MPA, driven mainly by myeloperoxidase antibodies (p-ANCA), is in most cases limited to the kidneys, whereas both GPA, in about 75% associated with proteinase-3 antibodies (c-ANCA), and EGPA, induced by eosinophiles and in 40% by ANCA, are usually expressed in the upper airways and lungs, with about 70% renal involvement in GPA and 25% in EGPA [1,2]. The gene discussed is PRTN3; the disease is microscopic polyangiitis.