Association Study Of Asthma And Polymorphisms In TIM Gene Family And PTGDR Gene In A Chinese Han Population

[Background]T cell immunoglobulin domain and mucin domain protein (TIM) gene and prostaglandin D2 receptor (PTGDR) gene were located in 5q33. 2 and 14q22.1 respectively; both chromosomal regions were found to be linked with asthma in previous studies. Functional studies of Tim-1, Tim-3 and Tim-4 (mouse ortholog of human TIM gene family members TIM-1, TIM-3 and TIM-4) suggested that these genes could regulate the proliferation and differentiation of CD4⁺ T cells, which were the main effector cells in the airway inflammations of asthma. And several polymorphisms in Tim-1 and Tim-3 were associated with the development of T_H2-biased immune responses and allergen-induced airway hyper reactivity (AHR). Ptgdr gene has been shown to be necessary for the development of asthma in an asthmatic mouse model, in which airway inflammatory response and AHR were highly inhibited when Ptgdr gene was knocked out. These studies suggested that TIM gene family members and PTGDR gene could also act as susceptibility genes in human asthma genesis. Some polymorphisms in these genes have already been shown to be associated with asthma susceptibility in different populations, but the association between polymorphisms of these genes and asthma in the Chinese Han population hasn't been well studied until now.[Objective]Using case-control study to determine the association between asthma and polymorphisms in TIM-1, TIMS, TIM-4 and PTGDR genes in a Chinese Han population, including two insertion/deletion polymorphisms in TIM-1 exon 4 (5383₅397ins/del and 5509₅511delCAA),one SNP IVS8+9G/A in TIM-1 intron 8, two SNPs T-882C and T-574G in TIM-3 promoter region, one SNP G-31A in TIM-4 promoter region and three SNPs T-549C, C-441T and T-197C in PTGDR promoter region.[Methods]1. Collect blood samples from asthma patients and healthy controls in the Chinese Han population and then extract DNA from the white blood cells in peripheral blood.2. Genotyping: (1) Two insertion/deletion polymorphisms in TIM-1 exon 4 (5383₅397ins/del and 5509₅511delCAA) and a SNP in intron 8 (IVS8+9G/A) were genotyped using PCR-PAGE and PCR-RFLP methods in 352 asthma patients and 309 healthy controls. (2)Two SNPs T-882C and T-574G in TIM-3 promoter region were genotyped using PCR-RFLP method in 449 asthma patients and 386 healthy controls. (3)A SNP G-31A in TIM-4 promoter region was genotyped using PCR-RFLP method in 264 asthma patients and 216 healthy controls. (4) Three SNPs T-549C, C-441T and T-197C in PTGDR promoter region were genotyped in 336 asthma patients and 264 healthy controls. SNPs T-549C and C-441T were genotyped using Tetra-primer ARMS-PCR method while SNP T-197C was genotyped using PCR-RFLP method.3. Evaluate each polymorphism for Hardy - Weinberg equilibrium (HWE) using chi-square test and make sure all the polymorphisms were at Hardy-Weinberg equilibrium in both asthma patients and healthy controls used in the study.4. Compare the distribution of different genotypes and alleles of every polymorphism in the two groups using chi-square test to determine whether the polymorphism was associated with asthma.5. Estimate linkage disequilibrium between different polymorphisms in the same gene (TIM-1, TIM-3 and PTGDR, respectively). Construct haplotypes and analyze whether the haplotype distribution in the two groups were statistically different.[Results]1.5383₅397ins/del, 5509₅511delCAA and IVS8+9G/A in TIM-1 gene were genetically polymorphic in Chinese Han population and were in Hardy-Weinberg equilibrium in both groups. 5383₅397ins/del and 5509₅511delCAA were in strong linkage disequilibrium. Neither genotype, allele or haplotype distribution was statistically different between asthma patients and healthy controls (all P>0.05).2. T-882C and T-574G in TIM-3 gene were genetically polymorphic in Chinese Han population and were in Hardy-Weinberg equilibrium in both groups. These two SNPs were in complete linkage disequilibrium. Both the genotype and allele distribution of the two SNPs were statistically different between asthma patients and healthy controls (P=0.045, P=0.047). The haplotype distribution between two groups was also statistically different (P=0.047).3. G-31A in TIM-4 gene was genetically polymorphic in Chinese Han population and was in Hardy-Weinberg equilibrium in both groups. Neither genotype nor allele distribution was statistically different between asthma patients and healthy controls (all P>0.05).4. T-549C, C-441T and T-197C in PTGDR promoter region were genetically polymorphic in Chinese Han population and were in Hardy-Weinberg equilibrium in both groups. T-549C and C-441T were in strong linkage disequilibrium. Neither genotype, allele or haplotype distribution of the three SNPs was statistically different between asthma patients and healthy controls (all P>0. 05).[Conclusions]1.None of 5383₅397ins/del, 5509₅511delCAA and IVS8+9G/A in TIM-1 gene was associated with asthma in Chinese Han population. But the probability that other polymorphisms in TIM-1 might be associated with asthma couldn't be excluded.2.T-882C and T-574G in TIM-3 gene were associated with asthma in ChineseHan population.3. G-31A in TIM-4 gene was not associated with asthma in Chinese Han population. But the probability that other polymorphisms in TIM-4 might be associated with asthma couldn't be excluded.4. None of T-549C, C-441T and T-197C-in PTGDR promoter region was associated with asthma in Chinese Han population. But the probability that other polymorphisms in PTGDR might be associated with asthma couldn't be excluded.