Individual and joint action of environmental factors and risk of MS.

In this review, the evidence for the leading environmental and lifestyle factors thought to play a role in multiple sclerosis (MS) onset, including Epstein-Barr virus, sun exposure or vitamin D, and smoking, will be discussed. The Causal Pie Model is used as a conceptual framework to understand the causation. Given that no single factor leads to the development of MS, the joint action or interaction of these factors, along with genetic factors, most particularly the HLA-DR15*1501 genotype, is a primary focus.