Ultra-rare genetic variation in relapsing polychondritis: a whole-exome sequencing study

Abstract

ObjectiveRelapsing polychondritis (RP) is a systemic inflammatory disease of unknown aetiology. The objective of this study was to examine the contribution of rare genetic variations to RP.MethodsWe performed a case–control exome-wide rare variant association analysis that included 66 unrelated European American cases with RP and 2923 healthy controls (HC). Gene-level collapsing analysis was performed using Firth’s logistics regression. Exploratory pathway analysis was performed using three different methods: Gene Set Enrichment Analysis, sequence kernel association test and higher criticism test. Plasma DCBLD2 levels were measured in patients with RP and HC using ELISA.ResultsIn the collapsing analysis, RP was associated with a significantly higher burden of ultra-rare damaging variants in theDCBLD2gene (7.6% vs 0.1%, unadjusted OR=79.8, p=2.93×10−7). Plasma DCBLD2 protein levels were significantly higher in RP than in HC (median 4.06 ng/µL vs 0.05 ng/µL, p<0.001). The pathway analysis revealed a statistically significant enrichment of genes in the tumour necrosis factor signalling pathway driven by rare damaging variants inRELB,RELAandRELusing higher criticism test weighted by eigenvector centrality.ConclusionsThis study identified specific rare variants in theDCBLD2gene as a putative genetic risk factor for RP. These findings should be validated in additional patients with RP and supported by future functional experiments.