TORONTO - Researchers at The Hospital for Sick Children (Sick Kids) have shown an association between paediatric multiple sclerosis (MS) and the Epstein-Barr virus (EBV), indicating that exposure to the virus at a certain time in childhood may be an important environmental trigger for the development of MS. This research is reported in the April 21, 2004 issue of JAMA (The Journal of the American Medical Association).
"Earlier studies suggested a relationship between childhood exposure to Epstein-Barr virus and the risk of developing MS. This is virtually impossible to quantify in adult MS patients, as nearly 90 per cent of the healthy adult population in Western countries has been exposed to EBV. In the paediatric patients, we can study viral exposures more easily, as children have fewer viral exposures due to their young age," said Dr. Brenda Banwell, the study's principal investigator, a Sick Kids neurologist and associate scientist, and an assistant professor in the Department of Paediatrics at the University of Toronto.
The research team found that 83 per cent of the paediatric MS patients showed evidence of a past EBV infection, compared with 42 per cent for the healthy control group. The paediatric MS patients also were less likely than the control subjects to have been exposed to herpes simplex virus. Epstein-Barr virus is very common and transmissible virus in the herpes family that causes infectious mononucleosis.
"We think the Epstein-Barr virus plays an important role in the development of MS, as the genetic code of the virus contains sequences that are identical to genetic sequences in the myelin basic protein, which is expressed in the brain, and destroyed in MS. It is conceivable that the immune system mounts a response to that genetic sequence in EBV, then sees it in myelin and targets it as well," added Dr. Banwell.
Multiple sclerosis (MS) is a disease of the brain, spinal cord, and optic nerves that can cause problems with muscle control and strength, vision, balance, sensation (such as numbness or tingling in your feet or hands), and mental functions such as thinking (cognition) and moods.
The symptoms of MS are caused by inflammation of the central nervous system and the destruction of myelin, the protein coating that surrounds and protects nerve fibres (axons).
MS is believed to involve a complex interplay between environmental triggers (such as infections), genetic predisposition, and an abnormal autoimmune response. At least five per cent of all MS patients experience the onset of their disease before the age of 18. It is estimated that 50,000 Canadians have MS. Multiple sclerosis is the most prevalent in countries that are furthest from the equator, such as Canada, northern Europe, and Australia.
"We suspect that it is the sequence and timing of viral exposure and how this modifies an individual's immune response that is important," said Dr. Banwell. "Children with MS are the closest to the biological onset of the disease, which allows us to look at a whole host of causative factors that are very difficult to study in adults."
Other members of the research team included Dr. Suad Alotaibi (now at the Al-Sabah Hospital in Kuwait), and Julia Kennedy, Dr. Raymond Tellier, and Derek Stephens, all from The Hospital for Sick Children.
This research was supported by The Hospital for Sick Children Foundation.
The Hospital for Sick Children, affiliated with the University of Toronto, is Canada's most research-intensive hospital and the largest centre dedicated to improving children's health in the country. Its mission is to provide the best in family-centred, compassionate care, to lead in scientific and clinical advancement, and to prepare the next generation of leaders in child health. For more information, please visit http://www.sickkids.ca.
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