High-resolution analysis of von Willebrand factor multimeric composition defines a new variant of type I von Willebrand disease with aberrant structure but presence of all size multimers (type IC)

In Type I von Willebrand disease, the whole series of von Willebrand factor (vWF) multimers is present in plasma, but all are decreased in quantity. No structural abnormality of individual multimers has been demonstrated so far in these patients. We now describe five individuals, from two unrelated families, who had this form of the disease and in whom the complex banding pattern of each vWF multimer was markedly abnormal. Inheritance was autosomal dominant and the clinical expression was mild. A bleeding history was elicited in three of the patients and included recurrent epistaxis, menometrorrhagia, and bleeding following tooth extraction. Replacement therapy had never been required. Although vWF levels in plasma were within the normal range in all of them, the ristocetin cofactor activity was decreased in four, and the bleeding time was prolonged in three. Analysis of vWF multimeric structure by agarose gel electrophoresis, including a newly developed high-resolution technique, demonstrated that the main band of each multimer was present, but a second, well-defined band always seen in normal individuals was missing in the patients. Two additional bands had altered mobility and were less well defined than in normal subjects, and a fifth, less intense band was also undetectable in the patients. Treatment with 1-deamino-8-D-arginine vasopressin (DDAVP) was assessed in two patients. It caused the circulating levels of vWF to increase and correct the bleeding time, but did not alter the structural abnormality. This study describes, therefore, a new variant form of Type I von Willebrand disease with aberrant structure of individual repeating multimers and an associated functional abnormality of vWF. In keeping with previously accepted terminology, the designation of Type IC von Willebrand disease has been adopted for this new variant.     

A new variant of dominant type II von Willebrand's disease with aberrant multimeric pattern of factor VIII-related antigen (type IID)

A new type II variant form of von Willebrand's disease has been recognized in a mother and daughter who have bleeding manifestations typical of von Willebrand's disease. Laboratory findings include consistently prolonged bleeding times, with normal levels of factor VIII procoagulant and antigen, but decreased ristocetin cofactor activity. Electrophoresis in SDS 1.5% agarose gel and reaction with 125I-labeled anti-factor VIII-related antigen rabbit IgG, followed by autoradiography, revealed that both plasma and platelets lack the large multimers of factor VIII-related antigen. In 2.5% gel, the propositus plasma lacked the normal "triplet" pattern. In 3.0% gel, a 5-band pattern was observed in normal, type IIA, and type IIB plasma, whereas type IIC plasma revealed a 2-band pattern. The patient's plasma revealed a 4-band pattern distinctly different from normal or other type II variants. We suggest that this new variant be labeled type IID, until a more appropriate nomenclature is developed.     

A variant of type II von Willebrand disease with an abnormal triplet structure and discordant effects of protease inhibitors on plasma and platelet von Willebrand factor structure

We have characterized the plasma and platelet von Willebrand factor (vWf) multimeric structure of a patient with von Willebrand disease (vWd) as having a long bleeding time, no aggregation of her platelet-rich plasma (PRP) to ristocetin, and very low plasma and platelet von Willebrand antigen (vWf Ag) and vWf activity. The abnormalities of the plasma and platelet vWf have not been previously described. In particular, the patient's plasma and platelet vWf lacked the intermediate and largest vWf multimers and the slowest migrating minor band (band 1) of the triplet was markedly diminished compared to the major band (band 2) and the fastest migrating band of the triplet (band 3). A similar multimeric structure was seen in the platelet vWf. Collection of the patient's blood in protease inhibitors prior to the analysis of the platelet and plasma vWf structure revealed that the plasma vWf multimeric structure did not change, while the patient's platelet vWf showed a marked change with the appearance of the intermediate and large multimers and almost total disappearance of the abnormal multimeric structure. Direct comparison of this patient's plasma with previously reported cases of type IIA, IIC, and IID revealed marked differences in their multimeric organization compared to our patient. Employing the presently accepted convention, we have designated this variant type of vWd type IIG.     

A new von Willebrand variant (type I, New York): increased ristocetin-induced platelet aggregation and plasma von Willebrand factor containing the full range of multimers

We report three members of a family who had reduced levels of plasma von Willebrand factor (vWF) and increased ristocetin-induced platelet aggregation (RIPA) (aggregation of platelet-rich plasma with ristocetin at a concentration of 0.45 mg/mL), as previously reported in type IIB and pseudo-von Willebrand's disease (vWD). However, in contrast to the latter two disorders in which the larger vWF multimers are absent in plasma, the entire range of vWF multimers was observed in the patients' plasma after sodium dodecyl sulfate-agarose gel electrophoresis, and all vWF multimers (including the largest) were present in the same proportion as in normal plasma and type I vWD. Thus, despite increased RIPA, the levels and multimeric pattern of vWF in this family's plasma were indistinguishable from those in type I vWD in which RIPA is usually decreased. Addition of ristocetin to the patients' platelet- rich plasma resulted in the removal of vWF (and, more selectively, of the large multimers) at lower concentrations of ristocetin than normal, as in type IIB and pseudo-vWD. The defect in the patients was localized to their vWF, which had an enhanced capacity for aggregating washed normal platelets in the presence of low concentrations of ristocetin and for aggregating pseudo-vWD platelets (in the absence of ristocetin). Both glycoproteins (GP) Ib and IIb-IIIa were involved in the enhanced aggregation response. RIPA (at low ristocetin concentrations) in the patients' platelet-rich plasma was abolished by a monoclonal antibody (AP1) to GPIb and was markedly reduced by monoclonal antibodies (10E5 and LJP9) that block adenosine diphosphate and thrombin-induced binding of vWF and fibrinogen to GPIIb-IIIa but was unaffected by an antibody (LJP5) that only blocks vWF binding. Partial inhibition of the initial aggregation slope (and complete inhibition of second phase aggregation) was achieved with creatine phosphate/creatine phosphokinase. EDTA blocked second-phase aggregation but was without effect on the initial slope. The findings in this family combine some features of both type I vWD (normal pattern of vWF multimers in plasma) and type IIB vWD (increased RIPA) and further demonstrate the increasing complexity of the structure-function relationships in vWD.     

Inverse relationship between plasma von Willebrand factor and soluble P selectin in patients with type 1 but not type 2 von Willebrand disease

P selectin is a component of endothelial Wiebel-Palade body membrane and platelet alpha granule membrane. Patients with von Willebrand disease (VWD) have low plasma von Willebrand factor (VWF). To examine the relationship between plasma P selectin and VWF, both were measured by ELISA in 38 patients with VWD and 40 controls. The patient had lower VWF (P < 0.001) but similar P selectin levels (P = 0.458). In 24 type 1 VWD patients, VWF and P selectin correlated inversely (P = 0.005) but in 14 type 2 VWD patients there was no correlation (P = 0.997). These data imply major differences in VWF/P-selectin regulation between types 1 and 2 VWD.     

Multimeric pattern discrepancy between platelet and plasma von Willebrand factor in type IIC von Willebrand disease

von Willebrand factor (vWF) from platelet lysate and plasma, collected in the presence of protease inhibitors, was studied in two patients with type IIC von Willebrand disease (vWD). Platelet and plasma vWF showed the smallest multimer increased, but the latter had a repeating single band whereas the former had a repeating "doublet." This platelet-plasma discrepancy observed for the first time in these patients suggests that the repeating "doublet" or single band described in other type IIC patients represent minor subgroups of type IIC vWD.     

Correction of the bleeding time in treated patients with severe von Willebrand disease is not solely dependent on the normal multimeric structure of plasma von Willebrand factor

Even though it is generally held that cryoprecipitate and fraction I-O correct the prolonged bleeding time (BT) in patients with von Willebrand disease (VWD), perusal of reported data indicates that the correction is usually short-lasting and often partial. We decided to do a controlled study of the relationship between the multimeric structure of von Willebrand factor (VWF) and the BT in five patients with severe (type III) VWD after infusion of three plasma concentrates ("wet" cryoprecipitate, lyophilized cryoprecipitate, and fraction I-O) given in random order. The dosage of concentrates was tailored from in vitro measurements to achieve post-infusion levels of ristocetin cofactor above the lower normal limit (50 U/dL) for at least 3 hours. The postinfusion BT became transiently normal in only two of five patients treated with wet cryoprecipitate, whereas it remained prolonged in all five patients treated with lyophilized cryoprecipitate or fraction I-O. For all the concentrates, the proportion of large VWF multimers calculated by scanning the electrophoretic gels were the same as those for normal standard plasmas. An intact multimeric structure was recovered in postinfusion plasmas of patients treated with wet cryoprecipitate, whereas there was a postinfusion loss of large multimers after lyophilized cryoprecipitate and fraction I-O. These findings indicate that the attainment of a normal BT is the exception rather than the rule after the infusion of three plasma fractions used in the treatment of severe VWD, and that an intact multimeric structure in concentrates and postinfusion plasmas is necessary but not sufficient to sustain a normal BT.     

New variant of von Willebrand disease type II with markedly increased levels of von Willebrand factor antigen and dominant mode of inheritance: von Willebrand disease type IIC Miami

A variant of von Willebrand disease (vWD) was identified in six members of a kindred spanning four generations. The proband was a 46-year-old woman with a lifelong history of bleeding, a prolonged bleeding time (> 15 minutes), markedly elevated von Willebrand factor (vWF) antigen (vWF:Ag = 2.09 U/mL), slightly reduced ristocetin cofactor activity, and a plasma vWF multimer pattern similar to that of vWD type IIC. Similar findings were observed in her three children, mother, and brother. In affected family members, platelet and plasma vWF multimer patterns were discrepant with higher molecular weight multimers observed in platelet vWF. Following a 1-Des-amino-8-D-arginine vasopressin (DDAVP) challenge, the proband failed to normalize her bleeding time even though vWF: Ag rose by 70% and higher molecular weight multimers were increased slightly. Genetic studies were consistent with autosomal dominant inheritance of a mutation within the vWF gene. By sequencing of cloned genomic DNA, mutations were excluded in exons 4, 5, 14, and 15, which encode regions of the vWF propeptide proposed to be important in multimer biosynthesis. Mutations also were excluded in exons 28 to 31, which encompass the known mutations that cause vWD types IIA, IIB, and B. This new variant of vWD, characterized by autosomal dominant inheritance, a qualitative defect that resembles vWD type IIC, and increased plasma vWF:Ag, was tentatively designated vWD type IIC Miami.     

In vitro correction of the abnormal multimeric structure of von Willebrand factor in type IIa von Willebrand''s disease.

Type IIa von Willebrand's disease (vWd) has been characterized by the absence of the largest and a reduction in the intermediate-sized multimers of the plasma and platelet von Willebrand factor (vWf) and by the diminished response of the platelet-rich plasma of these patients to ristocetin. Other recently demonstrated abnormalities include the presence of an abnormal triplet structure of vWf. We have studied the plasma and platelets from three patients with this form of vWd and have found that both their plasma and platelets manifest the previously described abnormalities. Because of the heterogeneity of the multimeric structure of the vWf in these patients, we considered the possibility that postsynthetic events may have modified the vWf. When blood was collected in 5 mM EDTA or 5 mM EDTA/leupeptin/N-ethylmaleimide, the abnormal multimeric structure of the plasma and platelet vWf was partially normalized in that the intermediate and the largest vWf multimers were increased, the abnormal multimer structure was no longer as apparent, and the fastest migrating band (an abnormality seen only in the type IIa vWd plasma and platelets) disappeared. The enzymatic activity responsible for this degradation can be classified as a calcium-dependent protease. Studies of normal radiolabeled vWf incubated with platelet lysates from normal subjects and these patients revealed that the patients' platelets did not contain increased amounts of calcium-dependent protease activity as assessed by degradation of normal vWf. These data suggest that patients with type IIa vWd synthesize an abnormal vWf protein that is susceptible to in vitro proteolytic degradation and that proteolytic degradation can play a significant role in the phenotypic expression of vWd by modifying the plasma and platelet vWf multimeric structure.     

A new von Willebrand factor (vWF) defect in a patient with factor VIII (FVIII) deficiency but with normal levels and multimeric patterns of both plasma and platelet vWF. Characterization of abnormal vWF/FVIII interaction

The patients with inherited bleeding diathesis related to quantitative, structural, and/or functional abnormalities of von Willebrand factor (vWF) are said to have von Willebrand's disease (vWD). We report here the clinical and laboratory features of a 50-year-old woman with a life-long history of excessive bleeding. Her particular laboratory data are factor VIII (FVIII) deficiency, subnormal bleeding time, and the presence of all plasma and platelet vWF multimers in normal amounts. Infused with FVIII/vWF concentrate, she showed a persistent increase in FVIII that led us to discard hemophilia A carrier or "acquired hemophilia" diagnoses. vWF devoid of FVIII purified from normal and patient's plasma by immunoaffinity on anti-vWF monoclonal antibody (MoAb) was immobilized onto polystyrene tubes that were further incubated with purified normal FVIII. The bound FVIII was evidenced using radiolabeled anti-FVIII MoAb. The data showed that the patient's vWF, in contrast to vWF purified from normal plasma, was unable to bind FVIII. Furthermore, no inhibitor of FVIII/vWF interaction was evidenced in incubating purified normal vWF with the patient's plasma before the addition of FVIII and anti-FVIII MoAb. These results support the concept that the bleeding diathesis of this patient appears to be due mainly to her abnormal vWF preventing FVIII/vWF interaction. This abnormality, which is not yet described in present classification of vWD, could be considered as a new variant of vWD.     

Heterogeneous phenotypes of platelet and plasma von Willebrand factor in obligatory heterozygotes for severe von Willebrand disease

To characterize the heterogeneity of severe (type III) von Willebrand disease (vWD), plasma and platelet von Willebrand factor antigen (vWF:Ag) and ristocetin cofactor activity (Ricof) were measured in 28 obligatory heterozygotes (ie, parents or children of probands from 15 different kindreds with severe vWD). On the average, heterozygotes had low levels of vWF in both platelets and plasma. There was, however, considerable heterogeneity, with four distinct patterns. Eleven heterozygotes had concordant reduction of vWF:Ag and Ricof in both plasma and platelets; five had low levels of vWF:Ag and Ricof in plasma contrasting with normal levels in platelets; eight had a peculiar pattern, the reverse of the above (ie, low levels in platelets and normal levels in plasma); and in one, both vWF measurements were normal in plasma and platelets. These patterns were genetically determined: they were consistent in four couples of consanguineous heterozygotes and in two couples carrying the same gene deletion. Only the remaining three heterozygotes had no clearly identifiable pattern. Other findings of this study were that although most of the heterozygotes had normal bleeding times, the 7 of 28 who had prolonged bleeding times had concordantly low levels of vWF measurements in both plasma and platelets. In conclusion, this large series of obligatory heterozygotes provides evidence for phenotypic and genotypic heterogeneity of severe vWD.     

Founder von Willebrand factor haplotype associated with type 1 von Willebrand disease

To date, no dominant mutation has been identified in a significant proportion of patients with type 1 von Willebrand disease (VWD). In this study, we examined 70 families as part of the Canadian Type 1 VWD Study. The entire VWF gene was sequenced for 1 index case, revealing 2 sequence variations: intron 30 (5312-19A>C) and exon 28 at Tyr1584Cys (4751A>G). The Tyr1584Cys variation was identified in 14.3% (10 of 70) of the families and was in phase with the 5312-19A>C variation in 7 (10.0%) families. Both variants were observed in 2 of 10 UK families with type 1 VWD, but neither variant was found in 200 and 100 healthy, unrelated persons, respectively. Mean von Willebrand factor antigen (VWF:Ag), VWF ristocetin cofactor (VWF:RCo), and factor VIII coagulant activity (FVIII:C) for the index cases in these families are 0.4 U/mL, 0.36 U/mL, and 0.54 U/mL, respectively, and VWF multimer patterns show no qualitative abnormalities. Aberrant VWF splicing was not observed in these patients, and both alleles of the VWF gene are expressed as RNA. Molecular dynamic simulation was performed on a homology model of the VWF-A2 domain containing the Tyr1584Cys mutation. This showed that no significant structural changes occur as a result of the substitution but that a new solvent-exposed reactive thiol group is apparent. Expression studies revealed that the Tyr1584Cys mutation results in increased intracellular retention of the VWF protein. We demonstrate that all the families with the Tyr1584Cys mutation share a common, evolved VWF haplotype, suggesting that this mutation is ancient. This is the first report of a mutation that segregates in a significant proportion of patients with type 1 VWD.     

Additional variant of type I von Willebrand disease

We introduce a family with a von Willebrand subgroup that has not been described before. All of the eight subjects examined had normal levels of factor VIII coagulant activity (FVIII:C), a moderate reduction in the level of von Willebrand factor antigen (VWF:Ag), which resulted in a high FVIII:C/VWF:Ag ratio, and normal crossed immunoelectrophoresis, with normal multimeric pattern. The ristocetin cofactor in plasma and platelets was very low. Bleeding time was prolonged in two subjects without clearcut linkage to laboratory findings. In addition, an abnormality of platelet aggregation in response to ADP was observed: a decreased initial response was followed by marked disaggregation.     

A new congenital platelet abnormality characterized by spontaneous platelet aggregation, enhanced von Willebrand factor platelet interaction, and the presence of all von Willebrand factor multimers in plasma

A case is reported of a 49-year-old woman with a mild bleeding tendency. Her bleeding time, platelet count and size, plasma ristocetin cofactor activity, von Willebrand factor (vWF) antigen, and vWF multimeric pattern are all within normal limits. Spontaneous platelet aggregation is observed when citrated platelet-rich plasma (PRP) is stirred in an aggregometer cuvette. This aggregation is completely is only slightly diminished by an antiglycoprotein (GP) IIb/IIIa or by an anti GPIb monoclonal antibody. The patient's PRP shows increased sensitivity to ristocetin. The distinct feature of this patient, also present in two family members studied, is that platelet aggregation is initiated by purified vWF in the absence of any other agonist. The vWF- induced platelet aggregation is abolished by anti-GPIb and anti- GPIIb/IIIa monoclonal antibodies and by EDTA (5 mmol/L). Apyrase inhibits the second wave of aggregation. Patient's platelets in PRP are four to six times more reactive to asialo vWF-induced platelet aggregation than normal platelets. The amount of radiolabeled vWF bound to platelets in the presence of either low concentration of ristocetin or asialo vWF was increased 30% compared with normal. The patient's platelet GPIb was analyzed by SDS page and immunoblotting and by binding studies with anti-GPIb monoclonal antibodies showed one band with slightly increased migration pattern and a normal number of GPIb molecules. Unlike the previously reported patients with pseudo or platelet-type von Willebrand disease, this patient has normal vWF parameters.     

Studies of multimerin in patients with von Willebrand disease and platelet von Willebrand factor deficiency

In normal platelet α-granules von Willebrand factor (VWF) is stored with multimerin and factor V in an eccentric electron-lucent zone. Because the platelet stores of VWF are deficient in 'platelet low' type 1 and type 3 von Willebrand disease (VWD), we investigated their electron-lucent zone proteins. The patients with VWD had partial to complete deficiencies of plasma and platelet VWF but normal α-granular multimerin and factor V, and normal α-granular fibrinogen, thrombospondin-1, fibronectin, osteonectin and P-selectin. In type 3 VWD platelets, α-granular electron-lucent zones lacking VWF-associated tubules were identified and multimerin was found in its normal α-granular location. These findings indicate that the formation of the electron-lucent zone and the sorting of multimerin to this region occur independent of VWF. The isolated abnormalities in VWF suggests a VWF gene mutation is the cause of 'platelet low' type 1 VWD.     

The prevalence of the cysteine1584 variant of von Willebrand factor is increased in type 1 von Willebrand disease: co-segregation with increased susceptibility to ADAMTS13 proteolysis but not clinical phenotype

The molecular pathogenesis of type 1 von Willebrand disease (VWD) is uncertain in most patients. We examined 30 type 1 VWD families in the UK Haemophilia Centre Doctors' Organization study. Heterozygosity for Y/C1584 was present in eight of 30 (27%) families and 19 of 76 (25%) individuals with type 1 VWD recruited into the study. Eighteen (95%) of these 19 individuals were blood group O. C1584 did not co-segregate with VWD in four families, and co-segregated in one family; the results were equivocal in three families. In all families increased susceptibility of von Willebrand factor (VWF) to a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS) 13 proteolysis co-segregated with C1584 in affected and unaffected individuals. These data show that C1584, associated with blood group O, is prevalent among patients with type 1 VWD but not necessarily causative of disease and should not be used in isolation to diagnose VWD. Increased susceptibility of C1584 VWF to ADAMTS13 proteolysis may be physiologically significant and increase an individual's risk of bleeding and presenting with VWD.     

Role of carbohydrate in multimeric structure of factor VIII/von Willebrand factor protein.

The carbohydrate moiety of the factor VIII/von Willebrand (vW) factor protein is important in the expression of vW factor activity and the intravascular survival of the protein. Studies of normal human factor VIII/vW factor protein indicate that there is a requirement of a full complement of penultimate galactose for the maintenance of a normal multimeric structure. Release of penultimate galactose by beta-galactosidase or modification by galactose oxidase results in loss of the largest molecular weight multimers and increased numbers of intermediate and smaller multimers. In contrast, terminal galactose on the factor VIII/vW factor protein does not appear to play a significant role in the maintenance of the multimer organization. The abnormalities in multimeric structure and molecular size were demonstrated by NaDodSO4/polyacrylamide/agarose gel electrophoresis, NaDodSO4/glyoxyl-agarose electrophoresis, and sucrose density ultracentrifugation. These studies indicate that the penultimate galactose plays a role in the maintenance of the largest multimers of the factor VIII/vW factor protein. This may explain why, in some patients with variant forms of vW disease, a carbohydrate abnormality also may affect the multimeric structure of the plasma factor VIII/vW factor protein.     

Changes in von Willebrand factor level and von Willebrand activity with age in type 1 von Willebrand disease

In a normal population, VWF plasma levels (VWF:Ag) and VWF activity (VWF:RCo) increase by approximately 0.17 and 0.15 IU mL^?1 per decade, but the influence of age is unknown in patients with type 1 von Willebrand disease (VWD). In a retrospective cohort study, the medical records of 31 type 1 VWD patients over the age of 30, who had been followed for ≥5 years, were reviewed for baseline clinical data and previously performed VWF:Ag, VWF:RCo and factor VIII levels (FVIII:C). VWF multimer analysis was normal in 28/31 cases performed. Mean age at diagnosis was 33 (range 16–60 years), and duration of follow‐up ranged from 5 to 26 years (mean 11 years). Patients had 2–10 time points of VWD testing (mean of 5.2). The mean VWF:Ag, VWF:RCo and FVIII:C at time of diagnosis were 0.44 IU mL^?1 0.34 IU mL^?1 and 0.75 IU mL^?1. At last follow‐up, the mean VWF:Ag, VWF:RCo and FVIII:C were significantly increased to 0.71 IU L^?1, 0.56 IU mL^?1 and 0.90 IU mL^?1 (P ≤ 0.001, <0.001, and 0.0081 respectively). Here 18/31 patients had VWF:Ag, VWF:RCo and FVIII: C levels that increased into the normal range. The rate of change in VWF:Ag, VWF:RCo and FVIII was 0.30 IU mL^?1 (0.21–0.39, CI 95%, P < 0.0001), 0.20 IU mL^?1 per decade (0.13–0.27, CI 95%, P = 0.0001) and 0.20 IU mL^?1 (0.11–0.29, CI 95%, P = 0.0011). Patients with type 1 VWD experience age‐related increases to VWF:Ag and VWF:RCo which can result in normalization of VWF levels. Further studies are required to determine if the bleeding phenotype resolves with the increases in VWF:Ag and VWF:RCo levels.