Association Study Of Asthma And Polymorphisms In STAT4 Gene, T-bet Gene And IL-2 Gene In A Chinese Han Population

[Background]Asthma is a chronic inflammatory disorder which is induced by IgE,involving several inflammatory cells such as eosinophile granulocytes,mast cells and T cells.It is a polygenic disease which is influenced by both hereditary and environmental factors,mainly characterized by airway responsiveness,variable airflow limitations, airway inflammation and airway reconstruction.Recurrent cough,wheezing and dyspnea can be observed on asthma patients who can usually be self-cured or be treated by drug.Differentiation of Th1 and Th2 cells is considered to be related to asthma development.STAT4(signal transducer and activator of transcription 4)---T-bet (T-box 21)and STAT6(signal transducer and activator of transcription 6)---GATA3 are the two major pathways for the differentiation.The differentiation balance can be disturbed if either goes abnormally.It is already known that Th2 cells are associated with asthma.In 2005,Park et al reported that a single nucleotide polymorphism(SNP) in STAT4 gene is significantly related to asthma,and it is one of the genetic causes to specific IgE.Susetta et al discovered that mice lacking T-bet gene,encoding an important transcription factor in Th1 differentiation,would develop spontaneous airway changes consistent with human asthma.Furthermore,in 2006,T-bet gene was reported to be associated with asthma and airway responsiveness in Americans. Japanese also observed in 2005,that a SNP in T-bet gene was involved in aspirin-induced asthma.IL-2 gene,which is located on 4q27,involving 4 exons,was first reported to be asthma candidate gene by Ulla Christensen in 2006.What is more, two SNPs on IL-2 gene were discovered to participate in IgE induced allergic diseases such as asthma.STAT4 gene,T-bet gene and IL-2 gene have already been shown to be associated with asthma and airway responsiveness in different populations,however, no report has shown the relationship between such candidate genes and asthma in Chinese Han population till now.[Objective]To examine the association between asthma and polymorphisms in STAT4,T-bet and IL-2 genes in a Chinese Han population,including one SNP—608 A＞G in STAT4 gene promoter region,one SNP--1993 T＞C in T-bet gene and one SNP—92T＞G in promoter region of IL-2 gene.[Methods]1.Blood samples were collected from asthma patients and normal controls in Chinese Han population and DNA was extracted from the white blood cells in peripheral blood.2.Genotyping:1)SNP in STAT4 gene was genotyped using PCR-RFLP (Restriction Fragment Length Polymorphism)in 220 asthma patients and 223 normal controls.2)Polymorphism in T-bet gene was genotyped by Tetra-primer ARMS-PCR method in 292 asthma patients and 272 normal controls while SNP in IL-2 gene were genotyped in 262 asthma patients and 248 controls with the same method.3.Hardy-Weinberg equilibrium(HWE)was tested using chi-square test to make sure all the polymorphisms were at Hardy-Weinberg equilibrium in both asthma patients and normal controls used in the study.4.Distribution of different genotypes and alleles of each polymorphism in the two groups was compared using chi-square test to determine whether the polymorphisms were associated with asthma.[Results]1.In the genotype analysis for -608 A＞G site in STAT4 gene,the frequencies of genotypes AA,AG and GG in asthma patients were 0.536,0.377 and 0.086,while 0.515,0.399 and 0.086 in normal controls,respectively.The frequencies ratios for allele A and G in asthma patients were 0.725 and 0.275,while 0.715 and 0.285 in normal controls,respectively.No significant difference was observed(P =0.089).2.For the SNP site -1993 T＞C in T-bet gene,genotype frequencies for TT, TC and CC were 0.630,0.315 and 0.055 in asthma patients,while 0.632,0.325 and 0.044 in normal controls,respectively.Frequencies of allele T and C were 0.788 and 0.212 in asthma patients,while 0.794 and 0.206 in normal controls,respectively.No significant difference was observed(P =0.837).3.For--92 T＞G site in IL-2 gene,genotype frequencies of TT,TG and GG were 0.344,0.511 and 0.145 in asthma patients,while 0.331,0.532 and 0.137 in normal controls,respectively.Allele frequencies for T and G displayed 0.599 and 0.401 in asthma patients,while 0.597 and 0.403 in normal controls,respectively.No significant difference was observed(P =0.894).[Conclusions]Polymorphism--608 A＞G in STAT4 gene,--1993 T＞C in T-bet gene and--92 T>G in IL-2 gene showed no association with asthma in a Chinese Han population, but probability that other polymorphisms in these three genes might be associated with asthma could not be excluded.