Background
Inflammatory bowel disease (IBD) was reported to be associated with hepatobiliary disease. Previous observational and Mendelian randomization (MR) studies suggested a causal association between IBD and primary sclerosing cholangitis (PSC). However, it is unclear whether IBD has causal association with primary biliary cholangitis (PBC): another autoimmune liver disease.
Methods
We obtained genome-wide association study (GWAS) statistics from published GWASs for PBC, UC and CD. We screened qualified instrumental variables (IVs) based on the three major assumptions of MR. To determine the causal relationship between UC or CD and PBC, two-sample MR analyses were performed using inverse variance weighted (IVW), MR-Egger, and weighted median (WM) methods, and sensitivity analyses were conducted to validate the robustness of the results. We also conducted reverse MR analysis to reveal the causal association between PBC and UC or CD.
Results
UC were associated with a higher risk of PBC (OR = 1.35, 95% CI: 1.05–1.73, P = 0.02) in IVW method. And CD was associated with an increased risk of PBC (OR = 1.18, 95% CI: 1.03–1.36, P = 0.02) in IVW method. The weighted median and MR-Egger regression of both diseases showed a consistent direction but not statistically significant. Results of reverse MR analysis did not suggest genetic susceptibility to psoriasis was associated with increased risk of UC (OR = 1.05, 95% CI: 0.95–1.17, P = 0.34) or CD (OR = 1.1, 95% CI: 0.99–1.20, P = 0.06).
Conclusion
The present study revealed that IBD subtypes could increase the incidence of PBC, but in turn PBC did not increase the incidence of IBD subtypes. Understanding that IBD and PBC constitute mutual risk factors can help with clinical management of both diseases.