Type IIB von Willebrand's disease presenting as thrombocytopenia during pregnancy

Type 2B von Willebrand disease mutations differentially perturb autoinhibition of the A1 domain

Type 2B von Willebrand disease (VWD) is an inherited bleeding disorder in which a subset of point mutations in the von Willebrand factor (VWF) A1 domain and recently identified autoinhibitory module (AIM) cause spontaneous binding to glycoprotein Ibα (GPIbα) on the platelet surface. All reported type 2B VWD mutations share this enhanced binding; however, type 2B VWD manifests as variable bleeding complications and platelet levels in patients, depending on the underlying mutation. Understanding how these mutations localizing to a similar region can result in such disparate patient outcomes is essential for detailing our understanding of VWF regulatory and activation mechanisms. In this study, we produced recombinant glycosylated AIM-A1 fragments bearing type 2B VWD mutations and examined how each mutation affects the A1 domain's thermodynamic stability, conformational dynamics, and biomechanical regulation of the AIM. We found that the A1 domain with mutations associated with severe bleeding occupy a higher affinity state correlating with enhanced flexibility in the secondary GPIbα-binding sites. Conversely, mutation P1266L, associated with normal platelet levels, has similar proportions of high-affinity molecules to wild-type (WT) but shares regions of solvent accessibility with both WT and other type 2B VWD mutations. V1316M exhibited exceptional instability and solvent exposure compared with all variants. Lastly, examination of the mechanical stability of each variant revealed variable AIM unfolding. Together, these studies illustrate that the heterogeneity among type 2B VWD mutations is evident in AIM-A1 fragments.

Challenges in the management of women with type 2B von Willebrand disease during pregnancy and the postpartum period: evidence from literature and data from an international registry and physicians' survey-communication from the Scientific and Standardization Committees of the International Society on Thrombosis and Haemostasis

BACKGROUND

Management of women with type 2B von Willebrand disease (VWD) during pregnancy is challenging because of dysfunctional von Willebrand factor (VWF) and the complexity resulting from discrepant VWF/factor VIII (VWF/FVIII) levels, impaired platelet-dependent VWF activity, progressive thrombocytopenia, and risks associated with the use of desmopressin. There is a lack of high-quality evidence to support clinical decision making.

OBJECTIVES

In this study, we examined the current diagnostic and management approaches and outcomes in women with VWD during pregnancy.

METHODS

Data were collected via 3 avenues: literature review, an international registry, and an international survey on physicians' practices for the management of pregnancy in women with VWD. The registry and survey were supported by the International Society on Thrombosis and Haemostasis.

RESULTS

Data on clinical and laboratory features, management and bleeding complications, and pregnancy outcomes of a total of 55 pregnancies from 49 women across the globe (literature: 35, registry: 20) and data reported by 112 physicians were analyzed. We describe the largest dataset on pregnancies in women with type 2B VWD available to date. The data highlight the following key issues: a) bleeding complications remain a concern in these patients, b) the target safe VWF level and the ideal monitoring approach are unknown, c) there is a wide range of hemostatic management practices in the type and timing of treatment, and d) physicians have diverse views on the mode of delivery and use of neuraxial anesthesia.

CONCLUSION

We conclude that an international consensus and guidance are critically required for better care and improved outcomes in this patient cohort.

Planning Pregnancy and Birth in Women with Inherited Bleeding Disorders

Inherited bleeding disorders are characterized by a diverse clinical phenotype within and across specific diagnoses. von Willebrand disease (VWD), hemophilia A, and hemophilia B comprise 95 to 97% of inherited bleeding disorders, with the remaining 3 to 5% attributed to rare bleeding disorders, including congenital fibrinogen disorders, factor deficiencies (affecting FII, FV, FV + FVIII, FVII, FX, FXI, and FXIII), and platelet function defects. The pregnancy, birth, and the puerperium may be adversely influenced in the setting of an inherited bleeding disorder depending on its type and clinical phenotype. Obstetric hemostatic challenges may sometimes also unmask the presence of a previously unknown inherited bleeding disorder. This review aims to address the approach to pregnancy and birth in the context of an inherited bleeding disorder and highlights the significance of multidisciplinary input into the care of these women.

Type 2B von Willebrand Disease in Pregnancy: A Systematic Literature Review

Our objective was to review the maternal characteristics and obstetric complications in women with type 2B von Willebrand disease (VWD). A systematic literature search was conducted using PubMed, Scopus, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov. We included all publications that addressed type 2B VWD in pregnancy. Our primary and secondary outcomes were incidence of postpartum hemorrhage (PPH) and incidence of thrombocytopenia in pregnancy. Two reviewers independently identified eligible studies and abstracted data including maternal characteristics, hematologic characteristics, treatment, and delivery outcomes. Twenty studies met inclusion criteria. There were 27 women (32 pregnancies) with type 2B VWD. Primary PPH was reported in 9/20 women (45%) and secondary PPH was reported in 6/13 women (46%). Thrombocytopenia in pregnancy was present in 27/28 women (96%); 23/27 women (85%) had platelet count <100 × 10⁹/L, mean 33.7 ± 22.7 × 10⁹/L. Factor concentrate treatment was administered before delivery (n = 16) and postpartum (n = 18), some women received both. Seventeen deliveries required blood products postpartum with 13/17 (76%) platelet transfusions and 6/17 (35%) red blood cell transfusions. No maternal mortality was reported. Women with type 2B VWD have significant morbidity in pregnancy related to high incidence of severe thrombocytopenia and primary and secondary PPH.

Thrombocytopenia: Perioperative Considerations for Patients Undergoing Cardiac Surgery

The etiologies of thrombocytopenia in patients presenting for cardiac surgery are extensive, but clinically relevant conditions generally can be categorized by those related to decreased platelet production or increased platelet destruction. Many causes require mere acknowledgment and availability of allogeneic platelet transfusion; others have unique considerations for which providers should be familiar. The purpose of this review is to provide an overview of the common causes of thrombocytopenia, summarize the literature, and discuss perioperative considerations for patients undergoing cardiac surgery.

Pregnancy and delivery in women with von Willebrand disease

Given the wide heterogeneity of phenotypes and of the underlying pathophysiological mechanisms associated with the disorder, pregnancy and delivery in von Willebrand disease (VWD) represent a significant clinical challenge. The variable pattern of changes observed during pregnancy of von Willebrand factor (VWF) and factor VIII (FVIII), the protein carried by VWF, prompts a careful evaluation of pregnant women with VWD to plan the most appropriate treatment at the time of parturition. However, there are also instances during pregnancy (amniocentesis, vaginal bleeding associated with placental detachment, sudden abortion) that may require urgent hemostatic treatment to prevent bleeding. Thus, women with VWD should start pregnancy after being well characterised as to their type, subtype and treatments. Women with VWD who have VWF and FVIII basal levels >30 U/dL typically normalise these levels at the end of pregnancy and specific anti-haemorrhagic prophylaxis is seldom required. On the contrary, those with basal levels <20 U/dL usually show a lesser increase and specific treatment is required. Some women with DNA variants associated with increased clearance can be treated with desmopressin, while those unresponsive or with contra-indications to this agent need replacement therapy. For these latter women, the risk of vaginal bleeding during pregnancy may be increased and prophylaxis with VWF concentrates required. Similarly, women with type 2 VWD who maintain reduced VWF activity throughout pregnancy require replacement therapy with FVIII/VWF concentrates. Delayed postpartum bleeding may occur when replacement therapy is not continued for some days. Tranexamic acid is useful at discharge to avoid excessive lochia.

Type 2B von Willebrand Disease: An Unusual Cause of Severe Neonatal Thrombocytopenia

An infant with presumed maternal immune thrombocytopenic purpura had persistent thrombocytopenia with platelet clumping. The patient had no significant bleeding symptoms in the first year of life and von Willebrand antigen and ristocetin cofactor activity were normal. Absent high molecular weight multimers ultimately led to a genetically proven diagnosis of type 2B von Willebrand disease (3964G>A VWF exon 28), highlighting the challenges of establishing this diagnosis in infants.

How I treat type 2 variant forms of von Willebrand disease

Type 2 von Willebrand disease (VWD) includes a wide range of qualitative abnormalities of von Willebrand factor structure and function resulting in a variable bleeding tendency. According to the current classification, 4 different subtypes can be identified, each with distinctive phenotypic and therapeutic characteristics. Current available laboratory methods allow a straightforward approach to VWD subtyping, and although the precise molecular characterization remains complex, it is not required for appropriate treatment of the vast majority of cases. Desmopressin can be useful only in a few type 2 cases compared with patients with actual quantitative deficiency (type 1), most often in variants with a nearly normal multimeric pattern (type 2M). However, since no laboratory test accurately predicts response to desmopressin, a trial test should always be performed in all type 2 VWD patients, with the exception of type 2B ones. Replacement therapy with plasma-derived von Willebrand factor-factor VIII concentrates represents the safe mainstay of treatment of all patients, particularly those not responding to desmopressin or requiring a sustained hemostatic correction because of major surgery or bleeding. A significant patient bleeding history correlates with increased bleeding risk and should be considered in tailoring the optimal antihemorrhagic prophylaxis in the individual patient.

Principles of care for the diagnosis and treatment of von Willebrand disease

Von Willebrand disease is a common autosomal inherited bleeding disorder caused by quantitative or qualitative defects of von Willebrand factor, a multi-adhesive protein that binds platelets to exposed subendothelium and carries factor VIII in circulation. As a result of von Willebrand factor deficiency or abnormality, levels of factor VIII, the protein deficient in hemophilia A, may be variably reduced. Clinical manifestations are mainly represented by mucous membrane and of soft tissue bleeding. Their severity is variable depending on the degree of von Willebrand factor and factor VIII reduction. While a clear-cut diagnosis is easy in severe von Willebrand factor reductions, the advantage of pursuing a definite diagnosis in mild or dubious cases should be weighed against the risk of over-medicalization. The aim of treatment is to correct the dual defect of hemostasis caused by the abnormal/reduced von Willebrand factor and the concomitant deficiency of factor VIII. Desmopressin is the treatment of choice for type 1 von Willebrand disease patients with factor VIII and von Willebrand factor levels of 10 U/dL or over who have proved responsive to a test-infusion with the compound. Von Willebrand factor/factor VIII concentrates are needed when desmopressin is ineffective (mainly type 2 and 3 von Willebrand disease).

Changes of von Willebrand Factor during Pregnancy in Women with and without von Willebrand Disease

Delivery in von Willebrand disease (VWD) represents a significant hemostatic challenge because of the variable pattern of changes observed during pregnancy of von Willebrand factor (VWF) and factor VIII (FVIII), the protein carried by VWF. Since a wide heterogeneity of phenotypes and of the underlying pathophysiological mechanisms is associated with this disorder, a prompt and careful evaluation of pregnant women with VWD is requested in order to plan the most appropriate treatment at time of parturition. VWF and FVIII increase significantly during pregnancy in normal women, already within the first trimester, reaching levels by far >100 U/dL by the time of parturition. Women with VWD, levels at baseline of VWF and FVIII >30 U/dL have us a high likelihood to achieve normal levels at the end of pregnancy; thus specific anti-hemorrhagic prophylaxis is seldom required. Women with basal level <20 U/dL usually have a poor increase since most of these women carry mutations associated with increased VWF clearance or are compound heterozygous for different VWF mutations; that prevent the achievement of satisfactory hemostatic levels. While women with mutations associated with increased clearance show a full, albeit transitory correction of their hemostatic deficiency after desmopressin administration, compound heterozygous need replacement therapy because they do not respond well to this agent. Patients with abnormal VWF:RCo/VWF:Ag ratio at baseline (e.g. <0.6), typically associated with type 2 VWD, maintain the abnormality throughout pregnancy and VWF:RCo usually does not attain safe levels ≥50 U/dL. These women require replacement therapy with VWF-FVIII concentrates. Delayed post-partum bleeding may occur when replacement therapy is not continued for some days. Tranexamic acid may be useful at discharge to avoid excessive lochia.

Pregnancy in type 2B VWD: a case series

Type 2B von Willebrand disease (VWD) is a rare, inherited bleeding disorder resulting from a qualitative defect in von Willebrand factor (VWF). There is very little published information on how to quantify bleeding risk and manage haemostasis in type 2B VWD patients during pregnancy. This article presents the changes in VWF parameters and details of patient management and delivery outcomes for four pregnancies in three women with two different mutations causing type 2B VWD. We report an unexpected rise in the VWF:Ag at 37 weeks gestation in two sisters with R1306W associated with significant thrombocytopenia. These patients were supported with platelet transfusions as well as intermediate purity VWF-FVIII plasma concentrates during the peri- and postpartum periods. No thrombocytopenia was observed in our third case with a mutation encoding an R1308C substitution; haemostatic support was with intermediate purity VWF-FVIII plasma concentrates alone. No adverse bleeding events occurred and in all cases a live healthy infant was delivered. One patient was readmitted post partum with bleeding symptoms due to retained placenta; no further haemostatic support was given at this time. This case series is the first to detail the progression of laboratory parameters, management and outcomes of pregnancy in patients with type 2B VWD. The cases illustrate some of the challenges posed by the increased production of a VWF variant with a gain-of-function effect. The rapid coagulation changes observed in this series illustrate the need for continual monitoring of VWF parameters and platelet count throughout pregnancy in women with type 2B VWD.

von Willebrand disease and pregnancy: a practical approach for the diagnosis and treatment

von Willebrand disease is caused by either a quantitative or qualitative defect in von Willebrand factor (VWF). Patients may have extensive mucosal bleeding (because of platelet dysfunction) and prolonged bleeding after surgery (because of factor VIII deficiency). Up to 6 different subtypes of the disease have been described, and diagnosis is based on clinical suspicion and laboratory confirmation. Accurate diagnosis is of paramount importance because therapy will vary according to the subtype. Bleeding complications during pregnancy are more frequent when levels of the von Willebrand ristocetin cofactor assay and factor VIII levels are <50 IU/dL. In such cases, therapy before any invasive procedure or delivery must be instituted. The mainstays of therapy are desmopressin and plasma concentrates that contain von Willebrand factor. Delayed postpartum hemorrhage may occur, despite adequate prophylaxis. Frequent monitoring and continued prophylaxis and/or treatment are recommended for at least 2 weeks after delivery.

Evidence-based recommendations on the treatment of von Willebrand disease in Italy

BACKGROUND

von Willebrand disease (VWD) is the most common hereditary bleeding disorder affecting both males and females. It arises from quantitative or qualitative defects of von Willebrand factor (VWF) and causes bleeding of mucous membranes and soft tissues. The aim of treatment is to correct the dual defect of haemostasis caused by the abnormal/reduced VWF and the concomitant deficiency of factor VIII (FVIII).

MATERIAL AND METHODS

This document contains evidence-based recommendations for the management of VWD compiled by AICE (the Italian Association of Haemophilia Centres). All the evidence supporting these recommendations are based on non-randomised comparative studies or case series, because randomised controlled clinical trials or meta-analyses are not available for this disease.

RESULTS AND CONCLUSIONS

Desmopressin (DDAVP) is the treatment of choice for patients with type 1 VWD with FVIII and VWF levels of 10 U/dL or more, while VWF/FVIII concentrates are indicated for those who are unresponsive or insufficiently responsive to DDAVP (severe type 1, type 2 and 3 VWD). VWF concentrates devoid of FVIII, not yet licensed in Italy, may be considered for short-term prophylaxis in elective surgery or for long-term secondary prophylaxis.

Management of von Willebrand disease: a guideline from the UK Haemophilia Centre Doctors' Organization

von Willebrand disease (VWD) is the commonest inherited bleeding disorder. The aim of therapy for VWD is to correct the two defects of haemostasis in this disorder, impaired primary haemostasis because of defective platelet adhesion and aggregation and impaired coagulation as a result of low levels of factor VIII. The objective of this guideline is to inform individuals making choices about the treatment and management of VWD including the use of therapeutic products. This is the second edition of this UK Haemophilia Centre Doctors' Organization (UKHCDO) guideline and supersedes the previous edition which was published in 1994.

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.

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.

von Willebrand disease and pregnancy

von Willebrand Disease (vWD) affects approximately 1% of Americans and as many as 25% of women referred for evaluation of menorrhagia. We briefly review the history of vWD, its molecular defects, and diagnostic criteria for each subtype of disease. We also address obstetric management of the patient with vWD. While there is a significant increased risk for postpartum hemorrhage, patients with vWD should not be discouraged to undertake pregnancy.

Thrombocytopenia in pregnancy

Thrombocytopenia is a common finding in normal pregnancy. The introduction of routine automated complete blood counting has clearly documented this. In the past, these patients would go undetected and be spared unnecessary testing, procedures, or medications. This article reviews the common causes of thrombocytopenia and offers criteria on which the diagnosis of clinically significant thrombocytopenia can be made. In addition, we will discuss therapeutic approaches to manage patients with pathologic thrombocytopenia.

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.

The generation of thrombin in vivo induces the selective loss of high molecular weight multimers of von Willebrand factor and the reversible sequestration of platelets

Various levels of thrombin generation were induced by the infusion of a combination of factor Xa (F.Xa) and phosphatidylcholine/phosphatidylserine (PCPS) vesicles into normal dogs and non-human primates. In the dog, an immediate loss of von Willebrand factor antigen (vWF:Ag) with a progressive recovery to normal levels by 45 min was observed. Multimeric assay demonstrated a selective loss of high molecular weight multimers (HMWM) with subsequent replacement. At low doses, in non-human primates (chimpanzees), identical changes to those seen in the dog were observed and this was associated with an equivalent loss of ristocetin co-factor activity (vWF:RCoF). At high dose a reversal of the wWF response occurred with levels increasing to twice that of baseline values by 2 min and multimeric analysis demonstrated the presence of abnormally large multimers and increased vWF:RCoF specific activity, suggesting that the response at each dosage reflected a net balance of consumption over release. This was supported by in vitro simulation where increasing thrombin generation was associated with a selective loss of HMWM without replacement. In both species, an immediate fall in platelet count occurred and this was directly correlated with the amount of thrombin generated. Full recovery occurred within 45 min and isotopic labelling studies demonstrated that platelet sequestration rather than consumption was occurring. These studies demonstrate that thrombin generation in vivo is associated with a selective loss of the multimeric forms of vWF known to interact with platelets and this may provide an in vivo model to characterize the physiology/pathophysiology of this primary event in haemostasis.

Type IIB von Willebrand's disease: gene mutations and clinical presentation in nine families from Denmark, Germany and Sweden

Type IIB of von Willebrand's disease (vWD) is a variant in which the structurally abnormal von Willebrand factor (vWF) shows an increased affinity for the platelet vWF receptor, glycoprotein Ib (GPIb). This may sometimes give rise to platelet aggregation and thrombocytopenia in vivo. In 20 patients from nine unrelated families with type IIB vWD from Denmark, Germany and Sweden we studied the molecular defect by amplification and direct sequencing of parts of exon 28 which encode for the vWF domain that interacts with platelet GPIb. Three different point mutations were identified one of which has not previously been reported. Fifteen patients from five families were heterozygous for the Arg543-->Trp substitution. The mutation had occurred independently in all five families and in two of them represented a de novo mutation. In one of these families the father, though asymptomatic and with normal laboratory test results, carried the mutation in heterozygous form. In three families, four affected members were found to be heterozygous for the Arg543-->Cys substitution. The mutations were of different origin at least in two of the families. The third substitution, Val551-->Leu, which has not previously been described, was found in one patient and was due to a de novo mutation. In most of the patients spontaneous thrombocytopenia had been recorded on at least one occasion. Five of the patients with the Arg543-->Trp substitution and the one with the Val555-->Leu substitution had all had bleeding associated with thrombocytopenia in the neonatal period of early infancy.

Recurring mutations at CpG dinucleotides in the region of the von Willebrand factor gene encoding the glycoprotein Ib binding domain, in patients with type IIB von Willebrand's disease

The mutant von Willebrand factor (vWf) molecule in type IIB von Willebrand's disease (vWd) has an increased binding affinity for the platelet receptor glycoprotein Ib (GpIb). In previous studies we have confirmed genetic linkage of this phenotype to the vWf gene and in this report we document three recurring missense mutations in the region of the gene that encodes the GpIb binding domain. Two families with type IIB vWd were found to have an arginine to tryptophan substitution at residue 543, three families had a valine to methionine substitution at residue 553, and one kindred had an arginine to glutamine change at amino acid 578. None of these sequence changes were found in 200 normal vWf genes and within each of the six families the mutations were only found in affected subjects. This is strong circumstantial evidence in support of these substitutions representing the disease causing mutations in these families. All three of these substitutions have occurred at CpG dinucleotide sequences, and their polymorphic associations indicate that they represent recurring new mutations. Missense mutations at these sites may represent the underlying genetic pathology in a large number of type IIB vWd families.

The molecular defect in type IIB von Willebrand disease. Identification of four potential missense mutations within the putative GpIb binding domain

Type IIB von Willebrand Disease (vWD) is characterized by the selective loss of large von Willebrand Factor (vWF) multimers from plasma, presumably due to their increased reactivity with platelets and subsequent clearance from the circulation. Using the PCR, one of a panel of four potential missense mutations was identified in each of the 14 patients studied from 11 unrelated families. None of these substitutions was encountered in a large panel of normal DNAs. These changes all represent C----T transitions at CpG dinucleotides, proposed "hot spots" for mutation in the human genome. The four resulting amino acid substitutions, Arg543----Trp, Arg545----Cys, Val553----Met, and Arg578----Gln, are all clustered within the GpIb binding domain of vWF. Disruption of this latter functional domain may explain the pathogenesis of Type IIB vWD. By sequence polymorphism analysis, the Arg543----Trp substitution was shown to have occurred as at least two independent mutational events. This latter observation, along with the identification of mutations in all 14 patients studied and their localization to the GpIb binding domain, all strongly suggest that these substitutions represent the authentic defects responsible for Type IIB vWD. This panel of mutations may provide a useful diagnostic tool for the majority of patients with Type IIB vWD.

Molecular basis of von Willebrand disease type IIB. Candidate mutations cluster in one disulfide loop between proposed platelet glycoprotein Ib binding sequences

Many variants of von Willebrand disease (vWD) with qualitatively abnormal von Willebrand factor (vWF) are recognized. In vWD type IIB, the abnormal protein displays enhanced affinity for a platelet vWF receptor, the glycoprotein Ib-IX complex. 14 patients from 7 unrelated families with vWD type IIB were studied to determine the molecular basis for this phenotype. Specific oligonucleotide primers were used to amplify portions of vWF exon 28 encoding a domain that interacts with the platelet glycoprotein Ib-IX complex. Candidate missense mutations were identified for all 14 patients by DNA sequencing, allele specific oligonucleotide hybridization, and restriction endonuclease digestion. These sequence changes occur in an 11 amino acid segment within a single disulfide loop bounded by Cys(509) and Cys(695). All of these sequence changes are C----T transitions within CG dinucleotides. Six patients from two unrelated families were heterozygous for the encoded sequence Arg(543)----Trp. Seven patients from four unrelated families were heterozygous for the encoded sequence Arg(545)----Cys; this sequence change appears to have occurred independently three times, once as a new spontaneous mutation. One patient with apparently sporadic vWD type IIB was heterozygous for the encoded sequence Val(553)----Met, and this appears to be a new mutation. None of these sequence changes was found in 100 normal alleles. These findings suggest that vWD type IIB may be caused by relatively few distinct mutations, that these mutations may cluster within a specific region of one disulfide loop in vWF domain A1, and that this region can modulate the affinity of vWF for the platelet glycoprotein Ib-IX complex.

Effect of a factor VIII concentrate on type IIB von Willebrand's disease-associated thrombocytopenia presenting during pregnancy in identical twin mothers

Marked thrombocytopenia developed during pregnancy in both identical twins mothers who had systemic lupus erythematosus (SLE) and also type IIB von Willebrand's disease (vWD). The proband's platelet count decreased in the third trimester of pregnancy. Large-dose gamma-globulin and prednisolone treatments were performed because of the suspicion of immune thrombocytopenic reaction associated with SLE. These treatments were not effective. Her platelet count returned to the normal range immediately after delivery. Postpartum examinations revealed the decreased ristocetin cofactor activity and the deficiency of large von Willebrand factor (vWF) multimers in preserved plasma samples from the third trimester. These abnormal findings improved after delivery. Investigation of family members revealed that the proband had inherited type IIB vWD from her mother. The other twin, who was also under treatment for SLE, became pregnant about 1 year after delivery in the proband and followed almost the same course as that observed in the proband. As bleeding tendency was observed a few days before delivery, a factor VIII concentrate (Haemate P) was administered to compete with her variant vWF. This concentrate could prevent the further decrease in her platelet count, thereby correcting the hemorrhagic tendency. It seems evident that factor VII concentrate would be effective in treating thrombocytopenia associated with type IIB vWD.

Severe thrombocytopenia in a pregnant patient with platelet-associated IgM, and known von Willebrand's disease; a case report

In this report, a patient with known von Willebrand's disease is presented with severe thrombocytopenia developing during pregnancy, which at first was believed to be caused by immune thrombocytopenic purpura. For several reasons this first diagnosis had to be rejected, but subtyping of von Willebrand's disease pointed out that the patient suffered from type IIB, which, according to recent literature, can lead to platelet destruction in pregnancy. Early subtyping of von Willebrand's disease can have a major influence on the management of pregnancy.

Spontaneous platelet aggregation during pregnancy in a patient with von Willebrand disease type IIB can be blocked by monoclonal antibodies to both platelet glycoproteins Ib and IIb/IIIa

Spontaneous platelet aggregation appeared in a patient with von Willebrand disease type IIB during the 37th week of pregnancy. This phenomenon was not associated with symptoms of thrombosis and the patient delivered by caesarean section with no complications. Her platelet-poor plasma (PPP) aggregated normal platelet-rich plasma (PRP) and washed platelets. Aggregation was inhibited by monoclonal antibodies with known specificity for the platelet receptors of von Willebrand factor (vWF), i.e. the glycoprotein Ib (GPIb) and the GPIIb/IIIa complex. A monoclonal antibody, which selectively inhibits the binding of vWF to the GPIIb/IIIa complex, did not block aggregation, suggesting that spontaneous aggregation is not dependent on the binding to GPIIb/IIIa of vWF from patient plasma. Aggregation induced by patient plasma could also be blocked either by two monoclonal antibodies raised against vWF or by a fragment derived from trypsin digestion of normal vWF which blocks the ristocetin-induced binding of normal vWF to platelets. These findings indicate that the spontaneous platelet aggregation in this patient results from the binding of her vWF to GPIb but is independent from the binding of her vWF to GPIIb/IIIa.

Investigation of a large kindred with type IIB von Willebrand's disease, dominant inheritance and age-dependent thrombocytopenia

Twenty-six members of four generations of one family in which a man was diagnosed in 1961 as having von Willebrand's disease (vWD) have been studied. Subtype IIB vWD and autosomal dominant inheritance was identified in 19 individuals with bleeding signs varying in severity and frequency. The absence of high molecular weight multimers of plasma von Willebrand factor (vWf) and the heightened interaction of plasma vWf with platelets in the presence of low ristocetin concentrations were consistent in all affected subjects. Nevertheless the degree of these abnormalities was variable without clearcut linkage to the severity of clinical symptoms. Thrombocytopenia was present only in the adult affected family members and the platelet count appeared to be age-dependent. The investigation of this family provides further evidence of the phenotypic variability in the vWf-platelet interactions within this vWD subtype.