Latitudinal variation in the prevalence of multiple sclerosis in Ireland, an effect of genetic diversity

Abstract

Background: Northern Ireland has a high and rising prevalence rate of multiple sclerosis (MS). The most recent survey in 1996 found a rate of 168.7/100 000. Recorded prevalence rates for the south of Ireland, including County Wexford, have been markedly lower and seemed to suggest the existence of a prevalence gradient within the island. Objectives: To compare the prevalence of multiple sclerosis in Co. Wexford in the south east of Ireland and Co. Donegal in the north west, and to establish whether a variation in prevalence of MS exists within Ireland. Methods: Patients were referred from multiple sources. Review of clinical case records and/or patient examination confirmed the diagnosis. Results: In Co. Wexford, 126 patients were found to have clinically definite or probable multiple sclerosis with a prevalence rate of 120.7/100 000 (95% confidence intervals (CI) 100.6 to 143.8), which is similar to other areas of similar latitude within the British Isles. In Co. Donegal, 240 people had clinically definite or probable MS with a prevalence rate of 184.6/100 000 (95% CI 162.0 to 209.5). The difference in prevalence rates is statistically significant (Z = 3.94, p = ,0.001). Conclusion: There is a latitudinal variation in the prevalence rate of MS between the north and the south of Ireland. The increased prevalence of MS seen in Co. Wexford is likely to represent better case ascertainment and improved diagnostic accuracy rather than an actual increase in prevalence. The north/ south variation in prevalence may represent a variation in the genetic predisposition to MS between the background populations of the two counties.

Population frequency of HLA haplotypes contributes to the prevalence difference of multiple sclerosis in Ireland

“…Subjects were enrolled during the course of an epidemiological study on two Irish counties, Donegal in the northwest and Wexford in the southeast [12]. Enrolment criteria included clinically definite or probable MS as defined by Poser's diagnostic criteria [15] and the patient's consent to venesection for HLA typing.…”

“…There is a debate as to whether environmental or genetic factors contribute more strongly to the variation in prevalence rates [18]. In a recent epidemiological study we identified a prevalence gradient for MS within the population of the Republic of Ireland [12]. In County Donegal in northwest Ireland the prevalence of MS was 184.6/100,000 (95 % Confidence Interval (CI): 162-209.5/100,000).…”

“…In County Wexford in the southeast of the island the prevalence figure for MS was 120.7/100,000 (95 % CI: 100.6-143.8/ 100,000). The difference in prevalence of 63.9/100,000 (95 % CI: 49.3-82.7/100,000) was significant (Z = 3.94, p ≤ 0.001) [12].…”

The immunogenetics of multiple sclerosis. The frequency of HLA-alleles class 1 and 2 is lower in Southern Brazil than in the European population

“…We believe that the mainly factor to our different results was the different ethnic backgrounds into Brazil which can really results in many possible genetic combinations in the Brazilian population. Furthermore, beside the type of HLA and ethnic diversity, probably climate with less sunlight, different environmental conditions and dietary habits could play a role in the triggering and incidence of MS in southern Brazil different from other countries 8,32,33,34,35 .…”

The Incidence and Prevalence of Neuromyelitis Optica

“…This is consistent with findings for MS in several regions, including Italy, Sweden, and Ireland. [25][26][27] Evidence supports an increased risk of MS in certain racial (white) and ethnic (Scandinavian and Scottish) groups, and resistance among others, including African Americans, Asians, and Maori. 5,28,29 Clinic-based series have suggested that the risk of NMO is higher among nonwhites than whites.…”