|Alt. symbols||XKR1, Kx, X1k|
|Locus||Chr. X p21.2-p21.1|
XK (also known as Kell blood group precursor) is a protein found on human red blood cells and other tissues which is responsible for the Kx antigen which helps determine a person's blood type. The Kx antigen plays a role in matching blood for blood transfusions. Absence of XK protein leads to McLeod syndrome, a multi-system disorder characterized by hemolytic anemia, myopathy, acanthocytosis, and chorea.