Scianna: the lucky 13th blood group system.

The Scianna system was named in 1974 when it was appreciated that two antibodies described in 1962 in fact identified antithetical antigens. However, it was not until 2003 that the protein on which antigens of this system are found and the first molecular variants were described. Scianna was the last previously serologically defined, protein-based blood group system to be characterized at the molecular level, marking the end of an era in immunohematology. This story highlights the critical role that availability of laboratory reagents for serologic testing has played in the initial characterization of a blood group and sets the stage for the development of new reagents, such as recombinant proteins, to assist in this process. The central role that genetics has played, both by classical pedigree analysis and by molecular techniques, in the discovery and characterization of this blood group is reviewed.