Environmental factors and their interactions with risk genotypes in MS susceptibility.

The area of multiple sclerosis (MS) epidemiology has expanded during the last few years. Established lifestyle and environmental factors influencing MS risk are Epstein-Barr virus infection, sun exposure/vitamin D, and smoking. We review these factors and a series of other potential candidates implicated in the pathogenesis of MS and how environmental factors interact with genetic susceptibility with regard to disease risk.

On top of established MS-associated factors, there is now strong evidence for influence of adolescent obesity, exposure to organic solvents and shift work, all demonstrating increased risk of disease. Other factors, such as nicotine, alcohol, and high coffee consumption are associated with decreased MS risk. A number of lifestyle/environmental factors, including smoking and obesity, seem to interact with MS risk human leukocyte antigen genes, conferring much stronger effects on disease risk among those exposed to both factors. Furthermore, an interaction between two environmental factors, obesity and infectious mononucleosis, with regard to MS risk, has been demonstrated in two independent studies.

MS is a complex disease for which both genetic susceptibility and lifestyle/environmental factors are important, and where the latter may be of great importance. Lifestyle and environmental factors can often be modified and may denote pathogenic pathways.