科研之友
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摘要
Human coagulation factor XII (FXII), also called Hageman factor, is a plasma plycoprotein that is functionally deficient in individuals with Hageman trait; which is an inherited trait discovered by chance during preoperative blood coagulation screening tests. FXII is a single-chain 596-amino-acid zymogen of a serine protease with an approximate molecular weight of 80 000 FXII appears to play an important role in blood coagulation, fibrinolysis and kinin generation. Contact of FXII with negatively charged surfaces leads to proteolytic cleavage and activation of the FXII molecule by plasma kallikrein at Arg353 - Val354. The generated FXIIa can initiate the rapid intrinsic coagulation pathway by activation of Factor XI and also seems to participate in the conversion of plasminogen to plasmin and bradykinin production pathways. Severe deficiency of FXII does not lead to an increased bleeding tendency, but has been associated with an increased risk for venous, as well as for arterial, thromboembolism.(1) @@@ We report here the genetic analysis of the FXII gene obtained from a patient with congenital FXII deficiency who died of recurrent, lethal cerebral thrombosis. After gene sequencing, we found that the present case of congenital FXII deficiency was the result of the homozygous C46T polymorphism site in the 5' untranslated region combined with a novel C73S heterozygous amino acid substitution in FXII protein.
