A nationwide survey of the prevalence of multiple sclerosis in immigrant populations of Sweden.
BACKGROUND
In 2008, immigrants constituted 14% of the population of Sweden, a high-risk area for multiple sclerosis (MS). We investigated the largest Swedish immigrant populations for the prevalence of MS.


METHODS
Data on foreign-born MS patients were retrieved from Swedish national health and population registers. We calculated observed versus expected numbers of MS patients and gender- and age-specific prevalence ratios (PR) between immigrant populations and the general population of Sweden and, where possible, of the countries of birth.


RESULTS
The 19 largest immigrant populations included 1327 MS patients. The global variation in MS prevalence was reflected in Sweden. The prevalence in immigrant populations who had moved to Sweden from countries with a lower MS risk was however higher than in their countries of birth. Notably, the MS prevalence in the population born in Iran was at least as high as in the general population of Sweden (men: PR = 1.10, 95% CI 0.81-1.46, p = 0.537, women: PR = 1.18, 95% CI 0.97-1.44, p = 0.855) and more than twice as high as in Isfahan, Iran (men: PR = 3.06 (95% CI 2.26-4.06), p <0.001, women: PR = 2.21 (95% CI 1.81-2.68), p <0.001).


CONCLUSIONS
The MS prevalence increased in migrants who moved to Sweden from countries with a lower MS risk. In the Iranian immigrant population the prevalence exceeded that in the general population of Sweden. This indicates that Iranians carry genetic factors that contribute to a higher MS risk when environmental-lifestyle MS risk factors change.
Institute of Neuroscience and Physiology, Department of Neurology, Sahlgrenska University Hospital, Gothenburg, Sweden. Cecilia.Ahlgren@neuro.gu.se
Cecilia
C
Ahlgren
Anders
A
Odén
Jan
J
Lycke
D054242:Emigrants and Immigrants / Q000706:statistics & numerical data*; D004777:Environment; D005260:Female; D020022:Genetic Predisposition to Disease; D006306:Health Surveys; D006801:Humans; D007492:Iran / Q000208:ethnology; D008019:Life Style; D008297:Male; D009103:Multiple Sclerosis / Q000175:diagnosis / Q000208:ethnology* / Q000235:genetics; D015995:Prevalence; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors