Xg antigen system

{{Short description|Blood group system}}

{{infobox protein

|name=Xg blood group

|image=File:Serology interpretation of antibody panel for blood group antigens.jpg

|caption=Interpretation of antibody panel to detect patient antibodies towards the most relevant human blood group systems, including Xg. {{further|Blood compatibility testing}}

|width=370

|HGNCid=12806

|Symbol=XG

|AltSymbols=PBDX

|EntrezGene=7499

|OMIM=

|RefSeq=NM_175569

|UniProt=

|PDB=

|ECnumber=

|Chromosome=X

|Arm=p

|Band=22.32

|LocusSupplementaryData=

}}

The XG antigen is a red blood cell surface antigen discovered in 1962.{{cite journal |vauthors=Tippett P, Ellis NA |title=The Xg blood group system: a review |journal=Transfus Med Rev |volume=12 |issue=4 |pages=233–57 | date=October 1998 |pmid=9798268 |doi= 10.1016/S0887-7963(98)80001-1}} by researchers at the MRC Blood Group Unit.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.

The PBDX gene that encodes the antigen is located on the short arm of the X chromosome.{{cite journal |vauthors=Ellis NA, Tippett P, Petty A, etal |title=PBDX is the XG blood group gene |journal=Nat. Genet. |volume=8 |issue=3 |pages=285–90 | date=November 1994 |pmid=7533029 |doi=10.1038/ng1194-285|s2cid=36695727 }}{{cite journal |vauthors=LINDSTEN J, FRACCARO M, POLANI PE, HAMERTON JL, SANGER R, RACE RR |title=Evidence that the Xg blood group genes are on the short arm of the X chromosome |journal=Nature |volume=197 |issue= 4868|pages=648–9 | date=February 1963 |pmid=13930842 |doi= 10.1038/197648a0|bibcode=1963Natur.197..648L |s2cid=4209911 }} 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.{{cn|date=December 2021}}