Aim
Interleukin (IL) 1 receptor-like 1, encoded by the IL1RL1 gene, is a receptor for IL-33. In European birth cohorts, IL1RL1 rs102082293, rs10204137 (rs4988955), rs13424006 and rs13431828 (rs13048661) variations were associated with asthma at school age. In a Dutch multi-centre study, IL1RL1 rs1921622 variation was associated with severe bronchiolitis. We evaluated the associations of these five IL1RL1 variations with asthma and lung function at school age after hospitalisation for bronchiolitis in infancy.

Methods
Follow-up data, including impulse oscillometry at age 5–7 and flow-volume spirometry at age 11–13 years, and the IL1RL1 genotype data were available for 141 children followed until 5–7 and for 125 children followed until 11–13 age years after bronchiolitis in infancy. The IL1RL1 rs10204137 and rs4988955, and the IL1RL1 rs13048661 and rs13431828, are 100% co-segregating in the Finnish population.

Results
The variant IL1RL1 rs13048661/13431828 genotype was constantly associated with increased asthma risk by various definitions at 5–7 and 11–13 years of ages. The result was confirmed with analyses adjusted for current confounders and early-life environment-related factors. Statistical significances were lost, when maternal asthma and atopic dermatitis in infancy were included in the model.

Conclusion
IL1RL1 rs13048661/13431828 variation was associated with post-bronchiolitis asthma outcomes at school age.