Alternative titles and symbols : Xg blood group system;
Description : The XG blood group system is the only blood group system assigned to the X chromosome.
The system consists of 2 antigens, Xg(a) and CD99, which are encoded by 2 adjacent
genes, XG and CD99 (313470). Xg(a) may be expressed only on red blood cells, whereas
CD99 is expressed on all tissue cells. The expression level of CD99 on red blood cells
is directly related to the presence or absence of Xg(a). Both anti-Xg(a) and anti-CD99
are rare. Anti-Xg(a) is considered clinically insignificant, and the clinical significance
of anti-CD99 is unknown (review by Johnson, 2011).;