Association Study In Air Pollutants, Genetic Varaiations Of Candidate Genes, And Childhood Asthma

OBJECTIVE:This program is aimed to study the association of childhood asthma in Chinese Beijing children and polymorphisms of asthma candidate gene TRPV1, SOCS3, and STAT6. Effects of allergens, genetic variations, and air pollutants on childhood asthma are to be assessed in this study.METHODS:426 subjects aged 14 and under were recruited in a case-control study.221 asthmatics were confirmed by physician diagnosis. Matched by age and gender,205 non-asthma controls without respiratory diseases and inflammation symptoms were chosen from the same hospital. A child was considered atopic by 1 or more positive antigen-specific IgE to allergens (Dermatophagoides pteronyssinus, D. farinae, cat or dog danders, Alternaria tenuis, cockroach, mixed tree pollen, and mixed grass pollens). Associations of asthma candidate gene polymorphisms and childhood asthma were measured by minor frequency of allele (MAF), genotype analysis, and haplotype analysis. Genotype distribution was tested by Hardy-Weinberg equilibrium, permutation tests, and genotype simulation. Outdoor air pollutant concentrations were calculated by API. Plasma total IgE and concentrations of air pollutants were logarithm transformed to base 10 before analysis. In order to investigate the pattern of linkage disequilibrium (LD) in the single neucleotide polymorphisms (SNP), the pairwise LD coefficient was calculated for each SNP pair by Haploview software. Statistical analyses were done by SAS 9.1 software. T test, anova, chi-square, and non-conditional logistic stepwise analysis (0.1 was set as selection significant level). All comparisons are two-tailed, and p-values less than 0.05 are considered significant. RESULTS1) SNPs at 3'-UTR of TRPV1 gene of Chinese children included rs4790521, rs4790522, rs402369 and ENSSNP11193515. MAF of 2 SNPs (rs4790521 and rs4790522) is higher than 0.05. Only MAF of rs4790521 had been seen significant difference in asthmatics and control subjects (p<0.05).Genetype analysis showed that carriers of recessive homozygote C/C of rs4790521 would have higher risks of asthma in order of 3.3 (3.32:1.53-7.21).Overdominant model and dominant model showed that carriers of heterozygote A/C may have significant lower risks of asthma than homozygote carriers (p<0.05). No significant associations were found in atopy and genotypes of rs4790521 and rs4790522 (p>0.05), so did serum total IgE level.LD (linkage disequilibrium) was found between rs4790521 and rs4790522 (D'=0.959, r2=0.120).3 haplotypes with frequency>=0.20 were built, but they were not significantly associated with childhood asthma (p>0.05).Logistic stepwise analysis showed that after controlling for confounding factors, SNP rs4790521, family history of asthma, atopic status, environmental tobacco smoking exposure, and SO2 (avrg 5 days) were important risks of childhood asthma. When exposures were in the same level to other risks, carriers of ressesive homozygote C/C of SNP rs4790521 may increase asthma risks in order of 2, ETS exposures, outdoor air pollutant exposures, and interactive items of air pollutant and SNPs (rs4790521, rs4790522) were not found significant differences between asthmatics and control subjects (p>0.05). PM10 was not found significantly associated with childhood asthma (p>0.05).2) SNPs of SOCS3 gene at 3'-UTR included rs2280148, rs4969169, and rs4969168. MAF of rs4969168 and rs4969169 were higher than 0.05. Significant difference of MAF of rs4969168 had been found between asthmatic and control subjects (p<0.05). No significant difference had been found in MAF of rs4969169 between cases and controls (p>0.05). Genotype analysis showed that genotype distributrion of rs4969168 was found significant difference between asthmatic and control subjects (Cochran-Mantel-Haenszel chisq, p<0.05). Overdominant model showed that genotype of rs4969169 was found to be significant associated with atopic asthma and atopy (p<0.05). Genotypes of rs4969169 and rs4969168 were not found to be significantly associated with serum total IgE level (p>0.05).Logistic stepwise analysis showed that after controlling for confounding factors, rs4969169, family history of asthma, atopic status, and outdoor SO2 (Avrg 5days) were important risks of childhood asthma (p<0.05). When other exposure were in the same level, carriers of heterozygote T/C of rs4969169 may increase asthma risk in order of 1 (p<0.05). ETS exposure and interactive item of outdoor air pollutant and SNPs (rs4969168, rs4969169) were not found sigficantly associated with childhood asthma (p>0.05).3) SNP association analysis showed that there were 2 blocks of LD in SNPs of TRPV1 and SOCS3 gene. Hapmap C/C were found to be significantly associated with childhood asthma (p<0.05).4) rs71802646 was the only SNP found at exon 1 of STAT6 gene in Chinese children. rs71802646 is a kind of short tandem repeat polymorphism.3 kinds of polymorisms of rs71802646 were found in Chinese children:13 GT repeat (A1),14 GT repeat (A2), and 15GT repeat (A3). Short tandem of GT repeat polymorisms were not found significantly associated with childhood asthma, atopy, and serum total IgE level (p>0.05).5) No registered SNPs of STAT6 gene at 3'-UTR were found in Chinese Beijing children. BlAST results showed that 2 new SNPs were SNPs of Chinese children: C258T (registered as ss185319345) and T710C (registerd as ss185319352). MAF of C258T and T710C were not found significantly associated with childhood asthma (p>0.05).Genotype analysis showed that genotypes of T710C were significantly associated with serum total IgE level (p<0.05), while genotypes of T710C were not significantly associated with childhood asthma and atopy (p>0.05). Genotypes of C258T had not been found significant association with childhood asthma, atopy, and serum total IgE level (p>0.05).6) Association of T710C genotypes with childhood asthma was confounded by family history of asthma, atopic status, and outdoor air pollutants.7) Logistic stepwise analysis showed that after controlling for confounding factors, SNPs of TRPV1 and GATA3, family history of asthma, atopic status, and indoor TVOC exposure level were important risks of childhood asthma (P<0.05).CONCLUSION:TRPV1 and SOCS3 were tested to be new promising candidate genes of childhood asthma. Polymorisms of STAT6 gene at UTR were not associated with childhood asthma. Air pollutants might have trigger effects on childhood asthma, the effects were not confounded by genetic risks and allergens. Asthma risks of Chinese children were tested to be genetic risks (40%), allergen (38%), respiratory inflections (9%), and indoor TVOC level (4%).