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Environmental factors may be playing a much greater role in the onset of multiple sclerosis (MS) than previously realised, according to research led by Queen Mary University of London and Barts Health NHS Trust...Read more - http://www.ms-uk.org/MSnews

What we're learning from the human genome project and other research is that it is not necessarily the genes that we are born with that elicits disease but rather it is environmental impact on genetic expression. Example given: vitamin D has an impact on over 2000 of our genes!

In the above article people with darker skin living in London got MS at a much higher rate than people living in their homeland. This is because they cannot produce a similar amount of vitamin D in their darker skin that would have been possible at a more southern latitude.

These results could also be partially explained by differences in diagnostic rates between those living in London, and those living in other countries.

As I recall there have been studies of identical twins with MS. The studies showed that if one twin got MS then there was about a 30% chance the other twin would get MS. If it was purely genetic the other twin would always get MS. But that's not the case so MS is not purely genetic.

OK I just came across this article about twins and MS http://www.nature.com/news/2010/100428/ ... 1259a.html
One of the conclusions is this:

There is no doubt that MS, which causes the body's own immune cells to attack the insulating sheath around nerve cells, has a genetic component. Relatives of people who have the disease have an increased risk of developing it; if a patient with MS has an identical twin, that twin's risk climbs to more than 25%. But when a team of US researchers compared the complete genomes of twin females with each other, they failed to find any genetic differences that might cause MS.