Two-sample Mendelian randomization analysis of the causal relationship between blood eosinophils and allergic rhinitis.

Objectives: Previous studies have revealed a correlation between eosinophils and allergic rhinitis, but the causal relationship has not been fully confirmed. This study aims to evaluate the causal link between blood eosinophils and allergic rhinitis using the Mendelian randomization (MR) method.

Methods: Summary data from the Genome-Wide Association Study Catalog (GWAS) for eosinophil count (exposure variable) and allergic rhinitis (outcome variable) were collected. GWAS data for the exposure variable were obtained from the IEU Open GWAS Project developed by the Integrative Epidemiology Unit at the University of Bristol, while data for the outcome variable were sourced from the FinnGen Biobank (Finland) database. The causal relationship between eosinophils and allergic rhinitis was analyzed using the two-sample MR method with inverse variance weighted (IVW) analysis. Sensitivity analyses were conducted using the weighted median method, MR-Egger regression, leave-one-out analysis, and funnel plots.

Results: An increase in blood eosinophil count showed a potential causal relationship with an increased risk of allergic rhinitis (OR=1.187, 95% CI 1.051 to 1.341, P=0.006). This finding was consistent across the weighted median method and MR-Egger regression. Leave-one-out analysis indicated that no single nucleotide polymorphism significantly influenced the causal inference.

Conclusions: There is a causal association between increased eosinophil count and a higher risk or worsening of allergic rhinitis.