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Venöse thromboembolische Erkrankungen ereignen sich bei ca. l von 1000 Individuen jährlich. Meist handelt es sich dabei um ein multi-faktorielles Geschehen, das durch Zusammenwirken erworbener bzw. exogener Risikofaktoren einerseits sowie genetisch bedingter Veränderungen andererseits verursacht ist. In den letzten Jahren wurden mehrere Risikofaktoren der hereditären Thrombophilie identifiziert, die inzwischen als etabliert gelten. Daneben gibt es jedoch eine Reihe weiterer genetischer Defekte, deren Beteiligung bei der Entstehung venöser Thrombosen wahrscheinlich oder zumindest theoretisch denkbar ist. In diesem Überblick werden als solche Lipoprotein (a), Thrombomodulin, Fibrinogen, der Thrombin-aktivierbare Fibrinolyse Inhibitor (TAFI),Gewebefaktor (Tissue Factor) sowie der Endothelzell-Protein C Rezeptor (EPCR) dargestellt, ihre biochemischen Eigenschaften sowie physiologischen Funktionen zusammengefaßt und bekannte Mutationen bzw. Polymorphismen der betreffenden Gene als mögliche Risikofaktoren der hereditären Thrombophilie diskutiert. Vorzugsweise werden die bisherigen Kenntnisse über ihre wahrscheinliche pathophysiologische Beteiligung bei der Entstehung venöser Gefäßverschlüsse kritisch gewürdigt.
Activated blood coagulation factor (F) XIII (FXIIIa), a transglutaminase comprised of two A and two B subunits in a tetrameric structure (A2B2) of 320 kd, has a central role in the haemostatic system by cross-linking fibrin monomers in the final step of blood coagulation, thus stabilizing the fibrin clot and increasing its resistance to fibrinolysis. In addition, FXIIIa is implicated in the cross-linking of several other proteins, such as a-2-antiplasmin, fibronectin, and collagen. The impact of genetic variations of FXIII in thrombotic disorders has not been studied until recently, when a common polymorphism was described as a new candidate genetic factor influencing the risk of thrombotic diseases. This polymorphism results from a G to T transition in codon 34 of exon 2 of the catalytic FXIII A-subunit gene, leading to the substitution of leucine for valine (FXHIVal34Leu) close to the thrombin activation site. Genotype at this polymorphism is closely related to FXIII fibrin cross-linking activity, and FXIIILeu is associated with increased thrombin activation of FXIII with associated changes in fibrin structure. Initially, FXIII Val34Leu was shown to be significantly less common in British patients with a history of myocardial infarction than in controls, suggesting for the first time a new role for FXIII in a polygenic thrombotic disease. In addition to its proposed protective effect against thrombotic heart diseases, the Leu34 allele has also been correlated with protection against venous thromboembolism and thrombotic cerebral artery occlusion, whereas it seems to confer an increased risk for intracerebral haemorrhage. Because this genetic variation is associated with a higher activity of the enzyme, the mechanism accounting for the putative anti-thrombotic effect of FXIII Val34Leu is not well understood. However, it has been hypothesized that increased rates of FXIII activation could lead to ineffective cross-linking, or that the kinetics of the cross-linking reactions may be disrupted because of the effects of FXIIIa on other proteins. Previous s'tudies have demonstrated that the FXIII Val34Leu polymorphism is highly prevalent in ^[[200~several Caucasian populations, with reported Leu34 allele frequencies of around 0.25, whereas it is less prevalent in populations of African and Asian origin. The known significant ethnic heterogeneity linked to the FXIII Val34Leu polymorphism is of relevance when analyzing its role in vascular diseases. In summary, published studies indicate that blood coagulation FXIII is involved in the multifactorial pathogenesis of vascular diseases and suggest a contribution of FXIII Val34Leu in determining the risk of myocardial infarction, stroke and venous thromboembolism.