This study finds that people living in countries further away from the equator develop symptoms of multiple sclerosis at an earlier age. Why? Causes may be both genetic and environmental, but the main finding in this study is that the higher the latitude, the earlier the age of multiple sclerosis onset. The study draws on data from more than 22,000 adult MS patients from 52 recruiting centers across 21 countries. The average age at which the disease began was 32.3 years.