Four haplotypes of SP-A1 (6A, 6A 2 , 6A 3 and 6A 4 ) and six of SP-A2 (1A, 1A 0 , 1A 1 , 1A 2 , 1A 3 and 1A 5 ) are found frequently (>1%) in the general population [15] . On the basis of the differences in non-synonymous SNPs (SFTPA1-aa19, -aa50, -aa219, SFTPA2-aa9, -aa91, -aa223) the most frequent conventional haplotypes of these genes, except 1A and 1A 5 , can be unambiguously identified (see Table E1 in Additional File 1). However, this method does not allow for the differentiation of some of these haplotypes from those rare haplotypes (frequency equal or lower than 1%) identified with the SNPs indicated in Table E1 in Additional File 1. For comparative purposes, in our study each haplotype was denoted by the name of the most frequent haplotype for a given combination of non-synonymous SNPs. Genomic DNA was isolated from whole blood according to standard phenol-chloroform procedure or with the Magnapure DNA Isolation Kit (Roche Molecular Diagnostics, Pleasanton, CA, USA). Genotyping of polymorphisms in SFTPA1 (aa19, aa50, aa219), SFTPA2 (aa9, aa91, aa223) and SFTPD (aa11) genes was carried out using minor modifications of previously reported procedures [15, 20] . The accuracy of genotyping was confirmed by direct sequencing in an ABI Prism 310 (Applied Biosystems, Foster City, CA, USA) sequencer.