Causal association between systemic lupus erythematosus and primary biliary cholangitis: A bidirectional Mendelian...

An association has been observed between systemic lupus erythematosus (SLE) and primary biliary cholangitis (PBC) in observational studies, however, the exact causal link remains unclear. We aim to evaluate the causal relationships between SLE and PBC through bidirectional Mendelian randomization (MR). Single-nucleotide polymorphisms (SNPs) were selected as instrumental variables from publicly accessible genome-wide association studies (GWAS) in European populations. The PBC and SLE GWAS data were obtained from the MRC IEU Open GWAS database, consisting of 24,510 and 14,267 samples, respectively. After a series of quality control and outlier removal, inverse variance weighted was used as the primary approach to evaluate the causal association between SLE and PBC. The horizontal pleiotropy and heterogeneity were examined by the MR-Egger intercept test and Cochran Q value, respectively. Seven SNPs were included to examine the causal effect of SLE on PBC. Genetically predicted SLE may increase the risk of PBC development, with an odds ratio (OR) of 1.324 (95% confidence interval [CI] 1.220 ∼ 1.437, P ˂ .001). Twenty SNPs were included to explore the causal effect of PBC on SLE. Genetically predicted PBC may increase the risk of SLE development, with an OR of 1.414 (95% CI 1.323 ∼ 1.511, P ˂ .001). Horizontal pleiotropy and heterogeneity were absent (P > .05) among SNPs. The robustness of our results was further enhanced by using the leave-one-out method. Our research has provided new insights into SLE and PBC, indicating bidirectional causal associations between the 2 diseases. These findings offer valuable contributions to future clinical studies.