Multiple sclerosis: New insights and trends

Although genetic susceptibility explains the clustering of multiple sclerosis (MS) cases within families and the sharp decline in risk with increasing genetic distance, it cannot fully explain the geographic variations in MS frequency and the changes in risk that occur with migration. Epidemiological data provide some support for the "hygiene hypothesis," but with the additional proviso for a key role of Epstein-Barr virus (EBV) in determining MS risk. We show that whereas EBV stands out as the only infectious agent that can explain many of the key features of MS epidemiology, by itself the link between EBV and MS cannot explain the decline in risk among migrants from high to low MS prevalence areas. This decline implies that either EBV strains in low-risk areas have less propensity to cause MS, or that other infectious or noninfectious factors modify the host response to EBV or otherwise contribute to determine MS risk. The role of infectious factors is discussed here; in a companion article, we will examine the possible role of noninfectious factors and provide evidence that high levels of vitamin D may have a protective role, particularly during adolescence. The primary purpose of these reviews is to identify clues to the causes of MS and to evaluate the possibility of primary prevention. Show more

Multiple sclerosis (MS) is a chronic immune-mediated demyelinating disease of the central nervous system characterized by relapses and remissions. The risk of acquiring this complex disease is associated with exposure to environmental factors in genetically susceptible individuals. The epidemiology of MS has been extensively studied. We review the geographic epidemiology of the disease, the influence of immigration, age at immigration, clustering and epidemics. Various presumptive risk factors are discussed such as ultraviolet radiation, vitamin D, Epstein-Barr virus and infectious mononucleosis, other infectious agents and non-infectious factors. Two different hypotheses, the hygiene hypothesis and the prevalence hypothesis, were proposed to explain these environmental risk factors for MS. The epidemiological data, combined with pathological and immunological data, may contribute to the debate whether MS is an autoimmune disease, a latent or persistent viral disease, or a neurodegenerative disease. 2009 Elsevier B.V. All rights reserved. Show more

The hypothesis that adequate vitamin D nutrition can contribute to the prevention of multiple sclerosis (MS) was originally proposed to explain the geographical distribution of MS, but only recently has the relation between various measures of vitamin D (eg, sun exposure, dietary sources, and serum concentrations of 25-hydroxyvitamin D) and risk of developing MS been rigorously investigated. Overall, the results of these studies support a protective effect of vitamin D, but there are uncertainties and many unanswered questions, including how vitamin D exerts a protective effect, how genetic variations modify the effect, and whether vitamin D can influence the course of MS progression. Copyright 2010 Elsevier Ltd. All rights reserved. Show more