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The American Society of Hematology-International Society on Thrombosis and Haemostasis-National Hemophilia Foundation-World Federation of Hemophilia 2021 International Guidelines (IGL) on von Willebrand disease (VWD) have pointed out many challenges, mainly in the diagnostic approach of VWD patients. To determine the impact of these IGL on the current clinical and laboratory diagnosis of Italian VWD patients, we have recently conducted a survey among 43 centers affiliated with the Italian Association of Hemophilia Centers (AICE). Directors and colleagues responsible for the management of VWD patients were invited to report in a detailed questionnaire how IGL recommendations about the assessment of the specific activities of von Willebrand Factor (VWF) could be applied at their local sites. Results from such a survey showed that bleeding assessment tools, VWF antigen, and factor VIII procoagulant are currently in use in all centers. The automated assays for platelet-dependent VWF activity with or without ristocetin described in IGL have been used since 2021 in 37/43 (86%) centers. Among other laboratory tests, VWF collagen binding, ristocetin-induced platelet agglutination, multimeric analysis, VWF propeptide, VWF:FVIII binding assay were available in 49, 63, 26, 7, and 28% of AICE, respectively. Analyses of VWF gene defects are available only at 3/43 (7%) centers. Desmopressin (DDAVP) infusion trials at diagnosis, with measurements of VWF activities at 1 and 4 hours post-DDAVP, is currently performed at 38/43 (88%) centers. Based on this information, a simplified clinical diagnosis using a few automated tests before and after DDAVP has been proposed. Such a diagnostic approach will be validated prospectively in a large cohort of Italian VWD patients.
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INTRODUCTION: Recent guidelines for von Willebrand Disease (VWD) highlighted the challenges in diagnosis and management. Identifying the number of persons with VWD (PwVWD) internationally will help target support to aid diagnosis of PwVWD. AIM: To examine international registration rates of PwVWD, the influence of income status, geographical region and the age and sex profile. Cumulatively, these data will be used to inform future strategy from the World Federation of Haemophilia (WFH) to address unmet clinical and research needs. METHODS: Data from the 2018/2019 WFH Annual Global Survey (AGS) were analysed, providing a global perspective on VWD registration. RESULTS: Registration rates are lowest in South Asia (0.6/million population) and highest in Europe/Central Asia (50.9/million population, 0.005%), but below the expected prevalence rate (0.1%). National economic status impacted VWD registration rates, reflecting variation in access to optimal healthcare infrastructure. Females represented the majority of PwVWD globally, however, in low-income countries (LIC) males predominated. Age profile varied, with markedly higher rates of paediatric registrations in North America, Middle East and North Africa and South Asia. Rates of type 3 VWD registrations were significantly influenced by economic status (81% of VWD diagnoses in LIC), suggesting only the most severe VWD types are diagnosed in resource limited settings. CONCLUSION: Significant variation in registration rates of PwVWD exist internationally and is influenced by income status and the presence of HTC networks. Improved understanding of registration rates will enable targeting of advocacy to improve awareness, diagnosis and support for PwVWD internationally. KEY POINTS: Registration rates of People with Von Willebrand Disease (PwVWD) vary internationally and are influenced by national income status Although females represent the majority of PwVWD globally, in low income countries (LIC) males predominated, possibly related to stigma surrounding gynaecological bleeding. Rates of type 3 VWD registration were significantly influenced by economic status (81% of VWD diagnoses in LIC), suggesting only the most severe VWD types are diagnosed in resource limited settings.
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Hemofilia A , Doença de von Willebrand Tipo 3 , Doenças de von Willebrand , Masculino , Feminino , Humanos , Criança , Doenças de von Willebrand/diagnóstico , Doenças de von Willebrand/epidemiologia , Hemorragia , Atenção à Saúde , Europa (Continente) , Fator de von WillebrandRESUMO
INTRODUCTION: The sixth Åland Islands Conference on von Willebrand disease (VWD) on the Åland Islands, Finland, was held from 20 to 22 September 2018. AIM: The meeting brought together experts in the field of VWD from around the world to share the latest advances and knowledge in VWD. RESULTS AND DISCUSSION: The topics covered both clinical aspects of disease management, and biochemical and laboratory insights into the disease. The clinical topics discussed included epidemiology, diagnosis and treatment of VWD in different countries, management of children with VWD, bleeding control during surgery, specific considerations for the management of type 3 VWD and bleeding control in women with VWD. Current approaches to the management of acquired von Willebrand syndrome were also discussed. Despite significant advances in the understanding and therapeutic options for VWD, there remain many challenges to be overcome in order to optimise patient care. In comparison with haemophilia A, there are very few registries of VWD patients, which would be a valuable source of data on the condition and its management. VWD is still underdiagnosed, and many patients suffer recurrent or severe bleeding that could be prevented. Awareness of VWD among healthcare practitioners, including non-haematologists, should be improved to allow timely diagnosis and intervention. Diagnosis remains challenging, and the development of fast, simple assays may help to facilitate accurate and rapid diagnosis of VWD.
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Doença de von Willebrand Tipo 3 , Doenças de von Willebrand , Criança , Congressos como Assunto , Feminino , Finlândia , Hemorragia , Humanos , Sistema de Registros , Doenças de von Willebrand/complicações , Doenças de von Willebrand/diagnóstico , Doenças de von Willebrand/tratamento farmacológico , Fator de von Willebrand/uso terapêuticoRESUMO
OBJECTIVES: The present review aims to summarize the state-of-the-art von Willebrand disease (VWD) treatment focusing on specific clinical settings (obstetrics, surgery, long-term prophylaxis and comorbidities) as well as on the use of a Von Willebrand factor (VWF) concentrate with low FVIII content. METHODS: Literature research and case reports. RESULTS AND CONCLUSIONS: Considering that patients affected by VWD have an intact ability to synthesize FVIII, in order to avoid excessive levels of FVIII, a highly purified plasma VWF concentrate with low FVIII content could be particularly useful in those patients and clinical circumstances at high thrombotic risk as well as for long-term prophylaxis. When deciding the optimal therapeutic strategy, physicians should take into account both the patient's history and the differences among available concentrates according to the clinical situations requiring treatment.
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Trombose , Doenças de von Willebrand , Prova Pericial , Fator VIII/uso terapêutico , Humanos , Trombose/tratamento farmacológico , Doenças de von Willebrand/terapia , Fator de von Willebrand/uso terapêuticoRESUMO
In this issue of Blood, Chung and colleagues demonstrate in vitro and in an animal model that von Willebrand factor (VWF) self-association under shear stress can be modulated by the high-density lipoprotein and apolipoprotein A-I (HDL/ApoA-I) complex, with significant reduction in the length and thickness of VWF fibers. These antiadhesive and antithrombotic properties of HDL/ApoA-I may connect the pathology of microvasculature with that of large vessels (atherosclerosis with arterial thrombosis) and might suggest novel approaches to these thrombotic disorders.
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Apolipoproteína A-I/metabolismo , Lipoproteínas HDL/metabolismo , Adesividade Plaquetária , Trombose/metabolismo , Fator de von Willebrand/metabolismo , Animais , HumanosRESUMO
Type 2B von Willebrand disease (VWD2B) is a rare, autosomal-dominant inherited bleeding disorder, characterized by an enhanced ristocetin-induced platelet aggregation in platelet-rich plasma and often with variable degree of thrombocytopenia and loss of high-molecular-weight multimers von Willebrand factor (VWF). All these phenomena are caused by a mutant VWF, normally synthesized and assembled by endothelial cells, but with heightened affinity binding to the platelet receptor glycoprotein Ib-α (GpIb-α). When this abnormal VWF is released into the circulation and under specific clinical circumstances, in vivo platelet clumping is observed. Mutations, invariably clustered in exon 28 of the VWF gene encoding for the VWF A1 domain involved in VWF binding to GpIb-α, are responsible for VWD2B phenotype. Clinical and laboratory phenotype appears strongly related to the type of VWF-causative mutations. However, recent evidences suggest that a true platelet defect is also present in this type, with several morphological and functional abnormalities being detected in a subset of VWD2B patients.
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Plaquetas/metabolismo , Mutação , Plasma , Complexo Glicoproteico GPIb-IX de Plaquetas/metabolismo , Doença de von Willebrand Tipo 2/sangue , Fator de von Willebrand/metabolismo , Plaquetas/patologia , Éxons , Humanos , Complexo Glicoproteico GPIb-IX de Plaquetas/genética , Doença de von Willebrand Tipo 2/genética , Doença de von Willebrand Tipo 2/patologia , Fator de von Willebrand/genéticaRESUMO
Analyses of the bleeding tendency by means of the bleeding score (BS) have been proposed until now to confirm diagnosis but not to predict clinical outcomes in patients with inherited von Willebrand disease (VWD). We prospectively followed up, for 1 year, 796 Italian patients with different types of VWD to determine whether the previous BS of European VWD1 is useful to predict the occurrence of spontaneous bleeds severe enough to require replacement therapy with desmopressin (DDAVP) and/or von Willebrand factor (VWF)/factor VIII concentrates. Among the 796 patients included, 75 (9.4%) needed treatment of 232 spontaneous bleeding events. BS >10 and VWF:ristocetin cofactor activity <10 U/dL were associated with the risk of bleeding, but only a BS >10 remained highly associated in a multivariable Cox proportional hazard model (adjusted hazard ratio: 7.27 [95% confidence interval, 3.83-13.83]). Although the bleeding event-free survival was different in VWD types, only a BS >10 could predict for each type which patient had bleeding events severe enough to require treatment with DDAVP and/or concentrates. Therefore, BS can be considered a simple predictor of clinical outcomes of VWD and may identify patients needing intensive therapeutic regimens.
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Desamino Arginina Vasopressina/administração & dosagem , Hemorragia , Hemostáticos/administração & dosagem , Índice de Gravidade de Doença , Doenças de von Willebrand , Fator de von Willebrand/administração & dosagem , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Criança , Pré-Escolar , Intervalo Livre de Doença , Fator VIII , Feminino , Seguimentos , Hemorragia/tratamento farmacológico , Hemorragia/epidemiologia , Hemorragia/mortalidade , Hemorragia/patologia , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Fatores de Risco , Taxa de Sobrevida , Doenças de von Willebrand/sangue , Doenças de von Willebrand/tratamento farmacológico , Doenças de von Willebrand/mortalidade , Doenças de von Willebrand/patologiaRESUMO
A 3-1/2-year-old male with no personal or family history of bleeding disorders presented with abdominal distension, epistaxis, and anemia (hemoglobin 8.2 g/dL). A magnetic resonance imaging scan of the abdomen demonstrated a mass arising from the left kidney. Preoperative laboratory studies revealed a prolonged activated partial thromboplastin time of 49.2 seconds, a normal prothrombin time of 12.4 seconds, and a platelet count of 230, 000/µL. Further testing revealed factor VIII (FVIII) activity of 16%, factor IX (FIX) activity of 74%, von Willebrand factor (VWF) activity of 12%, VWF antigen activity of 31%, and decreased high-molecular-weight VWF multimers consistent with acquired von Willebrand syndrome (AVWS). What is the best treatment for this child?
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Doenças de von Willebrand/etiologia , Doenças de von Willebrand/terapia , Autoanticorpos/imunologia , Doenças Cardiovasculares/complicações , Criança , Pré-Escolar , Efeitos Colaterais e Reações Adversas Relacionados a Medicamentos , Humanos , Hipotireoidismo/complicações , Hipotireoidismo/metabolismo , Neoplasias/complicações , Neoplasias/metabolismo , Fator de von Willebrand/metabolismoRESUMO
During posttranslational modifications of von Willebrand factor (VWF), the VWF propeptide (VWFpp) is cleaved. The ratio between VWFpp and VWF antigen (VWF:Ag) and the ratio between factor VIII (FVIII:C) and VWF:Ag may be used to assess synthesis and clearance of VWF. We analyzed the contribution of VWFpp and ratios of VWFpp/VWF:Ag and FVIII:C/VWF:Ag in the pathophysiological characterization of type 1 von Willebrand disease (VWD) in the Molecular and Clinical Markers for the Diagnosis and Management of Type 1 VWD (MCMDM-1VWD) study. The VWFpp/VWF:Ag and FVIII:C/VWF:Ag ratios were increased among patients compared with unaffected family members and healthy controls. The VWFpp/VWF:Ag ratio was higher in individuals heterozygous for missense mutations than in those heterozygous for null alleles. In contrast, the FVIII:C/VWF:Ag ratio was highest among heterozygotes for VWF null alleles. The ratios of VWFpp/VWF:Ag and FVIII:C/VWF:Ag indicate that the pathophysiological mechanisms of type 1 VWD include reduced production and accelerated clearance of VWF, but that often a combination of both mechanisms is implicated.
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Fator VIII/análise , Precursores de Proteínas/sangue , Doença de von Willebrand Tipo 1/sangue , Doença de von Willebrand Tipo 1/diagnóstico , Fator de von Willebrand/análise , Fator de von Willebrand/química , Estudos de Casos e Controles , Estudos de Coortes , Fator VIII/genética , Família , Triagem de Portadores Genéticos , Ligação Genética , Humanos , Mutação/fisiologia , Multimerização Proteica , Precursores de Proteínas/química , Precursores de Proteínas/genética , Precursores de Proteínas/metabolismo , Processamento de Proteína Pós-Traducional/genética , Doença de von Willebrand Tipo 1/genética , Fator de von Willebrand/genética , Fator de von Willebrand/metabolismoRESUMO
BACKGROUND: Postpartum hemorrhage (PPH) remains one of the leading causes of maternal morbidity and mortality worldwide, although the lack of a precise definition precludes accurate data of the absolute prevalence of PPH. STUDY DESIGN AND METHODS: An international expert panel in obstetrics, gynecology, hematology, transfusion, and anesthesiology undertook a comprehensive review of the literature. At a meeting in November 2011, the panel agreed on a definition of severe PPH that would identify those women who were at a high risk of adverse clinical outcomes. RESULTS: The panel agreed on the following definition for severe persistent (ongoing) PPH: "Active bleeding >1000 mL within the 24 hours following birth that continues despite the use of initial measures including first-line uterotonic agents and uterine massage." A treatment algorithm for severe persistent PPH was subsequently developed. Initial evaluations include measurement of blood loss and clinical assessments of PPH severity. Coagulation screens should be performed as soon as persistent (ongoing) PPH is diagnosed, to guide subsequent therapy. If initial measures fail to stop bleeding and uterine atony persists, second- and third-line (if required) interventions should be instated. These include mechanical or surgical maneuvers, i.e., intrauterine balloon tamponade or hemostatic brace sutures with hysterectomy as the final surgical option for uncontrollable PPH. Pharmacologic options include hemostatic agents (tranexamic acid), with timely transfusion of blood and plasma products playing an important role in persistent and severe PPH. CONCLUSION: Early, aggressive, and coordinated intervention by health care professionals is critical in minimizing blood loss to ensure optimal clinical outcomes in management of women with severe, persistent PPH.
Assuntos
Hemorragia Pós-Parto/diagnóstico , Hemorragia Pós-Parto/terapia , Prática Profissional , Transtornos Herdados da Coagulação Sanguínea/complicações , Transtornos Herdados da Coagulação Sanguínea/diagnóstico , Transtornos Herdados da Coagulação Sanguínea/terapia , Transfusão de Componentes Sanguíneos/estatística & dados numéricos , Prova Pericial , Feminino , Hemostáticos/uso terapêutico , Humanos , Trabalho de Parto , Hemorragia Pós-Parto/etiologia , Guias de Prática Clínica como Assunto , Gravidez , Prática Profissional/normas , Prática Profissional/estatística & dados numéricos , Fatores de RiscoRESUMO
Plasma-derived von Willebrand factor-containing factor VIII concentrates (pd-VWF/FVIII-C) are the mainstay of treatment in von Willebrand disease (VWD). Real-world data on efficacy and safety of these pd-VWF/FVIII-C are required. To retrospectively evaluate the efficacy and safety of pd-VWF/FVIII-C (Fanhdi® and Alphanate®, Grifols) in clinical practice in Italy. A multicentric, observational, retrospective study at 10 Italian centers was conducted. Eligible patients diagnosed with inherited VWD (ISTH criteria) were treated with either Fanhdi® or Alphanate® for bleeding episodes, prevention of surgical bleeding and secondary long-term prophylaxis (SLTP) according to clinical practice with medical records collected from January 2007 to December 2019. Efficacy/safety of pd-VWF/FVIII-C was assessed according to FDA-agreed objective criteria following regulatory procedures. Fifty-seven patients (M/F: 21/36) were enrolled in the study with the following VWD types: VWD1 (n = 29, 52%), VWD2A (n = 10, 18%), VWD2B (n = 7, 12%), VWD2M (n = 2, 4%), VWD2N (n = 1, 2%), VWD2 unclassified (n = 1, 2%), and VWD3 (n = 7, 12%). These pd-VWF/FVIII-C were used to manage 58 bleeding episodes (n = 24 patients), 100 surgeries (n = 47 patients), and 7 SLTP (n = 6 patients). Global clinical efficacy with these pd-VWF/FVIII-C was reported to be excellent/good in 85% of bleeding episodes, 98% of surgeries, and 100% of SLTP. As far as safety, no adverse-drug-related episodes, immunogenic or thrombotic events were reported. This study confirmed that Fanhdi® and Alphanate® were effective and safe in the management of bleeding episodes, the prevention of bleeding during surgeries and for SLTP in Italian patients with inherited VWD.
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Acquired von Willebrand syndrome (AVWS) is an acquired bleeding disorder, first reported in 1968, with clinical and laboratory features similar to inherited von Willebrand disease. This rare bleeding disorder occurs mainly in patients with underlying lymphoproliferative, cardiovascular, myeloproliferative, and immunologic disorders. In contrast to acquired hemophilia A, AVWS is rarely associated with measurable anti-von Willebrand factor inhibitors. In most instances, AVWS is identified because of bleeding complications: in fact, more than 80% of the patients with this syndrome are active bleeders. Recurrent bleeding episodes occur in approximately 20 to 33% of patients with AVWS, especially following major trauma and surgery. Because of the heterogeneous mechanisms of AVWS, more than one therapeutic approach is often required to prevent or treat acute bleedings. Remission from some forms of AVWS can be obtained when the underlying disorders are treated.
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Doenças de von Willebrand/diagnóstico , Doenças de von Willebrand/terapia , Humanos , Doenças de von Willebrand/sangue , Fator de von Willebrand/metabolismoRESUMO
The acquired von Willebrand syndrome (AVWS) is a bleeding disorder that is frequently unrecognized or is misdiagnosed as von Willebrand disease. AVWS is characterized by structural or functional defects of von Willebrand factor (VWF) that are secondary to autoimmune, lymphoproliferative or myeloproliferative, malignant, cardiovascular, or other disorders. VWF abnormalities in these disorders can result from (1) antibody-mediated clearance or functional interference, (2) adsorption to surfaces of transformed cells or platelets, or (3) increased shear stress and subsequent proteolysis. Diagnosis can be challenging as no single test is usually sufficient to prove or exclude AVWS. Furthermore, there are no evidence-based guidelines for management. Treatments of the underlying medical condition, including chemo/radiotherapy, surgery, or immunosuppressants can result in remission of AVWS, but is not always feasible and successful. Because of the heterogeneous mechanisms of AVWS, more than one therapeutic approach is often required to treat acute bleeds and for prophylaxis during invasive procedures; the treatment options include, but are not limited to, desmopressin, VWF-containing concentrates, intravenous immunoglobulin, plasmapheresis or recombinant factor VIIa. Here, we review the management of AVWS with an overview on the currently available evidence and additional considerations for typical treatment situations.
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Doenças Hematológicas/diagnóstico , Doenças Hematológicas/terapia , Hemostáticos/uso terapêutico , Doenças de von Willebrand/diagnóstico , Doenças de von Willebrand/terapia , Animais , Desamino Arginina Vasopressina/uso terapêutico , Fator VIIa/uso terapêutico , Doenças Hematológicas/epidemiologia , Doenças Hematológicas/patologia , Humanos , Imunoglobulinas Intravenosas/uso terapêutico , Plasmaferese , Proteínas Recombinantes/uso terapêutico , Síndrome , Doenças de von Willebrand/epidemiologia , Doenças de von Willebrand/patologia , Fator de von Willebrand/uso terapêuticoRESUMO
The platelet P2Y(12) purinoceptor (P2Y(12)R), which plays a crucial role in hemostasis, undergoes internalization and subsequent recycling to maintain receptor responsiveness, processes that are essential for normal platelet function. Here, we observe that P2Y(12)R function is compromised after deletion or mutation of the 4 amino acids at the extreme C-terminus of this receptor (ETPM), a putative postsynaptic density 95/disc large/zonula occludens-1 (PDZ)-binding motif. In cell line models, removal of this sequence or mutation of one of its core residues (P341A), attenuates receptor internalization and receptor recycling back to the membrane, thereby blocking receptor resensitization. The physiologic significance of these findings in the regulation of platelet function is shown by identification of a patient with a heterozygous mutation in the PDZ binding sequence of their P2Y(12)R (P341A) that is associated with reduced expression of the P2Y(12)R on the cell surface. Importantly, platelets from this subject showed significantly compromised P2Y(12)R recycling, emphasizing the importance of the extreme C-terminus of this receptor to ensure correct receptor traffic.
Assuntos
Plaquetas/fisiologia , Domínios PDZ/fisiologia , Ativação Plaquetária/fisiologia , Transporte Proteico/fisiologia , Receptores Purinérgicos P2Y12/metabolismo , Difosfato de Adenosina/metabolismo , Animais , Arrestina/metabolismo , Células CHO , Linhagem Celular Transformada , Clatrina/metabolismo , Cricetinae , Hemostasia/fisiologia , Humanos , Mutagênese/fisiologia , Estrutura Terciária de Proteína/fisiologia , Receptores Purinérgicos P2Y12/química , Receptores Purinérgicos P2Y12/genéticaRESUMO
Von Willebrand disease (VWD) is an inherited bleeding disorder caused by quantitative or qualitative deficiencies in von Willebrand factor (VWF). People with VWD may experience excessive, recurrent or prolonged bleeding, particularly during menstruation, childbirth, surgery or following trauma. However, many VWD patients are undiagnosed, and therefore inadequately treated. Reasons for the underdiagnosis of VWD include its relatively mild symptoms, complex diagnosis, lack of awareness among non-specialist healthcare providers and the general population, and a lack of prioritisation of disorders disproportionately affecting females. The vwdtest.com platform was launched as part of a global initiative to raise awareness and improve diagnosis of VWD. Besides providing VWD-specific educational resources, the website includes an online bleeding self-assessment tool and offers diagnostic support for individuals, and their providers, who have a score suggestive of a bleeding disorder. vwdtest.com helps to address these unmet needs, especially in regions with limited access to educational and diagnostic resources.
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Transtornos Hemorrágicos , Doenças de von Willebrand , Feminino , Humanos , Doenças de von Willebrand/diagnóstico , Doenças de von Willebrand/terapia , Doenças de von Willebrand/complicações , Fator de von Willebrand , Hemorragia/diagnóstico , Hemorragia/etiologia , Hemorragia/terapiaRESUMO
BACKGROUND: Type 3 von Willebrand disease (VWD) is the most severe form of this disease owing to the almost complete deficiency of von Willebrand factor (VWF). Replacement therapy with plasma-derived products containing VWF or recombinant VWF rarely cause the development of alloantibodies against VWF that may be accompanied by anaphylactic reactions. OBJECTIVE: The objective of this study was to assess the prevalence of anti-VWF alloantibodies in subjects with type 3 VWD enrolled in the 3WINTERS-IPS. METHODS: An indirect in-house enzyme-linked immunosorbent assay has been used to test all the alloantibodies against VWF. Neutralizing antibodies (inhibitors) have been tested with a Bethesda-based method by using a VWF collagen binding (VWF:CB) assay. Samples positive for anti-VWF antibodies were further tested with Bethesda-based methods by using the semiautomated gain-of-function glycoprotein-Ib binding (VWF:GPIbM) and a VWF antigen (VWF:Ag) enzyme-linked immunosorbent assay. RESULTS: In total, 18 of the 213 (8.4%) subjects tested positive for anti-VWF antibodies and 13 of 213 (6%) had VWF:CB inhibitors. These 13 were among the 18 with anti-VWF antibodies. Of the 5 without VWF:CB inhibitors, 3 had non-neutralizing antibodies, 1 only inhibitor against VWF:GPIbM, and one could not be tested further. Ten of the 13 subjects with VWF:CB inhibitors also had VWF:GPIbM inhibitors, 6 of whom also had VWF:Ag inhibitors. Subjects with inhibitors were homozygous for VWF null alleles (11/14), homozygous for a missense variant (1/14), or partially characterized (2/14). CONCLUSIONS: Anti-VWF antibodies were found in 8.4% of subjects with type 3 VWD, whereas neutralizing VWF inhibitors were found in 6%, mainly in subjects homozygous for VWF null alleles. Because inhibitors may be directed toward different VWF epitopes, their detection is dependent on the assay used.
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Doença de von Willebrand Tipo 2 , Doença de von Willebrand Tipo 3 , Doenças de von Willebrand , Humanos , Fator de von Willebrand/metabolismo , Doenças de von Willebrand/diagnóstico , Isoanticorpos , Complexo Glicoproteico GPIb-IX de Plaquetas/metabolismo , Doença de von Willebrand Tipo 2/diagnósticoRESUMO
von Willebrand factor (VWF) is an essential mediator of platelet adhesion to the vessel wall, but little is known about its role in megakaryocytopoiesis. VWF and its platelet receptor, glycoprotein Ibalpha (GPIbalpha), are both expressed during megakaryocyte (MK) maturation. This study was designed to evaluate whether the enhanced VWF-GPIbalpha interactions typical of patients with von Willebrand disease type 2B (VWD2B) modify platelet production. Platelets from 9 patients with VWD2B with 7 different gain-of-function mutations were examined by electron microscopy (EM) and immunofluorescence labeling. For the patients with VWD2B, EM characteristically showed variable numbers of structurally abnormal giant platelets, sometimes in agglutinates. Cultures of MKs from controls performed with or without purified VWF confirmed a positive influence of VWF on platelet production with specific inhibition by an antibody blocking VWF binding to GPIbalpha. VWD2B MK cultures examined by EM showed a disorganized demarcation membrane system and abnormal granule distribution. They produced platelets with structural abnormalities typical of VWD2B. Confocal examination of MK revealed limited extension of pseudopods with few large proplatelets. These results confirm that megakaryocytopoiesis is modified by the enhanced VWF-GPIbalpha interactions. These data obtained for controls and patients with VWD2B suggest a novel regulatory role of VWF-GPIbalpha interactions in platelet production.
Assuntos
Plaquetas/patologia , Megacariócitos/patologia , Glicoproteínas de Membrana/fisiologia , Trombopoese/fisiologia , Doença de von Willebrand Tipo 2/sangue , Fator de von Willebrand/fisiologia , Substituição de Aminoácidos , Plaquetas/ultraestrutura , Membrana Celular/ultraestrutura , Tamanho Celular , Células Cultivadas/ultraestrutura , Grânulos Citoplasmáticos/ultraestrutura , Humanos , Megacariócitos/efeitos dos fármacos , Microscopia Confocal , Microscopia Eletrônica , Mutação de Sentido Incorreto , Complexo Glicoproteico GPIb-IX de Plaquetas , Mutação Puntual , Mapeamento de Interação de Proteínas , Trombopoese/efeitos dos fármacos , Trombopoetina/farmacologia , Doença de von Willebrand Tipo 2/genética , Fator de von Willebrand/genética , Fator de von Willebrand/farmacologiaRESUMO
Type 3 von Willebrand disease (VWD3) is characterized by unmeasurable von Willebrand factor (VWF) levels in plasma and platelets and severe but variable hemorrhagic symptoms. To identify and characterize the causal mutations, we screened 10 Italian patients with VWD3 by several techniques including Multiplex Ligation-dependent Probe Amplification to identify large insertions and deletions, High Resolution Melting and PCR coupled with Sanger sequencing. Fourteen different mutations scattered throughout the VWF gene were identified, 10 of which were novel. As expected, most of these mutations caused null alleles: five were deletions (del exons 1-3, del exon 17, c.2157delA, c.2269delCT, and c.3940delG), three nonsense (p.Q1526X, p.E1549X, and p.C2448X) and three potential splice-site mutations (c.658-2A>G, c.7729+7C>T, and c.8155+1G>T). Three candidate missense mutations (p.C2184S, p.C2212R, and p.C2325S) were also identified. Missense mutations and the putative splice-site defects were confirmed to be disease related by in vitro expression studies and mRNA analysis. None of these patients have developed alloantibodies against VWF. This study extends our previous finding that most of the mutations that we identified in VWD3 patients arise independently and are scattered throughout the entire VWF gene.