What is the deficiency associated with Bernard-Soulier syndrome?

Bernard-Soulier syndrome is associated with a deficiency of the glycoprotein Ib (Gp1b) receptor on the surface of platelets. This receptor is crucial for the initial adhesion of platelets to the exposed subendothelium following vascular injury, as it binds to von Willebrand factor (vWF), which is presented in the vessel wall.

In patients with Bernard-Soulier syndrome, the absence or dysfunction of the Gp1b receptor leads to impaired platelet aggregation and a tendency to bleed due to the inability to properly adhere to the damaged endothelium. This condition is characterized by large platelets (macrothrombocytes) and a prolonged bleeding time, which can be identified through laboratory tests.

The other options are associated with different conditions or roles in hemostasis. Glycoprotein IIb/IIIa is involved in platelet aggregation but is not deficient in Bernard-Soulier syndrome. Factor VIII and Factor IX are clotting factors involved in the intrinsic pathway of coagulation and are not related to platelet function or to Bernard-Soulier syndrome.