Hence, serum KL-6 levels >10,000 U/mL in our patient at diagnosis were tremendously high and consistent with comorbid aPAP; however, peak serum KL-6 levels decreased at disease relapse, and this might suggest that the relapse was mainly FHP, although it was not histologically examined. The gene discussed is MUC1; the disease is autoimmune pulmonary alveolar proteinosis.