Endothelial Function in Patients With Von Willebrand Disease.

In patients with von Willebrand disease (vWD) the interest in age-related comorbidities has grown, because the life expectancy of these patients has increased. The research question of this study was whether patients with vWD show a different endothelial function compared to the general population. A total of 37 patients with type 1 (n = 23), type 2 (n = 10) and type 3 (n = 4) vWD, 14 controls and 38 patients with coronary artery disease (CAD) were included in this study. Five markers of endothelial dysfunction (MOED) were determined. Moreover, the endothelial function was examined using the Itamar Endo-PAT. The reactive hyperemia index (RHI) was calculated from the results. The markers soluble intercellular adhesion molecule-1 (p = 0.171), P-Selectin (p = 0.512), interleukin-6 (p = 0.734) and monocyte chemoattractant protein-1 (p = 0.761) showed higher levels in patients with vWD, but were not significantly different compared to the control group. RHI was impaired in CAD-patients (1.855), whereas vWD patients had mean results of 1.870 and controls 2.112 (p = 0.367). In this study, the endothelial function measurements of patients with von Willebrand disease were not significantly different compared to healthy controls.

Type 2B von Willebrand disease with or without large multimers: A distinction of the two sides of the disorder is long overdue.

Most, but not all patients with type 2B von Willebrand disease (VWD)-which features gain-of-function mutations in the A1 domain of von Willebrand factor (VWF)-have no circulating large VWF multimers. Similarities and differences were analysed in 33 type 2B patients, 12 with a normal and 21 with an abnormal multimer pattern, to see whether they should be considered separately. The minimum aggregating dose of ristocetin was similarly reduced in both patient groups, and modulated by their underlying VWF mutations. Platelet VWF content was normal in all patients lacking in large multimers, but sometimes reduced in those with a normal multimer pattern. All the former patients and none of the latter had persistent or transient thrombocytopenia. A short VWF half-life (affecting plasma VWF levels) was seen in both groups, but more pronounced in patients without large multimers. Bleeding scores were also high in all patients, but more so in those without large multimers, apparently regardless of their platelet count. The marked phenotypic heterogeneity of type 2B VWD concerns not only patients' VWF multimer pattern, but also their bleeding risk, and consequently their appropriate treatment too. Hence the need to clearly distinguish between type 2B VWD with normal or abnormal VWF multimers.

LIM kinase/cofilin dysregulation promotes macrothrombocytopenia in severe von Willebrand disease-type 2B.

von Willebrand disease type 2B (VWD-type 2B) is characterized by gain-of-function mutations of von Willebrand factor (vWF) that enhance its binding to platelet glycoprotein Ibα and alter the protein's multimeric structure. Patients with VWD-type 2B display variable extents of bleeding associated with macrothrombocytopenia and sometimes with thrombopathy. Here, we addressed the molecular mechanism underlying the severe macrothrombocytopenia both in a knockin murine model for VWD-type 2B by introducing the p.V1316M mutation in the murine Vwf gene and in a patient bearing this mutation. We provide evidence of a profound defect in megakaryocyte (MK) function since: (a) the extent of proplatelet formation was drastically decreased in 2B MKs, with thick proplatelet extensions and large swellings; and (b) 2B MKs presented actin disorganization that was controlled by upregulation of the RhoA/LIM kinase (LIMK)/cofilin pathway. In vitro and in vivo inhibition of the LIMK/cofilin signaling pathway rescued actin turnover and restored normal proplatelet formation, platelet count, and platelet size. These data indicate, to our knowledge for the first time, that the severe macrothrombocytopenia in VWD-type 2B p.V1316M is due to an MK dysfunction that originates from a constitutive activation of the RhoA/LIMK/cofilin pathway and actin disorganization. This suggests a potentially new function of vWF during platelet formation that involves regulation of actin dynamics.

Accelerated uptake of VWF/platelet complexes in macrophages contributes to VWD type 2B-associated thrombocytopenia.

Von Willebrand disease (VWD) type 2B is characterized by mutations causing enhanced binding of von Willebrand factor (VWF) to platelets. Bleeding tendency is associated with heterogeneous clinical manifestations, including moderate to severe thrombocytopenia. The underlying mechanism of the thrombocytopenia has remained unclear. Here, a mouse model of VWD type 2B was used to investigate pathways contributing to thrombocytopenia. Immunohistochemical analysis of blood smears revealed that mutant VWF was exclusively detected on platelets of thrombocytopenic VWD type 2B mice, suggesting that thrombocytopenic VWD type 2B mice were elevated two- to threefold upon chemical macrophage depletion. Colocalization of platelets with CD68-positive Kupffer cells and CD168-positive marginal macrophages in liver and spleen, respectively, confirmed the involvement of macrophages in the removal of VWF/platelet complexes. Significantly more platelets were found in liver and spleen of VWD type 2B mice compared with control mice. Finally, platelet survival was significantly shorter in VWD type 2B mice compared with control mice, providing a rationale for lower platelet counts in VWD type 2B mice. In conclusion, our data indicate that VWF type 2B binds to platelets and that this is a signal for clearance by macrophages, which could contribute to the thrombocytopenia in patients with VWD type 2B.

Inherited thrombocytopenias: an approach to diagnosis and management.

Inherited thrombocytopenias vary in their presentation, associated features, and molecular etiologies. An accurate diagnosis is important to provide appropriate therapy as well as counseling for the individual and their family members. As the genetic basis of more disorders is understood, it will be possible to diagnose a greater fraction of patients as well as learn more about the process of megakaryopoiesis and platelet production.

Diagnosis and therapeutic management in a patient with type 2B-like acquired von Willebrand syndrome.

Acquired von Willebrand syndrome (AVWS) usually mimics von Willebrand disease (VWD) type 1 or 2A. However, in rare cases, the characteristics of other VWD types can predominate in AVWS that might require careful consideration of differential treatment options. The diagnosis and the treatment of a case of type 2B-like AVWS are discussed. Diagnosis of AVWS was ascertained by determining ristocetin cofactor activity, ristocetin-induced platelet aggregation, von Willebrand factor antigen, collagen binding and characterization of von Willebrand factor (VWF) multimers. Inhibitor presence was sought through mixing experiments, the Bethesda method, and calculation of the in-vivo recovery and plasma half-life of VWF after administration of factor VIII/VWF concentrate. Mutations in the A1 domain of VWF were ruled out by sequencing of exon 28 of the VWF gene. A 34-year-old male patient, putatively diagnosed with type 2B VWD, and undergoing laparoscopic cholecystectomy, did not respond adequately to perioperative hemostatic treatment with desmopressin and high doses of factor VIII/VWF concentrate, requiring the administration of recombinant activated factor VII. Further diagnostic workup revealed AVWS mimicking type 2B VWD, most likely owing to an autoantibody developed in the course of underlying monoclonal gammopathy of undetermined significance. The presence of AVWS should be considered before a diagnosis of type 2B VWD is made, especially in patients with a history atypical for inherited disease.