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

Abstract

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 14.8/10(5) 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 1.4/10(5) (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 (21.0/10(5) versus 8.5/10(5)) and a higher incidence (2.0/10(5) versus 0.7/10(5)) 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.

Resistance to experimental autoimmune encephalomyelitis development in Lewis rats from a conventional animal facility

“…Epidemiological investigation revealed a dichotomous relationship between the global distribution of MS and parasitic infections (Fleming & Cook 2006). Also, longitudinal and migratory studies of MS have been consistent with the hygiene hypothesis, showing a paralleled increase in MS and improved sanitation (Cabre et al 2005). In this context we evaluated the presence of worm eggs in the feces and adult worms in the intestine of Lewis rats from both colonies.…”

Optic neuritis

“…[18][19][20] Some studies have shown that individuals who migrate before puberty have the incidence of MS in the area to which they have migrated. [20][21][22] This suggests a possible interaction between the ethnic origin of the patient, the latitude, and whatever is the factor (or factors) that triggers MS. Other studies have suggested that less sun exposure at increasing latitude might be a risk factor for MS, 23,24 and vitamin D deficiency is an additional potential explanation for some of the epidemiological differences in MS. 25,26 In addition, an increased incidence of ON during the spring season has been reported. 27,28 There are also some who postulate viruses as having a role in the pathogenesis of MS. 29,30 Diagnosis Clinical presentation (signs and symptoms)…”

Evidence-based guideline: Clinical evaluation and treatment of transverse myelitis: [RETIRED]

“…8,9,13,14 Only Class IV studies are available regarding the association between ethnicity and the cause of myelitis. 15,16 When comparing various types of myelitis, we found 2 studies showing no significant age differences and 2 studies with insufficient data to assess age differences concerning idiopathic TM vs MS presenting as myelitis (table e-2).…”