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For coeliac disease (CD) to manifest itself, certain common gene variants within the human leucocyte antigen (HLA) complex must be present. These HLA gene variants are necessary but not sufficient for the disease to develop, as both environmental factors and other gene variants play their role in CD. In order to determine the effect of environmental factors versus genetic factors in disease development, studies are conducted using twins. One such study of Italian twins suggests that very little of the risk of developing CD is due to environmental factors. In fact, the study indicates that CD is influenced by an unusually strong genetic component (heritability).1 In this issue, Kuja-Halkola et al2 provide a second evaluation of twin concordance rates and heritability of CD using Swedish twins. They were able to combine the national twin registry with data collected from all pathology departments in Sweden. This comprehensive data collection includes virtually every case of CD diagnosed in Sweden between the years 1969 and 2013, which allows for an accurate estimate as to the prevalence of diagnosed CD.
The results from Kuja-Halkola et al differ noticeably from the earlier Italian study. While Kuja-Halkola et al show a concordance rate in Swedish monozygotic twins of 49% and in …