Inherited defects of platelet function.

Inherited platelet defects bleeding syndromes underlie of varying severity. The Bernard-Soulier syndrome and Glanzmann thrombasthenia are disorders of membrane glycoproteins. In the former, a deficiency of the GPIb-IX-V complex leads to defective platelet adhesion, while in thrombasthenia, platelet aggregation does not occur in the absence of the integrin alphaIIbbeta3. Defects of primary receptors for stimuli are increasingly being described, and include a defect of a newly cloned Gi-protein-linked, seven transmembrane domain, ADP receptor. These lead to agonist-specific deficiencies in the platelet function response, as do abnormalities in the many intracellular signaling pathways of platelets. Defects affecting secretion from dense bodies and alpha-granules, of ATP production and generation of procoagulant activity, are also encountered. Some disorders are exclusive to megakaryocytes and platelets, while in others, such as the Chediak-Higashi, Hermansky-Pudlak and Wiskott-Aldrich syndromes; the molecular lesion extends to other cell types. Disorders affecting platelet morphology, the so-called "giant platelet" syndromes should also be considered. In familial thrombocytopenias, platelets are produced in insufficient quantities to assure hemostasis. Platelet disorders are examples of rare diseases; nevertheless they have provided essential information in the elucidation of the molecular basis of platelet function.