Pediatric Pyoderma Gangrenosum in Patients with a Novel Biallelic Mutation in OTULIN

Pyoderma gangrenosum (PG) is an understudied inflammatory skin condition that causes significant morbidity and rarely mortality. Treatment options for PG are limited due to our relatively poor understanding of its molecular mechanisms. Prior studies have suggested a genetic basis for PG, but causal genes have remained elusive. Through the study of siblings with severe recurrent PG in childhood, we identified a novel mutation in OTULIN. OTULIN is a linear deubiquitylase that regulates several immune signaling pathways in ways that are cell type specific. Interestingly, this mutation affects the PIM domain, responsible for protein–protein interactions, but does not impair catalytic functions of the OTU domain, thus its mechanism of action is distinct from previously reported OTULIN mutations. Through a combination of in vitro mechanistic studies that isolate the functional impact of the variant, together with single cell analyses of patient and healthy control PBMC samples, we demonstrate this novel OTULIN mutation causes PG via i) hyperactivation of the NLRP3 inflammasome and elevated IL-1b secretion from patients’ myeloid cells and ii) heightened keratinocyte sensitivity to TNF-driven cell death. The patients responded well to anti-TNF therapy and are now free of PG flares. This study establishes the first monogenic etiology of isolated PG of childhood, identifies the molecular mechanisms of disease, and suggests that TNF and/or IL-1b blockade may be effective therapeutic options.