Genetic determinants of type 1 diabetes: immune response genes.

Type 1 diabetes (T1D) is a polygenic autoimmune disease. Susceptibility to T1D is strongly linked to a major genetic locus that is the MHC, and several other minor loci including insulin, cytotoxic T-lymphocyte-associated antigen-4, PTPN22 and others that contribute to diabetes risk in an epistatic way. We have observed that there are three sets of DR3-positive autoimmunity-favoring haplotypes in the north-Indian population, including B50-DR3, B58-DR3 and B8-DR3. The classical Caucasian autoimmunity favoring AH8.1 (HLA-A1-B8-DR3) is rare in the Indian population, and has been replaced by a variant AH8.1v, which differs from the Caucasian AH8.1 at several gene loci. Similarly, there are additional HLA-DR3 haplotypes, A26-B8-DR3 (AH8.2), A24-B8-DR3 (AH8.3), A3-B8-DR3 (AH8.4) and A31-B8-DR3 (AH8.5), of which AH8.2 is the most common. The fact that disease-associated DR3-positive haplotypes show heterogeneity in different populations suggests that these might possess certain shared components that are involved in the development of autoimmunity.