Unveiling novel susceptibility genes for sarcoidosis by a cross-tissue transcriptome-wide association study

Sarcoidosis is a systemic granulomatous disease with heterogeneous clinical manifestations and unclear pathogenesis. Although genome-wide association studies (GWAS) have identified several immune-related loci, the functional interpretation of these signals remains limited. Integrative transcriptome-wide approaches may uncover novel susceptibility genes and provide mechanistic insights.

The primary objective of this study was to identify novel susceptibility genes for sarcoidosis and provide mechanistic insights into its pathogenesis through a comprehensive, cross-tissue transcriptome-wide approach.

We conducted a cross-tissue transcriptome-wide association study (TWAS) using the UTMOST framework, followed by single-tissue TWAS via FUSION. Candidate genes identified in both analyses were further evaluated using Multi-marker Analysis of Genomic Annotation (MAGMA), Mendelian randomization (MR), and Bayesian colocalization. Functional characterization was explored through gene-chemical-disease associations from the Comparative Toxicogenomics Database (CTD) and phenome-wide association studies (PheWAS) in the UK Biobank.

Cross-tissue TWAS identified 48 genes. Integrative analyses prioritized four novel susceptibility genes: RNF215, PLCL1, FAM117B, and RFTN2. MR and colocalization supported causal effects of RNF215 (risk-increasing), FAM117B and RFTN2 (protective), and tissue-dependent effects for PLCL1. CTD analyses revealed interactions of these genes with environmental chemicals including bisphenol A and tetrachlorodibenzodioxin, while PheWAS demonstrated pleiotropic associations with immune, respiratory, hematological, and cardiovascular traits.

This comprehensive integrative study identifies four biologically plausible susceptibility genes for sarcoidosis, expanding the genetic architecture of sarcoidosis and suggest potential targets for mechanistic and therapeutic investigation.