Jeroen Eikenboom

Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand Factor

Summary.  von Willebrand disease (VWD) is a bleeding disorder caused by inherited defects in the concentration, structure, or function of von Willebrand factor (VWF). VWD is classified into three primary categories. Type 1 includes partial quantitative deficiency, type 2 includes qualitative defects, and type 3 includes virtually complete deficiency of VWF. VWD type 2 is divided into four secondary categories. Type 2A includes variants with decreased platelet adhesion caused by selective deficiency of high‐molecular‐weight VWF multimers. Type 2B includes variants with increased affinity for platelet glycoprotein Ib. Type 2M includes variants with markedly defective platelet adhesion despite a relatively normal size distribution of VWF multimers. Type 2N includes variants with markedly decreased affinity for factor VIII. These six categories of VWD correlate with important clinical features and therapeutic requirements. Some VWF gene mutations, alone or in combination, have complex effects and give rise to mixed VWD phenotypes. Certain VWD types, especially type 1 and type 2A, encompass several pathophysiologic mechanisms that sometimes can be distinguished by appropriate laboratory studies. The clinical significance of this heterogeneity is under investigation, which may support further subdivision of VWD type 1 or type 2A in the future.

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

Summary.  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.

The Value of Family History as a Risk Indicator for Venous Thrombosis

BACKGROUND A positive family history of venous thrombosis may reflect the presence of genetic risk factors. Once a risk factor has been identified, it is not known whether family history is of additional value in predicting an individuals risk. We studied the contribution of family history to the risk of venous thrombosis in relation to known risk factors. METHODS In the Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis, a population-based case-control study, we collected blood samples and information about family history and environmental triggers from 1605 patients with a first venous thrombosis and 2159 control subjects. RESULTS A total of 505 patients (31.5%) and 373 controls (17.3%) reported having 1 or more first-degree relatives with a history of venous thrombosis. A positive family history increased the risk of venous thrombosis more than 2-fold (odds ratio [95% confidence interval], 2.2 [1.9-2.6]) and up to 4-fold (3.9 [2.7-5.7]) when more than 1 relative was affected. Family history corresponded poorly with known genetic risk factors. Both in those with and without genetic or environmental risk factors, family history remained associated with venous thrombosis. The risk increased with the number of factors identified; for those with a genetic and environmental risk factor and a positive family history, the risk was about 64-fold higher than for those with no known risk factor and a negative family history. CONCLUSIONS Family history is a risk indicator for a first venous thrombosis, regardless of the other risk factors identified. In clinical practice, family history may be more useful for risk assessment than thrombophilia testing.

Elevated Factor VIII Levels and the Risk of Thrombosis

In vivo, a delicate balance exists between fibrin formation and fibrinolysis. Reduced blood flow, changes in the vessel wall, and changes in blood composition (hypercoagulability)1 may all result in a disturbance of this balance, which favors fibrin formation and ultimately may lead to the formation of occlusive thrombi. Venous thromboembolism is the result of clot formation in a vein at sites of reduced blood flow. Arterial thrombosis involves the formation of platelet aggregates at high shear rates at sites of vessel-wall injury. Classic acquired risk factors for venous thrombosis include trauma, immobilization, pregnancy, surgery, malignancy, and infection. These are all factors that may cause tissue damage, stasis of the blood, or changes in blood composition. Inherited risk factors for venous thrombosis,2 3 4 5 most of which concern defects in the procoagulant and anticoagulant pathways, account for a substantial proportion of all thrombotic events. Table 1⇓ summarizes prevalences and relative risks of established genetic risk factors.6 7 8 9 View this table: Table 1. Genetic Risk Factors for Venous Thrombosis: Prevalence and Relative Risk These risk factors include factor V Leiden (resistance to activated protein C [APC]),9 prothrombin 20210A,8 and deficiencies in antithrombin,2 protein C,3 4 and protein S.5 10 11 Elevated fibrinogen,12 antiphospholipid antibodies,13 and mild hyperhomocysteinemia14 are examples of laboratory phenotypes associated with venous thrombosis. Some of these phenotypes have also been found to be associated with arterial thrombosis.15 16 17 Whether this is also true for genetic risk factors such as factor V Leiden or the prothrombin 20210A allele is still uncertain.18 19 20 21 22 23 24 25 26 Despite growing insight in the pathogenesis of thrombophilia, the cause of many thrombotic episodes remains unknown. Recently, new laboratory phenotypes that are associated with an increased risk of …

Functional architecture of Weibel-Palade bodies

Weibel-Palade bodies (WPBs) are elongated secretory organelles specific to endothelial cells that contain von Willebrand factor (VWF) and a variety of other proteins that contribute to inflammation, angiogenesis, and tissue repair. The remarkable architecture of WPBs is because of the unique properties of their major constituent VWF. VWF is stored inside WPBs as tubules, but on its release, forms strikingly long strings that arrest bleeding by recruiting blood platelets to sites of vascular injury. In recent years considerable progress has been made regarding the molecular events that underlie the packaging of VWF multimers into tubules and the processes leading to the formation of elongated WPBs. Mechanisms directing the conversion of tightly packaged VWF tubules into VWF strings on the surface of endothelial cells are starting to be unraveled. Several modes of exocytosis have now been described for WPBs, emphasizing the plasticity of these organelles. WPB exocytosis plays a role in the pathophysiology and treatment of von Willebrand disease and may have impact on common hematologic and cardiovascular disorders. This review summarizes the major advances made on the biogenesis and exocytosis of WPBs and places these recent discoveries in the context of von Willebrand disease.

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)

Summary.  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.

Identification of type 1 von Willebrand disease patients with reduced von Willebrand factor survival by assay of the VWF propeptide in the European study: Molecular and Clinical Markers for the Diagnosis and Management of Type 1 VWD (MCMDM-1VWD)

The decreased survival of von Willebrand factor (VWF) in plasma has been implicated as a mechanism in a subset of type 1 von Willebrand disease (VWD) patients. We have previously reported that the ratio of plasma levels of VWF and its propeptide (VWFpp) can be used to identify patients with reduced VWF survival. In this study, we report the assay of VWFpp and VWF:Ag in 19 individuals recruited from 6 European centers within the MCMDM-1VWD study. Eight individuals had a VWF:Ag level less than 30 IU/dL. Seven of these patients had a robust desmopressin response and significantly reduced VWF half-life that was predicted by a markedly increased steady-state plasma VWFpp/VWF:Ag ratio. VWF mutations previously associated with reduced VWF survival were identified in each of the 7 individuals. Thus, a substantially increased ratio of steady-state VWFpp/VWF:Ag predicted a reduced VWF half-life in patients with markedly decreased VWF:Ag levels. These data indicate that a reduced VWF survival is found in a subpopulation of patients with type 1 VWD. The systematic assay of both plasma VWF and the VWF propeptide in moderately severe type 1 VWD patients may identify patients with a reduced VWF survival phenotype.

Recessive inheritance of von Willebrand's disease type I

The inheritance of type I von Willebrands disease is thought to be autosomally dominant. The laboratory profile may, however, vary between affected people, even within a single family. There is also a large variation in the severity of clinical symptoms. To see if there is an association between the von Willebrand factor genotype, the laboratory profile, and the severity of the clinical symptoms we did a genetic analysis of four families with type I von Willebrands disease. The proband of each family proved to be a compound heterozygote for defects in the von Willebrand factor gene. Simple heterozygotes in these families were either symptomless or only mildly affected. One of the identified mutations, which was shared by the probands of three of the four families, may have a carrier prevalence of 1:50 in the general population. These results suggest that the inheritance of von Willebrands disease is often recessive rather than dominant and so have important implications for diagnosis and genetic counselling.

Cysteine-mutations in von Willebrand factor associated with increased clearance

Summary.  Background: von Willebrand disease (VWD) is a bleeding disorder caused by the decrease of functional von Willebrand factor (VWF). Low levels of VWF can result from decreased synthesis, impaired secretion, increased clearance or combinations thereof. Several mutations lead to impaired synthesis or secretion of VWF, however, little is known about the survival of VWF in the circulation. Objectives: To evaluate the effect of several VWF mutations on VWF clearance. Patients/methods: The effect of three cysteine‐mutations (C1130F, C1149R or C2671Y) on the in vivo survival of VWF was studied in patients carrying these mutations and in a VWF‐deficient mice model. Results: In patients carrying these mutations, we observed increased propeptide/mature VWF ratios and rapid disappearance of VWF from the circulation after desmopressin treatment. Detailed analysis of in vivo clearance of recombinant VWF in a VWF‐deficient mice model revealed a fourfold increased clearance rate of the mutants. The mutations C1130F, C1149R and C2671Y are each associated with reduced survival of VWF in the circulation. Detailed analysis of the recombinant mutant VWF demonstrated that increased clearance was not due to increased proteolysis by ADAMTS‐13. We did not identify functional or structural characteristics that the mutant proteins have in common and could be associated with the phenomenon of increased clearance. Conclusions: Cysteine‐mutations in VWF may result in reduced in vivo survival. The observation that various mutations are associated with increased in vivo clearance may have major implications for the therapeutic strategies that rely on the rise of endogenous VWF after desmopressin administration.

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

Summary.  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%.