Primary Hemostatic (Platelet Plug) Disorders

Defects of Platelet Adhesion


  von Willebrand disease
  Bernard-Soulier syndrome (absence of dysfunction of GpIb-IX-V)


Defects of Platelet Aggregation


  Glanzmann's thrombasthenia (absence or dysfunction of GpIIbIIIa)
  Afibrinogenemia


Defects of Platelet Secretion


  Decreased cyclooxygenase activity
    Drug-induced (aspirin, nonsteroidal anti-inflammatory agents)
    Inherited
  Granule storage pool defects
    Inherited
    Acquired
  Nonspecific drug effects
  Uremia
  Platelet coating (e.g., paraprotein, penicillin)


Defect of platelet coagulant activity
  Scott's syndrome

Scott syndrome is a rare congenital bleeding disorder that is due to a defect in a platelet mechanism required for blood coagulation.When normal platelets are activated, as may occur at sites of vascular injury, phosphatidylserine (PS) in the inner leaflet of the platelet membrane is transported to the outer membrane surface of the platelet, where it provides a binding site for plasma protein complexes, such as factor VIIIa-IXa (tenase) and factor Va-Xa (prothrombinase), that are involved in the conversion of prothrombin to thrombin.


In Scott syndrome, the mechanism for translocating PS to the platelet membrane is defective, resulting in impaired thrombinformation. A similar defect in PS translocation has also been demonstrated in Scott syndrome red blood cells and Epstein-Barr virus transformed lymphocytes, suggesting that the defect in Scott syndrome reflects a mutation in a stem cell that effects multiple hematological lineages. The basis for the defect in PS translocation is, at present, unknown. A candidate protein, scramblase, that may be involved in this process appears to be normal in Scott syndrome platelets.Other possible defects in PS translocation, reported in some patients, require further study. The initially reported patient with Scott Syndrome has been found to have a mutation at a splice-acceptor site of the gene encoding transmembrane protein 16F (TMEM16F)[9]. At present, the only treatment for episodes of bleeding is the transfusion of normal platelets.