P1PK (formerly: P) is a human blood group system (International Society of Blood Transfusion system 003) based upon the A4GALT gene on chromosome 22. The P antigen (later renamed P1) was first described by Karl Landsteiner and Philip Levine in 1927. The P1PK blood group system consists of three glycosphingolipid antigens: Pk, P1 and NOR. In addition to glycosphingolipids, terminal Gal¦Á1¡ú4Gal¦Â structures are present on complex-type N-glycans. The GLOB antigen (formerly P) is now the member of the separate GLOB (globoside) blood group system.

Reference
Wiki: Polyagglutinable erythrocyte syndrome