Xg antigen system

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

Xg blood group
Interpretation of antibody panel to detect patient antibodies towards the most relevant human blood group systems, including Xg. Further information: Blood compatibility testing
Identifiers
Symbol	XG
Alt. symbols	PBDX
NCBI gene	7499
HGNC	12806
RefSeq	NM_175569
Other data
Locus	Chr. X p22.32

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.^{[citation needed]}

Frequency

Population frequencies of Xa[5]
Population	Sample N	Xg %
Australian Aborigines	352	79
Chinese, mainland	171	60
North Europeans	5,388	66
Indians, Bombay	100	65
Israelis	201	66
American Indians	308	77
New-Guineans	263	85
New York's Afro-Americans	219	55
Sardinians	322	76
Taiwan Chinese	178	53
Taiwan Aborigines	164	38