Risk factors for increased multiple sclerosis susceptibility in the Iranian population

Multiple sclerosis (MS) is a complex autoimmune disease with increasing prevalence. Many factors have been assessed in relation to its development and its worldwide geographical and racial distribution. Therefore, we decided to conduct a nationwide case-control matched study to estimate the possible influence of putative risk factors on MS status in an Iranian MS population. Between January 2008 and September 2013, 1403 patients diagnosed with MS according to the Poser or McDonald criteria and 883 controls were studied. Of all patients, there were 921 women and 296 men (ratio 3.1:1) with a mean age of 32.6 ± 8.7 years. In the multivariate model adjusted for sex and age (±2 years), we found associated risk factors of MS to be: history of any allergic condition (Odds ratio (OR): 1.92, 95% Confidence interval (CI): 1.55-2.47, p < 0.001), and smoking (OR: 1.93, 95% CI: 1.31-2.73, p < 0.001). Sunlight exposure ≥3 hours was found to be associated with a reduced risk of MS (OR: 0.23, 95% CI: 0.15-0.31, p < 0.001). As expected, cases were more likely to have a positive family history of MS than controls (OR: 1.91, 95% CI: 1.33-2.75, p < 0.001). A significant association was found between family history of other autoimmune diseases and MS risk (OR: 1.57, 95% CI: 1.18-2.09, p = 0.002). These results support the hypothesis that sun exposure is associated with a decreased risk of MS while smoking, autoimmune family history, MS family history, and personal allergy history are risk factors for MS susceptibility.