A 12-year-old boy has recurrent epistaxis and gingival bleeding since childhood. Platelet count and morphology are normal. Bleeding time is prolonged. PT and aPTT are normal. Platelet aggregation studies show absent aggregation with ADP, collagen, epinephrine, and thrombin, but normal aggregation with ristocetin. Which platelet surface glycoprotein is deficient?

• A GPIb-IX-V
• B GPIV
• C GPIa/IIa
• D GPIIb/IIIa ✓

Explanation

Glanzmann thrombasthenia results from deficiency of GPIIb/IIIa (integrin alphaIIbbeta3), the receptor that binds fibrinogen to mediate platelet aggregation. Aggregation is absent with all agonists except ristocetin, which acts via GPIb-IX-V binding vWF. Bernard-Soulier syndrome involves GPIb-IX-V deficiency and shows absent ristocetin-induced aggregation.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.