Association between interleukin-18 gene polymorphism 105A/C and asthma

Background IL-18 has been shown to exert anti-allergic or allergy-promoting activities, but the existence of genetic polymorphisms in the coding regions of IL-18 gene has not been demonstrated. Objective The aim of this study was to investigate whether polymorphism is present in the coding regions of the IL-18 gene and, if so, to further analyse the association between polymorphism and asthma in a case-control study. Methods We screened the coding regions of the IL-18 gene for polymorphisms by using PCRsingle-stranded conformation polymorphism and direct sequencing of PCR products, followed by analysis of the association between polymorphism and asthma. Results We identified one polymorphism (105A/C) in the coding regions. The frequency of the 105A allele was significantly higher in asthmatic patients than in controls (P < 0.01; odds ratio (OR) = 1.83 (1.37-2.26)). Significant linkage disequilibrium was observed between the 105A/C and -137G/C polymorphisms in the 5' flanking region of the IL-18 gene (D = 0.58, P < 0.0001). However, in asthmatic patients the 105A allele was not associated with either total serum IgE or IL-18 levels. Conclusion The 105A/C polymorphism of the IL-18 gene may be associated with the pathogenesis of asthma.