INTRODUCTION

When a blood vessel is injured, platelets adhere to the exposed subendothelium (platelet adhesion), are activated (platelet activation), and secrete their granule contents (platelet secretion), including some platelet agonists [adenosine diphosphate (ADP), serotonin] that, by interacting with specific platelet receptors, contribute to the recruitment of additional platelets to form aggregates (platelet aggregation). In addition, platelets play a role in the coagulation mechanism, providing the necessary surface of procoagulant phospholipids (platelet procoagulant activity). Congenital or acquired abnormalities of platelet number or function are associated with a heightened risk of bleeding, proving that platelets play an important role in hemostasis. Typically, patients with platelet disorders have mucocutaneous bleeding of variable severity and excessive hemorrhage after surgery or trauma.

CLASSIFICATION OF CONGENITAL DISORDERS OF PLATELET FUNCTION

Inherited disorders of platelet function are generally classified based on the functions or responses that are abnormal. However, since platelet functions are intimately related, a clear distinction between disorders of platelet adhesion, aggregation, activation, secretion, and procoagulant activity is in many instances problematic. For example, platelets deficient in the glycoprotein (GP) complex Ib/IX/V, which is a receptor for von Willebrand factor (VWF), do not adhere normally to the subendothelium and are therefore generally included in the group of abnormalities of platelet adhesion. However, they also do not undergo normal activation and aggregation at high shear, do not aggregate normally to thrombin, and display abnormal procoagulant responses.