Other examples of diseases studied that may have less in common than PsA and axSpA are abundant; granulomatosis with polyangiitis (GPA), with myeloperoxidase- (MPO) or proteinase 3- (PR 3), or anti-neutrophil cystoplasmic antibody (ANCA), pneumoniae with several causative agents, or studies on IBD including both Crohn’s disease and ulcerative colitis. Here, MPO is linked to granulomatosis with polyangiitis.