Which disorder is defined by defective GPIIb/IIIa leading to impaired platelet aggregation with multiple agonists but normal ristocetin response?

Which disorder is defined by defective GPIIb/IIIa leading to impaired platelet aggregation with multiple agonists but normal ristocetin response?

• A. Glanzmann thrombasthenia
• B. Von Willebrand disease
• C. DIC
• D. TTP

Answer: (A)

Defective GPIIb/IIIa prevents platelets from crosslinking and forming aggregates in response to most activating signals. Because GPIIb/IIIa is the key receptor for fibrinogen bridging between platelets, its deficiency means aggregation fails when tested with ADP, epinephrine, collagen, and other agonists. However, ristocetin-induced aggregation relies on von Willebrand factor binding to the GPIb receptor, a pathway that does not require GPIIb/IIIa, so that response remains normal. This combination—impaired aggregation with multiple agonists but a normal ristocetin response—is characteristic of Glanzmann thrombasthenia, a congenital deficiency of GPIIb/IIIa. By contrast, von Willebrand disease mainly disrupts ristocetin-induced aggregation due to vWF defects, while DIC and TTP involve platelet consumption or microangiopathy rather than a specific platelet receptor deficiency.

Defective GPIIb/IIIa prevents platelets from crosslinking and forming aggregates in response to most activating signals. Because GPIIb/IIIa is the key receptor for fibrinogen bridging between platelets, its deficiency means aggregation fails when tested with ADP, epinephrine, collagen, and other agonists. However, ristocetin-induced aggregation relies on von Willebrand factor binding to the GPIb receptor, a pathway that does not require GPIIb/IIIa, so that response remains normal. This combination—impaired aggregation with multiple agonists but a normal ristocetin response—is characteristic of Glanzmann thrombasthenia, a congenital deficiency of GPIIb/IIIa. By contrast, von Willebrand disease mainly disrupts ristocetin-induced aggregation due to vWF defects, while DIC and TTP involve platelet consumption or microangiopathy rather than a specific platelet receptor deficiency.