Causal relationship between Faecalibacterium abundance and risk of Faecalibacterium-related diseases: a two-sample bi-directional Mendelian randomisation study.

Faecalibacterium is an essential probiotic in the human gut; changes in its abundance are associated with various disease states in many studies. However, the causal nature of such associations remains obscure. Therefore, we aimed to thoroughly investigate the causal relationships between Faecalibacterium and its related diseases. A two-sample bi-directional Mendelian randomisation analysis was conducted using publicly available genome-wide association studies summary statistics for Faecalibacterium and its related diseases. We found that Faecalibacterium was negatively correlated with the risk of ankylosing spondylitis (odds ratio [OR] = 0.526, 95% confidence interval [CI]:0.304-0.908, P = 0.021), atopic dermatitis (OR = 0.484, 95%CI: 0.261-0.898, P = 0.021) and heart failure (OR = 0.657, 95%CI: 0.467-0.924, P = 0.016), while Faecalibacterium was positively associated with autism spectrum disorder risk (OR = 2.529, 95%CI: 1.012-6.319, P = 0.047). The results of reverse Mendelian randomisation analysis showed that acute sinusitis (OR = 0.902, 95%CI: 0.839-0.970, P = 0.005) and Alzheimer's disease (OR = 0.976, 95%CI: 0.958-0.993, P = 0.008) was causally associated with lower Faecalibacterium abundance, respectively, while cirrhosis (OR = 1.154, 95%CI: 1.028-1.295, P = 0.015) and multiple myeloma (OR = 2.619 × 1012, 95%CI: 2.492-2.754 × 1024, P = 0.043) was causally associated with higher Faecalibacterium abundance. Our findings firstly showed that changes in Faecalibacterium abundance may contribute to the risk of ankylosing spondylitis, atopic dermatitis, heart failure and autism spectrum disorders, and potentially as a result of acute sinusitis, Alzheimer's disease, cirrhosis and multiple myeloma.