PubMed · 4969820
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P Speiser. 1967-09-22. [Plasmapheresis].. https://pubmed.ncbi.nlm.nih.gov/4969820/
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This chapter summarizes research data contributing to current understanding of disorders affecting alpha-granules of megakaryocytes and platelets. Diagnostic features of the gray platelet syndrome are well defined. Combined evidence suggests a defect, specific to the megakaryocyte cell lineage, causing a cytoskeletal abnormality and defective targeting of endogenously synthesized proteins to the alpha-granule. The abnormalities linked by signal transduction pathways. von Willebrand disease and afibrinogenaemia are disorders which highlight the functional importance of platelet storage pools of von Willebrand factor and fibrinogen, essential ligands in the process of adhesion and aggregation. The abnormality in the factor V Quebec disorder leads to a degradation of most proteins contained within the alpha-granule. The familial platelet disorder Paris-Trousseau thrombocytopenia is the only alpha-granule disorder associated with a cytogenetic abnormality, and it presents a useful model for exploring the genetic influence on regulation of thrombopoiesis. Study of these syndromes has elucidated aspects of the physiology of normal megakaryocyte maturation and platelet formation, including storage organelle biosynthesis.
Fibrinogen abnormalities can be classified as congenital or acquired. Each class manifests quantitative or qualitative alterations; the latter are known as dysfibrinogenemias. In dysfibrinogenemias, structural defects cause alterations in the conversion of fibrinogen to fibrin. Approximately 300 abnormal fibrinogens have been reported, and about 83 structural defects have been identified. The most common structural defect involve the fibrinopeptides and their cleavage sites, and the second most common involves the gamma-chain polymerization region. Approximately half of the mutants are clinically silent, whereas hemorrhage and thrombosis occur in almost equal numbers of cases. Study of the abnormal fibrinogens has provided insight into fibrinogen structure and fibrin formation and dissolution. Some of the structural abnormalities exhibit defective assembly and activation of components of the fibrinolytic system on the abnormal fibrin, resulting in impaired dissolution of fibrin, clinically associated with thrombosis.