A Study On Correlation Of SNP And Haplotype In IL-6R Gene With Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a complicated disease. Both hereditary factor and environmental factor contribute to the development of T2DM, which is the major type of diabetes mellitus. In the study, we plan to explore the association of interleukin 6 receptor (IL-6R) gene with the susceptibility of T2DM through investigating IL-6R polymorphisms.The IL-6R gene, mapped to human chromosome 1q21.3, encode IL-6R protein, which can bind specially to interleukin 6(IL-6) and form IL-6R/IL-6 complex caused corresponding signal transduction. IL-6 is a multifunctional cytokine, which can be produced by various cells, such as lymphocyte, adipocyte, endothelial cell, and so on. IL-6 plays an important role in immunifaction and inflammation. Hence, the disturbance of IL-6 may lead to a wide range of diseases. Studies have shown that high level of IL-6 can induce pancreaticβ-cell failure and insulin resistance(IR), so that it may contribute significantly to the genesis and development of diabetes mellitus. Yet the signal of IL-6 is mediated by IL-6R, so IL-6R is the key to the biological function of IL-6. It has reported that human chromosome 1q21.3 is a region of linkage well to T2DM. However, previous reports indicated that the correlation between IL-6R gene and T2DM exists race heterogeneity. Therefore, we tested the relation of IL-6R gene with T2DM in Chinese han population.ObjectivesIn the present study, we aimed to investigate single nucleotide polymorphism (SNP) and haplotype frequency distribution of IL-6R gene, and identify the association of two SNP sites with T2DM of Han population in southwestern China, which will accumulate more data of IL-6R polymorphisms and facilitate further exploration into the pathogenesis, precaution and treatment for T2DM.Methods(1) IL-6R gene nucleotide sequences and the corresponding SNP sites were obtained from GenBank of National Center for Biotechnology Information (NCBI). The primers were designed by Primer Premier 5.0 software and their specificity was tested by NCBI Blast 2.0 software.(2) The two SNP sites of IL-6R gene in the 106 T2DM cases and 102 normal controls were genotyped with Polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP) technique and analyzed by group-candidate gene method.(3) The genotypes combination distribution of two SNP sites of IL-6R gene was analyzed by clustering analysis method.Results(1)The genotypes frequency of SNP rs8192284 at the ninth exon D358A of IL-6R gene between cases and controls were AA 0.443/0.304, AC 0.415/0.421, CC 0.142/0.275 respectively, and the allele frequency were A 0.651/0.510 and C 0.349/0.490. Notably, There were significant differences between the two groups in the SNP site (chi-square(χ²)=7.149,P=0.029;χ²=8.511,P=0.04).The results indicated that the ninth exon D358A of IL-6R gene is a susceptible factor of T2DM among the Han population in southwestern China..(2)The genotypes frequency of SNP rs4845617 in the promoter-183 (G→A) of IL-6R gene between T2DM cases and control subjects were GG 0.387/0.451, GA 0.443/0.412, AA 0.170/0.137 respectively, and the allele frequency were G 0.585/0.657 and A 0.415/0.343. There were no significant differences between the two groups in the SNP site (χ²=0.992, P=0.634 ;χ²=2.285 , P=0.157).The results showed that rs4845617 polymorphism in the promoter-183 (G→A) of IL-6R gene is independence of T2DM.(3) Among the four haplotype (A1-G, A1-A2, C-G, C-A2) in southwestern Chinese Han population, which are composed of the two SNP sites [ rs8192284 at the ninth exon D358A and rs4845617 in the promoter-183(G→A)]of IL-6R gene, the most common was A1-G, the frequency of which between cases and controls was 0.418/0.293(χ²=1.738,P=0.187480). The haplotype frequency of C-A2 was 0.110/0.273 between cases and controls. And its P values was 0.036357. There was significant difference between the two groups. This study suggested that haplotype C-A₂ of IL-6R gene might be associated with T2DM among the Han population in southwestern China.Conclusions(1)The study first revealed the features of genotypes combination distribution and frequency distribution of the two SNP sites of IL-6R gene, thus explore the relation between IL-6R gene polymorphisms and T2DM among the Han population in southwestern China, which would supply valuable data for further studies on the association of SNP in IL-6R gene with the physiological function and pathologic condition.(2)We found a trend to correlation of IL-6R gene with genetic predisposition of T2DM among the Han population in southwestern China.