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

Abstract

A recent epidemiological study of multiple sclerosis in County Donegal in the northwest of Ireland and County Wexford in the southeast found a significant prevalence difference of 63.9/100,000 (95% CI 49.3-82.7/100,000) between the two regions (Z = 3.94, p <or= 0.001). County Donegal had a higher prevalence rate than County Wexford (184.6/100,000 vs. 120.7/ 100,000). The aim of this paper is to examine whether the MS prevalence difference between the two counties is due to population differences in the genetic predisposition to MS. Seventy-three MS patients from County Donegal and 45 from County Wexford participated in the study and 200 control subjects were enrolled from each county. Blood samples from both MS populations and control populations were HLA typed for DRB1 and DQB1 alleles. The strong association with the development of MS and the HLA DRB1*1501 and DQB1*0602 phenotypes was confirmed in both patient populations relative to controls. The Donegal sample control population also had a significantly higher carriage rate of the HLA DRB1*1501 - DQB1*0602 haplotype relative to the Wexford sample control population (chi(2) = 5.02, p <or= 0.05,OR = 1.616, CI 1.060-2.464, p = 0.05). Although the numbers tested in this study were small the results suggest one of the factors accounting for the difference in MS prevalence across the island of Ireland is likely to be variation in the genetic predisposition to MS within the Irish population.