Studies show that it is, but if you move from an area with higher risk to one of lower risk, you acquire the risk of your new home if the move happens before adolescence. This suggests exposure to something in the environment before puberty may make MS more likely. In both hemispheres, the prevalence or MS rises the farther you are from the equator. There have been MS "epidemics." One happened in people living off the coast of Denmark after WWII, suggesting an environmental cause.