Limitations of the ristocetin cofactor assay in measurement of von Willebrand factor function
Limitations of the ristocetin cofactor assay in measurement of von Willebrand factor function
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DOI：
10.1111/j.1538-7836.2009.03594.x
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发表时间：
2009-11-01
影响因子：
10.4
通讯作者：
Montgomery, R. R.
中科院分区：
文献类型：
--
作者：
Flood, V. H.;Friedman, K. D.;Montgomery, R. R.
背景资料：2 M型血管性血友病（VWD）的特征是血管性血友病因子（VWF）的定性缺陷，并通过与VWF抗原（VWF：Ag）相比，VWF瑞斯托康辅助因子活性（VWF：RCo）不成比例的降低来诊断。目的：我们在此报告一例VWF的瑞斯托菌素结合区序列变异的VWD误诊。患者/方法：索引病例的VWF：RCo为11 IU dL-1，VWF：RCo/VWF：Ag比值为0.09。DNA测序揭示了一个新的P1467 S突变在一个已知的瑞斯托菌素结合区的A1结构域。由于实验室检查结果与2 M型VWD一致，并且患者没有出血症状，因此进行了进一步的研究以确定这种突变是否影响VWF功能或仅仅降低其与利托那相互作用的能力。结果：重组VWF的研究显示，血小板与肉毒素的结合正常，但对利托那肽的结合显著降低。也不存在瑞斯托菌素诱导的与重组GPIb的结合，但当在不存在瑞斯托菌素的情况下使用功能获得性GPIb构建体时，观察到正常结合。用锥板分析仪（let）分析时，切应力下的VWF功能正常。结论：在P1467 S序列变异中观察到的VWF：RCo降低可能代表了使用利托那肽测量VWF活性的结果。在其他试验中正常的VWF功能与出血症状的缺乏相关，并建议需要更多的生理相关的VWF功能测定。
Background: Type 2M von Willebrand disease (VWD) is characterized by a qualitative defect in von Willebrand factor (VWF) and diagnosed by a disproportionate decrease in VWF ristocetin cofactor activity (VWF:RCo) as compared with VWF antigen (VWF:Ag). Objective: We report here on the spurious diagnosis of VWD in a patient with a sequence variation in the ristocetin-binding domain of VWF. Patients/methods: The index case had a VWF:RCo of 11 IU dL-1, with VWF:RCo/VWF:Ag ratio of 0.09. DNA sequencing revealed a novel P1467S mutation in a known ristocetin-binding region of the A1 domain. Because of the discrepancy between the laboratory findings, consistent with type 2M VWD, and the patient's lack of bleeding symptoms, further studies were performed to determine whether this mutation affected VWF function or merely reduced its ability to interact with ristocetin. Results: Studies with recombinant VWF showed normal platelet binding with botrocetin, but a significant decrease in binding in response to ristocetin. Ristocetin-induced binding to recombinant GPIb was also absent, but normal binding was seen when a gain-of-function GPIb construct was used in the absence of ristocetin. VWF function under shear stress was normal when analyzed with a cone and plate(let) analyzer. Conclusions: The decreased VWF:RCo seen with the P1467S sequence variation likely represents an artifact as a result of the use of ristocetin to measure VWF activity. The normal VWF function in other assays correlates with the lack of hemorrhagic symptoms, and suggests the need for more physiologically relevant assays of VWF function.