the likeliest explanation.

Clusters of MS have previously been noted in certain areas, including the Faroe Islands, Orkney and Shetland.

Researchers at Dundee University used a comprehensive register which recorded MS cases in Tayside over three decades to examine whether similar outbreaks would appear in a region where there was no prior knowledge of high incidences of the disease.

The study found peaks of MS occurring in both certain years and in geographical locations, which scientists claim supports the idea that a virus is involved in the development of MS.

Co-author Dr Peter Donnan, a senior lecturer in medical statistics at the university, said: "We were interested in whether there was any clustering of cases in time and [location].

"Nobody really knows what causes MS. It is a multifactorial condition and there are debates about the role of genetic susceptibility and certain childhood viral infection in those who are susceptible, along with unknown environmental factors.

"In some years there may be epidemics of viral infections and in some years you get less, so what we are looking to see is whether there are peaks in certain years and peaks in certain locations."

The study, which is published in this month's Multiple Sclerosis journal, found there were a total of 772 new cases of the disease.

Nearly three-quarters of those diagnosed were female and the average age of the onset of symptoms was 35.7 years.

Researchers found that there was a significant increase in cases between 1982 and 1995, with an annual incident rate of 8.2 per 100,000 population, compared to an overall average figure of 7.2 per 100,000. During the 30 years studied, cases also appeared to peak every two to three years.

In addition, there was an outbreak of cases during 19931995 in a location southwest of Perth, centred in the rural area of Auchterarder but also including part of central Perth.

During that time, the annual incident rate of cases there rose to 17.1 per 100,000 population.

Donnan said: "If a viral agent had a role in the development of MS, then you would expect clusters. If you just found that the number of cases was constant over time and areas, then that would tend to go against that hypothesis.

"What we concluded is that it demonstrated evidence consistent with a role for viral infectious agents in MS."

Further investigation, he added, would be needed to help explain why, for example, the incidence of MS appears to peak every three years.

"One possible explanation is that viral disease epidemics have a three-year cycle, " he said.

There are an estimated 10,500 people in Scotland with MS, the most common neurological disorder diagnosed among young adults. It attacks the central nervous system and usually strikes between the ages of 20 and 40 years.

Mark Hazelwood, director of the Multiple Sclerosis Society Scotland, said there had been suspicions that viruses have been involved in the development of MS for some time.

"There have been more than 20 different viruses researched over the past couple of decades, " he said. "Sadly there has not been anything which has been proved or disproved on the specific involvement of a particular virus.

"What this research does is that it shows evidence consistent with a possibility of a viral involvement, but it doesn't prove it and it really highlights the need for further research."

Hazelwood also revealed that, to help with such research, the charity is currently looking into the possibility of setting up a national database to record MS cases across Scotland.

"This study was only able to be done because Tayside has got the best records about the number of people who have got MS in an area, " he said.

"We are trying to establish a similar database which would go right across the Scottish population, so we can really look at MS in the Scottish population and start to understand why there is so much more here."

judith. duffy@sundayherald. com

Source: Sunday Herald

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