SFTPA2 and idiopathic pulmonary fibrosis: Among surfactant proteins variants of surfactant protein C (SP-C) [18,19,20,21], surfactant protein A2 (SP-A2) [22,23,24,25] and surfactant protein A1 (SP-A1) [26] have been associated to familiar pulmonary fibrosis, while they are rare in sporadic IPF [19].