**Question:** Glanzmann thrombasthenia is due to defect in:-

A. Platelet glycoprotein IIb/IIIa complex
B. Factor VIII
C. Factor IX
D. Factor XII

**Correct Answer:** A. Platelet glycoprotein IIb/IIIa complex

**Core Concept:** Glanzmann thrombasthenia is a rare autosomal recessive bleeding disorder characterized by impaired platelet function due to defects in the platelet glycoprotein (GP) IIb/IIIa complex. This complex is crucial for the formation of stable platelet aggregates during hemostasis.

**Why the Correct Answer is Right:** Glanzmann thrombasthenia results from mutations in the genes encoding for GPIIb/IIIa complex, which includes the alphaIIbbeta3 and alphaVbeta3 receptors. These receptors are essential for the binding of fibrinogen, von Willebrand factor, and other plasma proteins to the platelet surface during clot formation. A deficiency or dysfunction of these receptors leads to impaired platelet aggregation and prolonged bleeding time.

**Why Each Wrong Option is Incorrect:**

A. Platelet glycoprotein IIb/IIIa complex: As mentioned above, this complex is the correct answer and not a defect.

B. Factor VIII: Factor VIII is a coagulation factor, not a platelet receptor or component of the platelet surface. It plays a role in the intrinsic pathway of coagulation, not platelet function.

C. Factor IX: Factor IX is also a coagulation factor involved in the intrinsic pathway. It does not contribute to platelet function or hemostasis.

D. Factor XII: Factor XII is a part of the intrinsic coagulation pathway, not related to platelet function or hemostasis.

**Clinical Pearl:** Glanzmann thrombasthenia is an important differential diagnosis in patients presenting with prolonged bleeding time and mucocutaneous bleeding, especially when other causes of bleeding have been ruled out. Early diagnosis and management with desmopressin (DDAVP), which enhances platelet aggregation, can significantly improve clinical outcomes in these patients.