In this study, we introduce the Dispanin family, of which the IFITM genes constitute a subfamily. In addition to the IFITM genes we identify 10 novel human Dispanins and investigate the family's evolutionary history and suggest that the eukaryotic members are descending from bacteria through a horizontal gene transfer. Thus, the expansion and diversification of Dispanins in vertebrates may reflect the evolution of a larger functional repertoire, which is a supported by the distinct expression profiles Figure 3 . The protein features and topology of the Dispanin subfamilies. The picture shows the membrane topology and sequences features of a representative human member of each subfamily. Conserved motifs and residues are shown and those which have a sequence identity of more than 90% are framed in black and those with 80-90% sequence similarity are framed in blue. Predicted phosphorylation (Green) and glycosylation (orange) sites are shown. doi:10.1371/journal.pone.0031961.g003 of the subfamilies. By identifying homologs to the IFITM genes and establishing the Dispanins as a family together with a solid detailed and evolutionary based nomenclature for the vertebrate genes, we provide a fundament for future functional characterization these genes.