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


Toshio Tanaka, Department III of Internal Medicine, Osaka University Medical School, 2-2 Yamada-oka, Suita City, Osaka 565-0871, Japan. E-mail:


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.