Bernard-Soulier syndrome is associated with which of the following?

• A. Giant platelets and defective ristocetin-induced aggregation due to GPIb-IX-V deficiency
• B. Normal platelet size and increased ristocetin aggregation
• C. Decreased ADP aggregation
• D. Deficiency of GPIIb/IIIa

Answer: (A)

At the heart of this question is a defect in platelet adhesion. Bernard-Soulier syndrome results from a deficiency of the GPIb-IX-V receptor on the platelet surface, which normally binds von Willebrand factor to mediate platelet sticking to injured vessel walls. Because this receptor is lacking, platelets are abnormally large (giant platelets) and cannot bind von Willebrand factor effectively, leading to markedly reduced ristocetin-induced platelet aggregation. This combination—giant platelets with defective ristocetin-induced aggregation due to GPIb-IX-V deficiency—best fits the description.

The other scenarios point to different disorders: a deficiency of GPIIb/IIIa causes Glanzmann thrombasthenia, where ristocetin response is normal but aggregation with other agonists (ADP, collagen, epinephrine) is impaired; decreased ADP aggregation reflects other storage pool or secretion defects; normal platelet size with increased ristocetin aggregation does not describe Bernard-Soulier and is more compatible with other von Willebrand-related issues.