This includes the positivity of anti-PR3 ANCA in a high percentage of GPA, anti-MPO ANCA in around 60% of MPA and 1/3 of EGPA, or the presence of microaneurysms of the abdominal vessels on arteriography in PAN [57]. The gene discussed is PRTN3; the disease is eosinophilic granulomatosis with polyangiitis.