Molecular characterization of LEPR Q223R single nucleotide polymorphism (rs1137101) and salivary leptin levels in different facial skeletal patterns

Abstract

Leptin hormone regulates several key physiological processes which include signalling for energy homeostasis, endocrine function and bone metabolism and physiology. There is however a gap in the literature regarding leptin’s role and its association with the facial skeletal pattern that is heavily related to the dynamic of growth, bone deposition and bone resorption. The role of genetic factors in the growth of the maxilla and the mandible is also still largely being investigated. The Q223R (rs1137101) single nucleotide polymorphism (SNP) of the leptin receptor (LEPR) gene has previously been associated with abnormal growth of the maxilla. Limited studies have been done with regards to its association with mandibular growth. The aim of this study therefore is to determine the molecular characterization of the LEPR Q223R (rs1137101) SNP and salivary leptin levels in different classes of facial skeletal pattern. A total of 82 participants from Kuantan, Pahang were recruited to participate in this case control study with regards to the examination of the molecular characterization of the LEPR Q223R (rs1137101) SNP and a total of 62 participants from Kuantan, Pahang were recruited to participate in the case control study of leptin hormone levels in different classes of facial skeletal pattern. Based on the lateral cephalometric analysis, the subjects were grouped into Class I, II and III facial skeletal patterns, according to Eastman and Wits appraisal. For the genetic analysis, DNA extraction and isolation from the unstimulated saliva samples was done. The samples were then subjected to polymerase chain reaction (PCR) amplification. Subsequently, restriction fragment length polymorphism (RFLP) technique was used for the genotyping analysis using the MspI restriction enzyme. Statistical analysis with the Chi-square (χ2) test was used to compare genotype and allele frequencies between the different classes of facial skeletal pattern while the Hardy-Weinberg Equilibrium (HWE) was applied to assess distribution of genotype frequency between the classes of facial skeletal pattern. The results of the genetic study indicate no significant association between genotype frequency between the control group (Class I facial skeletal pattern) and Class II (p=0.48) and Class III (p=0.16) facial skeletal pattern. There was also no significant association between allele frequency between the control group (Class I facial skeletal pattern) and Class II (p=0.82) and Class III (p=0.32) facial skeletal pattern. For the leptin hormone analysis, unstimulated saliva samples were taken and purified to undergo leptin enzyme-linked immunosorbent assay (ELISA) analysis to determine the levels of leptin hormone. Statistical analysis using the Kruskal-Wallis test was used to analyse the data obtained. Results of the leptin hormone analysis indicate that there is a significant difference in the median levels of leptin hormone between the control group (Class I facial skeletal pattern) and Class II (p=0.004) and Class III (p=0.003) facial skeletal pattern. In conclusion, for the Malaysian population, there is no significant association between the Q223R (rs1137101) SNP of the LEPR gene in different classes of facial skeletal pattern. There is however a significant association between salivary leptin hormone levels between the control group and Class II and Class III facial skeletal pattern. This study suggests that leptin hormone may be used as an indicator to predict the growth of the facial skeletal pattern and to facilitate interceptive orthodontic treatment if necessary. More studies however are required to consolidate the results of both the genetic study and the study of leptin hormone in different classes of facial skeletal pattern.