Prospects of Mendelian randomization in hepatology: a comprehensive literature review with practice guidance

Mendelian randomization (MR), a powerful statistical tool for causal inference, has been widely applied in various fields of medical research, even extending to economics and psychology. In hepatology, MR has been utilized to identify risk factors and potential therapeutic targets for liver diseases, including metabolic dysfunction-associated steatotic liver disease, cholestatic and autoimmune liver diseases, and hepatobiliary cancer. MR can provide evidence of causation via associations between genetic variants, modifiable exposures and liver disease occurrence or outcomes, using large existing datasets. However, results from MR studies are sometimes scattered, biologically not plausible or even controversial between analyses, potentially reflecting a trend of inappropriate application of this method (e.g., inappropriate selection of genetic instruments, insufficient assessment of horizontal pleiotropy, compromised statistical power, and neglected genetic diversity among different populations), and thus hinder the translation of MR findings from bench to bedside. Assessing these critical issues and pinpointing <i>bona fide</i> evidence are essential but quite challenging for clinicians. In this review, we aim to introduce the MR method to hepatologists and provide a comprehensive overview of the current MR findings that are relevant for hepatologists. Furthermore, we will discuss how to evaluate the quality of MR publications, interpret MR findings, and illustrate good practice of using MR studies in hepatology.