The P1PK blood group system: revisited and resolved

This update on the P1PK blood group system (Hellberg Å, Westman JS, Thuresson B, Olsson ML. P1PK: the blood group system that changed its name and expanded. Immunohematology 2013;29:25–33) provides recent findings concerning the P1PK blood group system that have both challenged and confirmed old theories. The glycosphingolipids can no longer be considered the sole carriers of the antigens in this system because the P1 antigen has been detected on human red blood cell glycoproteins. New indications suggest that P1P^k synthase activity truly depends on the DXD motif, and the genetic background and molecular mechanism behind the common P₁ and P₂ phenotypes were found to depend on transcriptional regulation. Transcription factors bind the P¹ allele selectively to a motif around rs5751348 in a regulatory region of A4GALT, which enhances transcription of the gene. Nonetheless, unexplained differences in antigen expression between individuals remain.