Glanzmann Thromboasthenia: An autosomal recessive bleeding
disorder characterized by failure of platelet aggregation and absent or
diminished clot retraction. It has been classified clinically into types I
and II. In type I, platelets show absence of the glycoprotein IIb/IIIa
(GPIIb-IIIa) complexes at their surface and lack fibrinogen and clot
retraction capability. In type II, the platelets express the GPIIb-IIIa
complex at reduced levels (5-20% controls), have detectable amounts of
fibrinogen, and have low or moderate clot retraction capability. The
disorder is manifest soon after birth with episodic mucocutaneous bleeding
and unprovoked bruising. Epistaxis frequently occurs. Women experience
copious menstrual hemorrhage. Intracranial bleeding may occur. Bleeding time
is prolonged, with normal platelet count, platelet morphology, and
coagulation times. Platelets fail to aggregate, either spontaneously or in
response to agonists, such as ADP, thrombin, or epinephrine, although there
may be a transient response to ristocetin.