Objective: The nonclassical major histocompatibility complex (MHC) class I chain-related molecules (MICs), encoded within the MHC, function in immunity. The transmembrane polymorphism in MICA (MICA-STR) has been reported to be associated with type 1 diabetes. In this study, we directly sequenced both of the highly polymorphic MIC genes (MICA and MICB) in order to establish whether they are associated with type 1 diabetes independently of the known type 1 diabetes MHC class II genes HLA-DRB1 and HLA-DQB1.
Research design and methods: We developed a sequencing-based typing method and genotyped MICA and MICB in 818 families (2,944 individuals) with type 1 diabetes from the U.K. and U.S. (constructing the genotype from single nucleotide polymorphisms in exons 2-4 of MICA and 2-5 of MICB) and additionally genotyped the MICA-STR in 2,023 type 1 diabetic case subjects and 1,748 control subjects from the U.K. We analyzed the association of the MICA and MICB alleles and genotypes with type 1 diabetes using regression methods.
Results: We identified known MICA and MICB alleles and discovered four new MICB alleles. Based on this large-scale and detailed genotype data, we found no evidence for association of MICA and MICB with type 1 diabetes independently of the MHC class II genes (MICA P = 0.08, MICA-STR P = 0.76, MICB P = 0.03, after conditioning on HLA-DRB1 and HLA-DQB1).
Conclusions: Common MICA and MICB genetic variations including the MICA-STR are not associated, in a primary way, with susceptibility to type 1 diabetes.