Polymorphism of 8-oxoguanine DNA glycosylase -1(OGG1)in Iraqi Patients with Type2 Diabetes Mellitus

Abstract

Chronic hyperglycemia in type 2 diabetes mellitus leads to elevated oxidative stress. As a consequence , the accumulation of reactive oxygen species (ROS)may cause additional damage to various biological macromolecules, including DNA. Several studies have demonstrated that oxidative stress plays an important role in the pathogenesis of type2 diabetes mellitus. The aim of this study is to investigate the association of polymorphisms of 8- oxoguanine DNA glycosylase-1(OGG1) repair gene polymorphism to the susceptibility of type 2 DM in an Iraqi population with T2DM patients from Wasit Province. All samples were collected from the local community of Wasit province, Iraq. Forty five type 2 diabetes mellitus patients (22 males and 23 females) and 35 healthy controls (17 males and 18 females) were genotyped for 8-oxoguanine DNA glycosylase-1(OGG1) using PCR- RFLP technique. In both patients and control groups, the distribution frequencies of genotypes and alleles of 8-oxoguanine DNA glycosylase-1(OGG1) A/G was inconsistent with the Hardy-Weinberg equilibrium in T2DM patients(χ2=49.542,P=(0.00001); χ2=82.0185,P=(0.0001) respectively. The Cys/Cys(mt/mt) OGG1 genotype was significantly higher in patients than controls(mt/mt;33(37%)vs,0.00 in controls. The Ser/Cys (wt/mt) was 7(16%) and 6(17%) in patients and controls respectively and Ser/Ser genotypes wt/wt; decreased significantly in patients 5(11%) vs,29(83%) in controls. The wt and mt allele frequencies of OGG1were highly significant between the two groups P=0.00001. The wt allele was the major one in control group with a percent of (90.28) vs. (18.89) in patients group. Whereas the mt the frequent allele in patients with a percent of (81.11) vs. (18.89).This further analysis showed that the individuals carrying the homozygous Cys/Cys(mt/mt) genotype were more likely to have increased the risk of T2DM very significantly with OR= 190.02800 (CI95% 10.8329 to 3342.2603) ,P=0.0003. The genotypes Ser/Ser( wt/wt) and Ser/Cys(wt/mt) decrease the association with T2DM with OR=0.0259 (CI95% 0.0072 to 0.0930), and 0.8904 (CI95% 0.2701 to 2.9347 )respectively, P= 0.0001 and 0.08486 for each genotype respectively, These results suggest that mt allele may be considered as risk allele of T2DM whereas the wt allele is protective agent T2DM.Association analysis showed that the type2 diabetes mellitus risk of females with OGG1 gene Cys/Cys( mt/mt) genotype was highly significant 81.4000 fold higher than that in controls OR= 81.4000 (CI 95% 4.3089 to 1537.7322), P= 0.0033.Ser/Cys( wt/mt) genotype increase the probability of the disease with OR = 1.7647 (CI 95% 0.3745 to 8.3154), P = 0.4727.Similary,Ser/Ser(wt/wt) genotype decrease the association with T2DM with OR= 0.0091 (CI95% 0.0009 to 0.0959), P = 0.0001.Type2 diabetes mellitus patients particularly with Cys/Cys(mt/mt) genotype increases the association about more than 111 times in males patients than that in controls OR= 111.3636 ( CI95% 5.7135 to2170.6226), P = 0.0019 While, genotypes Ser/Cys(wt/mt) and Ser/Ser (wt/wt) reduce the likelihood of T2DM with OR= 0.2222 ( CI95% 0.0209 to 2.3585),P = 0.2120 and 0.0476( CI95% 0.0091 to 0.2484), P= 0.0003 respectively. the genetic model for OGG1 in comparison between T2DM patients and controls . The dominant model indicated that patients and controls of (wt/mt+mt/mt) genotype increased significantly the association with T2DM in patients: (5/7 and 33) comparing with control (29/6 and 0.00) with OR (38.666),P=0.0001.The recessive model revealed that patients carrier the genotype (wt/wt+wt/mt) declined significantly the association with the disease :(33/5 and 7) in patients versus (0.00/29 and 6) in controls,OR=0.0053,P=0.0003.The Over-dominant model showed that patients with the genotype (wt/wt+mt/mt) in creased non-significantly the association with the disease when compare patients (7/5 and 33) with controls(6/29 and 0.00) ,OR=1.123,P=0.848