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GP9 gene

glycoprotein IX platelet

Normal Function

The GP9 gene provides instructions for making a protein called glycoprotein IX (GPIX). This protein is one piece (subunit) of a protein complex called GPIb-IX-V, which plays a role in blood clotting. GPIb-IX-V is found on the surface of small cells called platelets, which circulate in blood and are an essential component of blood clots. The complex can attach (bind) to a protein called von Willebrand factor, fitting together like a lock and its key. Von Willebrand factor is found on the inside surface of blood vessels, particularly when there is an injury. Binding of the GPIb-IX-V complex to von Willebrand factor allows platelets to stick to the blood vessel wall at the site of the injury. These platelets form clots, plugging holes in the blood vessels to help stop bleeding.

To form the GPIb-IX-V complex, GPIX interacts with other protein subunits called GPIb-alpha, GPIb-beta, and GPV, each of which is produced from a different gene. GPIX is essential for assembly of the complex at the platelet surface and helps stabilize the complex once it is formed.

Health Conditions Related to Genetic Changes

Bernard-Soulier syndrome

At least 28 GP9 gene mutations have been found to cause Bernard-Soulier syndrome, a condition characterized by a reduced number of platelets that are larger than normal (macrothrombocytopenia) and excessive bleeding. These mutations lead to production of an altered GPIX subunit that is likely broken down too soon or that cannot get to the platelet surface. Lack of this subunit on the surface of platelets prevents formation of the GPIb-IX-V complex. Without GPIb-IX-V, platelets cannot come together at the site of an injury to form a clot, leading to the bleeding problems associated with Bernard-Soulier syndrome.

More About This Health Condition

Other Names for This Gene

  • CD42a
  • glycoprotein 9
  • glycoprotein IX (platelet)
  • GPIX
  • platelet glycoprotein IX precursor

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Geng H, Xu G, Ran Y, Lopez JA, Peng Y. Platelet glycoprotein Ib beta/IX mediates glycoprotein Ib alpha localization to membrane lipid domain critical for von Willebrand factor interaction at high shear. J Biol Chem. 2011 Jun 17;286(24):21315-23. doi: 10.1074/jbc.M110.202549. Epub 2011 Apr 20. Citation on PubMed or Free article on PubMed Central
  • Li R, Emsley J. The organizing principle of the platelet glycoprotein Ib-IX-V complex. J Thromb Haemost. 2013 Apr;11(4):605-14. doi: 10.1111/jth.12144. Citation on PubMed or Free article on PubMed Central
  • McEwan PA, Yang W, Carr KH, Mo X, Zheng X, Li R, Emsley J. Quaternary organization of GPIb-IX complex and insights into Bernard-Soulier syndrome revealed by the structures of GPIbbeta and a GPIbbeta/GPIX chimera. Blood. 2011 Nov 10;118(19):5292-301. doi: 10.1182/blood-2011-05-356253. Epub 2011 Sep 8. Citation on PubMed or Free article on PubMed Central
  • Savoia A, Kunishima S, De Rocco D, Zieger B, Rand ML, Pujol-Moix N, Caliskan U, Tokgoz H, Pecci A, Noris P, Srivastava A, Ward C, Morel-Kopp MC, Alessi MC, Bellucci S, Beurrier P, de Maistre E, Favier R, Hezard N, Hurtaud-Roux MF, Latger-Cannard V, Lavenu-Bombled C, Proulle V, Meunier S, Negrier C, Nurden A, Randrianaivo H, Fabris F, Platokouki H, Rosenberg N, HadjKacem B, Heller PG, Karimi M, Balduini CL, Pastore A, Lanza F. Spectrum of the mutations in Bernard-Soulier syndrome. Hum Mutat. 2014 Sep;35(9):1033-45. doi: 10.1002/humu.22607. Epub 2014 Jul 15. Citation on PubMed
  • Xu G, Shang D, Zhang Z, Shaw TS, Ran Y, Lopez JA, Peng Y. The Transmembrane Domains of beta and IX Subunits Mediate the Localization of the Platelet Glycoprotein Ib-IX Complex to the Glycosphingolipid-enriched Membrane Domain. J Biol Chem. 2015 Sep 4;290(36):22155-62. doi: 10.1074/jbc.M115.668145. Epub 2015 Jul 22. Citation on PubMed or Free article on PubMed Central

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.