AUTHOR=Xu Qian , Ni Jing-Jing , Han Bai-Xue , Yan Shan-Shan , Wei Xin-Tong , Feng Gui-Juan , Zhang Hong , Zhang Lei , Li Bin , Pei Yu-Fang TITLE=Causal Relationship Between Gut Microbiota and Autoimmune Diseases: A Two-Sample Mendelian Randomization Study JOURNAL=Frontiers in Immunology VOLUME=12 YEAR=2022 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2021.746998 DOI=10.3389/fimmu.2021.746998 ISSN=1664-3224 ABSTRACT=Background

Growing evidence has shown that alterations in gut microbiota composition are associated with multiple autoimmune diseases (ADs). However, it is unclear whether these associations reflect a causal relationship.

Objective

To reveal the causal association between gut microbiota and AD, we conducted a two-sample Mendelian randomization (MR) analysis.

Materials and Methods

We assessed genome-wide association study (GWAS) summary statistics for gut microbiota and six common ADs, namely, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, type 1 diabetes (T1D), and celiac disease (CeD), from published GWASs. Two-sample MR analyses were first performed to identify causal bacterial taxa for ADs in discovery samples. Significant bacterial taxa were further replicated in independent replication outcome samples. A series of sensitivity analyses was performed to validate the robustness of the results. Finally, a reverse MR analysis was performed to evaluate the possibility of reverse causation.

Results

Combining the results from the discovery and replication stages, we identified one causal bacterial genus, Bifidobacterium. A higher relative abundance of the Bifidobacterium genus was associated with a higher risk of T1D [odds ratio (OR): 1.605; 95% CI, 1.339–1.922; PFDR = 4.19 × 10−7] and CeD (OR: 1.401; 95% CI, 1.139–1.722; PFDR = 2.03 × 10−3), respectively. Further sensitivity analyses validated the robustness of the above associations. The results of reverse MR analysis showed no evidence of reverse causality from T1D and CeD to the Bifidobacterium genus.

Conclusion

This study implied a causal relationship between the Bifidobacterium genus and T1D and CeD, thus providing novel insights into the gut microbiota-mediated development mechanism of ADs.