Smoking and Multiple Sclerosis: A Matter of Global Importance

Abstract

els [1] . However, these data largely stem from studies in North American and European populations. In this edition of Neuroepidemiology, Maghzi et al. [3] report the results of a well-powered sibling case-control study of cigarette smoking and MS in Iran. MS in Iran is gaining attention due to reports of a recent substantial prevalence increase [4] . If true, causal factors may be more easily discovered in this population. The authors found that smoking history was associated with MS risk. Overall this is a similar finding to that reported by a previous case-control study conducted in multiple centres across Iran [5] . However, there are a number of unexplained discrepancies; Maghzi et al. report a positive association with a history of smoking drawn almost exclusively from the association observed in men since the frequency of smoking amongst women in the study was very low. In contrast, the other Iranian study found that smoking was significantly associated with MS susceptibility only in women and not in men. The two studies are quite similar in demographical characteristics and, indeed, the controls used in the first study were often family members, but the smoking rate in females reported by Maghzi et al. is much lower than that seen The aetiology of multiple sclerosis (MS) arises from the interaction of multiple different genetic and environmental risk factors [1] . Large-scale genome-wide association studies have identified multiple genetic risk loci but by far the most important association in MS susceptibility is with the class II human leukocyte antigen (HLA) region, specifically HLA-DRB1 * 1501 bearing haplotypes [2] . The environmental factors most consistently associated with risk of MS are Epstein-Barr virus infection, particularly infectious mononucleosis, cigarette smoking and low vitamin D levPublished online: December 7, 2011