The causality between C-reactive protein and asthma: a two-sample Mendelian randomization analysis.

Purpose This study sought to investigate the causal effects of circulating C-reactive protein (CRP) level on risk of asthma and its subtypes by two-sample Mendelian randomization (MR) analysis. Methods We utilized single nucleotide polymorphisms (SNPs) associated with both CRP and outcomes of asthma, allergic asthma, and obesity-related asthma as genetic variables via a genome-wide summary association study (GWAS). MR analysis mainly based on the inverse variance weighted (IVW) method was performed to infer the causal relationship between exposure and outcomes. Cochran's Q test and MR-Egger regression analysis were performed to determine respectively the heterogeneity and pleiotropy among instrumental variables (IVs), and leave-one-out analysis was conducted to determine the stability of the MR results. Results In our study, 42 SNPs were identified as IVs for MR analyses. According to the primary inference results by IVW methods, circulating CRP was demonstrated to be significantly associated with risk of asthma [odds ratio (OR): 1.046; 95% confidence interval (95% CI): 1.004–1.090; P  = .030] and obesity-related asthma (OR: 1.072; 95% CI: 1.009–1.138; P  = 0.025), whereas no distinct causality with allergic asthma was found (OR: 1.051; 95% CI: 0.994–1.112; P  = .081). Sensitivity analyses indicated that there was no horizontal pleiotropy among IVs, and the MR results were proved to be robust by leave-one-out sensitivity analysis, despite the presence of heterogeneity. Conclusion The present study suggested that higher CRP might genetically predict an increased risk of developing asthma and obesity-related asthma, without causality with allergic asthma. Key message What is already known on this topic C-reactive protein (CRP) plays a critical role in asthma development and is usually elevated in asthmatic patients. However, the causal association between CRP and asthma remains unknown. What this study adds This Mendelian randomization study demonstrated that circulating CRP causally increased the risk of asthma, especially obesity-related asthma. How this study might affect research, practice, or policy The findings of our study carry the implication for clinicians that controlling circulating CRP levels might be a promising strategy for reducing the risk of asthma and obesity-related asthma. [ABSTRACT FROM AUTHOR]