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Scott syndrome

Field	Value
synonyms	Platelet factor X receptor deficiency
name	Scott syndrome
image	Autosomal recessive - en.svg
caption	This condition is inherited in an autosomal recessive manner

Scott syndrome is a rare congenital bleeding disorder that is due to a defect in a platelet mechanism required for blood coagulation.

Normally when a vascular injury occurs (i.e., a cut, scrape or other injury that causes bleeding), platelets are activated and phosphatidylserine (PS) in the inner leaflet of the platelet membrane is transported to the outer leaflet of the platelet membrane, where it provides a binding site for plasma protein complexes that are involved in the conversion of prothrombin to thrombin, such as factor VIIIa-IXa (tenase) and factor Va-Xa (prothrombinase).

In Scott syndrome, the mechanism for translocating PS to the platelet membrane is defective, resulting in impaired thrombin formation. 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 affects 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 anoctamin 6 (ANO6, transmembrane protein 16F, TMEM16F). At present, the only treatment for episodes of bleeding is the transfusion of normal platelets.

References

Weiss HJ. Scott syndrome: a disorder of platelet coagulant activity (PCA). ''Sem Hemat'' 1994; 31:312–319
Zwaal FA, Comfurius P, Bevers EM. Scott syndrome, a bleeding disorder caused by defective scrambling of membrane phospholipids. ''Biochem Bioph Acta'' 2004; 1636:119–128
Rosing J, Bevers EM, Comfurius P, [[Coen Hemker. Hemker HC]], von Dieijen G, Weiss HJ, et al. Impaired factor X and prothrombin activation associated with decreased phospholipid exposure in platelets from a patient with a bleeding disorder. ''Blood'' 1985; 65:1557–1561.
Toti F, Satta N, Fressinaud E, Meyer D, Freyssinet JM. Scott syndrome, characterized by impaired transmembrane migration of procoagulant phosphatidylserine and hemorrhagic complications, is an inherited disorder. ''Blood'' 1996; 87:1409-1415
Elliott JI, Mumford AD, Albrecht C, Collins PW, Giddings JC, Higgins CF et al. Characterization of lymphocyte responses to Ca2+ in Scott syndrome. ''Thromb Haemost'' 2004; 91:412-415
Sims PJ, Wiedmer T. Unraveling the mysteries of phospholipid scrambling. ''Thromb Haemost'' 2001; 86:266–275
Zhou Q, Sims PJ, Wiedmer T. Expression of proteins controlling transbilayer movement of plasma membrane phospholipids in the B lymphocytes from a patient with Scott syndrome. ''Blood'' 1998; 92:1707–1712
Weiss, HJ: Impaired platelet procoagulant mechanisms in patients with bleeding disorders. ''Sem. Thromb. Hemost.'' 35:233–241, 2009
Suzuki J, Umeda M, Sims PJ, Nagata S. Calcium-dependent phospholipid scrambling by TMEM16F. ''Nature'' online, November 24, 2010

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coagulopathies rare-diseases syndromes

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