An update on the GLOB blood group system (and former GLOB collection).

The main change that has occurred in the GLOB blood group system since the GLOB review published in this journal in 2013 is the addition of an antigen. The high-prevalence PX2 antigen, originally recognized as the x2 glycosphingolipid, is expressed on red blood cells of most individuals and is elevated in the rare PP1Pk-negative p blood group phenotype. P synthase, encoded by B3GALNT1, was found to elongate paragloboside to PX2 by adding the terminal β3GalNAc moiety. Hence, PX2 was moved from the GLOB collection to the GLOB system. The presence of naturally-occurring anti-PX2 was noted in P1k and P2k individuals exhibiting nonfunctional P synthase. Although the clinical significance of this specificity remains unclear, a recommendation to avoid transfusing Pk patients with p phenotype blood has been made. Currently, 13 mutations at the highly conserved B3GALNT1 locus have been found to abolish P synthase function and are recognized as null alleles by the International Society of Blood Transfusion. A new allele with a missense mutation but resulting in normal expression of P has been assigned GLOB*02. Finally, the GLOB collection was made obsolete after the move of LKE antigen to the 901 series.