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Glanzman thrombosthenia

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Glanzman thrombasthenia platelet aggregation GPIIb/IIIa defect

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"Glanzmann thrombasthenia"

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Glanzmann thrombasthenia GPIIb/IIIa diagnosis treatment 2024 2025

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Glanzmann thrombasthenia platelet aggregation defect

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Glanzmann Thrombasthenia

Overview Glanzmann thrombasthenia (GT) is a rare, autosomal-recessive inherited platelet function disorder caused by mutations in the ITGA2B and ITGB3 genes, which encode the two subunits (αIIb and β3) of the platelet integrin αIIbβ3, also known as glycoprotein GPIIb/IIIa (CD41/CD61) - the major fibrinogen receptor on the platelet surface (Goldman-Cecil Medicine, p. 1668; Henry's Clinical Diagnosis and Management by Laboratory Methods).
Pathophysiology GPIIb/IIIa mediates the final common pathway of platelet aggregation by binding fibrinogen (and other ligands such as von Willebrand factor, fibronectin, vitronectin) and cross-linking adjacent activated platelets. In GT this receptor is absent or dysfunctional, so platelets adhere normally to the vessel wall (via GPIb-IX-V binding vWF) but cannot aggregate with one another, regardless of which agonist activates them - this contrasts with disorders like Bernard-Soulier syndrome, where the adhesion step is defective (Henry's Clinical Diagnosis, p. 2270-2272).
Two molecular subtypes are recognized:
  • Type I: essentially complete absence of GPIIb/IIIa
  • Type II: receptor present at 10-20% of normal levels
  • A variant type exists with normal receptor quantity but abnormal function
Clinical Features
  • Bleeding tends to be severe and begins in childhood
  • Predominantly mucocutaneous: epistaxis, gingival bleeding, easy bruising, menorrhagia, GI bleeding
  • Platelet count and platelet morphology/size are normal (distinguishing it from thrombocytopenic disorders and from Bernard-Soulier syndrome's macrothrombocytopenia)
  • Severity is variable even within the same genotype
Laboratory Diagnosis
  • Platelet count and peripheral smear: normal
  • Bleeding time: prolonged
  • Light transmission platelet aggregometry: virtually absent aggregation to ADP, collagen, epinephrine, and arachidonic acid; normal response to ristocetin (since this depends on GPIb-IX-V, which is intact) - this ristocetin-sparing pattern is the classic diagnostic clue (Henry's Clinical Diagnosis, p. 1909-1932)
  • Flow cytometry: confirms reduced/absent GPIIb/IIIa receptor density and is used to distinguish Type I vs Type II
  • Genetic testing of ITGA2B/ITGB3 confirms the diagnosis
  • The platelet antigen PlA1 (on GPIIIa) is typically decreased
Management
  • Preventive: avoid antiplatelet agents (aspirin, NSAIDs); iron/folate supplementation for chronic blood loss anemia; hepatitis B vaccination given repeated transfusion exposure
  • Minor bleeding: local measures (pressure, fibrin sealants, topical thrombin), antifibrinolytics (tranexamic acid, including as a mouthwash for gingival bleeding), desmopressin
  • Severe bleeding/surgery: platelet transfusion remains first-line, though repeated transfusions carry a risk of alloimmunization (anti-HLA and anti-αIIbβ3 antibodies), which can render future transfusions ineffective and cause transfusion reactions
  • Recombinant activated factor VII (rFVIIa, NovoSeven RT) is FDA-approved for bleeding refractory to platelet transfusion, or in patients who have developed antibodies to GPIIb/IIIa
  • Refractory alloimmunized cases may use HLA-matched platelets or immunoadsorption to remove anti-αIIbβ3 antibodies
Differential diagnosis includes Bernard-Soulier syndrome, von Willebrand disease, Hermansky-Pudlak syndrome, Scott syndrome, gray platelet syndrome, and acquired platelet dysfunction (e.g., NSAID use, uremia).
Recent evidence (last 2-3 years) A 2025 systematic review in Haemophilia on rFVIIa efficacy/safety in GT and a 2026 systematic review/case report on pulmonary thromboembolism in GT (an emerging concern given increasing use of rFVIIa and other procoagulant support, since GT patients can still develop thrombotic complications despite their bleeding tendency) both support and refine the current treatment framework above - PMID 39604156 and PMID 41591555. These don't contradict the textbook approach but add nuance around rare thrombotic risk with rFVIIa/factor therapy in GT patients.
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