Platelet aggregation at sites of vascular injury is essential for the formation of the primary haemostatic plug.

The mechanism of platelet aggregation under conditions of physiological flow is a complex multistep process, which requires the synergistic action of several different platelet receptors.

Platelet interaction with collagen at sites of damage to the vascular endothelium involves adhesion, activation, secretion of platelet granular contents and finally aggregation.

Other agonists other than collagen, such as fibrinogen, vWF and soluble agonists released from activated platelets (thromboxane A2 (TXA2) and ADP) are involved in platelet aggregation.

Platelets express a variety of receptors including GP Ib-IX-V, GP VI, GP Ia-IIa and GP IIb-IIIa. One aspect of this complexity of function is the variety of inherited defects of platelet function.

Types

 hereditary disorders of platelet adhesion

• Bernard-Soulier syndrome
• von Willebrand disease

 inherited disorder of platelet aggregation

• Glanzmann thrombasthenia

 defects in collagen receptors
 defects in ADP receptors
 defects in TXA2 receptors
 defects in TXA2 production
 generation of procoagulant activity
 secretion from dense bodies and alpha-granules

 defects in platelet storage granules

• Chediak-Higashi disease
• Hermansky-Pudlak disease
• Wiskott-Aldrich disease

References

 Ramasamy I. Inherited bleeding disorders: disorders of platelet adhesion and aggregation. Crit Rev Oncol Hematol. 2004 Jan;49(1):1-35. PMID: #14734152#