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GP9 gene

Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

GP9 gene

The GP9 gene provides instructions for making glycoprotein IX, a protein subunit essential for the formation of blood clots.

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.

Other Names for This Gene

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

Frequently Asked Questions

Bernard-Soulier syndrome, which can result from mutations in the GP9 gene, is characterized by macrothrombocytopenia, meaning patients have a low number of abnormally large platelets. The most common clinical manifestation is a tendency to bleed excessively, which may present as frequent nosebleeds, bleeding gums, easy bruising, or prolonged bleeding after minor cuts, dental work, or surgery. Newborns may experience significant bleeding at birth, and women may have heavy menstrual periods. How is Bernard-Soulier syndrome diagnosed if it is suspected due to GP9 gene mutations?::Diagnosis typically begins with a complete blood count (CBC) that reveals a low platelet count and an increased mean platelet volume (MPV), indicating large platelets. Further confirmation involves a bleeding time test, which is usually prolonged, and platelet aggregation studies that show a lack of response to ristocetin. Definitive diagnosis is achieved through genetic testing to identify specific mutations in the GP9 gene, as well as flow cytometry to detect the absence or reduction of the GPIb-IX-V complex on the platelet surface. Can individuals with GP9-related Bernard-Soulier syndrome lead a normal life with proper management?::Yes, with appropriate medical management, many individuals with Bernard-Soulier syndrome can lead normal, active lives. Management strategies include avoiding medications that impair platelet function, such as aspirin and non-steroidal anti-inflammatory drugs (NSAIDs). For minor bleeding, local pressure and topical hemostatic agents are often sufficient. For major bleeding or surgical procedures, platelet transfusions or desmopressin (DDAVP) may be required to control bleeding. Genetic counseling is also recommended for family planning. How does a GP9 mutation affect the structure and function of the GPIb-IX-V complex?::The GP9 gene provides instructions for glycoprotein IX (GPIX), a subunit essential for the assembly and stability of the GPIb-IX-V complex on the platelet surface. Mutations in GP9 can lead to the production of an altered GPIX protein that is either degraded prematurely or fails to reach the cell surface. Without GPIX, the GPIb-IX-V complex cannot form properly, preventing platelets from binding to von Willebrand factor. This binding is the critical first step in primary hemostasis, so its absence results in the bleeding tendencies seen in Bernard-Soulier syndrome.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.