Background: Established genetic susceptibility loci for type 1 diabetes are important in immune regulation and may play a role also in atopic disorders, potentially explaining the inverse association between childhood eczema and subsequent risk for type 1 diabetes previously reported.
Objective: We aimed to directly assess whether HLA-DQ, CTLA4, and PTPN22 genes could explain the putative association between childhood eczema and lower subsequent risk of type 1 diabetes observed in several case-control studies.
Methods: We designed a case-control study with 339 incident cases of type 1 diabetes identified in the Norwegian childhood diabetes registry, and 985 population-based control children. DNA was collected, and physician-diagnosed childhood eczema was ascertained by a questionnaire administered to the parents of children with and without type 1 diabetes.
Results: The previously reported association between childhood eczema and lower risk of type 1 diabetes was confirmed (odds ratio,OR, 0.61, 95% confidence interval, CI, 0.40-0.95] and this was consistent in subgroups defined by HLA-DQ, CTLA4, and PTPN22 genotypes. The OR was essentially not influenced by adjustment for genetic variation at these loci (OR simultaneously adjusted for the three genetic loci: 0.55, 95% CI: 0.32-0.92). The ratio of the unadjusted to adjusted OR was 1.12, with a corresponding 95% CI from 0.84 to 1.50.
Conclusion: In this first study of its kind, we demonstrated directly that the observed inverse association between childhood eczema and type 1 diabetes is not likely to be explained by the established diabetes susceptibility genes HLA-DQ, CTLA4, or PTPN22.