Dental Fluorosis And Its Relationship With The CLCN7Gene Polymorphism

The endemic fluorosis is a common environmental related endemic disease whichmay affect skeleton (skeletal fluorosis) or teeth (dental fluorosis). The etiology ofendemic fluorosis lays in that people who live a high fluorine environment intake toomuch fluorine leading to chronic fluorosis. Recent years our group carried out theepidemiological investigation concerning dental fluorosis in Shaanxi local districts Wefocused on the clinical manifestation, the prevalence of dental fluorosis and its relatedgene background. Here we continued our genetic studies in the patients in endemicfluorosis area, explored the relationship between pathogenic mechanism of dentalfluorosis and chloride channels.Methods:1. We collected132blood samples of Shaanxi health individuals, and obtained thegenomic DNA. Three tag SNPs (rs11645645, rs2235579, rs2745001) of CLCN7genewere selected and genotyped by Sequenom MassArray genotyping platform. The correlations among these polymorphisms from Hapmap were compared with Chinesepopulations, Japanese populations and European populations.2. Epidemiological investigation was carried out in the Ziyang County, City ofAnkang, Shaanxi Province. Peripheral blood was also obtained from samples. Weextracted genomic DNA from blood samples by magnetic bead methods. Based on someof our previous dental fluorosis samples and new collected samples, we chose three tagSNPs of CLCN7and test their distribution in the control as well as dental fluorosissamples. Genetic typing of SNP was determined by Mass array. Statistical significancewas analyzed between patients and normal control in considering above testing indexes.Finally we compared the classification results to CHB, JPT and CEU in Hapmapdatabase.3. We randomly selected100blood samples (50from patients and50from normalcontrol), extracted the mRNA, and tested the mRNA expression level of CLCN7throughreal-time PCR in order to determine the expression difference between these two groups.Results:1. The genotypes of CLCN7in132Shaanxi healthy samples were similar to that inChinese populations (P>0.05), but were different to that in European populations(P<0.05).2. Total1723samples were investigated in this study.889cases were diagnosed asdental fiourosis, other834were controls. Male is909and female is814. The age of thesamples varied from12to77, and the average age is38. The genotype distribution ofthree SNPs were not different between patients and normal group (P>0.05).3. Results of real-time PCR indicated that the mRNA expression level for CLCN7inpatients with dental fluorosis was lower than normal control.Conclusions:1. The samples in our research are representative of general Chinese, andrs11645645、rs2235579、rs2745001may be used as the tag SNPs of CLCN7for further experiments.2. There is no significant correlation between the genotyping of CLCN7genepolymorphism and dental fluorosis based on the three tag SNP genotyping. The selectedthree tag SNPs, rs11645645and rs2235579are not functional SNPs, and the rs2235579site may cause the ESE changes of the CLCN7mRNA levels. Thus we need furtherexperiment to exclude the final contribution of CLCN7in the development of dentalfluorosis.3. In the investigated area, the mRNA expression level for CLCN7in patients withdental fluorosis was lower than normal control, which showed a positive relationshipbetween dental fluorosis and ClC-7. The decreased CLCN7level might be a direct effectof fluoride, also might be an epigenetic regulation result.Here we explored the relationship between dental fluorosis and ClC-7, and wefound a decreased CLCN7mRNA level in the dental fluorosis populations, whilst anegative relationship between three tag SNPs of CLCN7gene and dental fluorosispopulation. We suggested that there might an epigenetic regulation mechanism betweendental fluorosis and CLCN7gene.