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What triggers MS in the genetically predisposed?

Narrator:    This is Science Today. Researchers studying multiple sclerosis are beginning to discover genes that may affect how severe the disease will be in patients. Dr. Ari Green, assistant director of the Multiple Sclerosis Center at the University of California, San Francisco, says the genetic side of the disease that's less understood is what actually causes multiple sclerosis in those who are genetically predisposed to the disease.

Green:    There are a few factors that may play a role there. The two most important that have come out in the last few years are the timing of infection, particularly one virus known as Epstein-Barr virus and the other is sunlight exposure.

Narrator:    Green explains that sunlight triggers the production of vitamin D in our bodies.

Green:    Vitamin D plays an important role in the functionality of our immune system and may even play an important role in the function of our nervous system. And it's clear that people who have very low levels of vitamin D are predisposed to developing MS.

Narrator:    For Science Today, I'm Larissa Branin.