Exploring causality in the association between gut microbiota and irritable bowel syndrome risk: a large Mendelian randomization study

In the past, some observational studies have highlighted the correlation between gut microbiota and irritable bowel syndrome (IBS). However, it is still unknown if the composition of gut microbiota shows a causal effect on the risk of IBS. To conduct Mendelian randomization (MR) analysis of the samples to study the probable causal relationship between the gut microbiota, their taxonomic groups, and the risk of IBS. In this study, the summarized data regarding 211 gut microbiota and their IBS genome-wide association studies (GWAS) were collected from public databases. The causal estimates were determined using five MR techniques, where Inverse Variance Weighted (IVW) regression was employed as the major MR technique. Herein, MR-PRESSO and MR-Egger intercept tests were conducted to prevent horizontal pleiotropy. Cochran's test was used to evaluate heterogeneity using the IVW and MR-Egger techniques. IVW results showed that gut microbes, belonging to Class ( = 0.04; OR = 1.45), Family XIII ( = 0.03; OR = 1.34), Family ( = 0.003; OR =1.24), and UCG004 ( = 0.049; OR = 1.19) increased the risk of IBS, while ( = 0.03; OR = 0.83, 95% CI: 0.69-0.98) and ( = 0.02; OR = 0.86, 95% CI: 0.76-0.98) decreased the risk of IBS. This study presented novel insights that highlighted the causal relationship between gut microbiota and IBS, and offered new treatment strategies for preventing or treating IBS.