SFTPA2 and idiopathic interstitial pneumonia: Mutations in the surfactant protein-C gene (SFTPC); surfactant protein A2, SFTPA2; and ATP-binding cassette member A3, ABCA3, whose product is expressed exclusively by alveolar type 2 (AT2) cells, suggest that defects in AT2 cell function may play critical roles in IPF pathogenesis.