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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed May 2008

What is the official name of the XK gene?

The official name of this gene is “X-linked Kx blood group.”

XK is the gene's official symbol. The XK gene is also known by other names, listed below.

What is the normal function of the XK gene?

The XK gene provides instructions for producing a protein that is found in various tissues of the body, particularly the brain, muscle, and heart. This protein is also present on the surface of red blood cells and carries a molecule known as the Kx blood group antigen. Blood group antigens are found on the surface of red blood cells and determine a number of blood types. When blood cells with unfamiliar antigens enter the bloodstream, the body's immune system recognizes the cells as foreign and may trigger an immune reaction that destroys the foreign blood cells.

The function of the XK protein is unclear; researchers believe that it might play a role in transporting substances into and out of cells. On red blood cells, the XK protein attaches to another blood group protein, the Kell protein. The function of this blood group complex is unknown.

Does the XK gene share characteristics with other genes?

The XK gene belongs to a family of genes called blood group (blood group antigens).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

How are changes in the XK gene related to health conditions?

McLeod neuroacanthocytosis syndrome - caused by mutations in the XK gene

Approximately 30 mutations in the XK gene have been found to cause McLeod neuroacanthocytosis syndrome. Most of these mutations lead to the production of an abnormally short, nonfunctional XK protein or cause no XK protein to be produced at all. Missing or abnormal XK protein also affects another blood group antigen, the Kell protein, causing it to be less prevalent on the surface of red blood cells. How mutations in the XK gene cause the misshapen red blood cells and movement problems characteristic of McLeod neuroacanthocytosis syndrome is unknown.

Where is the XK gene located?

Cytogenetic Location: Xp21.1

Molecular Location on the X chromosome: base pairs 37,685,781 to 37,732,130

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The XK gene is located on the short (p) arm of the X chromosome at position 21.1.

The XK gene is located on the short (p) arm of the X chromosome at position 21.1.

More precisely, the XK gene is located from base pair 37,685,781 to base pair 37,732,130 on the X chromosome.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about XK?

You and your healthcare professional may find the following resources about XK helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the XK gene or gene products?

  • Kell blood group precursor (McLeod phenotype)
  • KX
  • Kx antigen
  • membrane transport protein XK
  • X1k
  • XK, Kell blood group complex subunit (McLeod syndrome)
  • XKR1
  • XK-related protein 1
  • X-linked Kx blood group (McLeod syndrome)

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding XK?

antigens ; gene ; immune system ; molecule ; phenotype ; precursor ; protein ; subunit ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Clapéron A, Hattab C, Armand V, Trottier S, Bertrand O, Ouimet T. The Kell and XK proteins of the Kell blood group are not co-expressed in the central nervous system. Brain Res. 2007 May 25;1147:12-24. Epub 2007 Feb 2. (
  • Danek A, Rubio JP, Rampoldi L, Ho M, Dobson-Stone C, Tison F, Symmans WA, Oechsner M, Kalckreuth W, Watt JM, Corbett AJ, Hamdalla HH, Marshall AG, Sutton I, Dotti MT, Malandrini A, Walker RH, Daniels G, Monaco AP. McLeod neuroacanthocytosis: genotype and phenotype. Ann Neurol. 2001 Dec;50(6):755-64. (
  • Lee S. The value of DNA analysis for antigens of the Kell and Kx blood group systems. Transfusion. 2007 Jul;47(1 Suppl):32S-9S. Review. (
  • NCBI Gene (
  • Russo DC, Lee S, Reid ME, Redman CM. Point mutations causing the McLeod phenotype. Transfusion. 2002 Mar;42(3):287-93. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: May 2008
Published: February 8, 2016