Assessing causal relationships between oral microbiota and asthma: evidence from two-sample mendelian randomization analysis

Accumulating evidence indicates that alterations in the composition of the oral microbiota are associated with asthma. However, it remains uncertain whether these associations reflect causal relationships. The study aimed to investigate the causal relationship between oral microbiota and asthma at the genetic level. A two-sample Mendelian randomization (MR) analysis was conducted using genome-wide association studies (GWAS) data on the oral microbiota and asthma within the East Asian population. Inverse-variance weighted (IVW), MR-Egger, weighted median, and weighted mode methods were utilized to examine the potential causal relationship between oral microbiota and asthma. Additionally, pleiotropy and heterogeneity tests were conducted to assess the robustness of the findings. Among the 3,117 bacterial taxa analyzed, nine genera, comprising 18 oral microbiota, exhibited causal effects on asthma. Twelve oral microbiota, including Streptococcus_umgs_1936, Porphyromonas_mgs_3421, and Campylobacter_A_umgs_3382, demonstrated positive causal associations with asthma. Conversely, six oral microbiota, including Parvimonas_umgs_2046, and Parvimonas_umgs_3325, were negatively related to asthma. Enrichment was observed in three genera: Parvimonas, Streptococcus, and TM7x. No pleiotropy or heterogeneity was detected among the instrumental variables (IVs) throughout the study. The findings suggest a causal relationship between oral microbiota and asthma. These results provide novel insights into the mechanisms underlying asthma that are mediated by the oral microbiota.