A review of the JR blood group system.

The JR blood group system (ISBT 032) consists of one antigen,Jra, which is of high prevalence in all populations. The rare Jr(a-) phenotype has been found mostly in Japanese and other Asian populations, but also in people of northern European ancestry, in Bedouin Arabs, and in one Mexican. Anti-Jra has caused transfusion reactions and is involved in hemolytic disease of the fetus and newborn. The Jra antigen is located on ABCG2 transporter, a multipass membrane glycoprotein (also known as the breast cancer resistance protein, BCRP), which is encoded by the ABCG2 gene on chromosome 4q22.1. The Jr(a-) phenotype mostly results from recessive inheritance of ABCG2 null alleles caused by frameshift or nonsense changes.