Although disease pathogenesis/progression is not currently well‐described, auto‐immune dysregulation has classically been implicated in GPA, with anti‐neutrophil cytoplasmic auto‐antibodies (ANCA) against serum protease proteinase 3 (PR3) present in 80‐90% of cases.51 Here, PRTN3 is linked to granulomatosis with polyangiitis.