HLA‐DQ relative risks for coeliac disease in European populations: a study of the European Genetics Cluster on Coeliac Disease

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Abstract
Coeliac disease is an enteropathy due to an intolerance to gluten. The association between HLA-DQ genes and CD is well established. The majority of patients carry the HLA-DQ heterodimer encoded by DQA1*05/DQB1*02, either in cis or in trans. The remaining patients carry either part of the DQ heterodimer or DQA1*03-DQB1*0302. The aim of the study was to estimate the risks associated with different DQ genotypes in European populations. HLA information was available for 470 trio families from four countries: France (117), Italy (128), and Norway and Sweden (225). Five DQA1-DQB1 haplotypes were considered and control haplotype frequencies were estimated from the set of parental haplotypes not transmitted to the affected child. The possible genotypes were grouped into five genotype groups, based on the hierarchy of risk reported in the literature. A north–south gradient in the genotype group frequencies is observed in probands: homogeneity is strongly rejected between all country pairs. For each country, the relative risks associated with each genotype group were computed taking into account the control haplotype frequencies. Homogeneity of relative risks between countries was tested pairwise by maximum likelihood ratio statistics. The hypothesis of homogeneity of relative risks is rejected (P is approximately 10−6) for all country pairs. In conclusion, the gradient in the genotype group frequencies in probands is not only due to differences in haplotype frequencies but also due to differences in genotype relative risks in the studied populations; the relative risks associated with each DQ genotype group are different between northern and southern European countries; neither are they ordered in the same way.