Additionally, elevated circulating anti-MPO concentrations were accompanied by a relevant clinical phenotype compatible with either a typical diagnosis of MPA with pulmonary involvement as assessed by positive renal biopsy and diffuse alveolar alveolar hemorrhage leading to respiratory failure or a more occult clinical phenotype encompassing asymptomatic microscopic hematuria with normal renal function and mild hypoxemia. The gene discussed is MPO; the disease is respiratory failure.