SFTPA1 and idiopathic pulmonary fibrosis: 2) After comparison of IPF and HP, i) three SFTPA1 and one SFTPB SNP were found to associate with decreased or increased risk in IPF and HP and one SFTPA1 SNP to associate with decreased risk in both IPF and HP, ii) a number of three-SNP interactions with the same or different effect pattern associated with IPF and/or HP susceptibility; iii) one of the three-SNP interactions that involved SNPs of SFTPA2, SFTPA1, and SFTPD, with the same effect pattern, was associated with a disease-specific outcome, a decreased and increased risk in HP and IPF, respectively.