Laboratory diagnosis of von Willebrand's disease

[Von Willebrand disease. Molecular biology and diagnosis]

BACKGROUND

Von Willebrand disease is the most common inherited disorder of the coagulation proteins in humans. There are three types: 1, 2A, 2B, 2N, 2M and 3. It is associated with mutations on chromosome 12 in the region p13.2, encoding the von Willebrand factor (VWF), which is synthesized in endothelial cells and megakaryocytes.

DISCUSSION

The VWF gene has been characterised using molecular biology techniques, which have acquired an important role in diagnosis von Willebrand disease, as well as in the investigation of alterations in other genes, which may be involved in regulating the synthesis, processing, and secretion of VWF. However, there are still no strategies to integrate the molecular biology diagnostic tests available. Analysis of VWF multimers is a methodology that meets the characteristics for diagnosis, but it is not easy to standardise. Considering that even in tertiary centres in our country, von Willebrand patients do not have a definitive diagnosis, it is necessary to implement these methodologies to study and improve diagnosis.

CONCLUSIONS

Von Willebrand disease is highly heterogeneous due to the molecular mechanisms that produce the various clinical and laboratory phenotypes. In Mexico there are few studies related to this disease; therefore it is essential to conduct a comprehensive study including clinical, basic, and special testing laboratory tests, in order to establish a correct diagnosis, develop new therapeutic approaches, and offer the appropriate medical care and genetic counselling.

Von Willebrand disease: an overview

Most commonly inherited bleeding disorder, first described in Aland Islands by Erik von Willebrand. It occurs as a result of decrease in plasma levels or defect in von Willebrand factor which is a large multimeric glycoprotein. Monomers of this glycoprotein undergo N-glycosylation to form dimers which get arranged to give multimers. Binding with plasma proteins (especially factor VIII) is the main function of von Willebrand factor. The disease is of two forms: Inherited and acquired forms. Inherited forms are of three major types. They are type 1, type 2, and type 3; in which type 2 is sub-divided into 2A, 2B, 2M, 2N. Type 1 is more prevalent than all other types. Mucocutaneous bleeding is mild in type 1 whereas it is mild to moderate in types 2A, 2B, and 2M. Type 2N has similar symptoms of haemophilia. The pathophysiology of each type depends on the qualitative or quantitative defects in von Willebrand factor. The diagnosis is based on von Willebrand factor antigen, von Willebrand factor activity assay, FVIII coagulant activity and some other additional tests. Results should be analyzed within the context of blood group. von Willebrand factor multimer analysis is essential for typing and sub typing the disease. The management of the disease involves replacement therapy, non-replacement therapy and other therapies that include antifibrinolytics and topical agents.

A practical approach to genetic testing for von Willebrand disease

von Willebrand disease (vWD) is the most commonly diagnosed congenital bleeding disorder. The laboratory diagnosis of type 2 variants and type 3 vWD is reasonably well defined, and characterization of the von Willebrand factor (vWF) gene has facilitated definition of their molecular basis. However, for type 1 vWD, the laboratory diagnosis poses a diagnostic dilemma, and knowledge of its molecular basis is evolving. Characterization of the vWF gene and refinement of genetic techniques have led to an evolving repertoire of genetic tests. Genetic testing is costly, and thus judicious use will be increasingly important for appropriate genetic-counseling of patients with vWD and their family members. This article provides a practical approach to utilization of genetic testing in vWD.

The molecular biology of von Willebrand disease

von Willebrand disease (VWD) is a common autosomally inherited bleeding disorder associated with mucosal or trauma-related bleeding in affected individuals. VWD results from either a quantitative or qualitative deficiency of von Willebrand factor (VWF)--a glycoprotein with essential roles in primary haemostasis and as a carrier of coagulation factor VIII (FVIII) in the circulation. In recent years the identification of mutations in the VWF gene in patients with VWD has improved our understanding of the structure and function of the VWF protein, and has illustrated the importance of specific regions of VWF for its interaction with other components of the vasculature. The underlying genetic lesions and associated molecular pathology have been identified in many cases of type 2A, type 2B, type 2M, type 2N and type 3 VWD. However in the most common variant, type 1 VWD, the causative molecular defect is unknown in the large majority of cases. In the absence of an understanding of the molecular pathology underlying type 1 VWD, precise diagnosis and classification of this common disorder remains problematic.

Successful treatment with recombinant factor VIIa of therapy-resistant severe bleeding in a patient with acquired von Willebrand disease

We describe an elderly man who presented with life-threatening hematuria and gastrointestinal bleeding caused by acquired von Willebrand disease associated with monoclonal gammopathy of undetermined significance (MGUS). Standard therapy with desmopressin, von Willebrand factor-containing factor VIII concentrate, tranexamic acid, and immunoglobulin failed to achieve adequate hemostasis. However, treatment with recombinant activated factor VII (rFVIIa) arrested the bleeding completely. Since acquired von Willebrand disease can lead to life-threatening hemorrhage, clinicians should consider rFVIIa as an effective treatment option if standard therapy fails.

Hemorrhagic problems in obstetrics, exclusive of disseminated intravascular coagulation

During pregnancy many physiologic changes occur that result in an increase in coagulation factors and a decrease in fibrinolytic activity. Because hemorrhage during pregnancy is a major cause of maternal morbidity, it is important to recognize and understand the pathophysiology of hereditary and acquired bleeding disorders. This article reviews von Willebrand's disease types 1, 2, and 3 and acquired hemophilia.

Coagulation and Bleeding Disorders: Review and Update

Hemostasis is initiated by injury to the vascular wall, leading to the deposition of platelets adhering to components of the subendothelium. Platelet adhesion requires the presence of von Willebrand factor and platelet receptors (IIb/IIIa and Ib/IX). Additional platelets are recruited to the site of injury by release of platelet granular contents, including ADP. The “platelet plug” is stabilized by interaction with fibrinogen. In this review, I consider laboratory tests used to evaluate coagulation, including prothrombin time, activated partial thromboplastin time, thrombin time, and platelet count. I discuss hereditary disorders of platelets and/or coagulation proteins that lead to clinical bleeding as well as acquired disorders, including disseminated intravascular coagulation and acquired circulating anticoagulants.

The molecular basis of von Willebrand disease

von Willebrand disease (VWD) is a clinically heterogeneous bleeding disorder that reflects a wide array of defects. Quantitative subtypes of the disorder, including types 1 and 3 VWD, result in bleeding due to reduced levels of circulating von Willebrand factor (VWF) protein. Qualitative subtypes, defined as type 2 VWD, act through altered VWF function. A range of molecular defects are responsible for many of these subtypes, including missense, nonsense, splicing, insertion, and deletion mutations, resulting in either dominant or recessive inheritance. While many mutations correspond to selected variants, the basis for variation in expression and the imperfect correlations between genotype and phenotype remain to be understood.

Congenital disorders of platelet function: disorders of signal transduction and secretion

Congenital defects in platelet function are associated with bleeding manifestations of variable intensity and arise by diverse mechanisms. Defects in platelet-vessel wall interaction (disorders of adhesion) may arise because of qualitative or quantitative abnormalities in plasma von Willebrand factor (von Willebrand disease) or in platelet glycoprotein Ib, the binding site on platelets for von Willebrand factor (Bernard-Soulier syndrome). Disorders characterized by abnormal platelet-platelet interaction (disorders of aggregation) arise because of absence of plasma fibrinogen (congenital afibrinogenemia) or because of qualitative or quantitative abnormalities in platelet glycoprotein IIb-IIIa complex (Glanzmann's thrombasthenia). Patients with abnormalities in platelet secretion and signal transduction are a heterogeneous group characterized by impaired aggregation responses and secretion of granule contents. A small proportion of these patients have deficiency of granule stores (storage pool deficiency [SPD]) or impaired production of thromboxane A2; in most, the mechanisms underlying the platelet dysfunction are unknown. Evidence is accumulating that at least some patients have abnormalities in early signal transduction events. Abnormalities in phospholipase C activation, G-protein activation, and other events (eg, protein phosphorylation) have been documented. Platelets play a major role in blood coagulation, and in Scott syndrome, there is an abnormality in platelet contribution to the mechanisms leading to thrombin generation. In most patients with inherited platelet dysfunction, the underlying mechanisms remain to be delineated. Future studies of these patients should yield valuable new information on normal platelet mechanisms.

Acquired von Willebrand disease: concise review of occurrence, diagnosis, pathogenesis, and treatment

Acquired von Willebrand disease (AvWD) is a rare complication of an autoimmune or neoplastic disease. It is associated mostly with a lymphoid or plasma cell proliferative disorder. The clinical manifestations are similar to congenital von Willebrand disease. Diagnosis is confirmed by the demonstration of decreased levels of factor VIII coagulant activity (VIII:C), ristocetin cofactor activity (vWF:RCo), and von Willebrand factor (vWF) antigen (vWF:Ag). vWF multimer analysis usually reveals a type II defect with decreased abundance of higher molecular weight vWF multimers. Various pathogenetic mechanisms have been described, including the development of anti-vWF antibodies and adsorption of vWF by tumor cells. Successful management approaches have included treatment of the underlying disorder, infusion of high-dose gamma globulin, replacement therapy with factor VIII/vWF concentrates, intravenous infusion of desmopressin, and administration of corticosteroids.

von Willebrand disease

Considerable progress has been made in characterizing the specific molecular defects responsible for the heterogeneous disorder known as von Willebrand disease (VWD). A large number of molecular defects have been identified and precise characterization may now be possible in the majority of type 2A, type 2B, type 2N, and potentially also type 3 VWD cases. However, the most common variant, type 1 VWD, still remains a major challenge. Continued progress in this area will improve our understanding of the pathogenesis of VWD and lead to more rapid and precise diagnosis and classification for this common disorder. The problems of incomplete VWD penetrance and poor diagnostic sensitivity and accuracy for the currently available clinical laboratory tests provide strong incentives for the development of DNA-based diagnostics. In addition, prenatal diagnosis is now possible either at the level of single point mutations (for some subtypes) or by RFLP analysis (assuming linkage to the von Willebrand factor [VWF] gene) and will probably be applied with increasing frequency for VWD type 3 (17, 133, 175). Understanding the molecular basis of VWD also has important implications for VWF structure and function and is helping to define critical binding domains within the VWF molecule. Insights gained from these studies may eventually lead to improved therapeutic approaches not only for VWD, but also for a variety of other genetic and acquired hemorrhagic and thrombotic disorders.

A novel modifier gene for plasma von Willebrand factor level maps to distal mouse chromosome 11

Type 1 von Willebrand disease (VWD), characterized by reduced levels of plasma von Willebrand factor (VWF), is the most common inherited bleeding disorder in humans. Penetrance of VWD is incomplete, and expression of the bleeding phenotype is highly variable. In addition, plasma VWF levels vary widely among normal individuals. To identify genes that influence VWF level, we analyzed a genetic cross between RIIIS/J and CASA/Rk, two strains of mice that exhibit a 20-fold difference in plasma VWF level. DNA samples from F2 progeny demonstrating either extremely high or extremely low plasma VWF levels were pooled and genotyped for 41 markers spanning the autosomal genome. A novel locus accounting for 63% of the total variance in VWF level was mapped to distal mouse chromosome 11, which is distinct from the murine Vwf locus on chromosome 6. We designated this locus Mvwf for "modifier of VWF." Additional genotyping of as many as 2407 meioses established a high resolution genetic map with gene order Cola1-Itg3a-Ngfr-Mvwf/Gip-Hoxb9-Hoxb1++ +-Cbx'rs2-Cox5a-Gfap. The Mvwf candidate interval between Ngfr and Hoxb9 is approximately 0.5 centimorgan (cM). These results demonstrate that a single dominant gene accounts for the low VWF phenotype of RIIIS/J mice in crosses with several other strains. The pattern of inheritance suggests a gain-of-function mutation in a unique component of VWF biosynthesis or processing. Characterization of the human homologue for Mvwf may have relevance for a subset of type 1 VWD cases and may define an important genetic factor modifying penetrance and expression of mutations at the VWF locus.

von Willebrand disease in children and adolescents

The term von Willebrand disease includes many bleeding disorders caused by abnormalities of vWF. Frequent or severe bleeding may be indicative of vWD or other bleeding conditions. Primary care practitioners need to be familiar with vWD and evaluate possibly affected individuals with appropriate laboratory studies. Patients with vWD should be educated about their disorder and preventive measures to limit its effect. Medications are available that can treat or prevent bleeding complications for most patients with vWD. Intervention with blood products is occasionally necessary.

Case report: recurrent hematuria and hematospermia due to prostatic telangiectasia in classic von Willebrand's disease

A previously healthy 32-year-old man presented with recurrent exercise induced painless gross hematuria and hematospermia. An extensive evaluation demonstrated classic von Willebrand's disease associated with vascular telangiectasia of the prostate gland as the locus of hemorrhage. The bleeding resolved spontaneously and without recurrence. The coexistence of von Willebrand's disease and vascular telangiectasia has been described previously, although it is a rare occurrence. However, a review of the English literature revealed no report of vascular telangiectasia involving the prostate gland, and therefore is the subject of this report. The prostate gland now should be added to the list of viscera associated with vascular telangiectasia and von Willebrand's disease.