PRTN3 and microscopic polyangiitis: In Europe, GPA is typically associated with polymorphisms in the genes encoding HLA-DP, SERPINA-1 and PRTN-3 leading to the production of ANCA directed against proteinase 3 (PR3), whereas MPA is more commonly associated with polymorphisms in the HLA-DQ gene and ANCA against myeloperoxidase (MPO) [1, 3, 4].