Tachyphylaxis and reproducibility of desmopressin response in perioperative persons with nonsevere hemophilia A: implications for clinical practice

Background

Desmopressin is frequently used perioperatively in persons with nonsevere hemophilia A. However, increase in factor (F)VIII:C after desmopressin use is interindividually highly variable. Tachyphylaxis has only been reported in test setting for persons with hemophilia A, with a remaining response of approximately 70% after a second dose compared with that after a first dose.

Objectives

To study tachyphylaxis of FVIII:C response after multiple administration(s) of desmopressin in perioperative persons with nonsevere hemophilia A.

Methods

We studied FVIII:C levels after desmopressin before (day 0 [D0]) and on days 1 (D1) and 2 (D2) after surgery in 26 patients of the DAVID and Little DAVID studies. We studied tachyphylaxis by comparing the responses at D1 and D2 with that at D0. We also assessed the reproducibility of the D0 response in comparison to an earlier performed desmopressin test.

Results

The median absolute FVIII:C increase was 0.50 IU/mL (0.35-0.74; n = 23) at D0, 0.21 IU/mL (0.14-0.28; n = 17) at D1, and 0.23 IU/mL (0.16-0.30; n = 11) at D2. The median percentage of FVIII increase after the second administration (D1) compared with the first (D0) was 42.9% (29.2%-52.5%; n = 17) and that of the third (D2) compared with the first (D0) was 36.4% (23.7%-46.9%; n = 11). The FVIII:C desmopressin response at D0 was comparable with the desmopressin test response in 74% of the patients.

Conclusion

Tachyphylaxis in the surgical setting was considerably more pronounced than previously reported, with FVIII:C at D1 and D2 of 36% to 43% of the initial response. Our results may have important implications for monitoring repeated desmopressin treatment when used perioperatively.

Clinical and computed tomography characteristics of COVID-19 associated acute pulmonary embolism: A different phenotype of thrombotic disease?

INTRODUCTION

COVID-19 infections are associated with a high prevalence of venous thromboembolism, particularly pulmonary embolism (PE). It is suggested that COVID-19 associated PE represents in situ immunothrombosis rather than venous thromboembolism, although the origin of thrombotic lesions in COVID-19 patients remains largely unknown.

METHODS

In this study, we assessed the clinical and computed tomography (CT) characteristics of PE in 23 consecutive patients with COVID-19 pneumonia and compared these to those of 100 consecutive control patients diagnosed with acute PE before the COVID-19 outbreak. Specifically, RV/LV diameter ratio, pulmonary artery trunk diameter and total thrombus load (according to Qanadli score) were measured and compared.

RESULTS

We observed that all thrombotic lesions in COVID-19 patients were found to be in lung parenchyma affected by COVID-19. Also, the thrombus load was lower in COVID-19 patients (Qanadli score -8%, 95% confidence interval [95%CI] -16 to -0.36%) as was the prevalence of the most proximal PE in the main/lobar pulmonary artery (17% versus 47%; -30%, 95%CI -44% to -8.2). Moreover, the mean RV/LV ratio (mean difference -0.23, 95%CI -0.39 to -0.07) and the prevalence of RV/LV ratio >1.0 (prevalence difference -23%, 95%CI -41 to -0.86%) were lower in the COVID-19 patients.

CONCLUSION

Our findings therefore suggest that the phenotype of COVID-19 associated PE indeed differs from PE in patients without COVID-19, fuelling the discussion on its pathophysiology.

AB0430 MORTALITY IN PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS AND NEUROPSYCHIATRIC SYMPTOMS

Background:

Little is known about mortality in patients with systemic lupus erythematosus (SLE) presenting with neuropsychiatric (NP) symptoms.

Objectives:

We aimed to evaluate all-cause and cause-specific mortality in patients with SLE and NP symptoms.

Methods:

All patients with the clinical diagnosis of SLE of 18 years and older that visited the tertiary referral NPSLE clinic of the Leiden University Medical Center between 2007-2018 and signed informed consent were included in this study. Patients were classified as NPSLE if NP symptoms were attributed to SLE and immunosuppressive or anticoagulant therapy was initiated, otherwise patients were classified as non-NPSLE. Municipal registries were checked for current status (alive/deceased). Electronical medical files were studied for clinical characteristics and cause of death. Standardized mortality ratios (SMRs) and 95% confidence intervals were calculated using data from the general Dutch population. In addition, a rate ratio (RR) was calculated using direct standardization to compare mortality in NPSLE with non-NPSLE patients.

Results:

351 patients with the clinical diagnosis of SLE were included, of which 149 patients were classified as NPSLE (42.5%). Compared with the general population, mortality was increased five times in NPSLE (SMR 5.0, 95% CI: 2.6-8.5) and nearly four times in non-NPSLE patients (SMR 3.7, 95% CI: 2.2-6.0), as shown in Table 1. Risk of death due to cardiovascular disease (CVD) was increased in non-NPSLE patients (SMR 6.2, 95% CI: 2.0-14.6) and an increased risk of death to infections was present in both NPSLE and non-NPSLE patients ((SMR 29.9, 95% CI: 3.5 – 105) and SMR 91.3 (95% CI: 18.8 – 266) respectively). However, mortality did not differ between NPSLE and non-NPSLE patients (RR 1.0, 95% CI: 0.5 – 2.0).

Table 1.

All-cause mortality in SLE patients presenting with neuropsychiatric symptoms attributed to SLE (NPSLE) or to other causes (non-NPSLE)

NPSLE(N = 149)Non-NPSLE(N = 202)Deaths (N, %)13 (8.7)17 (8.4)Age at death (median, range)49 (32 – 79)59 (20 – 89)Follow-up time (years)9061047Crude mortality rate (per 1000 PY)14.316.2All-cause mortality*Female5.5 (2.8 – 9.6)3.4 (1.9 – 5.7)Male2.3 (0.1 - 12.8)6.2 (1.3 – 18.2)Combined5.0 (2.6 – 8.5)3.7 (2.2 – 6.0)

*Standardized mortality ratio, ratio of the observed and expected number of deaths

Conclusion:

Mortality was increased in both NPSLE and non-NPSLE patients in comparison with the general population, but there was no difference in mortality between NPSLE and non-NPSLE patients. Risk of death due to infections was increased in both groups.

Disclosure of Interests:

Rory Monahan: None declared, Rolf Fronczek: None declared, Jeroen Eikenboom: None declared, Huub Middelkoop: None declared, L.J.J. Beaart- van de Voorde: None declared, Gisela Terwindt: None declared, Nic van der Wee: None declared, Frits Rosendaal: None declared, Thomas Huizinga Grant/research support from: Ablynx, Bristol-Myers Squibb, Roche, Sanofi, Consultant of: Ablynx, Bristol-Myers Squibb, Roche, Sanofi, Margreet Kloppenburg: None declared, G.M. Steup-Beekman: None declared

AB0383 EXTREME FATIGUE IN PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS AND NEUROPSYCHIATRIC SYMPTOMS

Background:

Fatigue is commonly described in chronic illnesses, especially auto-immune disorders such as systemic lupus erythematosus (SLE).

Objectives:

We aim to study the prevalence of fatigue in SLE patients with NP symptoms and compare fatigue in SLE patients with NP symptoms attributed to major organ involvement due to SLE (NPSLE) with SLE patients with NP symptoms not caused by major nervous system involvement (non-NPSLE).

Methods:

All patients visiting the tertiary referral center for NPSLE in the LUMC between 2007-2019 with the clinical diagnosis of SLE and age >18 years that signed informed consent were included in this study. Patients underwent a standardized multidisciplinary assessment, including two questionnaires: SF-36 (2007-2019) and multidimensional fatigue index (MFI, 2011-2019). Patients were classified as NPSLE in this study if NP symptoms were attributed to SLE and immunosuppressive or anticoagulant therapy was initiated, otherwise patients were classified as non-NPSLE. The vitality (VT) domain of the SF-36 domain was used to assess fatigue, which generates a score from 0-100, 100 representing the complete absence of fatigue. Patients with a score more than 1 standard deviation (SD) removed from age-related controls of the Dutch general population were classified as fatigued; patients more than 2 SD removed were classified as extremely fatigued1. The MFI was also used, which consists of 5 subdomain scores between 0-20, leading to a total score between 0-100, 100 representing the most extreme fatigue. All scores are presented as mean and standard deviation.

Results:

373 patients fulfilled the inclusion criteria and SF-36 questionnaires of 328 patients were available (88%). The majority of these patients was female (87%) and 98 were classified as NPSLE (30%). In NPSLE patients, average age was 41 ± 13 years and in non-NPSLE the average age was 45 ± 14 years. The average score of the SF-36 vitality domain was 36.0 ± 20.7 in NPSLE vs 33.9 ± 18.8. in non-NPSLE. Overall, 73.5% of the patients were fatigued and 46.9% extremely fatigued in NPSLE vs 77.8% fatigued and 45.7% extremely fatigued in non-NPSLE.

The MFI questionnaire and VAS score were available for 222 patients, of which 65 patients were classified as NPSLE (29.3%). Table 1 depicts the scores of NPSLE and non-NPSLE patients on the MFI subdomains and the VAS score.

Table.

Patient characteristics at registry entry.

NPSLE(N = 65)Non-NPSLE (N = 157)MFI(mean, sd)General Fatigue10.8 (1.8)11.1 (1.5)Physical Fatigue11.4 (2.4)12.3 (1.9)Reduced Activity9.6 (2.9)10.7 (2.2)Reduced Motivation10.7 (2.6)11.1 (1.9)Mental Fatigue9.5 (3.0)9.8 (2.7)Total score51.8 (9.9)54.9 (6.9)SF-36 Vitality (mean, sd)35 (20.7)32.7 (18.2)

Conclusion:

Nearly half of patients with SLE and NP symptoms are as extremely fatigued as only 2.5% of the general Dutch population. Extreme fatigue is not influenced by major nervous system involvement.

References:

[1]Aaronsonet al.J Clin Epidemiol. Vol. 51, No. 11, pp. 1055–1068, 1998

Disclosure of Interests:

Rory Monahan: None declared, Rolf Fronczek: None declared, Jeroen Eikenboom: None declared, Huub Middelkoop: None declared, L.J.J. Beaart- van de Voorde: None declared, Gisela Terwindt: None declared, Nic van der Wee: None declared, Thomas Huizinga Grant/research support from: Ablynx, Bristol-Myers Squibb, Roche, Sanofi, Consultant of: Ablynx, Bristol-Myers Squibb, Roche, Sanofi, Margreet Kloppenburg: None declared, G.M. Steup-Beekman: None declared

Acquired haemophilia A in a patient with breast cancer and lung carcinoma: a case report and literature review

Acquired haemophilia A is a rare disorder caused by spontaneous formation of auto-antibodies (inhibitors) against coagulation factor VIII. This can lead tolife-threatening haemorrhages. Six to twenty-two percent of patients with acquired haemophilia have an underlying malignancy. We describe a 69-year-old woman with metastatic breast cancer and non-small cell lung carcinoma who presented at the emergency room with spontaneous bruising, and who was using a vitamin K antagonist. She had a prolonged activated partial thromboplastin time (aPTT) due to a coagulation factor VIII deficiency caused by factor VIII antibodies. She was treated with prednisone and cyclophosphamide.

Diagnosing and treating antiphospholipid syndrome: a consensus paper

INTRODUCTION

The antiphospholipid syndrome (APS) is defined by the occurrence of venous and/or arterial thrombosis and/or pregnancy-related morbidity, combined with the presence of antiphospholipid antibodies (aPL) and/or a lupus anticoagulant (LAC). Large, controlled, intervention trials in APS are limited. This paper aims to provide clinicians with an expert consensus on the management of APS.

METHODS

Relevant papers were identified by literature search. Statements on diagnostics and treatment were extracted. During two consensus meetings, statements were discussed, followed by a Delphi procedure. Subsequently, a final paper was written.

RESULTS

Diagnosis of APS includes the combination of thrombotic events and presence of aPL. Risk stratification on an individual base remains challenging. 'Triple positive' patients have highest risk of recurrent thrombosis. aPL titres > 99th percentile should be considered positive. No gold standard exists for aPL testing; guidance on assay characteristics as formulated by the International Society on Thrombosis and Haemostasis should be followed. Treatment with vitamin K-antagonists (VKA) with INR 2.0-3.0 is first-line treatment for a first or recurrent APS-related venous thrombotic event. Patients with first arterial thrombosis should be treated with clopidogrel or VKA with target INR 2.0-3.0. Treatment with direct oral anticoagulants is not recommended. Patients with catastrophic APS, recurrent thrombotic events or recurrent pregnancy morbidity should be referred to an expert centre.

CONCLUSION

This consensus paper fills the gap between evidence-based medicine and daily clinical practice for the care of APS patients.

Are serum autoantibodies associated with brain changes in systemic lupus erythematosus? MRI data from the Leiden NP-SLE cohort

OBJECTIVE

The effect of serum autoantibodies on the brain of systemic lupus erythematosus (SLE) patients remains unclear. We investigated whether serum autoantibodies, individually and assessed in groups, are associated with specific brain-MRI abnormalities or whether these structural changes are associated with other SLE-related or traditional cardiovascular disease risk factors.

METHODS

All patients underwent brain 3Tesla-MRI. White matter hyperintensities (WMHs), ischemic lesions, inflammatory-like lesions and cerebral atrophy were scored. Serum autoantibodies analyzed included lupus anticoagulant (LAC), anticardiolipine (aCL) IgG and IgM (first 3 also grouped into antiphospholipid autoantibodies (aPL)), anti-dsDNA, anti-SSA, anti-SSB, anti-RNP, and anti-Sm (the latter 5 grouped into SLE-related autoantibodies). Associations were assessed using logistic regression analysis adjusted for potential confounders. Furthermore, a sensitivity analysis including anti-Beta2 glycoprotein-1 antibodies (anti-β2GP1) in the aPL group was performed and the potential modification role of the neuropsychiatric clinical status in the model was assessed.

RESULTS

325 patients (mean age 42 years (SD 14), 89% female) were included. The following MRI-brain abnormalities were found: WMHs (71%), lacunar infarcts (21%), gliosis (11%), micro-hemorrhages (5%), large hemorrhages (2%), inflammatory-like lesions (6%) and atrophy (14%). No associations were found between individual or total SLE-related autoantibodies and inflammatory-like lesions. A higher number of positive aPL was associated with lacunar infarcts (OR 1.37 (95%CI 1.02-1.99) and gliosis (OR 2.15 (1.37-3.37)). LAC was associated with lacunar infarcts in white matter (OR 3.38 (1.32-8.68)) and atrophy (OR 2.49 (1.01-6.15)), and aCL IgG with gliosis (OR 2.71 (1.05-7.02)). Among other variables, SLE patients with hypertension presented a higher chance for WMHs (OR 5.61 (2.52-12.48)) and lacunar infarcts in WM (OR 2.52 (1.10-5.74)) and basal ganglia (OR 8.34 (2.19-31.70)), while cumulative SLE-damage was correlated with lacunar infarcts in WM (OR 1.43 (1.07-1.90)), basal ganglia (OR 1.72 (1.18-2.51)) and cerebellum (OR 1.79 (1.33-2.41)). These associations were confirmed in the sensitivity analysis.

CONCLUSIONS

Brain abnormalities in SLE represent different underlying pathogenic mechanisms. aPL are associated with ischemic brain changes in SLE, while the presence of SLE-related serum autoantibodies is not related to inflammatory-like lesions. Hypertension and cumulative SLE-damage associate with ischemic MRI-brain changes in SLE, suggesting the importance of accelerated atherosclerosis in this process.

Clinically relevant differences between assays for von Willebrand factor activity

Essentials It is unclear whether there are differences between von Willebrand factor (VWF) activity assays. We compared the four most used VWF activity assays in 661 von Willebrand disease (VWD) patients. All assays correlated excellently, but a discrepant classification was seen in 20% of patients. Differences between VWF activity assays have a large impact on the classification of VWD. SUMMARY: Background Measuring the ability of von Willebrand factor (VWF) to bind to platelets is crucial for the diagnosis and classification of von Willebrand disease (VWD). Several assays that measure this VWF activity using different principles are available, but the clinical relevance of different assay principles is unclear. Objective To compare the four most widely used VWF activity assays in a large VWD patient population. Methods We measured VWF:RCo (ristocetin to activate VWF + whole platelets), VWF:GPIbR (ristocetin + platelet glycoprotein Ib receptor [GPIb] fragments), VWF:GPIbM (gain-of-function GPIb fragments that bind VWF spontaneously without ristocetin) and VWF:Ab (monoclonal antibody directed against the GPIb binding epitope of VWF to mimic platelets) in 661 VWD patients from the nationwide 'Willebrand in the Netherlands' (WiN) Study. Results All assays correlated excellently (Pearson r > 0.9), but discrepant results led to a different classification for up to one-fifth of VWD patients. VWF:RCo was not sensitive enough to classify 18% of patients and misclassified half of genotypic 2B VWD patients, especially those with p.Arg1306Trp. VWF:GPIbR was more sensitive, accurately classified the vast majority of patients, and was unaffected by the p.Asp1472His variant that causes artificially low VWF:RCo. VWF:GPIbM was the most precise assay but misclassified over a quarter of genotypic 2A, 2B and 3 patients. VWF:Ab, often not considered an actual VWF activity assay, performed at least equally to the other assays with regard to accurate VWD classification. Conclusion Although the different VWF activity assays are often considered similar, differences between assays have a large impact on the classification of VWD.

Correction of a dominant-negative von Willebrand factor multimerization defect by small interfering RNA-mediated allele-specific inhibition of mutant von Willebrand factor

Essentials Substitution therapy for von Willebrand (VW) disease leaves mutant VW factor (VWF) unhindered. Presence of mutant VWF may negatively affect phenotypes despite treatment. Inhibition of VWF by allele-specific siRNAs targeting single-nucleotide polymorphisms is effective. Allele-specific inhibition of VWF p.Cys2773Ser improves multimerization.

SUMMARY

Background Treatment of the bleeding disorder von Willebrand disease (VWD) focuses on increasing von Willebrand factor (VWF) levels by administration of desmopressin or VWF-containing concentrates. Both therapies leave the production of mutant VWF unhindered, which may have additional consequences, such as thrombocytopenia in patients with VWD type 2B, competition between mutant and normal VWF for platelet receptors, and the potential development of intestinal angiodysplasia. Most cases of VWD are caused by dominant-negative mutations in VWF, and we hypothesize that diminishing expression of mutant VWF positively affects VWD phenotypes. Objectives To investigate allele-specific inhibition of VWF by applying small interfering RNAs (siRNAs) targeting common single-nucleotide polymorphisms (SNPs) in VWF. This approach allows allele-specific knockdown irrespective of the mutations causing VWD. Methods Four SNPs with a high predicted heterozygosity within VWF were selected, and siRNAs were designed against both alleles of the four SNPs. siRNA efficiency, allele specificity and siRNA-mediated phenotypic improvements were determined in VWF-expressing HEK293 cells. Results Twelve siRNAs were able to efficiently inhibit single VWF alleles in HEK293 cells that stably produce VWF. Transient cotransfections of these siRNAs with two VWF alleles resulted in a clear preference for the targeted allele over the untargeted allele for 11 siRNAs. We also demonstrated siRNA-mediated phenotypic improvement of the VWF multimerization pattern of the VWD type 2A mutation VWF p.Cys2773Ser. Conclusions Allele-specific siRNAs are able to distinguish VWF alleles on the basis of one nucleotide variation, and are able to improve a severe multimerization defect caused by VWF p.Cys2773Ser. This holds promise for the therapeutic application of allele-specific siRNAs in dominant-negative VWD.

Analysis of current perioperative management with Haemate® P/Humate P® in von Willebrand disease: Identifying the need for personalized treatment

INTRODUCTION

Patients with Von Willebrand disease (VWD) are regularly treated with VWF-containing concentrates in case of acute bleeding, trauma and dental or surgical procedures.

AIM

In this multicentre retrospective study, current perioperative management with a von Willebrand factor (VWF)/Factor VIII (FVIII) concentrate (Haemate^® P) in patients with VWD was evaluated.

PATIENTS/METHODS

Patients with VWD undergoing minor or major surgery between 2000 and 2015, requiring treatment with a VWF/FVIII concentrate (Haemate^® P), were included. Achieved VWF activity (VWF:Act) and FVIII during FVIII-based treatment regimens were compared to predefined target levels in national guidelines.

RESULTS

In total, 103 patients with VWD (148 surgeries) were included: 54 type 1 (73 surgeries), 43 type 2 (67 surgeries) and 6 type 3 (8 surgeries). Overall, treatment resulted in high VWF:Act and FVIII levels, defined as ≥0.20 IU/mL above predefined levels. In patients with type 1 VWD, respectively, 65% and 91% of trough VWF:Act and FVIII levels were higher than target levels. In patients with type 2 and type 3 VWD, respectively, 53% and 57% of trough VWF:Act and 72% and 73% of trough FVIII levels were higher than target level. Furthermore, FVIII accumulation over time was observed, while VWF:Act showed a declining trend, leading to significantly higher levels of FVIII than VWF:Act.

CONCLUSION

High VWF:Act and accumulation of FVIII were observed after perioperative FVIII-based replacement therapy in patients with VWD, both underlining the necessity of personalization of dosing regimens to optimize perioperative treatment.

Von Willebrand disease and Weibel-Palade bodies

Von Willebrand factor (VWF) is a pivotal haemostatic protein mediating platelet adhesion to injured endothelium and carrying coagulation factor VIII (FVIII) in the circulation to protect it from premature clearance. Apart from the roles in haemostasis, VWF drives the formation of the endothelial cell specific Weibel-Palade bodies (WPBs), which serve as a regulated storage of VWF and other thrombotic and inflammatory factors. Defects in VWF could lead to the bleeding disorder von Willebrand disease (VWD).

Extensive studies have shown that several mutations identified in VWD patients cause an intracellular retention of VWF. However, the effects of such mutations on the formation and function of its storage organelle are largely unknown. This review gives an overview on the role of VWF in WPB biogenesis and summarizes the limited data on the WPBs formed by VWD-causing mutant VWF.

Health-related quality of life, developmental milestones, and self-esteem in young adults with bleeding disorders

Background

The treatment of bleeding disorders improved in the last decades. However, the effect of growing up with bleeding disorders on developmental, emotional, and social aspects is understudied. Therefore, this study assesses HRQOL, developmental milestones, and self-esteem in Dutch young adults (YA) with bleeding disorders compared to peers.

Methods

Ninety-five YA (18–30 years) with bleeding disorders (78 men; mean 24.7 years, SD 3.5) and 17 women (mean 25.1 years, SD 3.8) participated and completed the Pediatric Quality of Life Inventory Young Adult version, the Course of Life Questionnaire, and the Rosenberg Self-Esteem Scale. Differences between patients with bleeding disorders and their peers, and between hemophilia severity groups, were tested using Mann–Whitney U tests.

Results

YA men with bleeding disorders report a slightly lower HRQOL on the total scale, physical functioning, and school/work functioning in comparison to healthy peers (small effect sizes). YA men with severe hemophilia report more problems on the physical functioning scale than non-severe hemophilia. YA men with bleeding disorders achieved more psychosexual developmental milestones than peers, but show a delay in ‘paid jobs, during middle and/or high school.’ A somewhat lower self-esteem was found in YA men with bleeding disorders in comparison to peers (small effect size). For YA women with bleeding disorders, no differences were found on any of the outcomes in comparison to peers.

Conclusion

This study demonstrates some impairments in HRQOL and self-esteem in YA men with bleeding disorders. By monitoring HRQOL, problems can be identified early, especially with regard to their physical and professional/school functioning.

Comparison of haemostatic function of PAS-C-platelets vs. plasma-platelets in reconstituted whole blood using impedance aggregometry and thromboelastography

BACKGROUND AND OBJECTIVES

There are concerns about the haemostatic function of platelets stored in platelet additive solution (PAS). Aim of this study was to compare the haemostatic function of PAS-C-platelets to plasma-platelets in reconstituted whole blood.

MATERIALS AND METHODS

In our experiment, whole blood was reconstituted with red blood cells, solvent-detergent (SD) plasma and either PAS-C-platelets or plasma-platelets (n = 7) in a physiological ratio. On storage days 2, 5, 8 and 13, the agonist-induced aggregation (multiple electrode aggregometry), clot formation (thromboelastography) and agonist-induced CD62P responsiveness (flow cytometry) were measured.

RESULTS

Samples with PAS-C-platelets showed significantly lower aggregation than plasma-platelets when induced with adenosine diphosphate, -6 U (95% confidence interval: -8; -4) or thrombin receptor-activating protein, -15 U (-19; -10). Also when activated with collagen and ristocetin, the PAS-C-platelets showed less aggregation, although not statistically significant. All samples with PAS-C-platelets showed significantly lower agonist-induced CD62P responsiveness than samples with plasma-platelets. However, there was no difference regarding all TEG parameters.

CONCLUSION

Our findings demonstrate that the function - aggregation and CD62P responsiveness - of PAS-C-platelets in reconstituted whole blood is inferior to that of plasma-platelets, which may have implications in the setting of massive transfusions.

Developments in the diagnostic procedures for von Willebrand disease

Von Willebrand disease (VWD) is the most common inherited bleeding disorder but its diagnosis can be challenging due to the heterogeneity of the disease. VWD is mainly associated with mild mucocutaneous bleeding, although there are more severe phenotypes with bleeding from the gastrointestinal tract or even the joints. Also, surgical interventions and trauma may lead to critical bleeding events. These bleeding episodes are all related to quantitative or qualitative defects of von Willebrand factor (VWF), a multimeric glycoprotein produced by endothelial cells and megakaryocytes, which mediates platelet adhesion and aggregation and binds factor VIII (FVIII) in the circulation. This review describes the diagnostic procedures required for correct diagnosis. Accurate diagnosis and classification is required for proper treatment and counseling. Assessment of bleeding starts with the medical history. After a positive bleeding or family history, subsequent laboratory investigations will start with a panel of standard screening tests for hemostatic defects. Patients suspected of having VWD will be tested for plasma VWF antigen levels, the ability of VWF to bind platelets and FVIII activity. When VWD is confirmed, a set of subtyping tests can classify the patients as VWD types 1, 2 (A, B, M or N) or 3. The performance of some additional assays and analyses, such as VWF propeptide measurement or genetic analysis, may help in identifying the pathological mechanism behind certain defects or can guide in the choice of treatment.

Angiogenic characteristics of blood outgrowth endothelial cells from patients with von Willebrand disease

BACKGROUND

Endothelial von Willebrand factor (VWF) inhibits angiogenesis. Accordingly, blood outgrowth endothelial cells (BOECs) isolated from von Willebrand disease (VWD) patients showed enhanced in vitro angiogenesis when compared with healthy control BOECs. Characterization of the angiogenic response of VWD BOECs is limited and differences between the different types of VWD have not been investigated in detail.

OBJECTIVES

The aim of this study was to further explore the potential pathogenic effect of VWF mutations on angiogenesis.

METHODS

BOECs were isolated from four healthy individuals, 10 patients with VWD and one heterozygous carrier of a type 2N mutation. Cell migration and tube formation were measured.

RESULTS

Migration velocity and total tube formation were similar between VWD patients and controls in general. BOECs from the type 3 VWD patient and one type 2B patient showed increased migratory velocity and tube formation compared with BOECs from other patients and healthy controls. Directional migration was impaired in eight out of 10 VWD BOECs and the ability to form tubes was limited to early passage numbers, but not for BOECs from healthy controls.

CONCLUSION

BOECs can be a useful tool for ex vivo assessment of endothelial cell function in patients with different types of VWD, but possible limitations, such as early loss of angiogenic capacity, should be recognized. BOECs from most VWD patients consistently showed impairment in the directionality of migration. This is the first report on angiogenic properties of a type 3 VWD BOEC, which showed increased in vitro angiogenesis.

CLEC4M and STXBP5 gene variations contribute to von Willebrand factor level variation in von Willebrand disease

BACKGROUND

von Willebrand factor (VWF) levels in healthy individuals are influenced by variations in genetic loci other than the VWF gene, whose contribution to VWF levels in patients with von Willebrand disease (VWD) is largely unknown.

OBJECTIVES

To investigate the association between single-nucleotide polymorphisms (SNPs), VWF levels, and bleeding phenotype.

PATIENTS/METHODS

In 364 type 1 VWD and 240 type 2 VWD patients from the nationwide cross-sectional 'Willebrand in The Netherlands' (WiN) study, we studied the association between eight SNPs in STXBP5, SCARA5, ABO, VWF, STAB2, STX2, TC2N, and CLEC4M, and VWF antigen (VWF:Ag), VWF activity (VWF:Act), and bleeding phenotype as assessed with the Tosetto bleeding score.

RESULTS

In type 1 patients, STXBP5 was associated with a lower VWF:Ag level (adjusted difference of -3.0 IU dL(-1) per allele; 95% confidence interval [CI] -6.0 to 0.1) and CLEC4M with both a lower VWF:Ag level (-4.3 IU dL(-1) per allele; 95% CI -7.9 to -0.6) and lower VWF:Act (-5.7 IU dL(-1) per allele; 95% CI -10.9 to -0.5). In type 2 patients, none of the SNPs was associated with VWF levels. None of the genetic variants was associated with bleeding score.

CONCLUSIONS

Genetic variations in STXBP5 and CLEC4M are associated with VWF level variation in type 1 VWD, but not in type 2 VWD. This study increases our understanding of the pathophysiology of VWD, and provides a further indication of the involvement of STXBP5 and CLEC4M in determining VWF levels in VWD.

Joint bleeds in von Willebrand disease patients have significant impact on quality of life and joint integrity: a cross-sectional study

BACKGROUND

Joint bleeds (JB) are reported in a minority of patients with von Willebrand disease (VWD) but may lead to structural joint damage. Prevalence, severity and impact of JB in VWD are largely unknown.

OBJECTIVES

The aim of this study was to assess JB prevalence, onset, treatment and impact on health-related quality of life (HR-QoL) and joint integrity in moderate and severe VWD.

METHODS

In the Willebrand in the Netherlands study 804 moderate and severe VWD patients [von Willebrand factor (VWF) activity ≤30U dL(-1)] completed a questionnaire on occurrence, sites and consequences of JB. To analyse JB number, onset, treatment and impact on joint integrity we additionally performed a patient-control study on medical file data comparing patients with JB to age, gender, factor VIII (FVIII)- and VWF activity matched VWD patients without JB.

RESULTS

Of all VWD patients 23% (184/804) self-reported JB. These 184 patients reported joint damage more often (54% vs. 18%, P < 0.001) and had lower HR-QoL (SF36, P < 0.05) compared to VWD patients not reporting JB. Of 55 patients with available JB data, 65% had the first JB before age 16. These 55 patients used more clotting factor concentrate (CFC; median dose 43 vs. 0 IE FVIII kg(-1) year(-1) , P < 0.001), more often had X-ray joint damage (44% vs. 11%, P = 0.001] and chronic joint pain (44% vs. 18%, P = 0.008) compared to 55 control VWD patients without JB.

CONCLUSION

In conclusion, joint bleeds are reported by 23% of moderate and severe VWD patients, mostly start in childhood, are associated with more CFC use, joint pain, lower HR-QoL and significantly more radiological and self-reported joint damage.

No evidence for a direct effect of von Willebrand factor's ABH blood group antigens on von Willebrand factor clearance

BACKGROUND

One of the major determinants of von Willebrand factor (VWF) plasma levels is ABO blood group status, and individuals with blood group O have ~ 25% lower plasma levels. The exact mechanism behind this relationship remains unknown, although effects on clearance have been postulated.

OBJECTIVES

To determine whether clearance of VWF is directly dependent on the presence of ABH antigens on VWF.

METHODS

Three type 3 von Willebrand disease (VWD) patients were infused with Haemate-P, and the relative loading of VWF with ABH antigens at different time points was measured. VWF-deficient mice were injected with purified plasma-derived human VWF obtained from donors with either blood group A, blood group B, or blood group O.

RESULTS

In mice, we found no difference in clearance rate between plasma-derived blood group A, blood group B and blood group O VWF. Faster clearance of the blood group O VWF present in Haemate-P infused in type 3 VWD patients would have resulted in a relative increase in the loading of VWF with A and B antigens over time. However, we observed a two-fold decrease in the loading with A and B antigens in two out of three patients, and stable loading in the third patient.

CONCLUSION

There is no direct effect of ABH antigens on VWF in VWF clearance. We demonstrate that, in a direct comparison within one individual, blood group O VWF is not cleared faster than blood group A or blood group B VWF. Clearance differences between blood group O and non-blood group O individuals may therefore be related to the blood group status of the individual rather than the ABH antigen loading on VWF itself.

Primary postpartum haemorrhage in women with von Willebrand disease or carriership of haemophilia despite specialised care: a retrospective survey

Pregnant women with bleeding disorders require specialised peripartum care to prevent postpartum haemorrhage (PPH). If third trimester coagulation factor levels are <0.50 IU mL(-1) , prophylactic treatment is indicated and administered according to international guidelines. However, optimal dose and duration are unknown and bleeding may still occur. The aim of this study was to investigate the outcome in women with von Willebrand disease (VWD) or haemophilia carriership treated according to current practice guidelines. From the period 2002-2011, 185 deliveries in 154 VWD women or haemophilia carriers were retrospectively included. Data on blood loss, bleeding disorder characteristics and obstetric risk factors were obtained. The outcome was primary PPH, defined as blood loss ≥500 mL within 24 h postpartum and severe PPH as blood loss ≥1000 mL. Primary PPH was observed in 62 deliveries (34%), 14 (8%) of which resulted in severe PPH. In 26 deliveries prophylactic treatment was administered due to factor levels below the 0.50 IU mL(-1) cut-off in the third trimester, 14 of which (54%) were complicated by PPH. We found an increased PPH risk in deliveries given prophylactic treatment compared with deliveries without (OR 2.7, 95% CI 1.2-6.3). In conclusion, PPH incidence was highest in deliveries with the lowest factor levels in the third trimester. Currently, delivery outcome in women with bleeding disorders is unsatisfactory, given the high PPH incidence despite specialised care. Future studies are required to optimise management of deliveries in this patient population.

Towards the imaging of Weibel-Palade body biogenesis by serial block face-scanning electron microscopy

Electron microscopy is used in biological research to study the ultrastructure at high resolution to obtain information on specific cellular processes. Serial block face-scanning electron microscopy is a relatively novel electron microscopy imaging technique that allows three-dimensional characterization of the ultrastructure in both tissues and cells by measuring volumes of thousands of cubic micrometres yet at nanometre-scale resolution. In the scanning electron microscope, repeatedly an image is acquired followed by the removal of a thin layer resin embedded biological material by either a microtome or a focused ion beam. In this way, each recorded image contains novel structural information which can be used for three-dimensional analysis.

Here, we explore focused ion beam facilitated serial block face-scanning electron microscopy to study the endothelial cell–specific storage organelles, the Weibel–Palade bodies, during their biogenesis at the Golgi apparatus. Weibel–Palade bodies predominantly contain the coagulation protein Von Willebrand factor which is secreted by the cell upon vascular damage. Using focused ion beam facilitated serial block face-scanning electron microscopy we show that the technique has the sensitivity to clearly reveal subcellular details like mitochondrial cristae and small vesicles with a diameter of about 50 nm. Also, we reveal numerous associations between Weibel–Palade bodies and Golgi stacks which became conceivable in large-scale three-dimensional data. We demonstrate that serial block face-scanning electron microscopy is a promising tool that offers an alternative for electron tomography to study subcellular organelle interactions in the context of a complete cell.

von Willebrand disease and aging: an evolving phenotype

BACKGROUND

Because the number of elderly von Willebrand disease (VWD) patients is increasing, the pathophysiology of aging in VWD has become increasingly relevant.

OBJECTIVES

To assess age-related changes in von Willebrand factor (VWF) and factor VIII (FVIII) levels and to compare age-related differences in bleeding phenotype between elderly VWD patients and those < 65 years. We also studied co-morbidity in elderly patients.

PATIENTS/METHODS

We included VWD patients with VWF levels ≤ 30 U dL(-1) in the nationwide cross-sectional 'Willebrand in the Netherlands' (WiN-) study. Patients reported bleeding episodes and treatment of VWD in the year preceding inclusion and during life. This was compared between VWD patients older (n = 71) and younger (16-64 years, n = 593) than 65 years. In elderly patients, age-related changes in VWF and FVIII levels were studied longitudinally by including all historically measured levels. All medical records were examined for co-morbidity.

RESULTS

In elderly type 1 patients, a decade age increase was associated with a 3.5 U dL(-1) (95% CI, -0.6 to 7.6) VWF:Ag increase and 7.1 U dL(-1) (95% CI, 0.7 to 13.4) FVIII:C increase. This increase was not observed in elderly type 2 patients. Elderly type 2 patients reported significantly more bleeding symptoms in the year preceding inclusion than younger patients (16/27, 59% vs. 87/221, 39%; P = 0.048), which was not observed in type 1 VWD.

CONCLUSIONS

von Willebrand factor parameters and bleeding phenotype evolve with increasing age in VWD. VWF and FVIII levels increase with age in type 1 patients with no mitigation in bleeding phenotype. In type 2 patients VWF parameters do not increase with age and in these patients aging is accompanied by increased bleeding.

Phosphatidylinositol-3,4,5-triphosphate-dependent Rac exchange factor 1 regulates epinephrine-induced exocytosis of Weibel-Palade bodies

BACKGROUND

Weibel-Palade bodies (WPBs) function as storage vesicles for von Willebrand factor (VWF) and a number of other bioactive compounds, including angiopoietin-2 and insulin-like growth factor-binding protein 7. WPBs release their content following stimulation with agonists that increase the level of intracellular Ca²⁺, such as thrombin, or agonists that increase intracellular levels of cAMP, such as epinephrine.

OBJECTIVE

Previously, we have shown that the exchange protein activated by cAMP, exchange protein activated by cAMP, and the small GTPase Rap1 are involved in cAMP-mediated release of WPBs. In this study, we explored potential downstream effectors of Rap1 in cAMP-mediated WPB release.

METHODS

Studies were performed in primary human umbilical vein endothelial cells. Activation of the small GTP-binding protein Rac1 was monitored by its ability to bind to the CRIB domain of the serine/threonine kinase P21-activated kinase (PAK)1. Downstream effectors of Rap1 were identified with a proteomic screen using a glutathione-S-transferase fusion of the Ras-binding domain of RalGDS. Functional involvement of candidate proteins in WPB release was determined by RNA interference (RNAi)-mediated knockdown of gene expression.

RESULTS

Depletion of Rac1 by RNAi prevented epinephrine-induced VWF secretion. Also, the Rac1 inhibitor EHT1864 reduced epinephrine-induced WPB release. We identified the phosphatidylinositol-3,4,5-triphosphate-dependent Rac exchange factor 1 (PREX1) and the regulatory β-subunit of phosphatidylinositol 3-kinase (PI3K) as downstream targets of Rap1. The PI3K inhibitor LY294002 reduced epinephrine-induced release of VWF. RNAi-mediated downregulation of PREX1 abolished epinephrine-induced but not thrombin-induced release of WPBs.

CONCLUSION

Our findings show that PREX1 regulates epinephrine-induced release of WPBs.

[Von Willebrand disease in the Netherlands: the WiN study]

Von Willebrand disease is the most common inherited bleeding disorder and is characterised by mucocutaneous bleeding. Von Willebrand disease is caused by reduced levels or reduced function of von Willebrand factor. Depending on the cause, von Willebrand disease is distinguished into various types with their own characteristics and treatment options. The frequency and severity of bleeding in patients with von Willebrand disease is strongly determined by von Willebrand factor levels, factor VIII levels and the type of von Willebrand disease. Eighty-five percent of all adult females with von Willebrand disease reports menorrhagia. A high percentage have postpartum excessive blood loss (37% of all deliveries). The quality of life is reduced in patients with von Willebrand disease. Patients with von Willebrand disease have a reduced risk of arterial thrombosis such as a myocardial or cerebral infarction.

von Willebrand factor remodeling during exocytosis from vascular endothelial cells

BACKGROUND

In vascular endothelial cells, high molecular weight multimers of von Willebrand factor (VWF) are folded into tubular structures for storage in Weibel-Palade bodies. On stimulation, VWF is secreted and forms strings to induce primary hemostasis. The structural changes composing the transition of stored tubular VWF into secreted unfurled VWF strings are still unresolved even though they are vital for normal hemostasis. The secretory pod is a novel structure that we previously described in endothelial cells. It is formed on stimulation and has been postulated to function as a VWF release site. In this study, we investigated the actual formation of secretory pods and the subsequent remodeling of VWF into strings.

METHODS

Human umbilical vein endothelial cells were stimulated and studied using various imaging techniques such as live-cell imaging and correlative light and electron microscopy.

RESULTS

We found by using live-cell imaging that secretory pods are formed through the coalescence of multiple Weibel-Palade bodies without involvement of other large structures. Secreted VWF expelled from secretory pods was found to adopt a globular conformation. We visualized that VWF strings derive from those globular masses of VWF. Flow experiments showed that, on secretion, the globular masses of VWF move to the edge of the cell, where they anchor and generate VWF strings.

CONCLUSION

On secretion, VWF adopts a globular conformation that remodels into strings after translocation and anchoring at the edge of the cell. This finding reveals new pathophysiological mechanisms that could be affected in patients with von Willebrand disease.

Genome-wide linkage scan in affected sibling pairs identifies novel susceptibility region for venous thromboembolism: Genetics In Familial Thrombosis study

BACKGROUND

Venous thromboembolism (VTE) is a multicausal disorder involving environmental and genetic risk factors. In many thrombophilic families the clustering of thrombotic events cannot be explained by known genetic risk factors, indicating that some remain to be discovered.

OBJECTIVES

We aimed to identify novel thrombosis susceptibility alleles in a large panel of small thrombophilic families: the Genetics In Familial Thrombosis (GIFT) study.

PATIENTS/METHODS

In the GIFT study, 201 families were recruited consisting of 438 siblings with an objectively confirmed VTE at a young age. Multipoint linkage analysis (402 SSR markers) and fine mapping were performed, followed by genotyping of tagging SNPs in positional candidate genes.

RESULTS

Established genetic risk factors such as factor V Leiden, ABO blood group non-O, prothrombin 20210A, fibrinogen gamma 10034T and deficiencies of antithrombin, protein C and protein S were more frequent in GIFT patients than in unselected VTE patients. Linkage supported the presence of novel thrombosis susceptibility loci on 7p21.3-22.2 (LOD score = 3.23) and Xq24-27.3 (LOD score = 1.95). Simulation analysis showed that the chr7 signal was genome-wide statistically significant (P = 0.022). Tagging SNPs (n = 157) in eight positional candidate genes (LOD drop 1.5 regions) were genotyped in GIFT patients and 332 healthy controls. Five chr7 SNPs associated with VTE. SNP THSD7A rs2074597 was responsible for part of the chr7 signal.

CONCLUSIONS

The GIFT panel is rich in established genetic risk factors for VTE, but genetic factors remain unidentified in many families. Genome-wide linkage failed to identify the previously established genetic risk factors for VTE, but identified a novel VTE susceptibility locus on chr7.

Reduced prevalence of arterial thrombosis in von Willebrand disease

BACKGROUND

High von Willebrand factor (VWF) levels are an established risk factor for arterial thrombosis, including coronary heart disease and ischemic stroke. It has been hypothesized that von Willebrand disease (VWD) patients are protected against arterial thrombosis; however, this has never been confirmed in clinical studies.

OBJECTIVES

To investigate the prevalence of arterial thrombosis in VWD patients relative to the general population.

PATIENTS/METHODS

We included 635 adult patients with VWF levels ≤ 30 U dL(-1) , aged 16-85 years, from the nationwide cross-sectional 'Willebrand in the Netherlands' (WiN) study and compared the prevalence of arterial thrombosis with two reference populations from the general Dutch population adjusted for age and sex as standardized morbidity ratios (SMRs).

RESULTS

Twenty-nine arterial thrombotic events occurred in 21 patients (3.3%). Five patients suffered an acute myocardial infarction and three an ischemic stroke. Unstable angina pectoris was recorded 12 times, transient ischemic attack nine. The prevalence of all arterial thrombotic events combined (acute myocardial infarction, ischemic stroke and coronary heart disease) was 39% and 63% lower than in the two reference populations. The prevalence of cardiovascular disease in VWD was lower than in the general population, SMR 0.60 (95% CI, 0.32-0.98) for coronary heart disease and SMR 0.40 (95% CI, 0.13-0.83) for acute myocardial infarction. For ischemic stroke the prevalence was 35-67% lower compared with two reference populations, SMR 0.65 (95% CI, 0.12-1.59) and 0.33 (95% CI, 0.06-0.80), respectively.

CONCLUSIONS

This is the first study showing that VWD patients have a reduced prevalence of arterial thrombosis and provides important insights into the role of VWF in the pathogenesis of arterial thrombosis.

Weibel-Palade bodies: a window to von Willebrand disease

Weibel-Palade bodies (WPBs) are the storage organelles for von Willebrand factor (VWF) in endothelial cells. VWF forms multimers that assemble into tubular structures in WPBs. Upon demand, VWF is secreted into the blood circulation, where it unfolds into strings that capture platelets during the onset of primary hemostasis. Numerous mutations affecting VWF lead to the bleeding disorder von Willebrand disease. This review reports the recent findings on the effects of VWF mutations on the biosynthetic pathway of VWF and its storage in WPBs. These new findings have deepened our understanding of VWF synthesis, storage, secretion, and function.

Formation of platelet-binding von Willebrand factor strings on non-endothelial cells

BACKGROUND AND OBJECTIVE

Von Willebrand factor (VWF) forms strings on activated vascular endothelial cells that recruit platelets and initiate clot formation. Alterations in VWF strings may disturb hemostasis. This study was aimed at developing a flexible model system for structure-function studies of VWF strings.

METHODS

VWF strings were generated by inducing exocytosis of pseudo-Weibel-Palade bodies from VWF-transfected HEK293 cells, and the properties of these strings under static conditions and under flow were characterized.

RESULTS

Upon exocytosis, VWF unfurled into strings several hundred micrometers in length. These strings could form bundles and networks, and bound platelets under flow, resembling authentic endothelial VWF strings. Anchorage of the platelet-decorated VWF strings was independent of P-selectin and integrin α(V) β(3). Translocation of platelets along the strings, elongation and fragmentation of the strings frequently occurred under flow. Furthermore, VWF variants with the p.Tyr87Ser and p.Cys2773Ser mutations, which are defective in multimer assembly, did not give rise to VWF strings. Also, insertion of the green fluorescent protein into VWF inhibited string formation.

CONCLUSIONS

HEK293 cells provide a flexible and useful model system for the study of VWF string formation. Our results suggest that structural changes in VWF may modulate string formation and function, and contribute to hemostatic disorders.

Prospective evaluation of the clinical utility of quantitative bleeding severity assessment in patients referred for hemostatic evaluation

BACKGROUND

Quantitative bleeding assessment tools (BATs) have been used to describe the severity of the bleeding phenotype in patients with von Willebrand disease.

OBJECTIVES

To evaluate the clinical usefulness of a BAT for the diagnosis of mild bleeding disorders (MBDs) in previously undiagnosed patients.

METHODS

We prospectively assessed 215 patients who were consecutively referred for evaluation of bleeding symptoms (n=71), abnormal laboratory clotting test results (n=105) or family investigation (n=39) at two second-level centers. The bleeding history was assessed by a young investigator who administered the BAT instrument, and also by a senior physician who independently evaluated the patient and made the final diagnoses. Sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) were computed for a predefined bleeding score (BS) cut-off (BS of >3). Receiver operating characteristic curves were used to establish a diagnostic prediction rule.

RESULTS

Assuming the prevalence of MBD in the general population to be ∼1%, a normal BS (≤3) had a very high NPV (99.2%). The PPVs in patients referred for hemostatic or family evaluation at second-level clinics were estimated to be 71.0% and 77.5% (assuming MDB prevalences of 20% and 50%, respectively, in these settings). Measurement of BS in addition to activated partial thromboplastin time significantly increased the diagnostic efficiency of the BAT instrument (NPV of 99.6%).

CONCLUSIONS

BAT use improves the evaluation of patients with suspected MBD, and we propose its use in a clinical prediction guide based on BAT and activated partial thromboplastin time for the exclusion of patients with suspected MBD in a low-prevalence setting.

von Willebrand factor variant p.Arg924Gln marks an allele associated with reduced von Willebrand factor and factor VIII levels

BACKGROUND

von Willebrand factor (VWF) variant c.2771G>A; p.R924Q has been described as a benign polymorphism or a possible marker for a null allele and been associated with mild bleeding phenotypes. It was identified in several patients in recent type 1 von Willebrand disease (VWD) studies.

OBJECTIVES

To determine whether the p.R924Q allele contributes to reduced VWF levels and type 1 VWD.

METHODS

One thousand one hundred and fifteen healthy controls and 148 index cases from the MCMDM-1VWD study were genotyped for c.2771G>A; VWF and FVIII levels were analyzed in ABO blood group stratified individuals and the p.R924Q variant was expressed in 293 EBNA cells.

RESULTS

c.2771G>A was present in six index cases, five of whom had a second VWF variant which probably contributed to the phenotype. A common core haplotype identified in families, which included the rare G allele of c.5843-8C>G, was present in the majority of 35 c.2771G>A heterozygous controls. c.2771G>A contributed about 10% variance in VWF and FVIII levels in controls and 35% variance when co-inherited with blood group O. Recombinant p.R924Q VWF had no effect on in vitro expression and heterozygous family members had normal VWF-FVIII binding and normal clearance of VWF and FVIII.

CONCLUSIONS

The allele bearing c.2771A leads to reductions in VWF and FVIII levels particularly in combination with blood group O. Its inheritance alone may be insufficient for VWD diagnosis, but it appears to be associated with a further VWF level reduction in individuals with a second VWF mutation and it contributes to population variance in VWF and FVIII levels.

Von Willebrand disease and Weibel-Palade bodies

Von Willebrand factor (VWF) is a pivotal haemostatic protein mediating platelet adhesion to injured endothelium and carrying coagulation factor VIII (FVIII) in the circulation to protect it from premature clearance. Apart from the roles in haemostasis, VWF drives the formation of the endothelial cell specific Weibel-Palade bodies (WPBs), which serve as a regulated storage of VWF and other thrombotic and inflammatory factors. Defects in VWF could lead to the bleeding disorder von Willebrand disease (VWD). Extensive studies have shown that several mutations identified in VWD patients cause an intracellular retention of VWF. However, the effects of such mutations on the formation and function of its storage organelle are largely unknown. This review gives an overview on the role of VWF in WPB biogenesis and summarizes the limited data on the WPBs formed by VWD-causing mutant VWF.

Expression of 14 von Willebrand factor mutations identified in patients with type 1 von Willebrand disease from the MCMDM-1VWD study

BACKGROUND

Candidate von Willebrand factor (VWF) mutations were identified in 70% of index cases in the European study 'Molecular and Clinical Markers for the Diagnosis and Management of type 1 von Willebrand Disease'. The majority of these were missense mutations.

OBJECTIVES

To assess whether 14 representative missense mutations are the cause of the phenotype observed in the patients and to examine their mode of pathogenicity.

METHODS

Transfection experiments were performed with full-length wild-type or mutant VWF cDNA for these 14 missense mutations. VWF antigen levels were measured, and VWF multimer analysis was performed on secreted and intracellular VWF.

RESULTS

For seven of the missense mutations (G160W, N166I, L2207P, C2257S, C2304Y, G2441C, and C2477Y), we found marked intracellular retention and impaired secretion of VWF, major loss of high molecular weight multimers in transfections of mutant constructs alone, and virtually normal multimers in cotransfections with wild-type VWF, establishing the pathogenicity of these mutations. Four of the mutations (R2287W, R2464C, G2518S, and Q2520P) were established as being very probably causative, on the basis of a mild reduction in the secreted VWF or on characteristic faster-running multimeric bands. For three candidate changes (G19R, P2063S, and R2313H), the transfection results were indistinguishable from wild-type recombinant VWF and we could not prove these changes to be pathogenic. Other mechanisms not explored using this in vitro expression system may be responsible for pathogenicity.

CONCLUSIONS

The pathogenic nature of 11 of 14 candidate missense mutations identified in patients with type 1 VWD was confirmed. Intracellular retention of mutant VWF is the predominant responsible mechanism.

Detailed von Willebrand factor multimer analysis in patients with von Willebrand disease in the European study, molecular and clinical markers for the diagnosis and management of type 1 von Willebrand disease (MCMDM-1VWD)

BACKGROUND

Type 1 von Willebrand disease (VWD) is a congenital bleeding disorder characterized by a partial quantitative deficiency of plasma von Willebrand factor (VWF) in the absence of structural and/or functional VWF defects. Accurate assessment of the quantity and quality of plasma VWF is difficult but is a prerequisite for correct classification.

OBJECTIVE

To evaluate the proportion of misclassification of patients historically diagnosed with type 1 VWD using detailed analysis of the VWF multimer structure.

PATIENTS AND METHODS

Previously diagnosed type 1 VWD families and healthy controls were recruited by 12 expert centers in nine European countries. Phenotypic characterization comprised plasma VWF parameters and multimer analysis using low- and intermediate-resolution gels combined with an optimized visualization system. VWF genotyping was performed in all index cases (ICs).

RESULTS

Abnormal multimers were present in 57 out of 150 ICs; however, only 29 out of these 57 (51%) had VWF ristocetin cofactor to antigen ratio below 0.7. In most cases multimer abnormalities were subtle, and only two cases had a significant loss of the largest multimers.

CONCLUSIONS

Of the cases previously diagnosed as type 1 VWD, 38% showed abnormal multimers. Depending on the classification criteria used, 22 out of these 57 cases (15% of the total cohort) may be reclassified as type 2, emphasizing the requirement for multimer analysis compared with a mere ratio of VWF functional parameters and VWF:Ag. This is further supported by the finding that even slightly aberrant multimers are highly predictive for the presence of VWF mutations.

Impact of plasma von Willebrand factor levels in the diagnosis of type 1 von Willebrand disease: results from a multicenter European study (MCMDM-1VWD)

BACKGROUND

Presence of bleeding symptoms, inheritance and reduced von Willebrand factor (VWF) contribute to the diagnosis of type 1 von Willebrand disease (VWD). However, quantitative analysis of the importance of VWF antigen (VWF:Ag) and ristocetin cofactor activity (VWF:RCo) levels in the diagnosis is lacking.

OBJECTIVES

To evaluate the relative contribution of VWF measurement to the diagnosis of VWD.

PATIENTS AND METHODS

From the MCMDM-1VWD study cohort, 204 subjects (considered as affected by VWD based on the enrolling Center diagnoses and the presence of linkage with the VWF locus) were compared with 1155 normal individuals. Sensitivity, specificity and diagnostic positive likelihood ratios (LR) of VWF:Ag and VWF:RCo were computed.

RESULTS

ABO blood group was the variable most influencing VWF levels, but adjustment of the lower reference limit for the ABO group did not improve sensitivity and specificity of VWF:Ag or VWF:RCo. The lower reference limit (2.5th percentile) was 47 IU dL(-1) for both VWF:Ag and VWF:RCo and showed similar diagnostic performance [receiver-operator curve area: 0.962 and 0.961 for VWF:Ag and VWF:RCo, respectively; P = 0.81]. The probability of VWD was markedly increased only for values below 40 IU dL(-1) (positive LR: 95.1 for VWF:Ag), whereas intermediate values (40 to 60 IU dL(-1)) of VWF only marginally indicated the probability of VWD.

CONCLUSIONS

Although the conventional 2.5 lower percentile has good sensitivity and specificity, only VWF:Ag or VWF:RCo values below 40 IU dL(-1) appear to significantly indicate the likelihood of type 1 VWD. The LR profile of VWF level could be used in a diagnostic algorithm.

A quantitative analysis of bleeding symptoms in type 1 von Willebrand disease: results from a multicenter European study (MCMDM-1 VWD)

BACKGROUND

A quantitative description of bleeding symptoms in type 1 von Willebrand disease (VWD) has never been reported.

OBJECTIVES

The aim was to quantitatively evaluate the severity of bleeding symptoms in type 1 VWD and its correlation with clinical and laboratory features.

PATIENTS AND METHODS

Bleeding symptoms were retrospectively recorded in a European cohort of VWD type 1 families, and for each subject a quantitative bleeding score (BS) was obtained together with phenotypic tests.

RESULTS

A total of 712 subjects belonging to 144 families and 195 controls were available for analysis. The BS was higher in index cases than in affected family members (BS 9 vs. 5, P < 0.0001) and in unaffected family members than in controls (BS 0 vs. -1, P < 0.0001). There was no effect of ABO blood group. BS showed a strong significant inverse relation with either von Willebrand ristocetin cofactor (VWF:RCo), von Willebrand antigen (VWF:Ag) or factor VIII procoagulant activity (FVIII:C) measured at time of enrollment, even after adjustment for age, sex and blood group (P < 0.001 for all the four upper quintiles of BS vs. the first quintile, for either VWF:RCo, VWF:Ag or FVIII:C). Higher BS was related with increasing likelihood of VWD, and a mucocutaneous BS (computed from spontaneous, mucocutaneous symptoms) was strongly associated with bleeding after surgery or tooth extraction.

CONCLUSIONS

Quantitative analysis of bleeding symptoms is potentially useful for a more accurate diagnosis of type 1 VWD and to develop guidelines for its optimal treatment.

Linkage analysis in families diagnosed with type 1 von Willebrand disease in the European study, molecular and clinical markers for the diagnosis and management of type 1 VWD

BACKGROUND

von Willebrand disease (VWD) type 1 is a congenital bleeding disorder caused by genetic defects in the von Willebrand factor (VWF) gene and characterized by a reduction of structurally normal VWF. The diagnosis of type 1 VWD is difficult because of clinical and laboratory variability. Furthermore, inconsistency of linkage between type 1 VWD and the VWF locus has been reported.

OBJECTIVES

To estimate the proportion of type 1 VWD that is linked to the VWF gene.

PATIENTS AND METHODS

Type 1 VWD families and healthy control individuals were recruited. An extensive questionnaire on bleeding symptoms was completed and phenotypic tests were performed. Linkage between VWF gene haplotypes and the diagnosis of type 1 VWD, the plasma levels of VWF and the severity of bleeding symptoms was analyzed.

RESULTS

Segregation analysis in 143 families diagnosed with type 1 VWD fitted a model of autosomal dominant inheritance. Linkage analysis under heterogeneity resulted in a summed lod score of 23.2 with an estimated proportion of linkage of 0.70. After exclusion of families with abnormal multimer patterns the linkage proportion was 0.46. LOD scores and linkage proportions were higher in families with more severe phenotypes and with phenotypes suggestive of qualitative VWF defects. About 40% of the total variation of VWF antigen could be attributed to the VWF gene.

CONCLUSIONS

We conclude that the diagnosis of type 1 VWD is linked to the VWF gene in about 70% of families, however after exclusion of qualitative defects this is about 50%.