Found this interesting tidbit on a site which in general, I really agree with on so many levels. Some interesting thoughts, although not well-cited as are many other sections of that site...
One of the causes of magnesium deficiency is a diet high in grains, such as wheat, that have phytic acid. Phytic acid binds magnesium making it unavailable to the body. Wheat is an arid crop. It does not grow, and subsequently is not a staple food, in tropical countries. MS is also uncommon in tropical countries. Interestingly, wheat is a staple food in many of the countries in which MS frequently occurs.
Gluten intolerance has also been implicated in MS, and MS does occur more frequently in countries with high gluten diets. Gluten intolerance can lower absorption of minerals like magnesium. Perhaps not coincidentally, MS is uncommon in Asian countries like China and Japan, where the main starch is rice. Rice does not contain gluten.