Association Between PMCA2, HOGG1Gene Polymorphisms And Noise-induced Hearing Loss In A Chinese Population

Noise-induced hearing loss (NIHL) also known as occupational noise-induced deafness, is a slowly, progressively sensorineural hearing loss that often caused by daily exposure to detrimental levels of noise in the course of work. NIHL is a common occupational disease that endangers the health of workers and affects the quality of life. Since the industrial revolution, NIHL has become one of the most important occupational disease. In the United States, approximately10%of the total population (30million workers) is exposed daily to hazardous noise levels in their work environment; relevant data shows, there are approximately10million workers who are working under the environment with excessive levels of noise in our country at present, and about one million people among them suffer from varying degrees of occupational deafness. Therefore, NIHL has become the second most frequent form of sensorineural hearing loss, after age-related hearing impairment (ARHI). It is well known that working in the hazardous noisy environment for a long time without any protective measures may lead to permanent and irreversible hearing impairment. Accompanied by the process of industrialization, the morbidity of NIHL increases constantly in some developing countries, the number of disputes caused by NIHL ranks only second to that caused by pneumoconiosis, and it has negative influence on social stability. It brings a heavy economic burden and serious health damage for individuals and society as well. NIHL is a disorder that can be prevented, but once developed, it is permanent and irreversible. There is no effective treatment for NIHL at present. Hence, the most important task of Center for Disease Control and Prevention is to decrease the morbidity of NIHL and to prevent it effectively.In human study, it has been found that the occurrence of NIHL is associated with the amount of noise exposure. That is to say, the higher noise level and the longer noise period is, the more serious hearing loss is. Beside noise, there are many other responsible environmental factors involved in NIHL. These include chemicals, like organic solvents and heavy metals, ototoxic substances (such as aminoglycosides and carbon monoxide), heat, vibration, smoking, and medical factors such as increased blood pressure, and cholesterol, all of these factors have their effect on the development of NIHL. Research indicates that individuals show different susceptibility to noise damage even when exposed to identical harmful levels of noise and other similar environmental factors. Not all individuals exposed to a given noise level develop the same degree of hearing loss. Thus, NIHL is a complex disease that results from the interaction of genetic and environmental factors. If we can identify the susceptible genes of NIHL, we can make it possible that the individuals who are predisposed to NIHL can be screened out before exposing to prolonged occupational noise. Thereby, the incidence of NIHL may be reduced effectively. It is of profound significance for protecting the health of workers, raising Labor Productivity and reducing the medical expenses of enterprise.With the application of molecular biological techniques in the NIHL study, several kinds of genetic variants associated with NIHL susceptibility have been found in recent years. These possible susceptibility genes include genes encoding potassium ion channels (KCNQ4and KCNE1), catalase (CAT), protocadherin15(PCDH15), myosin14(MYH14), heat shock protein (HSP70), paraoxonase-2(PON2), glutathione S-transferases (GST) and Superoxide dismutase (SOD) and so on. In this study, we are aimed to investigate the relationship between common polymorphisms of plasma membrane Ca2+-ATPase isoform2(PMCA2) gene, human8-oxoG DNA glycosylasel (hOGG1) gene and the susceptibility to NIHL in a larger Chinese Han population, providing scientific proof and theoretical basis for future association studies on NIHL and other relevant diseases.Objectives:The aim of this case-control study was to test the hypothesis that polymorphisms of the PMCA2and hOGGl gene may be associated with increased risk of developing NIHL in the Chinese population and provide theoretical foundation for screening out the individuals who are susceptibility to NIHL.Materials and Methods:1. Study subjectsA case-control study was conducted in a Chinese Han population. According to GBZ49-2002, the average hearing threshold worse than25dB in high frequency was defined as cases, the average hearing threshold better than or equal to25dB in high frequency was defined as controls. The controls were matched with cases by age, sex, smoking status, drinking status, exposure level, and exposure time.2. DNA extraction and SNP selectionGenomic DNA was isolated from the donated venous blood samples by using Tiangen DNA extraction kit. The PMCA2(also known as ATP2B2) is located on human chromosome3p25.3. The hOGG1is located on human chromosome3p26.2. In this study, we selected representative SNPs of PMCA2and hOGGl from the data for Chinese in the NCBI SNP database (http://www.ncbi.nlm.nih.gov). Selection criteria are as follows:(1) those located in potential functional regions such as the promoter region,5’UTR, exon,3’UTR and so on.(2) Chinese Han population with a minor allele frequency (MAF)>0.05.3. Genotyping of PMCA2and hOGGl polymorphismsThe individual genotypes were determined using a TaqMan MGB probe assay performed on a96-well ABI PRISM7900HT Fast Real-Time polymerase chain reaction (PCR) System from Applied Biosystems Inc.(Foster City, CA, USA). The allelic discrimination was executed with SDS2.4software.4. Statistical analysis Epidata3.0software was used for data entry and all statistical analyses were performed with Statistics Analysis System software (SAS9.1.3). Chi-square (χ2) test was used to analyze the distribution differences of qualitative data and Student’s t-test was used to analyze quantitative data. Unconditional logistic regression analysis was done to obtain crude and adjusted ORs and their95%confidence intervals (CIs). Hardy-Weinberg equilibrium was tested by a goodness-of-fit χ2test. A criterion of P <0.05was chosen to define differences as statistically significant.Results1. General characteristics of the study populationThis study collected1230eligible subjects, including615controls and615cases. There was no significant difference in the distributions of age (P=0.978) and gender (P=0.686), noise exposure time and exposure level (P=0.391,0.807, respectively), smoking and drinking status,(P=0.594,0.780, respectively). However, the average threshold value of NIHL cases was more than two times higher than that of controls (37.2±11.8dB[A] vs14.1±4.1dB [A], P<0.001).2. Hardy-Weinberg equilibriumThe allele frequencies and genotype frequencies of these polymorphisms among the controls and cases were all in agreement with Hardy-Weinberg equilibrium (P>0.05).3. Associations of hOGGl polymorphisms with the susceptibility to NIHLThe selected SNP of hOGGl were analyzed in1230noise-exposed workers (615cases and615controls). The genotype frequencies of hOGG1gene rs1052133locus among cases and controls were statistically significantly difference (P=0.028).The GG genotype was statistically significantly associated with NIHL risk. To eliminate the effects of age, sex, smoking and drinking, we used logistic regression analysis. After adjusted for these confounding factors, the values of OR and95%CI were1.53(1.12-2.11, P=0.008), individuals with the GG genotype had a1.53-fold risk of NIHL compared with individuals carrying CC/CG genotype.4. Associations of PMCA2polymorphisms with the susceptibility to NIHL The selected SNPs of PMCA2were analyzed in1230noise-exposed workers(615cases and615controls). The genotype frequencies of PMCA2gene rs3209637locus among the cases and controls were statistically significantly difference (P=0.015). PMCA2gene rs3209637locus showed a dangerous effect in recessive modelcomparison. After adjusted for age, sex, smoking and drinking, the values of OR and95%CI were1.52(1.14-2.01, P=0.004), individuals with the CC genotype had ahigher risk of NIHL compared with individuals carrying CT/TT genotype.5. Stratification analysis between hOGG1polymorphisms and risk of NIHL Furthermore, we detected the hOGG1SNP versus noise exposure time, noiseexposure level, smoking, drinking and age interactions. Significant differences werefound in the genotype distributions between NIHL cases and controls for the groupsin noise exposure time (15-25years and>25years), exposure level (85-92dB [A]),smoking, drinking and age>45years. The GG genotype might be the risk factor forNIHL.6. Stratification analysis between PMCA2polymorphisms and risk of NIHL Furthermore, we detected the PMCA2SNPs versus noise exposure time, noiseexposure level, smoking, drinking and age interactions. Significant differences werefound in the SNP rs3209637genotype distributions between NIHL cases and controlsfor the groups in noise exposure time (15-25years), exposure level (>92dB [A]),smoking, drinking and age (35-45years). The individuals with CC genotype had ahigher risk of NIHL compared with individuals carrying CT/TT genotype.Conclusions In Chinese Han Population,1. We found that hOGG1gene rs1052133GG genotype might be risk factor forNIHL. And PMCA2gene rs3209637CT/TT genotype might be risk factor for NIHL.2. PMCA2and hOGG1versus noise exposure time, exposure level, smoking anddrinking had interaction effects on NIHL susceptibility. Higher exposure time andexposure level might expand the NIHL risk of individuals with hOGGl susceptibilitySNP and PMCA2susceptibility SNP. 3. In a preliminary conclusion, the genetic variation in the hOGGl gene and PMCA2gene may contribute to the susceptibility of NIHL.