2.1 Study design
We systematically evaluated the causal association between gut microbiota and the risk of MN through a two-sample MR analysis. Figure 1 showed an overview of this study design, which complied with three key assumptions: (1) the instrumental variables were associated with exposures; (2) the instrumental variables were not related to the confounders; (3) the instrumental variables influenced the outcome only through exposures [11]. The second and third assumptions were performed to ensure the independence of this study, which could be detected by various statistical methods.