Association Study Of SNPs Within G Protein-Coupled Receptor 65 Gene And Ankylosing Spondylitis In A Chinese Han Population

Objective:Ankylosing Spondylitis is a chronic inflammatory autoimmune disease that can affect a variety of tissues of patients,and lead to spinal mobility limitation and disability.Genetic studies have confirmed that the existence of risk gene overlap between AS and inflammatory bowel disease(IBD).A growing number of studies have showed that G protein-coupled receptor 65 is associated with IBD disease susceptibility.This study aimed to assess the association between two tag single nucleotide polymorphisms(SNPs)(rs68177277 and rs11624293)of G protein coupled-receptor 65(GPR65)gene and the susceptibility and severity of ankylosing spondylitis(AS)in a Chinese Han population.Methods:Using a case-control study design,700 patients with AS diagnosed by doctor with deputy director and above according to the 1984 modified New York criteria,and all of these cases were from outpatient clinics at the First Affiliated Hospital of Anhui Medical University,Hefei,China.A total of 700 participants that were frequency matched age and gender with cases were from Blood stations of Hefei.Two tag SNPs(rs68177277 and rs11624293)were selected from GPR65 gene using Haploview 4.2 software.SNP genotyping for rs68177277 and rs11624293 loci were performed using the SNPscan technique.The distributions of genotype and allele of rs68177277 and rs11624293 polymorphisms were compared between AS cases and healthy controls using?~2-test.Besides,binary logistic regression models were performed to analyze the the distributions of genotype and allele of rs68177277 and rs11624293 loci between AS patients and healthy controls with adjustment of age and gender.Dominant,recessive and over-dominant inheritance models were conducted to analyze the distributions of genotype of rs68177277 and rs11624293 loci between AS patients and healthy controls.Based on the different incidence of patents with AS among gender,stratified analysis was conducted using gender with a stratifying factor.Finally,in AS patients,Kruskal-Wallis H test were performed to analyze the association between genotype distribution and AS phenotypes,including ESR,CRP,BASDAI,BASFI,finger to floor distance,and occiput-wall distance.Additionally,we further analyzed the association between genotype distribution and BASFI and BASDAI scores after stratifying by BASDAI score.Quantitative data were described as mean±standard deviation(SD)if it conforms to normal distribution;if not,the data were described as median and inter-quartile range(IQR).And,qualitative data were described as frequency and percentage.All analyses were performed in SPSS 17.0 software(SPSS,Int.,Chicago,IL,USA),and two side p-value<0.05 was considered as a significant association.Bofferoni correction was performed to correct theα-value of multiple comparision that was set at 0.05/n,where n indicates the number of comparisons.Results:In the genotyping test,40 blood samples were failed and the success rate of genotyping was 97.1%.A total of 673 AS cases and 687 healthy controls were included into this study.The average ages of patients with AS and healthy controls were 28.62±7.76 years and 28.58±9.31 years,respectively;and the sex ratio(M/F)of healthy controls were 548/125 and 560/127,respectively.The positive rate of HLA-B27 of patients with AS was 61.4%.The average of disease course,BASFI and BASDAI was3.3(0.8,8.0)years,0.90(0.00,2.60)cm,2.00(0.60,3.80),respectively.According to the value of BASDAI,23%(152)individuals were identified as patients with high disease activity.The results of Hardy-Weinberg equilibrium(HWE)test indicated that rs68177277 and rs11624293 loci of GPR65 gene in healthy controls were in agreement with HWE(P=0.1822 and P=0.9434,respectively).Genotype distribution and allele frequencies of rs11624293 loci but not rs68177277 loci were significantly different between the patients with AS and healthy controls(P=0.004;P=0.002),and these differences were still significant after Bonferroni correction.Stratifying by gender,the associations between genotype and allele frequencies distribution of rs11624293 loci and AS suscetibility were just found among male patients and male healthy controls(P=0.013;P=0.010),but not observed in female patients and female healthy controls(P=0.188;P=0.062).In Logistic regression models,we observed that the individuals who was carring C/T genotype and C allele of rs11624293 loci had a significant increased risk for developing AS after adjustment for age and gender(OR=1.527,95%CI:1.190-1.958;OR=1.515,95%CI:1.183-1.942,respectively).In dominant and over-dominant inheritance model,genotype of rs11624293 loci was significantly related to AS susceptibility,and the differences were still statistically significant after Bonferroni correction(χ~2=11.169,P=0.001;χ~2=10.793,P=0.001;respectively).Stratifying by gender,we observed that the significant differences of genotype distribution in dominant and over-dominant inheritance model were only found among the patients with AS and healthy controls in males(P=0.004;P=0.003;respectively),and the differences were still statistically significant after Bonferroni correction.In analysis of clinical phenotypes,we did not found that a significant association between genotype of rs11624293 loci and clinical phenotypes of AS patients(P>0.05).Stratifying by gender,this association was stil not significant.Additionally,subgroup analysis was performed using BASDAI scores(BASDAI<4 or BASDAI≥4)as a stratification factor,and the result indicated that the genotype of rs11624293 loci was significantly associated with BASFI scores(P=0.007).ConclusionsThe present study found that rs11624293 polymorphisms of GPR65 gene are associated with the susceptibility of AS in a Chinese Han population.And the statistic significance was only found in males.Besides,the polymorphisms of rs11624293 may affect the severity of patients with AS.