Domain Distribution of Type 1 VWD Sequence Variants and Impact on Clinical and Laboratory Phenotype in the Zimmerman Program
Pamela A. ChristophersonVeronica H. FloodSandra L. HaberichterDaniel B. BellissimoKenneth D. FriedmanJoan Cox GillRupa UdaniRobert R. Montgomery
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von Willebrand Disease
von Willebrand Disease
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The bleeding disorder von Willebrand disease (VWD) is caused by mutations of von Willebrand factor (VWF), a multimeric glycoprotein essential for platelet-dependent primary haemostasis. VWD type 2A-associated mutations each disrupt VWF biosynthesis and function at different stages, depending on the VWF domain altered by the mutation. These effects cause considerable heterogeneity in phenotypes and symptoms. To characterise the molecular mechanisms underlying the specific VWF deficiencies in VWD 2A/IIC, IID and IIE, we investigated VWF variants with patient-derived mutations either in the VWF pro-peptide or in domains D3 or CK. Additionally to static assays and molecular dynamics (MD) simulations we used microfluidic approaches to perform a detailed investigation of the shear-dependent function of VWD 2A mutants. For each group, we found distinct characteristics in their intracellular localisation visualising specific defects in biosynthesis which are correlated to respective multimer patterns. Using microfluidic assays we further determined shear flow-dependent characteristics in polymer-platelet-aggregate formation, platelet binding and string formation for all mutants. The phenotypes observed under flow conditions were not related to the mutated VWF domain. By MD simulations we further investigated how VWD 2A/IID mutations might alter the ability of VWF to form carboxy-terminal dimers. In conclusion, our study offers a comprehensive picture of shear-dependent and shear-independent dysfunction of VWD type 2A mutants. Furthermore, our microfluidic assay might open new possibilities for diagnosis of new VWD phenotypes and treatment choice for VWD patients with shear-dependent VWF dysfunctions that are currently not detectable by static tests.
von Willebrand Disease
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Patients with von Willebrand disease (VWD) type 2A or acquired von Willebrand syndrome (aVWS) as a consequence of implantation of left ventricular assist devices (LVAD) are both characterized by a loss of von Willebrand factor (VWF) function. Loss of VWF function is however more severe in VWD type 2A than in LVAD patients.To compare VWF function in patients with VWD type 2A and LVAD-induced aVWS to highlight the differences in VWF activity and to stress the importance of VWF multimer analysis for correct diagnosis of aVWS in LVAD patients.Plasma samples from nine VWD type 2A, nine LVAD patients, and 20 healthy donors (HD) were analyzed for VWF function (VWF:CB/VWF:Ag and VWF:RCo/VWF:Ag) and loss of high molecular weight (HMW) VWF multimers.A severely impaired VWF function was indeed confirmed in all VWD 2A patients. HMW VWF multimers were severely reduced compared to HD (0% [0, 12.29] vs 34.19% [31.68, 38.88] for HD, P < 0.001) and this loss was reflected by VWF:CB/VWF:Ag and VWF:RCo/VWF:Ag ratios <0.7. In contrast, VWF function was less affected in LVAD patients. Although HMW VWF multimers were reduced in all patients (20.31% [15.84, 21.71], vs 34.19% [31.68, 38.88] for HD, P < 0.001), six out of nine LVAD patients had normal VWF:CB/VWF:Ag or VWF:RCo/VWF:Ag ratios (>0.7).VWF:CB/VWF:Ag or VWF:RCo/VWF:Ag analysis allows detection of impaired VWF function in VWD type 2A but not always in LVAD-induced aVWS patients. In contrast, VWF multimeric analysis allows detection of the loss of HMW VWF multimers in both groups of patients. Hence, performing VWF multimer analysis is crucial to detect aVWS in LVAD patients.
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von Willebrand Disease
Platelet adhesion
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von Willebrand Disease
Ristocetin
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von Willebrand Disease
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Abstract von Willebrand disease (VWD) is the most common autosomally inherited bleeding disorder. The disease represents a range of quantitative and qualitative pathologies of the adhesive glycoprotein von Willebrand factor (VWF). The pathogenic mechanisms responsible for the type 2 qualitative variants of VWF are now well characterized, with most mutations representing missense substitutions influencing VWF multimer structure and interactions with platelet GPIbα and collagen and with factor VIII. The molecular pathology of type 3 VWD has been similarly well characterized, with an array of different mutation types producing either a null phenotype or the production of VWF that is not secreted. In contrast, the pathogenetic mechanisms responsible for type 1 VWD remain only partially resolved. In the hemostasis laboratory, the measurement of VWF:Ag and VWF:RCo are key components in the diagnostic algorithm for VWD, although the introduction of direct GPIbα-binding assays may become the functional assay of choice. Molecular genetic testing can provide additional benefit, but its utility is currently limited to type 2 and 3 VWD. The treatment of bleeding in VWD involves the use of desmopressin and plasma-derived VWF concentrates and a variety of adjunctive agents. Finally, a new recombinant VWF concentrate has just completed clinical trial evaluation and has demonstrated excellent hemostatic efficacy and safety.
von Willebrand Disease
Desmopressin
Platelet disorder
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von Willebrand Disease
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The International Society of Thrombosis Haemostasis (ISTH) classification separated Von Willebrand Disease (VWD) into type 1 and type 2 by the use of four insensitive Von Willebrand Factor (VWF) assays Ristocetine Co-factor (VWF:RCo), VWF Antigen (VWF:Ag), Ristocetine Induced Platelet Agglutination (RIPA) and VWF multimers in a low resolution gel. A complete set of VWF parameters is mandatory to discriminate between all variants of VWD type 1, 2 and 3 and includes Bleeding Time (BT), PFA-100 closure times, FVIII:C, VWF:RCo activity, VWF Collagen Binding (VWF:CB), RIPA, VWF propeptide (VWF:pp), multimeric analysis of VWF and the response of FVIII:C and VWF parameters to DDAVP. We here translate the ISTH into European, Clinical, Laboratory and Molecular (2020 ECLM) classification of the Von Willebrand Disease (VWD) related to the domain location of the Molecular (M) efect in the VWF gene to detect all variants of VWD.
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Agglutination (biology)
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