Journal Article

Role of return migration in the emergence of multiple sclerosis in the French West Indies

P. Cabre, A. Signate, S. Olindo, H. Merle, D. Caparros-Lefebvre, O. Béra and D. Smadja

in Brain

Published on behalf of The Guarantors of Brain

Volume 128, issue 12, pages 2899-2910
Published in print December 2005 | ISSN: 0006-8950
Published online September 2005 | e-ISSN: 1460-2156 | DOI: http://dx.doi.org/10.1093/brain/awh624
Role of return migration in the emergence of multiple sclerosis in the French West Indies

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The emergence of multiple sclerosis in island societies has been investigated only in a few Caucasian populations living in temperate regions. The effect of human migration on the risk of developing this disease is still an open question because of possible genetic selection. We conducted an epidemiological study of the multiple sclerosis population in the French West Indies (Martinique and Guadeloupe), a population which includes large numbers of West Indians who have returned after emigrating to metropolitan France. Standardized incidence ratios (SIRs) for multiple sclerosis among migrants were calculated and their genetic characteristics were compared to those of non-migrants. The crude prevalence of multiple sclerosis was 14.8/105 on December 31, 1999 (95% CI: 11.9–17.7); and its crude mean annual incidence for the period July 1, 1999 to June 30, 2002 was 1.4/105 (95% CI: 1.0–1.8), confirming its emergence in the French West Indies. Recurrent neuromyelitis optica, which is virtually the only form of multiple sclerosis in black African populations in tropical regions, represented not >17.8% of these cases. During the 1 440 000 person-years of follow-up, 33 incidence cases were identified in migrants. Since the number of expected cases was 19.3, the overall SIR was 1.71 (95% CI: 1.19–2.38; P < 0.01) among migrants. The increase in the SIR was more marked if the stay was made before the age of 15 years (4.05, 95% CI: 2.17–6.83; P < 0.0001). European ancestry in the two migrating and non-migrating populations was similar. Martinique, which has a higher rate of return migration, has a higher prevalence of multiple sclerosis (21.0/105 versus 8.5/105) and a higher incidence (2.0/105 versus 0.7/105) than Guadeloupe. The emergence of the disease in the French West Indies is of environmental rather than genetic origin. It may be explained either through the introduction by migrants of precipitating environmental factors that operate in a critical way before the age of 15 years, and/or by the recent disappearance from the French West Indies of protective environmental factors acting before this age.

Keywords: emergence; multiple sclerosis; neuromyelitis optica; migration; French West Indies; HLA = human leucocyte antigen; RNMO = relapsing neuromyelitis optica; SIR = standardized incidence ratio; SPR = standardized prevalence ratio

Journal Article.  7862 words.  Illustrated.

Subjects: Neurology ; Neuroscience

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