Evaluation of high-risk type 1 diabetes HLA-DR and DQ haplotypes using three single nucleotide polymorphisms in a population from Southern Brazil

Abstract

Background: Type 1 diabetes mellitus (T1D) accounts for ∼10% of all diabetes cases, and it is caused by autoimmune destruction of pancreatic beta-cells, which leads to insulin deficiency and fates individuals to require insulin treatment to survive. The triggering of autoimmunity against betacells is caused by interaction between environmental and genetic risk factors. Among the several loci associated with T1D, the human leukocyte antigen (HLA) class II DR/DQ locus is the main genetic risk factor for T1D, accounting for 30-50% of genetic risk for this disease. Other genes have been associated with minor effects on T1D risk when compared with HLA, with different studies indicating that the effect of non-HLA polymorphisms on predisposition for T1D may be different according to HLA DR/DQ types. In this scenario, a recent study identified a minimum set of three polymorphisms (rs3104413, rs2854275, rs9273363) which can predict highrisk HLA-DR/DQ types relevant to T1D. Objective: To evaluate frequencies of high-risk T1D HLA-DR/DQ haplotypes in a Southern Brazilian population using a minimum set of HLA polymorphisms (rs3104413C/G, rs2854275A/C and rs9273363A/C). Materials and methods: We analyzed 387 T1D patients (cases) and 375 healthy blood-donor subjects (controls). The local ethics committee approved the protocol, and all patients signed an informed consent form. Polymorphisms of interest were genotyped by allelic discrimination - RTPCR technique using TaqMan MGB probes (Life Technologies). Haplotype combinations of the three analyzed polymorphisms were used for defining the HLA types relevant to T1D (Nguyen et al∗), distinguishing the highest-risk DR4-DQ8 and DR3/4-DQ types. Results: Minor alleles frequencies of rs3104413, rs2854275, rs9273363 were increased in T1D patients as compared to non-diabetic subjects (rs3104413C: 44.4% vs. 11.2%; rs2854275A: 12.9% vs. 1.9%; rs9273363A: 43.9% vs. 9.9%; all P <0.0001).The frequency of high-risk DR4-DQ8 type was 66.7% in T1D cases and 15.3% in controls (OR=11.059, 95%CI 6.68- 18.29; P <0.0001).The high-risk DR3/4-DQ8 heterozygous haplotype was observed in only one T1D patients and in none control subject. Conclusion: As expected, the high-risk HLA-DR4/DQ8 haplotype is associated with increased risk for T1D in our population. The genetic risk of non-HLA genes on T1D in Southern Brazil can now be correct for different high-risk HLA-DR/DQ types.