The human SP-A locus consists of two similar genes, SFTPA1 and SFTPA2, located on chromosome 10q21-24, within a cluster that includes the SP-D gene (SFTPD) [11] . The nucleotide sequences of human SFTPA1 and SFTPA2 differ little (96.0 to 99.6%) [14] . Single nucleotide polymorphisms (SNP) at the SFTPA1 codons 19, 50, 62, 133 and 219, and at the SFTPA2 codons 9, 91, 140 and 223 have been used to define the SP-A haplotypes, which are conventionally denoted as 6A n for the SFTPA1 gene and 1A n for the SFTPA2 gene (see Table E1 in Additional File 1) [15] . Variability at the SFTPD gene has been also reported. Particularly, the presence of the variant amino acid (aa)-11 (M11T) has been shown to lead to low SP-D levels [16] .