van 't Veer C, Golden N J, Kalafatis M, Simioni P, Bertina R M, Mann K G
Department of Biochemistry, University of Vermont, Burlington 05405-0068, USA.
Blood. 1997 Oct 15;90(8):3067-72.
The classification of factor VIII deficiency, generally used based on plasma levels of factor VIII, consists of severe (<1% normal factor VIII activity), moderate (1% to 4% factor VIII activity), or mild (5% to 25% factor VIII activity). A recent communication described four individuals bearing identical factor VIII mutations. This resulted in a severe bleeding disorder in two patients who carried a normal factor V gene, whereas the two patients who did not display severe hemophilia were heterozygous for the factor V(LEIDEN) mutation, which leads to the substitution of Arg506 --> Gln mutation in the factor V molecule. Based on the factor VIII level measured using factor VIII-deficient plasma, these two patients were classified as mild/moderate hemophiliacs. We studied the condition of moderate to severe hemophilia A combined with the factor V(LEIDEN) mutation in vitro in a reconstituted model of the tissue factor pathway to thrombin. In the model, thrombin generation was initiated by relipidated tissue factor and factor VIIa in the presence of the coagulation factors X, IX, II, V, and VIII and the inhibitors tissue factor pathway inhibitor, antithrombin-III, and protein C. At 5 pmol/L initiating factor VIIa x tissue factor, a 10-fold higher peak level of thrombin formation (350 nmol/L), was observed in the system in the presence of plasma levels of factor VIII compared with reactions without factor VIII. Significant increase in thrombin formation was observed at factor VIII concentrations less than 42 pmol/L (approximately 6% of the normal factor VIII plasma concentration). In reactions without factor VIII, in which thrombin generation was downregulated by the addition of protein C and thrombomodulin, an increase of thrombin formation was observed with the factor V(LEIDEN) mutation. The level of increase in thrombin generation in the hemophilia A situation was found to be dependent on the factor V(LEIDEN) concentration. When the factor V(LEIDEN) concentration was varied from 50% to 150% of the normal plasma concentration, the increase in thrombin generation ranged from threefold to sevenfold. The data suggested that the analysis of the factor V genotype should be accompanied by a quantitative analysis of the plasma factor V(LEIDEN) level to understand the effect of factor V(LEIDEN) in hemophilia A patients. The presented data support the hypothesis that the factor V(LEIDEN) mutation can increase thrombin formation in severe hemophilia A.
通常根据血浆中凝血因子 VIII 的水平对其缺乏症进行分类，包括重度（凝血因子 VIII 活性 <正常水平的 1%）、中度（凝血因子 VIII 活性为 1%至 4%）或轻度（凝血因子 VIII 活性为 5%至 25%）。最近有一篇通讯报道了四名携带相同凝血因子 VIII 突变的个体。其中两名携带正常凝血因子 V 基因的患者出现了严重的出血性疾病，而另外两名未表现出严重血友病的患者是凝血因子 V（莱顿）突变的杂合子，该突变导致凝血因子 V 分子中的 Arg506 被 Gln 取代。根据使用缺乏凝血因子 VIII 的血浆测得的凝血因子 VIII 水平，这两名患者被归类为轻度/中度血友病患者。我们在凝血酶生成的组织因子途径的重组模型中，对中度至重度血友病 A 合并凝血因子 V（莱顿）突变的情况进行了体外研究。在该模型中，在存在凝血因子 X、IX、II、V 和 VIII 以及抑制剂组织因子途径抑制剂、抗凝血酶 III 和蛋白 C 的情况下，由重组组织因子和因子 VIIa 启动凝血酶生成。在起始因子 VIIa×组织因子浓度为 5 pmol/L 时，与没有凝血因子 VIII 的反应相比，在存在血浆水平凝血因子 VIII 的系统中观察到凝血酶形成的峰值水平高 10 倍（350 nmol/L）。在凝血因子 VIII 浓度低于 42 pmol/L（约为正常血浆凝血因子 VIII 浓度的 6%）时，观察到凝血酶形成显著增加。在没有凝血因子 VIII 的反应中，通过添加蛋白 C 和血栓调节蛋白下调了凝血酶生成，而凝血因子 V（莱顿）突变导致凝血酶形成增加。发现血友病 A 情况下凝血酶生成的增加水平取决于凝血因子 V（莱顿）的浓度。当凝血因子 V（莱顿）浓度在正常血浆浓度的 50%至 150%之间变化时，凝血酶生成的增加幅度在三倍至七倍之间。数据表明，对凝血因子 V 基因型的分析应同时对血浆凝血因子 V（莱顿）水平进行定量分析，以了解凝血因子 V（莱顿）在血友病 A 患者中的作用。所呈现的数据支持凝血因子 V（莱顿）突变可增加重度血友病 A 中凝血酶形成的假说。
