Xg antigen system

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Xg blood group
Symbol XG
Alt. symbols PBDX
Entrez 7499
HUGO 12806
RefSeq NM_175569
Other data
Locus Chr. X p22.32

The XG antigen is a red blood cell surface antigen discovered in 1962.[1] by researchers at the MRC Blood Group Unit.[2]

The PBDX gene that encodes the antigen is located on the short arm of the X chromosome.[3][4] Since males normally have one X chromosome they are considered hemizygotes. Since women have two copies of the gene and could be heterozygotic for the presence or absence of the functioning gene they could (through the process of lyonisation) express the functioning protein on just some of their red blood cells.


  1. ^ Tippett P, Ellis NA (October 1998). "The Xg blood group system: a review". Transfus Med Rev 12 (4): 233–57. doi:10.1016/S0887-7963(98)80001-1. PMID 9798268. 
  2. ^ Mann, J. D., Cahan, A., Gelb, A. G., Fisher, N., Hamper, J., Tippett, P., Sanger, R., Race, R. R A sex-linked blood group. Lancet. 1962;279:8.
  3. ^ Ellis NA, Tippett P, Petty A, et al. (November 1994). "PBDX is the XG blood group gene". Nat. Genet. 8 (3): 285–90. doi:10.1038/ng1194-285. PMID 7533029. 
  4. ^ LINDSTEN J, FRACCARO M, POLANI PE, HAMERTON JL, SANGER R, RACE RR (February 1963). "Evidence that the Xg blood group genes are on the short arm of the X chromosome". Nature 197 (4868): 648–9. doi:10.1038/197648a0. PMID 13930842.