Confirmation of association of IL-15 with pediatric asthma and comparison of different controls

Background: Interleukin (IL)-15 is an important mediator in chronic inflammatory diseases. Recently, we have described the association of IL-15 haplotypes with bronchial asthma. Asthma genetics is highly complex - about every second candidate gene is not confirmed in consecutive studies. We were interested in whether association of asthma with IL-15 holds in a second population. Furthermore, we sought to investigate the effect of different controls. Methods: Five IL-15 polymorphisms were genotyped on the German Multicenter Allergy Study (MAS) cohort consisting of 886 children who were followed up from birth to 10 years of age. At 10 years of age, 96 were found to be asthmatic. MAS children who never had any wheezing symptoms (n = 576), who were never diagnosed with asthma (n = 790) and 129 super controls who had never had any atopic disorder were used as controls. Finally, 270 randomly chosen adults served as controls. Results: Association was confirmed with single polymorphism and haplotypes. The super controls showed the highest difference to the asthmatics regarding haplotype frequencies. However, the effect escaped statistical significance, most likely because of the small sample size. Conclusion: Association of IL-15 with asthma was confirmed. Although super controls might be the most suitable, more numbers are needed. This might hamper the value of these controls especially when investigating common diseases.