Evaluation of Insulin receptor (INSR), Leptin receptor (LEPR) and β3-adrenergic receptor (ADRB3) gene polymorphisms in Diabetes Mellitus patients of Kashmir valley

Abstract

The prevalence of type 2 diabetes mellitus has reached epidemic proportions worldwide. This complex disorder is characterized by defects in insulin secretion and insulin resistance. Type 2 diabetes is a consequence of complex interactions among multiple genetic variants and environmental risk factors. The genetic basis of type 2 diabetes is still poorly understood. The overarching aim of this study was to investigate various polymorphisms in Insulin receptor (INSR), leptin receptor (LEPR) and β3-adrenergic receptor (ADRB3) genes and evaluate their role in the incidence and progression of type 2 diabetes. Three single nucleotide polymorphisms (233, 234 and 276) in the exon 3 of INSR gene, a CTTTA pentanucleotide repeat Del/Ins polymorphism in the 3@ UTR of LEPR gene and a single nucleotide polymorphism (Trp64Arg) in the ADRB3 gene were analysed. The study comprised of 500 local subjects including 200 type 2 diabetes patients and 300 age and gender matched healthy controls. Restriction fragment length polymorphism and single stranded conformation polymorphism techniques were used for genotyping and the results were validated by direct sequencing assay. We observed that codon 233, 234 and 276 of INSR gene were monomorphic in our population thereby ruling out any possible association with type 2 diabetes. However we found an association of LEPR and ADRB3 gene polymorphisms with risk factors and severity of type 2 diabetes, such as obesity, abnormal lipid profile, hypertension, elevated HbA1c levels and serum creatinine levels. The frequency of Del allele was 89.7% and 59.3% in cases and controls respectively (p<0.001; odds ratio 6.0; 95% confidence interval 3.61 - 9.97). The wild allele (Del) in the LEPR gene showed a positive association with the disease as well as associated risk factors. The genotypes for Del/Ins polymorphism did not satisfy Hardy and Weinberg equilibrium (χ2=57.22). In ADRB3 gene, frequency of variant C (Arg) allele was observed to be 40% and 10.2% in cases and controls respectively (p<0.001; odds ratio 5.89; 95% confidence interval 3.69-9.39). Presence of C (Arg) allele was observed to be a risk factor, where as the wild T (Trp) allele exerted a protective effect against type 2 diabetes in our population. Presence of C allele was directly related to higher BMI, WHR, dyslipidemia and uncontrolled diabetes. Genotypes for Trp64Arg polymorphism were in Hardy and Weinberg equilibrium (χ2=0.48). The study signifies that Del allele in LEPR gene and Arg allele in ADRB3 are genotypic risk factors that confer susceptibility to type 2 Diabetes Mellitus in ethnic Kashmiri population