Vitamin D And Genetic Polymorphisms In Its Metabolic Pathway In Association With The Risk And Prognosis Of Tuberculosis

Background and Objective: Tuberculosis is a chronic infectious disease caused byMycobacterium tuberculosis infection. Different clinical manifestations ofMycobacterium tuberculosis infection reflect a balance between the pathogenicity ofthe Mycobacterium tuberculosis and host immune response. The compromisedimmunity can reduce the ability of clearing the pathogen. Before the invention ofeffective anti-tuberculosis drugs, people had found that sunlight had an effect ontreating tuberculosis. Scientists gradually realized a molecular pathway from thesunlight to vitamin D metabolism and then to the anti-tuberculosis immune response.Vitamin D could regulate the calcium metabolism and bone mineral density. Inaddition, it is also an important immune regulatory factor. Vitamin D metabolism is acomplex process, which requires the participation of multiple genes. Geneticpolymorphisms of these genes may lead to individual different genetic susceptibilityto tuberculosis. In recent years, great progress has been made on studies betweenvitamin D receptor gene polymorphism and genetic susceptibility of tuberculosis.However, few studies have addressed other genes, such as GC, RXRA and RXRB, onthe vitamin D metabolic pathway. Gene-gene and gene-environment interactions wererarely studied. The role of vitamin D intake and genetic polymorphism of itsmetabolic pathway genes on the prognosis of tuberculosis has not been reported inChina yet. Based on the above background, we selected a series of important genes involved in vitamin D metabolic pathway and performed a large sample size basedcase-control study together with a prospective cohort study, by using the fieldinvestigation methods and molecular epidemiological techniques, with aims (1) toexplore the relationships between VDR, GC, RXRA and RXRB gene polymorphisms,to detect serum vitamin D level and genetic susceptibility to tuberculosis, and toprovide scientific evidences for identifying high risk individuals and controllingtuberculosis;(2) to explore the effect of vitamin D metabolism pathway geneticpolymorphisms and vitamin D level on the prognosis of patients with tuberculosis,and to provide a theoretical basis and population research data for furtherindividualized vitamin D based anti-tuberculosis treatment.Methods: This study used a case-control study design and a prospective cohort studydesign. A total of1584patients with active pulmonary tuberculosis (including sputumsmear-positive and sputum smear-negative cases) were recruited from Taixing,Zhenjiang, Wujin, Zhangjiagang and Nanjing of Jiangsu from2008to2012. We alsorecruited1566controls from a pool of individuals who participated in the localcommunity-based health examination program in Taixing, Zhenjiang, Nanjing, andWujin. Controls were frequency-matched to the cases by sex and age. They had nohistory of tuberculosis and malignancy. After getting written informed consents fromall the participants, questionnaires were used to collect epidemiological data, andvenous blood samples were collected for vitamin D measurement and genotyping. Allpatients were followed up during the whole episode of standard anti-tuberculosistreatment (usually for6to8months) or to the end point of the outcome. Serum25-hydroxyvitamin D concentration was measured by Aidisi TM25hydroxyvitaminD kit (OCTEIA25-OH-VD). We selected four key genes in vitamin D metabolicpathway, which included VDR, GC, RXRA and RXRB. SNPs in these genes wereselected for genotyping by using the following criteria: the reported potentialfunctional polymorphic loci; potential functional polymorphic loci in dbSNP database(exon region missense mutations,5’UTR,5’near gene,3’UTR and so on),heterogeneity≥0.10, and the MAF of Chinese Han population≥0.05. Finally,14SNPs were chosen, including seven SNPs from VDR gene: rs2228570, rs7975232, rs757343, rs11568820, rs731236, rs1544410and rs739837; four SNPs form GC gene:rs16847024, rs3733359, rs4588and rs7041; two SNPs form RXRA gene: rs62576288and rs117846790; and one SNP form RXRB gene: rs2076310. Genotyping wasperformed by using TaqMan allelic discrimination technology on the ABI7900Real-Time PCR System (Applied Biosystems, Foster City, CA). Data were doubleentered with EpiData3.1(Denmark) and all analyses were performed using the SPSSsoftware (SPSS Inc., USA). We used the chi-square test or t test to compare thedistribution of demographic characteristics, smoking, alcohol consumption and otherfactors between cases and controls. We also compared the difference of alleles andgenotypes between cases and controls. Univariate and multivariate logistic regressionanalysis were used to calculate odds ratio (OR) and95%confidence interval (CI).Results:(1) Serum25-hydroxyvitamin D concentration was2.94±23.35nmol/L incases, which was lower than that among controls (41.79±16.57nmol/L). Thedifference between cases and controls was statistically significant (t=6.768, P<0.001).Univariate analysis found that variant genotypes of rs739837, rs757343andrs7975232in VDR gene were significantly associated with the reduced risk oftuberculosis. Compared with GG genotype of rs739837, the individuals carryinghomozygous TT genotype had a26%decreased risk (adjusted OR=0.74,95%CI:0.55-0.99).(2) Follow-up analysis revealed that serum25-hydroxyvitamin Dconcentration was associated with treatment outcome of patients (P=0.043). Singlelocus analysis found that variant genotypes of rs2076310in RXRB gene weresignificantly associated with the prognosis with OR (95%CI) of2.27(1.09-4.73).Conclusions: Serum25-hydroxyvitamin D concentration and genetic polymorphismsof vitamin D metabolic pathway genes are associated with the risk of tuberculosis aswell as the prognosis of disease. Our study not only provided a scientific basis for theetiological prevention of tuberculosis and screening for high-risk population, but alsoprovided evidences individualized therapy for tuberculosis in the future.