Pulmonary alveolar proteinosis: A review

Pulmonary alveolar proteinosis (PAP) is a disorder that rapidly leads to respiratory failure, because the alveolar spaces fill with a lipid-rich, proteinaceous material that impedes gas exchange. The pathogenesis of this life-threatening process remained an enigma for decades. Recent analysis of the lung pathology and molecular genetics of affected families has provided a molecular basis for some cases of PAP-deficiency of surfactant protein SP-B. This lack results from mutations in the gene for SP-B. The common mutation, 121ins2, is present in about two-thirds of the patients with SP-B deficiency. Additional insights into the mechanism for this lipoproteinaceous accumulation within alveoli were contributed by serendipity in a granulocyte-macrophage-colony stimulating factor (GM-CSF) knock-out mouse model developed to study basal hematopoiesis. In this model, hematopoiesis was unaffected, but the animals developed pulmonary alveolar proteinosis. Subsequently, mutations in the genes for GM-CSF or its receptor were identified as the cause for pulmonary alveolar proteinosis in some patients. In our review, we discuss the known clinical, pathologic, and molecular genetic aspects of pediatric PAP and consider avenues for future research.