Among previous genetic studies for asthma, inconsistent findings were often reported. We used a new approach to examine an integrated effect of haplotype blocks, newly termed ‘haplotype cluster’ over two different types of receptors which share common intracellular pathways on airway hyperresponsiveness (AHR). We recruited 165 young atopic adults without respiratory symptoms and measured airway responsiveness to methacholine and classified them into two groups, those with AHR (PC20 <8.0 mg/ml) and without AHR. In addition, we identified haplotype blocks or cluster tagging single nucleotide polymorphisms (SNPs) through two genes, epidermal growth factor receptor (EGFR) and protease activated receptor (PAR)-1, in all subjects, and compared the frequencies of haplotype block or cluster between subject groups. Significant differences in the frequencies were observed in the haplotype blocks within the EGFR gene (rs4947972, rs12718945 and rs2072454; rs4947972, rs12718945 and rs2227983; and rs4947972, rs12718945 and rs2293347) and the PAR-1 gene (rs37243 and rs253072). An integrated effect was also observed in one haplotype cluster consisting of both regions of the EGFR gene (rs2293347) and the PAR-1 gene (rs253072) (P=0.0426). Our results suggest the possibility that the integrated effect of functionally-related EGFR and PAR-1 genes (haplotype cluster) is associated with susceptibility to AHR.

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