Congenital von Willebrand disease type I: definition, phenotypes, clinical and laboratory assessment

The Influence of Hypothyroid Metabolic Status on Blood Coagulation and the Acquired von Willebrand Syndrome

The intent of this prospective study aimed to identify the influence of hypothyroid metabolic status on the coagulation and fibrinolytic system and association with the acquired von Willebrand syndrome (VWS-ac). We compared 54 patients without substitution therapy after radical thyroidectomy with 58 control subjects without pathological thyroid-stimulating-hormone (TSH)-values. Patients with TSH > 17.5 mU/L over a period of >4 weeks were included. The control-collective was selected based on age and sex to match the patient-collective. The data were collected using laboratory coagulation tests and patient questionnaires; a bleeding score was determined. There were significant differences in the measurement of activated-partial-thromboplastin-time (aPTT/p = 0.009), coagulation-factor VIII (p < 0.001) and von-Willebrand-activity (VWF-ac/p = 0.004) between the patient and control groups. The patient cohort showed an increased aPTT and decreased factor VIII and VWF-ac. 29.7% of the patient-collective compared to 17.2% of the control subjects met the definition of VWS-Ac (p = 0.12). The bleeding score showed significantly more bleeding symptoms in patients with a laboratory constellation of VWS-ac (no family history; p = 0.04). Our results suggest hypocoagulability in hypothyroid patients. Hypothyroidism appears to have a higher incidence of VWS-ac. The increased risk of bleeding complications in hypothyroid patients may be of relevant importance for the outcome, especially in the context of invasive interventions.

rVWF: treatment finally reaches the modern age

In this issue of Blood, Gill et al describe the results of the first phase 3 clinical trial evaluating recombinant von Willebrand factor (rVWF) for the treatment of hemorrhagic events in all patients with von Willebrand disease (VWD).

Characterization of multiple platelet activation pathways in patients with bleeding as a high-throughput screening option: use of 96-well Optimul assay

Up to 1% of the population have mild bleeding disorders, but these remain poorly characterized, particularly with regard to the roles of platelets. We have compared the usefulness of Optimul, a 96-well plate-based assay of 7 distinct pathways of platelet activation to characterize inherited platelet defects in comparison with light transmission aggregometry (LTA). Using Optimul and LTA, concentration-response curves were generated for arachidonic acid, ADP, collagen, epinephrine, Thrombin receptor activating-peptide, U46619, and ristocetin in samples from (1) healthy volunteers (n = 50), (2) healthy volunteers treated with antiplatelet agents in vitro (n = 10), and (3) patients with bleeding of unknown origin (n = 65). The assays gave concordant results in 82% of cases (κ = 0.62, P < .0001). Normal platelet function results were particularly predictive (sensitivity, 94%; negative predictive value, 91%), whereas a positive result was not always substantiated by LTA (specificity, 67%; positive predictive value, 77%). The Optimul assay was significantly more sensitive at characterizing defects in the thromboxane pathway, which presented with normal responses with LTA. The Optimul assay is sensitive to mild platelet defects, could be used as a rapid screening assay in patients presenting with bleeding symptoms, and detects changes in platelet function more readily than LTA. This trial was registered at www.isrctn.org as #ISRCTN 77951167.

Utility of the ISTH bleeding assessment tool in predicting platelet defects in participants with suspected inherited platelet function disorders

BACKGROUND

The ISTH bleeding assessment tool (ISTH-BAT) was developed to record bleeding symptoms and to aid diagnosis in patients with a possible bleeding disorder.

OBJECTIVES

To investigate the utility of the ISTH-BAT in predicting functional defects in platelet activation in participants with suspected inherited platelet function disorders.

PATIENTS/METHODS

Participants with clinical evidence of excessive bleeding and suspected inherited platelet function disorders and healthy volunteers were recruited to the Genotyping and Phenotyping of Platelets study (GAPP; ISRCTN 77951167). The ISTH-BAT questionnaire was applied by a trained investigator prior to lumiaggregometry.

RESULTS

One hundred participants were included (79 with suspected inherited platelet function disorders, and 21 healthy volunteers). The ISTH-BAT score in participants with suspected inherited platelet function disorders (median 12; interquartile range [IQR] 8-16) was significantly higher than in healthy volunteers (median 0; IQR 0-0). There was no difference between participants with suspected inherited platelet function disorders with a platelet defect detected by lumiaggregometry (median 11; IQR 8-16) and those with normal platelet function (median 12; IQR 8-14) (P > 0.05). The ISTH-BAT score was not associated with a demonstrable platelet defect on platelet function testing (area under the receiver operating characteristic curve = 0.501 [95% confidence interval 0.372-0.630, P = 0.98] and odds ratio 1.01 [95% confidence interval 0.93-1.09, P = 0.91]).

CONCLUSIONS

The ISTH-BAT is a powerful tool for documenting lifelong bleeding history. However, the score obtained is not predictive of the presence of a platelet defect on lumiaggregometry in patients with suspected inherited platelet function disorders.

Advances in the diagnosis and management of type 1 von Willebrand disease

Von Willebrand disease (VWD) is an autosomally inherited bleeding disorder caused by a deficiency and/or abnormality of von Willebrand factor (VWF). VWF is a multimeric adhesive protein that plays an important role in primary hemostasis by promoting platelet adhesion to the subendothelium at sites of vascular injury and platelet-platelet interactions at high-shear rate conditions. Furthermore, VWF is the carrier of factor VIII, thus indirectly contributing to the coagulation process. Most cases have a partial quantitative deficiency of VWF (type 1 VWD) with variable bleeding tendency, whereas qualitative variants (type 2 VWD), due to a dysfunctional VWF, are clinically more homogeneous and account for approximately 20-30% of cases. Type 3 VWD is rare and these patients have moderate-to-severe bleeding diathesis, display a recessive pattern of inheritance and virtual absence of VWF. The diagnosis of VWD may be difficult, especially in type 1 disease, since the laboratory phenotype of the disorder is very heterogeneous and confounded by the influence on VWF levels by factors outside the VWF gene (e.g., blood group). An array of tests are usually required to characterize the several types of the disorder in order to predict the best treatment modality. Desmopressin is the treatment of choice for most patients with type 1 VWD because it corrects the the dual defects of hemostasis, that is, abnormal coagulation expressed by low levels of factor VIII and abnormal platelet adhesion expressed by the reduction of VWF.

Evidence-based diagnosis of type 1 von Willebrand disease: a Bayes theorem approach

The diagnosis of type 1 von Willebrand disease (VWD) is based on the presence of bleeding symptoms, reduced von Willebrand factor (VWF) levels, and autosomal inheritance of the phenotype. To better appreciate the contribution of clinical and laboratory data to the final diagnosis of VWD, we computed the likelihoods of having VWD as a function of the bleeding score (LRscore), of VWF level (LRVWF), and of number of first-degree family members with reduced VWF levels (LRfamily). The 3 likelihoods were therefore combined using the Bayes theorem, giving the final probability (odds) of having VWD. LRfamily and LRVWF were the 2 factors mostly influencing the final probability of having VWD. Data from the present study provide an evidence-based description of the minimal criteria for the diagnosis of type 1 VWD. As an example, presence of VWF levels lower than 40 IU/dL in at least 2 family members (including the proband) and a bleeding score of at least 1 were found to be required for a final odd of VWD higher than 2.0 (false-positive rate less than one-half). Validation of this approach and of its clinical utility is, however, required by analysis in other cohorts of well-characterized type 1 VWD patients.

[Preoperative evaluation of the bleeding history. Recommendations of the working group on perioperative coagulation of the Austrian Society for Anaesthesia, Resuscitation and Intensive Care]

Unexpected bleeding in the perioperative period is largely caused by impaired inherited or drug-induced primary haemostasis. Standard tests for plasma coagulation are predominantly employed to gauge the risk of bleeding. In accordance with several reports the subcommittee for perioperative coagulation (AGPG) of the Austrian Society of Anaesthesia, Resuscitation and Intensive Care (OGARI) recommends the use of a standardised questionnaire to detect an increased risk of bleeding. Accordingly, healthy patients of the American Society of Anesthesiologists (ASA) grades I and II without any suspicion of impaired haemostasis who are scheduled for procedures without expected transfusion requirements, need no standard tests for coagulation. In all other patients (including patients taking medication affecting coagulation, or patients who are unable to provide adequate information) platelet count, platelet function, aPTT, PT, and fibrinogen levels should be assessed.

How to estimate bleeding risk in mild bleeding disorders

The concept of mild bleeding disorders (MBD) has evolved in contrast to severe hemophilia A and B to indicate less severe disorders, characterized by the presence of more frequent and/or more prominent bleeding symptoms than in the normal population. These symptoms occur mostly after a recognizable challenge and do not lead to major discomfort or organ damage, even in the absence of specific medical intervention. However, it has become clear that, from the most severe to the mildest hemostatic disorders, there is a continuous spectrum of bleeding manifestations, which overlap with the occasional bleeding occurring in people without any identifiable hemostatic abnormality. By reviewing the principal hemorrhagic disorders we have tried to identify those entities that could fit a diagnosis of MBD and result, at the same time, in a net benefit for treatment or prophylaxis of patients rather than being simply accurate. This goal can usually be achieved by comparing the patient's phenotype with known nosological entities. However, limitations of this approach are evident, considering the paucity of clinical data and the biases of most published reports on the different disorders. In addition, in a partial deficiency of a clotting factor, a reliable relationship between the residual activity and bleeding severity is not invariably found. Molecular characterization of the defects is also generally useless. Accordingly, an accurate bleeding history in the propositus and his/her family remains of major importance. For this purpose, new standardized and possibly quantitative tools are being developed in several institutions. Innovative approaches, combining into a single probability phenotypic and genetic data, could possibly estimate better the bleeding risk in specific disorders.

Autosomal recessive von Willebrand disease associated with compound heterozygosity for a novel nonsense mutation (2908 del C) and the missense mutation C2362F: definite evidence for the non-penetrance of the C2362F mutation

A novel null mutation (2908del C in exon 22) of the von Willebrand factor (VWF) gene was identified in compound heterozygosity with the missense mutation G7335T (C2362F) in exon 42 in a propositus from a new family with autosomal recessive von Willebrand disease (VWD). The propositus, referred at age 2 for severe epistaxis and prolonged bleeding after a tongue bite, had factor VIII:C 14-21 IU/dL, VWF Antigen 3-8 IU/dL and Ristocetin Cofactor activity < 3 IU/dL. Multimeric pattern showed the lack of triplet pattern and a faster mobility of central band, while heterozygotes for C2362F showed intermediate mobility compared to normal plasma and plasma from the propositus. In the propositus' family 5 subjects were heterozygotes for the C2362F mutation and 5 were heterozygotes for the cytosine deletion. Bleeding score was assessed with a detailed questionnaire in 28 heterozygotes for C2362F, 23 of whom identified in 5 previously reported families and 5 in the present one, and found to be similar to what is observed in normal controls and heterozygotes for null allele. In conclusion, the mutation C2362F is frequently observed in compound heterozygosity with null alleles in patients with recessive VWD in the Veneto region and cause bleeding only in the compound heterozygous or homozygous state.

Hemorrhagic symptoms and bleeding risk in obligatory carriers of type 3 von Willebrand disease: an international, multicenter study

OBJECTIVES

We undertook an international, multicenter study to describe the clinical picture and to estimate the bleeding risk in a group of obligatory carriers of type 3 von Willebrand disease (VWD).

PATIENTS AND METHODS

Obligatory carriers (OC) of type 3 VWD were identified by the presence of offspring with type 3 VWD or by being an offspring of a type 3 patient. Normal controls were age- and sex-matched with the obligatory carriers. A physician-administered standardized questionnaire was used to evaluate hemorrhagic symptoms at presentation. A score system ranging from 0 (no symptom) to 3 (hospitalization, replacement therapy, blood transfusion) was used to quantitate bleeding manifestations. Odds ratios were computed for each symptom.

RESULTS

Ten centers participated to the study, enrolling a total of 35 type 3 VWD families, with 70 OC. A total of 215 normal controls and 42 OC for type 1 VWD were also included. About 40% of type 3 OC had at least one bleeding symptom compared to 23% of normal controls and 81.8% of type 1 OC (P < 0.0001 by chi-squared test), showing that type 3 OC clearly represent a distinct population from type 1 OC. The clinical situations associated with an increase of bleeding risk in type 3 OC were epistaxis [odds ratio 3.6; 90% confidence intervals (CI) 1.84-21.5], cutaneous bleeding (odds ratio 5.5; 90% CI 2.5-14.1) and postsurgical bleeding (odds ratio 16.3; 90% CI 4.5-59). The severity of bleeding score correlated with the degree of factor (F) VIII reduction in plasma.

CONCLUSIONS

OC for type 3 VWD represent a distinctive population from type 1 OC. These patients, however, present with more frequent bleeding symptoms in comparison to normal controls, especially in case of significantly low FVIII. Desmopressin and/or tranexamic acid might be useful to prevent or treat bleeding in these cases.

Genetics of von Willebrand disease type 1

The most common form of von Willebrand disease (VWD) is reported to be type 1, accounting for as much as 80% of reported cases. With prevalence estimates as high as 1.6% in the general population, upwards of 4.5 million Americans may be affected. Unfortunately, VWD type 1 is also the most difficult type to diagnose. Despite the continuing progress in defining the genetic lesions responsible for VWD types 2 and 3, identification of the genetic determinants of VWD type 1 remains elusive. Herein the phenomenon known as VWD is summarized, the challenges associated with the diagnosis of type 1 VWD are described, and the role of genetic research in meeting these challenges is explored. The authors identify key gaps in the current genetics literature and suggest new avenues for future research. Lastly, they explore the role of nurses in this research and clinical endeavor. To the authors'knowledge, this review is the first to address these complex issues in nursing research.

Coagulation Defects

The present understanding of the coagulation process emphasizes the final common pathway and the proteolytic systems that result in the degradation of formed clots and the prevention of unwanted clot formations, as well as a variety of defense systems that include tissue repair, autoimmune processes, arteriosclerosis, tumor growth, the spread of metastases, and defense systems against micro-organisms. This article discusses diagnosis and management of some of the most common bleeding disorders. The goals are to provide a simple guide on how best to manage patients afflicted with congenital or acquired clotting abnormalities during the perioperative period, present a brief overview of the methods of testing and monitoring the coagulation defects, and discuss the appropriate pharmacologic or blood component therapies for each disease.

Comparison of a new automated von Willebrand factor activity assay with an aggregation von Willebrand ristocetin cofactor activity assay for the diagnosis of von Willebrand disease

von Willebrand disease (VWD) is caused by quantitative and/or qualitative defects of von Willebrand factor (VWF). The HemosIL von Willebrand Factor Activity assay, a new automated immunological test to measure VWF activity, was implemented on STAC and compared with the von Willebrand ristocetin cofactor activity (VWF:RCo) aggregation method. Imprecision and dilution studies were also performed. Within-run imprecision was 17.2% and between-run imprecision was 8.3% (coefficients of variation). Dilution studies showed a linearity between 12.5 and 100%. Passing and Bablok regression comparing the HemosIL von Willebrand Factor Activity assay and the aggregation method yielded a slope of 1.25 (95% confidence interval: 1.11-1.38) and intercept of -1.40 (95% confidence interval: -8.07 to 0.00). The correlation coefficient was 0.84 (95% confidence interval: 0.78-0.89). With a cut-off value of 50% for VWF activity, the assay has a sensitivity of 94.1% and a specificity of 92.8%, compared with the VWF:RCo aggregation assay with a cut-off value of 60% producing a sensitivity of 100.0% (specificity 87.6%). With a cut-off value of 60%, the HemosIL von Willebrand Factor Activity assay on STAC is a reliable assay for VWD. VWF:RCo or other functional testing is still required to confirm the diagnosis and for further classification of VWD.

Evaluation of a rapid automated assay for analysis of von Willebrand ristocetin cofactor activity

A commercially available turbidometric assay has been evaluated for the measurement of von Willebrand factor ristocetin cofactor activity (VWF:RCo). The assay is simple, rapid, and can be cost-effectively performed on automated coagulation analyzers. This study's aim is to illustrate the performance of the automated VWF:RCo assay and its capacity to identify patients with von Willebrand disease (VWD). By direct comparison with a conventional VWF:RCo assay, performed on an aggregometer, the concordance between the two assays was 96%. With minor modifications, the automated assay showed a detection level of 0.03 kIU/L with linearity to 2.00 kIU/L. The imprecision of the automated assay was reduced compared to the conventional assay procedure with CV of 6.8% at the 1.00 kIU/L level and 8.6% at the 0.30 kIU/L level. The automated VWF:RCo assay was also suitable as a screening test to detect VWD in patients investigated for the cause of an increased bleeding tendency. In this situation the automated VWF:RCo assay was tested simultaneously with an automated immunoassay for von Willebrand antigen. Receiver operating curves for the diagnosis of VWD showed a greater area under the curve for the automated VWF:RCo assay compared to the immunoassay, 0.98 vs. 0.94, although the difference did not reach significance. In conclusion, the modified automated VWF:RCo assay shows better precision, lower detection limit, is faster to perform with a lower cost per test compared to the conventional aggregometer based VWF:RCo activity method and is an alternative to an antigen immunoassay as a screening test for VWD.

Genetic analysis of 31 Swedish type 1 von Willebrand disease families reveals incomplete linkage to the von Willebrand factor gene and a high frequency of a certain disease haplotype

BACKGROUND

The most common type of von Willebrand disease (VWD), type 1, has in only a few cases been explained by an identified causative mutation in the von Willebrand factor (VWF) gene. The ABO blood group and other modifier loci outside the VWF gene may contribute to the development of type 1 VWD.

OBJECTIVES AND METHODS

Our aim was to determine whether there was genetic linkage to the VWF gene in 31 Swedish type 1 VWD families. Stringent diagnostic criteria in accordance with ISTH guidelines were used. Genetic linkage was investigated by using two highly informative dinucleotide microsatellite markers, which we have recently identified, located in introns six and 15 of the VWF gene. We also investigated the existence of common disease haplotypes and the relation between type 1 VWD and ABO blood group.

RESULTS

We found genetic linkage to the VWF gene in 27 (87%) of the families. However, in four (13%) of the families, there was clearly no genetic linkage. We found the 4751A>G (Tyr1584Cys) sequence variation in exon 28, which is a common mutation in the Canadian VWD population (14.3%), in only one of the 31 families (3.2%). A possible common mutation was identified in six of the 27 (22%) families with genetic linkage. Blood group O was over-represented among type 1 VWD patients.

CONCLUSION

We conclude that there is linkage between the VWF gene and hereditary type 1 VWD in a majority of families.

The evolving classification of von Willebrand disease

The classification of von Willebrand disease (VWD) has been refined since its first description in the 1920s, as knowledge regarding clinical symptoms and tests of von Willebrand factor (VWF) activity and multimer composition have increased. Current molecular approaches have allowed better understanding of the biosynthesis and function of VWF, and made possible phenotype-genotype studies of VWD subtypes. Improved classification of this heterogeneous disorder based on reproducible correlations between specific genetic mutations and recognized phenotypes should aid in determining appropriate management of patients with VWD.

Haemostatic management of intraoral bleeding in patients with von Willebrand disease

OBJECTIVES

To develop plans for the haemostatic management of intraoral bleeding in patients with von Willebrand disease (VWD).

SUBJECTS AND METHODS

Thirty-seven episodes of haemostatic management of intraoral bleeding in 19 VWD patients were analysed retrospectively based on the medical records.

RESULTS AND CONCLUSIONS

When performing tooth extractions in patients with type 1 or 2A VWD [responsive to 1-deamino-8-D-arginine-vasopressin (DDAVP)], 0.35-0.4 microg kg(-1) of DDAVP should be administered intravenously at three times. In patients with type 2A VWD (unresponsive to DDAVP) or patients with type 2B or 2N VWD, 50-90 U [as ristocetin cofactor (VWF:RCof)] kg(-1) of a factor VIII concentrate containing von Willebrand factor (FVIII/VWF concentrate) should be administered twice in routine extractions, and four to six times in surgical extractions. Gingival bleeding related to primary teeth can be mostly managed by pressure haemostasis alone. However, when treating gingival bleeding caused by marginal periodontitis, it is often necessary to administer 0.4 microg kg(-1) of DDAVP or 40-70 U (as VWF:RCof) kg(-1) of a FVIII/VWF concentrate. As local haemostasis is difficult to achieve in bleeding from the tongue or labial or mandibular haematoma, it is necessary to administer 0.4 microg kg(-1) of DDAVP or 60-80 U (as VWF:RCof) kg(-1) of a FVIII/VWF concentrate. In addition, oral administration of 20 mg kg(-1) day(-1) of tranexamic acid should be combined with the regimens described above.

Phenotypic and genotypic diagnosis of von Willebrand disease: a 2004 update

In the last two decades, progress in the diagnosis of von Willebrand disease (VWD) came from the rapidly developing field of molecular techniques that allowed the first phenotype-genotype correlations. In particular, structural and functional defects of von Willebrand factor (VWF) that underlie VWD type 2 and their molecular basis not only helped to understand the pathophysiology of VWD but also the complex post-translation processing of VWF and the multiple VWF functions. In contrast to the dramatic development of molecular techniques, improvement of methods for phenotypic description, a prerequisite for phenotype-genotype comparisons, has been neglected. The gold standard to differentiate VWD type 2 from type 1 and between diverse type 2 subtypes is the electrophoretic analysis of VWF multimers, a demanding technique that itself is not easily standardized but of crucial relevance for correct classification. This article summarizes the current knowledge on phenotype-genotype correlations as well as up-to-date phenotypic and genotypic methods in the diagnosis of VWD.

Treatment of von Willebrand disease

The bleeding tendency in von Willebrand disease (VWD) is heterogeneous and some patients with the mildest form of the disease have no significant bleeding symptoms throughout their lives. In some cases, the most difficult task for a clinician is to decide whether any treatment is actually required. However, cases with moderate to severe factor VIII (FVIII) and von Willebrand factor (VWF) deficiency usually require treatment to stop or prevent bleeding. Increasing autologous FVIII/VWF by desmopressin administration or providing normal allogeneic VWF through the infusion of plasma-derived concentrates can correct FVIII and VWF deficiencies and normalize or shorten bleeding time (BT). FVIII levels are the best predictors of soft tissue or surgical bleeding, while BT normalization, reflecting the correction of platelet-dependent functions of VWF, is considered a reliable indicator of an effective treatment of mucosal bleeding. Recombinant concentrates of FVIII are not indicated (apart from cases with alloantibodies against exogenous VWF), since they are devoid of VWF and lack its stabilizing effect on circulating FVIII. A very-high-purity concentrate of VWF has recently been made available, but its advantages over conventional concentrates containing both FVIII and VWF moieties are not obvious. The best way to select the appropriate treatment is to perform a test infusion with desmopressin in any patient with clinically significant VWD, provided that he/she has no contraindication to the compound or belongs to subtype with an anticipated lack of response (for example, type 3 VWD with FVIII/VWF lower than 5%).

Is the assessment of von Willebrand disease prevalence an achievable challenge? The example of the French Basque Country where blood group O and factor XI deficiency are highly prevalent

The diagnosis of type I von Willebrand disease (VWD) is not straightforward because of the absence of a single clear-cut biological criteria and the interference of several acquired conditions on phenotype expression. We illustrate here this challenge with the French Basque population characterised by a marked high frequency in both blood group O and factor XI deficiency. From this example one may question the validity of epidemiological studies reporting on VWD prevalence.

Clinical diagnosis of von Willebrand disease

von Willebrand disease (VWD) is the most frequent inherited bleeding disorder and is caused by quantitative (Types 1 and 3) or qualitative (Type 2) defects of von Willebrand factor (VWF). VWD is inherited by autosomal dominant or recessive pattern, but women with milder VWD forms seem to be more symptomatic than men. Mild VWD forms are both under- and misdiagnosed. The clinical expression of VWD is usually mild in Type 1, increasing in severity in Types 2 and 3. Mucocutaneous bleeding (epistaxis, menorrhagia) is a typical manifestation of the disease, and bleeding after dental extraction is the most frequent postoperative bleeding type. Because FVIII levels are usually only slightly reduced in most VWD types, spontaneous haemarthroses or haematomas are rare in VWD Types 1, 2A and 2B, whereas in Type 3 the severity of bleeding may resemble haemophilia. In Type 1 VWD, bleeding after delivery is rare because FVIII/VWF levels become normal at the end of pregnancy. Post-operative bleeding may not occur in Type 1 VWD patients, but in Type 3 VWD, prophylaxis is always required. Only a few retrospective studies on clinical diagnosis of VWD are available. In the 1234 cases enrolled by an Italian retrospective study, diagnosis of Types 1, 2 and 3 VWD occurred in young adults (83%), mainly in women (57%). Mucosal bleeding (64%) was more frequent than haematomas or haemarthrosis (15%), and 63% of patients did not require transfusions. In a more recent Italian prospective study (815/1234 cases observed for 1 year in 6/16 Italian centres), only 147 (18%) VWD patients showed bleeding episodes (n = 318) and minor or major surgeries (n = 87).

Haemophilias A and B

The haemophilias are inherited disorders in which one of the coagulation factors is deficient. Although deficiencies of factor VIII (haemophilia A) and factor IX (haemophilia B) are well recognised, von Willebrand's disease is much more common. Rare defects can occur in any of the coagulation factors. In the past, men with haemophilia were likely to die in their youth. With advances in diagnosis, and especially with development of safe and effective treatment, affected individuals can now look forward to a normal life expectancy. Complications of the disorder, particularly the development of antibodies that make treatment ineffective, and of treatment, such as transfusion-transmitted infections, have taken a severe toll on these patients. The future holds the realistic possibility of gene therapy. However, we must not forget that haemophilia is a worldwide disorder that requires significant economic resources not available for the majority.

von Willebrand disease: still an intriguing disorder in the era of molecular medicine

von Willebrand disease (vWD) is a single-locus disorder resulting from a deficiency of von Willebrand factor (vWF): a multimeric multifunctional protein involved in platelet adhesion and platelet-to-platelet cohesion in high shear stress vessels, and in protecting from proteolysis and directing circulating factor VIII (FVIII) to the site of injury. vWD is the most frequent bleeding disorder, with an estimated prevalence in the general population of 1%. Almost all these cases are represented by a partial quantitative deficiency of von Willebrand factor (vWF) (type 1 vWD). Type 1 is transmitted as an autosomal dominant trait with an extremely variable penetrance and expressivity. A consensus figure for the prevalence of cases with significant bleeding symptoms, requiring some form of treatment, is approximately 100 cases million-1. Among these cases, more than 70-80% are represented by type 1 and respond to deamino-D-arginine vasopressin (DDAVP; desmopressin) administration. The remaining cases are represented by type 2 vWD (qualitative), some of which require substitutive treatment. Only 3-5 cases million-1 result from a total deficiency of vWF in plasma and platelets because of the recessive inheritance of two defective alleles. These cases may have severe bleeding episodes and may require frequent substitutive treatment. The molecular basis of type 2 (missense mutation in the functional domains of the vWF subunit) and type 3 (nonsense or large deletions) is quite well understood. On the contrary the molecular basis for most type 1 cases remains largely unknown, and many genetic factors (e.g. ABO blood group) and environmental or circumstantial factors (e.g. age, stress, drugs, pregnancy, and inflammation) are superimposed on to the genetic background determined by the vWF gene to produce a continuous spectrum from normality to mild type 1 cases. It is extremely difficult to make a clear distinction between mild type 1 cases and normal people because of the wide 'normal' range of laboratory measurements (e.g. length of bleeding time, and levels of vWF and FVIII) and of bleeding symptoms. Molecular testing is useless in this situation, and only good history-taking and repeated laboratory testing of vWF-related measurements in the propositus and his/her family members can help in clinical diagnosis, albeit imprecisely. This difficult task is the main focus of this review which is aimed at alerting the physician toward a balanced approach that should take into consideration both the risk of over- and under-diagnosis of this frequent disorder and the unavoidable production of a number of false positive and false negative cases.

Von Willebrand factor and von Willebrand disease

von Willebrand disease (vWD) is caused by quantitative and/or qualitative defects of the von Willebrand factor (vWF), a multimeric high molecular weight glycoprotein. Typically, it affects the primary hemostatic system, which results in a mucocutaneous bleeding tendency simulating a platelet function defect. The vWF promotes its function in two ways: (i) by initiating platelet adhesion to the injured vessel wall under conditions of high shear forces, and (ii) by its carrier function for factor VIII in plasma. Accumulating knowledge of the different clinical phenotypes and the pathophysiological basis of the disease translated into a classification that differentiated between quantitative and qualitative defects by means of quantitative and functional parameters, and by analyzing the electrophoretic pattern of vWF multimers. The advent of molecular techniques provided the opportunity for conducting genotype-phenotype studies which have recently helped, not only to elucidate or confirm important functions of vWF and its steps in post-translational processing, but also many disease causing defects. Acquired von Willebrand syndrome (avWS) has gained more attention during the recent years. An international registry was published and recommendation by the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis in 2000. It concluded that avWS, although not a frequent disease, is nevertheless probably underdiagnosed. This should be addressed in future prospective studies. The aim of treatment is the correction of the impaired hemostatic system of the patient, ideally including the defects of both primary and secondary hemostasis. Desmopressin is the treatment of choice in about 70% of patients, mostly with type 1, while the others merit treatment with concentrates containing vWF.