The PEL blood group system consists of one high-prevalence antigen, PEL, initially included in the 901 series. It is carried on the ABCC4 protein (ATP-binding cassette sub-family C member 4), member of the superfamily of ATP-binding cassette transporters. ABCC4 is also known as the multidrug resistance-associated protein 4 (MRP4). ABC proteins transport various molecules across extra- and intra-cellular membranes. This multi-pass protein consists of 1325 amino acids, with predicted 12 transmembrane domains and 6 extracellular loops. The protein is encoded by ABCC4, 281,641 bases, chromosome 13q32.1(chr13:95,019,835-95,301,475) (GRCh38/hg38). The rare PEL– null phenotype is associated with a moderately impaired platelet aggregation.