Cross‐Phenotype Genome‐Wide Association Study on the Shared Genetic Susceptibility to Systemic Sclerosis and Primary Biliary Cholangitis

Objective An increased risk of primary biliary cholangitis (PBC) has been reported in patients with systemic sclerosis (SSc). Our study aims to investigate the shared genetic susceptibility between the two disorders and to define candidate causal genes using cross‐phenotype genome‐wide association study (GWAS) meta‐analysis. Methods We performed cross‐phenotype GWAS meta‐analysis and Bayesian colocalization analysis for patients with SSc and patients with PBC. We performed both genome‐wide and locus‐based analysis, including tissue and pathway enrichment analyses, fine‐mapping, Bayesian colocalization analyses with expression quantitative trait loci and protein quantitative trait loci (pQTL) datasets, and phenome‐wide association studies. Finally, we used an integrative approach to prioritize candidate causal genes from the novel loci. Results We detected a strong genetic correlation between SSc and PBC (global genetic correlation = 0.84, P = 1.7 × 10 −6 ). In the cross‐phenotype GWAS meta‐analysis, we identified 44 nonhuman leukocyte antigens loci that reached genome‐wide significance ( P < 5 × 10 −8 ). Evidence of shared causal variants between patients with SSc and patients with PBC was found for nine loci, five of which were novel. Integrating multiple sources of evidence, we prioritized CD40 , ERAP1 , PLD4 , SPPL3 , and CCDC113 as novel candidate causal genes. The CD40 risk locus colocalized with trans‐pQTLs of multiple plasma proteins involved in B cell function. Conclusion Our study supports a strong shared genetic susceptibility between SSc and PBC. Using cross‐phenotype analyses, we have prioritized several novel candidate causal genes and pathways for these disorders.