Aim: The aim of this study was to test the microsatellites in the Type 1 Diabetes Genetics Consortium major histocompatibility complex (MHC) data set for association with type 1 diabetes (T1D) independent of the HLA-DRB1, -DQA1 and -DQB1 genes.
Methods: The data set was edited to contain only one affected child per family, and broad ethnic subgroups were defined. Genotypes for HLA-DRB1, -DQA1 and -DQB1 were replaced by a haplotype code spanning all three loci, with phase inferred based on common haplotypes. The final data set contained 8190 samples in 2301 families, 59 microsatellites and the DRB1-DQA1-DQB1 haplotype code. Statistical analyses consisted of conditional logistic regression and haplotype estimations and linkage disequilibrium calculations.
Results: The data set was screened using a main effects test approach adjusted for DRB1-DQA1-DQB1, and significant results tested for validity. After these procedures, four markers remained significant at the Bonferroni-corrected threshold: D6S2773 (p = 0.00014), DG6S185 (p = 0.00015), DG6S398 (p = 0.00043) and D6S2998 (p = 0.00015). These results were supported by allelic tests conditioned on DRB1-DQA1-DQB1 haplotypes, except for DG6S185, which may contain artefacts.
Conclusions: We have identified three microsatellites that mark additional risk factors for T1D at highly significant levels in the MHC. Further analyses are needed to establish the relationship with other possible genetic determinants in this region.