Normal Function
The ITGA2B gene provides instructions for making one part, the alphaIIb subunit, of a receptor complex called integrin alphaIIb/beta3 (αIIbβ3), which is found on the surface of small cells called platelets. Platelets circulate in blood and are an essential component of blood clots. The alphaIIb subunit attaches (binds) to the beta3 subunit, which is produced from the ITGB3 gene, to form integrin αIIbβ3. It is estimated that 80,000 to 100,000 copies of integrin αIIbβ3 are present on the surface of each platelet.
During clot formation, integrin αIIbβ3 binds to a protein called fibrinogen. Attachment of integrin αIIbβ3 from adjacent platelets to the same fibrinogen protein helps platelets cluster together (platelet cohesion) to form a blood clot. Blood clots protect the body after injury by sealing off damaged blood vessels and preventing further blood loss. Integrin αIIbβ3 can also bind other proteins on platelets and in blood as well as proteins within the intricate lattice that forms in the space between cells (extracellular matrix) to ensure proper clot formation and promote wound healing.
Health Conditions Related to Genetic Changes
Glanzmann thrombasthenia
At least 200 mutations in the ITGA2B gene have been found to cause Glanzmann thrombasthenia, which is a rare bleeding disorder. The mutations that cause this disorder occur in both copies of the gene in each cell and impair the production or activity of the alphaIIb subunit, which disrupts the formation of functional integrin αIIbβ3. A shortage (deficiency) of functional integrin αIIbβ3 prevents sufficient binding of fibrinogen or other proteins, impairing the formation of blood clots. A lack of platelet cohesion leads to prolonged or spontaneous bleeding episodes experienced by people with Glanzmann thrombasthenia.
More About This Health ConditionOther disorders
Mutations in the ITGA2B gene can also cause another rare bleeding disorder called platelet-type bleeding disorder 16. People with this disorder have signs and symptoms similar to Glanzmann thrombasthenia (described above), including frequent nosebleeds (epistaxis), bleeding from the gums, or red or purple spots on the skin caused by bleeding underneath the skin (petechiae), but the episodes are typically milder.
Unlike Glanzmann thrombasthenia, this disorder results from a mutation in only one copy of the ITGA2B gene in each cell, and the mutations result in the formation of some integrin αIIbβ3 that is abnormally turned on (active), even when no clot is being formed. This abnormally active protein is unable to reach the surface of the platelet where it is needed to bind to other platelets during clot formation. The overactive integrin αIIbβ3 binds inappropriately to clotting proteins within the cell during the formation of platelets, causing the platelets to become misshapen and large. The abnormally shaped platelets have a shortened lifespan, so platelet numbers are often reduced, which impairs clot formation. (The combination of reduced numbers of enlarged platelets is referred to as macrothrombocytopenia.)
Because the mutation that causes this disorder affects only one copy of the ITGA2B gene, some normal integrin is formed and normal platelets produced, which accounts for the mild signs and symptoms in affected individuals.
Other Names for This Gene
- alphaIIb protein
- CD41
- CD41B
- GP2B
- GPIIb
- integrin alpha 2b
- integrin alpha-IIb preproprotein
- integrin, alpha 2b (platelet glycoprotein IIb of IIb/IIIa complex, antigen CD41)
- integrin, alpha-2B
- platelet fibrinogen receptor, alpha subunit
- platelet glycoprotein IIb
- platelet membrane glycoprotein IIb
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- Kunishima S, Kashiwagi H, Otsu M, Takayama N, Eto K, Onodera M, Miyajima Y, Takamatsu Y, Suzumiya J, Matsubara K, Tomiyama Y, Saito H. Heterozygous ITGA2B R995W mutation inducing constitutive activation of the alphaIIbbeta3 receptor affects proplatelet formation and causes congenital macrothrombocytopenia. Blood. 2011 May 19;117(20):5479-84. doi: 10.1182/blood-2010-12-323691. Epub 2011 Mar 31. Citation on PubMed
- Nurden AT, Fiore M, Nurden P, Pillois X. Glanzmann thrombasthenia: a review of ITGA2B and ITGB3 defects with emphasis on variants, phenotypic variability, and mouse models. Blood. 2011 Dec 1;118(23):5996-6005. doi: 10.1182/blood-2011-07-365635. Epub 2011 Sep 13. Citation on PubMed
- Nurden AT, Pillois X, Fiore M, Alessi MC, Bonduel M, Dreyfus M, Goudemand J, Gruel Y, Benabdallah-Guerida S, Latger-Cannard V, Negrier C, Nugent D, Oiron RD, Rand ML, Sie P, Trossaert M, Alberio L, Martins N, Sirvain-Trukniewicz P, Couloux A, Canault M, Fronthroth JP, Fretigny M, Nurden P, Heilig R, Vinciguerra C. Expanding the Mutation Spectrum Affecting alphaIIbbeta3 Integrin in Glanzmann Thrombasthenia: Screening of the ITGA2B and ITGB3 Genes in a Large International Cohort. Hum Mutat. 2015 May;36(5):548-61. doi: 10.1002/humu.22776. Citation on PubMed
- Nurden AT, Pillois X, Fiore M, Heilig R, Nurden P. Glanzmann thrombasthenia-like syndromes associated with Macrothrombocytopenias and mutations in the genes encoding the alphaIIbbeta3 integrin. Semin Thromb Hemost. 2011 Sep;37(6):698-706. doi: 10.1055/s-0031-1291380. Epub 2011 Nov 18. Citation on PubMed
- Pillitteri D, Pilgrimm AK, Kirchmaier CM. Novel Mutations in the GPIIb and GPIIIa Genes in Glanzmann Thrombasthenia. Transfus Med Hemother. 2010;37(5):268-277. doi: 10.1159/000320258. Epub 2010 Sep 15. Citation on PubMed or Free article on PubMed Central
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