© 2002 American College of Chest Physicians by guest on July 13, 2011 chestjournal. chestpubs. org Downloaded from identical to a familial mutation in infants with the same phenotype strongly supports the hypothesis that the mutations were causally related to their lung disease. Missense SP-C mutations that resulted in amino-acid substitutions in residues highly conserved across species (P30 L, I73T, G100V, Y104H, P115 L, I126R, T187N, and L188R), as well as a frameshift mutation (140delA) associated with expression of a stable transcript, were identified in 10 other infants, 6 of whom had a family history of lung disease. None of the identified mutations were found on 100 control chromosomes, indicating that they are not common polymorphisms. We conclude that mutations in the SP-C gene are a cause of both familial and sporadic ILD. While the pathophysiologic mechanisms remain to be elucidated, the finding of mutations on one allele suggests a dominant negative effect on SP-C or pro-SP-C function or metabolism.