Localization of type 1 diabetes susceptibility to the MHC class I genes HLA-B and HLA-A

Abstract

The MHC complex, occupying a sizeable section of human chromosome 6, is linked to almost all known autoimmune disorders. A new study uses a large data set from the Wellcome Trust Case Control Consortium to focus more closely on the MHC genes linked to a specific disease, childhood diabetes. Two susceptibility genes emerge: HLA-A and HLA-B. The discovery clarifies the aetiology of type 1 diabetes and points to a class of peptides worth studying in the search for vaccination strategies. New methods and larger sample groups are used to precisely determine the alleles in the HLA complex which contribute susceptibility to type 1 diabetes. The major histocompatibility complex (MHC) on chromosome 6 is associated with susceptibility to more common diseases than any other region of the human genome, including almost all disorders classified as autoimmune. In type 1 diabetes the major genetic susceptibility determinants have been mapped to the MHC class II genes HLA-DQB1 and HLA-DRB1 (refs 1–3), but these genes cannot completely explain the association between type 1 diabetes and the MHC region4,5,6,7,8,9,10,11. Owing to the region’s extreme gene density, the multiplicity of disease-associated alleles, strong associations between alleles, limited genotyping capability, and inadequate statistical approaches and sample sizes, which, and how many, loci within the MHC determine susceptibility remains unclear. Here, in several large type 1 diabetes data sets, we analyse a combined total of 1,729 polymorphisms, and apply statistical methods—recursive partitioning and regression—to pinpoint disease susceptibility to the MHC class I genes HLA-B and HLA-A (risk ratios >1.5; Pcombined = 2.01 × 10-19 and 2.35 × 10-13, respectively) in addition to the established associations of the MHC class II genes. Other loci with smaller and/or rarer effects might also be involved, but to find these, future searches must take into account both the HLA class II and class I genes and use even larger samples. Taken together with previous studies4,5,6,7,8,10,11,12,13,14,15,16 , we conclude that MHC-class-I-mediated events, principally involving HLA-B*39, contribute to the aetiology of type 1 diabetes.