Brugge J M, Simioni P, Bernardi F, Tormene D, Lunghi B, Tans G, Pagnan A, Rosing J, Castoldi E
Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, Netherlands.
J Thromb Haemost. 2005 Dec;3(12):2695-702. doi: 10.1111/j.1538-7836.2005.01634.x.
Functional defects of the protein C pathway, detectable in plasma as activated protein C (APC) resistance, are a prevalent risk factor for venous thrombosis. The factor V (FV) Leiden mutation causes APC resistance by interfering with the APC-mediated inactivation of both FVa and FVIIIa. Co-inheritance of FV Leiden and quantitative FV deficiency on different alleles, a rare condition known as pseudo-homozygous APC resistance, is associated with pronounced APC resistance and 50% reduced FV levels, because of non-expression of the non-Leiden FV allele.
The role of normal FV in modulating the APC resistance phenotype in carriers of FV Leiden was investigated in patients with pseudo-homozygous APC resistance and in model systems.
PATIENTS/METHODS: Four functional plasma assays probing both components of APC resistance (susceptibility of FVa to APC and cofactor activity of FV in FVIIIa inactivation) were employed to compare seven clinically and genetically characterized FV Leiden pseudo-homozygotes to 30 relatives with different FV genotypes (including 12 FV Leiden heterozygotes and seven carriers of FV deficiency) and to 32 unrelated FV Leiden homozygotes.
All assays consistently indicated that FV Leiden pseudo-homozygotes are significantly more APC-resistant than heterozygotes and indistinguishable from homozygotes. Thrombin generation measurements in FV-deficient plasma reconstituted with purified normal FV and FV Leiden confirmed these observations and showed that the expression of the normal FV allele is an important modulator of APC resistance in FV Leiden heterozygotes. These findings provide an explanation for the higher thrombotic risk of FV Leiden pseudo-homozygotes when compared with heterozygotes.
蛋白C途径的功能缺陷在血浆中表现为活化蛋白C（APC）抵抗，是静脉血栓形成的常见危险因素。因子V（FV）Leiden突变通过干扰APC介导的FVa和FVIIIa失活而导致APC抵抗。FV Leiden与不同等位基因上的定量FV缺乏共同遗传，这种罕见情况称为假纯合子APC抵抗，与明显的APC抵抗和FV水平降低50%有关，这是由于非Leiden FV等位基因不表达。
在假纯合子APC抵抗患者和模型系统中研究正常FV在调节FV Leiden携带者的APC抵抗表型中的作用。
患者/方法：采用四种功能性血浆检测方法来检测APC抵抗的两个组成部分（FVa对APC的敏感性以及FV在FVIIIa失活中的辅因子活性），以比较7例临床和基因特征明确的FV Leiden假纯合子与30名具有不同FV基因型的亲属（包括12名FV Leiden杂合子和7名FV缺乏携带者）以及32名无关的FV Leiden纯合子。
所有检测均一致表明，FV Leiden假纯合子比杂合子对APC的抵抗性明显更强，且与纯合子无差异。用纯化的正常FV和FV Leiden重构的FV缺乏血浆中的凝血酶生成测量结果证实了这些观察结果，并表明正常FV等位基因的表达是FV Leiden杂合子中APC抵抗的重要调节因子。这些发现解释了与杂合子相比，FV Leiden假纯合子血栓形成风险更高的原因。
