Pulmonary surfactant associated proteins promote alveolar stability by lowering the surface tension at the air-liquid interface in the peripheral air spaces. The disease is caused by variants affecting the gene represented in this entry. Disease susceptibility may be associated with variants affecting the gene represented in this entry. Pulmonary surfactant consists of 90% lipid and 10% protein. There are 4 surfactant-associated proteins: 2 collagenous, carbohydrate-binding glycoproteins (SP-A and SP-D) and 2 small hydrophobic proteins (SP-B and SP-C).