NKX2-1 and pulmonary alveolar proteinosis: Mutations in the genes for surfactant protein-B (SFTPB), surfactant protein-C (SFTPC), member A3 of the ATP-binding cassette family of transporters (ABCA3) [6], and sometimes thyroid transcription factor 1 (NKX2-1) [7] lead to PAP in combination with abnormalities in the pulmonary interstitial tissue [8].