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The first large population study of coeliac disease (CD) among twins has confirmed that genetic makeup is more important than environmental influence in this disorder. Using twinship as the first selection criterion and CD as the second allowed the true extent of genetic influence to be determined.
Twenty twin pairs were monozygotic and 27 were dizygotic. The ratio of monozygotic pairs to dizygotic pairs of the same sex and to dizygotic pairs of opposite sex was very close to the expected population ratio, confirming a truly population based sample. Concordance for CD was 86% probandwise, 74% pairwise for monozygotic twins and 20% probandwise, 11% pairwise for dizygotic twins.
The odds of concordance in the non-index twin after adjusting for age, sex, number of shared HLA haplotypes, and zygosity were for genotype DQA1*0501/DQB1*0201, specifying the DQ2 heterodimer, 3.3 (95% confidence interval 0.4 to 30.0) and for DQA1*0301/DQB1*0302, specifying DQ8, 1.4 (0.0 to 41.0). In monozygotic pairs the odds when adjusted for DQ genotype were 17.0 (2.1 to 134.0), indicating another, separate genetic influence.
Patients were identified from the Italian Twin Registry—with 1.6m names—cross matched with approximately 6000 names listed in a large CD patient support group. Forty seven of 58 twin pairs were studied. Each pair was tested for antibody markers and had an intestinal biopsy, if necessary, to confirm CD status, and was tested for HLA type. Same sex pairs were tested to confirm their zygosity.
Previous studies in twins, based on volunteers or case series, have the disadvantage of recruiting bias.
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