The remainder consist of secondary PAP, which is associated with various disorders (e.g., chronic inflammatory syndromes, immunodeficiencies, certain hematological diseases and solid tumors, immunoglobulin A deficiency); hereditary PAP that arises from mutations in genes for CSF2RA and CSF2RB; and congenital PAP, associated with mutations in genes for surfactant proteins (SFTPA, SFTPB, SFTPC), ATP-binding cassette subfamily A member 3 (ABCA3), and thyroid transcription factor-1 (TTF1). The gene discussed is NKX2-1; the disease is pulmonary alveolar proteinosis.