Association of polymorphisms in leptin receptor gene with obesity and type 2 diabetes in the local population of Coimbatore

Background: Candidate gene association studies are very relevant to the area of clinical pharmacology. As information on candidate genes and candidate single nucleotide polymorphisms increases, a number of such candidates can be studied in a population to explore their association with their susceptible disease. One such attractive and popular Single Nucleotide Polymorphism (SNP) candidate for obesity is the gene coding for leptin receptor. The leptin receptor gene (LEPR) polymorphism plays an important role in obesity and type 2 diabetes. But the role of this polymorphism is not yet studied in Indian population. Hence, the study focused to explore the association of leptin receptor polymorphisms (K109R, Q223R and K656N) with obesity and type 2 diabetes in both diabetic and non-diabetic subjects recruited from the local population of Coimbatore. Materials and Methods: Genotypic analysis for the three polymorphisms has been made for 300 subjects (150 diabetic and 150 non-diabetic) with the age range of 40-60 years using conventional Polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) techniques in a case-control fashion. Allele frequencies were estimated based on the gene count method. Correlation was made with phenotypic variables including body mass index (BMI), waist-to-hip ratio (WHR), insulin and leptin levels for those polymorphisms. Results and Conclusion: Among the polymorphisms tested in this study, significant association with BMI (P < 0.05), WHR (P < 0.05) leptin (P < 0.001) and insulin (P < 0.0001) was observed for the SNP Q223R, whereas in the case of the other two polymorphisms the association was not statistically significant. The significance value was calculated based on the χ2 test. The controls are also found to have a higher frequency of homozygous mutants for Q223R and are significantly associated with obesity. These findings support the hypothesis that Q223R polymorphism is associated with obesity. It can be speculated that the controls showing the same allele may develop Type 2 diabetes at a later stage and Q223R can act as a strong marker