Inherited variants of factor-VIII-related protein in von Willebrand's disease

How much do we really know about von Willebrand disease?

PURPOSE OF REVIEW

In the last nine decades, large advances have been made toward the characterization of the pathogenic basis and clinical management of von Willebrand disease (VWD), the most prevalent inherited bleeding disorder. Pathological variations at the von Willebrand factor (VWF) locus present as a range of both quantitative and qualitative abnormalities that make up the complex clinical spectrum of VWD. This review describes the current understanding of the pathobiological basis of VWD.

RECENT FINDINGS

The molecular basis of type 2 (qualitative abnormalities) and type 3 VWD (total quantitative deficiency) have been well characterized in recent decades. However, knowledge of type 1 VWD (partial quantitative deficiency) remains incomplete because of the allelic and locus heterogeneity of this trait, and is complicated by genetic variability at the VWF gene, interactions between the VWF gene and the environment, and the involvement of external modifying loci. Recent genome wide association studies and linkage analyses have sought to identify additional genes that modify the type 1 VWD phenotype.

SUMMARY

Understanding the pathogenic basis of VWD will facilitate the development of novel treatment regimens for this disorder, and improve the ability to provide complementary molecular diagnostics for type 1 VWD.

Translational medicine advances in von Willebrand disease

Following the recognition of von Willebrand disease (VWD) in 1926 and the cloning of the gene for von Willebrand factor (VWF) in 1985, significant advances have been made in our fundamental knowledge of both the disease and the protein. Some of this new knowledge has also begun to impact the clinical management of VWD. First, the progressive increase in our understanding of the molecular genetic basis of VWD has resulted in rational applications of molecular testing to complement the current range of phenotypic tests for VWD. These molecular genetic strategies are most effectively directed at the prenatal diagnosis of type 3 VWD and confirmatory testing for types 2B and 2N disease. In contrast, the use of molecular testing to clarify the diagnosis of type 1 VWD is of marginal benefit, at best. In terms of VWD therapies, a new recombinant VWF concentrate has recently completed successful clinical trials and is now awaiting more widespread application. There have even been some preclinical successes with VWF gene transfer although the clinical rationale for this therapeutic strategy needs careful consideration. Much more remains to be learnt about the biology of VWF and further translational advances for the enhancement of VWD care will inevitably be realized.

The molecular characterization of von Willebrand disease: good in parts

Since the cloning of the gene that encodes von Willebrand factor (VWF), 27 years ago, significant progress has been made in our understanding of the molecular basis of the most common inherited bleeding disorder, von Willebrand disease (VWD). The molecular pathology of this condition represents a range of genetic mechanisms, some of which are now very well characterized, and others that are still under investigation. In general, our knowledge of the molecular basis of type 2 and 3 VWD is now well advanced, and in some instances this information is being used to enhance clinical management. In contrast, our understanding of the molecular pathogenesis of the most common form of VWD, type 1 disease, is still at an early stage, with preliminary evidence that this phenotype involves a complex interplay between environmental factors and the influence of genetic variability both within and outside of the VWF locus.

Acquired von Willebrand's disease caused by a monoclonal antibody

A 67-year-old man with malignant lymphoma and acquired von Willebrand's disease is described. His bleeding symptoms started late in life and at this time a monoclonal IgGK serum protein was found. He had a prolonged bleeding time, decreased platelet adhesiveness, low values for factor VIII clotting activity (VIII:C), factor VIII related antigen (VIIIR:Ag) and ristocetin co-factor activity (VIII:Rcof). Infusion of factor VIII concentrates (fraction I-0) did not correct the abnormalities. No inhibitory activity in vitro of the patient's plasma or IgG fraction could be demonstrated against VIII:C, VIIIR:Ag and VIII:Rcof. In order to demonstrate an antibody that binds factor VIII without inhibiting its biological activities in vitro, advantage was taken of the fact that staphylococcal protein A strongly binds the Fc part of IgG molecules. Addition of staphylococci to mixtures of patient IgG and a factor VIII preparation resulted in removal of all factor VIII activities (VIII:C, VIIIR:Ag, VIII:Rcof) from the supernatant at sedimentation of the bacteria. The active binding principle was the M-component, i.e. probably a monospecific antibody molecule. We hypothesize that the complex is formed in vivo and eliminated at an accelerated rate.

Classification and characterization of hereditary types 2A, 2B, 2C, 2D, 2E, 2M, 2N, and 2U (unclassifiable) von Willebrand disease

All variants of type 2 von Willebrand disease (VWD) patients, except 2N, show a defective von Willebrand factor (VWF) protein (on cross immunoelectrophoresis or multimeric analysis), decreased ratios for VWF:RCo/Ag and VWF:CB/Ag and prolonged bleeding time. The bleeding time is normal and FVIII:C levels are clearly lower than VWF:Ag in type 2N VWD. High resolution multimeric analysis of VWF in plasma demonstrates that proteolysis of VWF is increased in type 2A and 2B VWD with increased triplet structure of each visuable band (not present in types 2M and 2U), and that proteolysis of VWF is minimal in type 2C, 2D, and 2E variants that show aberrant multimeric structure of individual oligomers. VWD 2B differs from 2A by normal VWF in platelets, and increased ristocetine-induced platelet aggregation (RIPA). RIPA, which very likely reflects the VWF content of platelets, is normal in mild, decreased in moderate, and absent in severe type 2A VWD. RIPA is decreased or absent in 2M, 2U, 2C, and 2D, variable in 2E, and normal in 2N. VWD 2M is usually mild and characterized by decreased VWF:RCo and RIPA, a normal or near normal VWF multimeric pattern in a low resolution agarose gel. VWD 2A-like or unclassifiable (2U) is distinct from 2A and 2B and typically featured by low VWF:RCo and RIPA with the relative lack of high large VWF multimers. VWD type 2C is recessive and shows a characteristic multimeric pattern with a lack of high molecular weight multimers, the presence of one single-banded multimers instead of triplets caused by homozygosity or double hereozygosity for a mutation in the multimerization part of VWF gene. Autosomal dominant type 2D is rare and characterized by the lack of high molecular weight multimers and the presence of a characteristic intervening subband between individual oligimers due to mutation in the dimerization part of the VWF gene. In VWD type 2E, the large VWF multimers are missing and the pattern of the individual multimers shows only one clearly identifiable band, and there is no intervening band and no marked increase in the smallest oligomer. 2E appears to be less well defined, is usually autosomal dominant, and accounts for about one third of patients with 2A in a large cohort of VWD patients.

The 80th anniversary of von Willebrand's disease: history, management and research

The history of von Willebrand's disease (VWD) is fascinating because it demonstrates how good clinical observations, genetic studies and biochemical skills can improve basic understanding of a disease and its management. The continuous efforts of scientists and clinicians during the last 80 years have significantly improved the knowledge of von Willebrand factor (VWF) structure and function and the management of VWD. Diagnosis of phenotype and genotype is now available in many countries and treatment is becoming more specific according to the VWD type. Any therapeutic agents must correct the dual defect of haemostasis, i.e. the abnormal platelet adhesion due to reduced and/or dysfunctional and low levels of factor VIII (FVIII) associated with VWF defects. Desmopressin (DDAVP) is the treatment of choice for type 1 VWD because it induces release of VWF from cellular compartments. Plasma virally inactivated VWF concentrates containing FVIII are effective and safe in patients unresponsive to DDAVP. There are advanced plans to develop a recombinant VWF but this product will require the concomitant administration of FVIII for the control of acute bleeds. Basic research studies on cellular biology, biochemistry and immunology have confirmed the role of VWF as a crucial participant in both haemostasis and thrombosis as its main biological activity is to support platelet adhesion-aggregation in the circulation. Retrospective and prospective clinical research studies, including bleeding history and laboratory markers for diagnosis as well as the use of DDAVP and VWF concentrates to manage or prevent bleeds in patients with VWD have been essential to provide general guidelines for VWD management. The large number of publications quoting VWD and VWF emphasizes the important role of VWF in medicine.

Maladie de Willebrand de type 2B et pseudomaladie de Willebrand de type 2B ; à propos de trois observations

Increased affinity of Von Willebrand factor (VWF) for its platelet receptor GPIb-GPIX complex is responsible of an hemorrhagic disease, which is the Von Willebrand disease (VWD) type 2B when the molecular abnormality is located on the VWF, and the platelet-type 2B VWD when the mutation concern the platelet receptor. Haemostatic abnormalities in these bleeding disorders are similar; prolonged bleeding time, fluctuating thrombocytopenia, decreased factor VIII-VWF complex, and an increased response to low dose of ristocetin in platelets rich plasma. High molecular weight VWF multimers are decreased. We report here 2 cases of type 2B VWD and 1 case of platelet type 2B VWD. The distinction between these 2 diseases was established by studying platelet aggregation with weak doses of ristocetin in mixtures of washed platelets (of normal control or patient)+poor platelets plasma (normal or patient). In one case, VWD 2B was discovered late in a 49 years old man, and the factor VIIIC-VWF complex was not diminished. The distinction between these two congenital diseases is important for the treatment of bleeding manifestations which need VWF concentrates infusions in type 2B VWD and administration of platelets concentrates in pseudo type 2B VWD.

Inheritance and prevalence of von Willebrand's disease severe form in a Brazilian population

Reviewed data suggest that the prevalence of severe von Willebrand's disease is influenced by ethnic and geographic factors. In the State of Rio Grande do Sul, Brazil, seven genealogies in which 11 individuals had a severe expression of von Willebrand's disease were localized. These affected subjects had similar laboratory results and all of them seemed to have resulted from double genetic defects, but the genealogic examination revealed that four of them probably resulted from combinations of autosomal recessive genes, while in the remaining the presence of dominant genes was likely and the involvement of genes for types I or II of von Willebrand's disease was possible. All of their examined relatives were asymptomatic but some of them presented unusual laboratory results, indicative of heterozygosis. The prevalence of severe cases in the surveyed population was higher than expected even when only the recessive forms were considered. It entered the expected values when it was presumed that these were all the cases currently living in the State. Genetic heterogeneity of the severe form was confirmed and it is suggested that the designations 'severe von Willebrand's disease' and 'type III von Willebrand's disease' should not be used as synonyms.

Hereditary combined deficiency of clotting factors V and VIII with involvement of von Willebrand factor

A family is described in which two brothers, with a significant haemorrhagic disorder, are affected by combined factor V/VIII deficiency. In one of these patients an abnormal decrease of von Willebrand factor was also observed. Family studies suggest that both of the brothers are homozygous for a recessive gene. Normal laboratory results were found in eight other family members although seven of them had reported a mild bleeding tendency. The results indicate that hereditary combined factor V/VIII deficiency is a heterogeneous disorder and that defects of von Willebrand factor might be involved in the aetiology of the disease in some families.

von Willebrand disease

von Willebrand disease (vWD) is a bleeding disorder characterized by a complex hemostatic defect. Abnormal platelet function, usually reflected by a prolonged bleeding time, is the result of a quantitative or qualitative defect of von Willebrand factor (vWF). A secondary deficiency of factor VIII procoagulant protein (factor VIII) may occur leading to a coagulation defect as well. These two glycoprotein macromolecules circulate as a complex in plasma. This article will review current understanding of structures and functions of vWF factor and factor VIII as they relate to the pathogenesis, diagnosis, classification and therapy of vWD.

The physiology and pathophysiology of the factor VIII complex

The factor VIII complex consists of two noncovalently linked proteins: von Willebrand factor (VWF) and factor VIII (FVIII). VWF plays an important role in primary hemostasis by mediating the adherence of blood platelets to the damaged vessel wall. A review of the literature on VWF is given with regard to its physicochemical properties and mode of action. FVIII acts as a cofactor in the factor Xa-generating enzyme complex of the intrinsic coagulation cascade. Starting with the recently published primary structure of FVIII, the literature is reviewed for structural information on FVIII. Also, an effort is made to characterize the interaction of FVIII with VWF and to discuss the possible physiological significance of FVIII-VWF complex formation. Interaction of FVIII with the clotting factors of the intrinsic pathway of coagulation is described in detail. Hemophilia and von Willebrand's disease (VWD) are both congenital bleeding disorders affecting a great many people. The different variants of these diseases are described with some reference to therapy and detection.

Investigation of a kindred with a new autosomal dominantly inherited variant type von Willebrand's disease (possible type IID)

A further type II variant of von Willebrand's disease has been identified in five family members who have the clinical symptoms of von Willebrand's disease. This variant is characterised by loss of high molecular weight VIIIR:AG multimers and the replacement of the normal triplet multimer configuration by a single dense band. In addition, variable minor bands are seen. These variants appear similar to those recently reported by Kinoshita et al and designated as type IID.

An immunoradiometric assay for human factor VIII/von Willebrand factor (VIII:vWF) using a monoclonal antibody that defines a functional epitope

A murine monoclonal antibody has been produced (RFF-VIII:R/2) that binds specifically to human factor VIII-related antigen (VIII:RAg) in plasma and in vascular endothelial cells but has no reactivity with factor VIII procoagulant antigen (VIII:cAg). This antibody is a potent inhibitor of von Willebrand factor activity (VIII:vWF) in that it can totally neutralize ristocetin-induced aggregation of platelet rich plasma and inhibit platelet adhesion at high flow rates. RFF-VIII:R/2 can be used in a one-stage, fluid phase immunoradiometric assay that can detect VIII:RAg at concentrations of 0.001 u/ml. This method has been used to analyse plasma from patients with von Willebrand's disease (vWD). Results obtained in these patients showed a high degree of correlation between the monoclonally-defined epitope and VIII:vWF levels measured by ristocetin-induced aggregation of washed platelets. This correlation was maintained in those patients with the 'variant' types of vWD who exhibit highly disparate VIII:vWF and VIII:RAg levels when the latter is determined using polyclonal antisera. It appears that this monoclonal antibody recognizes a site on the VIII:RAg molecule which is associated with its interaction with the platelet membrane. Immunoradiometric assays using RFF-VIII:R/2 offer a simplified, reproducible means of detecting functionally-active VIII:RAg as an alternative or supplement to techniques involving platelet interactions.

Factor V (Quebec): a bleeding diathesis associated with a qualitative platelet Factor V deficiency

Studies were performed on a French-Canadian family afflicted with a bleeding disorder exhibiting an autosomal dominant inheritance pattern and a severe bleeding diathesis after trauma. Clinical laboratory coagulation tests were unimpressive; the only persistent abnormalities include mild thrombocytopenia and moderately reduced Factor V clotting activities. Some individuals had prolonged Stypven times when platelet-rich plasma was used, suggesting that their platelets could not support functional prothrombinase complex assembly. Detailed studies were performed by use of plasma and isolated, washed platelets from a sister and brother. Bioassay data indicate that both individuals had Factor V activities of approximately 40 and 36% of normal, respectively. A comparison of the Factor V radioimmunoassay and bioassay data on the brother's plasma indicated that the circulating amount of Factor V functional activity was low relative to Factor V antigen concentration (approximately 65-75%). In both individuals, the platelet Factor V functional activities were extremely low (2-4%) relative to antigen levels present as determined by radioimmunoassay. These discrepancies between Factor V activities and antigen concentration do not appear to be due to an unstable Factor V molecule or to the presence of a Factor V or Factor Va inhibitor or inactivator. Kinetics of prothrombin activation by use of purified clotting factors indicated that thrombin-activated platelets from both individuals supported prothrombinase complex assembly identical to controls in the presence of added purified Factor Va. Consequently, their bleeding diathesis appears to reflect their platelet, rather than their plasma, Factor V activity. These results suggest that platelet Factor V is an essential component in maintaining stable and prolonged hemostasis after trauma.

Lack of correlation between factor VIII related antigen multimeric analysis pattern and parallel or non-parallel dose response curves in an ELISA factor VIII related antigen assay

Factor VIII related antigen has been measured and epitope distribution has been explored by testing the degree of parallelism between standard and test plasma dose response curves using an enzyme immunoassay. Normal plasma, plasma fractions, and plasma from patients with haemophilia and von Willebrand's disease have been tested. All showed parallelism except for plasma from patients with the variant type IIA von Willebrand's disease, of which 10 had parallel and five had non-parallel dose response curves when compared with that of normal plasma. In one family plasma from seven members showed parallelism but from four others did not. An unrelated patient was tested on three occasions, and although the samples were parallel to each other, no sample was parallel to the standard. No correlation was found between parallelism as shown by the enzyme immunoassay and differences in factor VIII related antigen multimeric pattern, including triplet configuration, seen in the type IIA patients.

Von Willebrand factor multimer patterns in von Willebrand's disease

The von Willebrand factor antigen (factor VIII-related antigen, VIIIR:Ag) multimer pattern has been analysed by SDS-agarose electrophoresis of plasmas from 116 patients (47 families) with von Willebrand's disease. In addition to previously recognized patterns, a subclassification was established between plasmas that had a type Ia pattern (VIIIR:Ag multimer pattern like that of normal plasma) and those that had a type Ib pattern in which there was a relative reduction in the concentration of the larger VIIIR:Ag multimers even though all multimeric forms were present. The different patterns were consistent within families and were inherited by autosomal dominant transmission. Von Willebrand's disease heterogeneity was apparent in the distribution of these plasmas: type Ia, 43 patients in 18 families; type Ib, 39 patients in 15 families; type II, 22 patients in 10 families, one of which was further classified as type IIB, one of which was type IIC, and three were IIA. Seven patients with severe von Willebrand's disease were also studied. In general, the interpretation of SDS-agarose multimer patterns corresponded to those previously obtained by crossed immunoelectrophoresis, but the former technique was more sensitive and could identify differences that were not apparent by crossed immunoelectrophoresis.

Acquired von Willebrand's disease: demonstration of a circulating inhibitor to the factor VIII complex in four cases

We have studied four patients suffering from acquired von Willebrand's disease. All patients had a severe bleeding diathesis with recurrent life-threatening haemorrhages. Three of the patients had a monoclonal gammopathy and one of these developed multiple myeloma. In three patients tested, a plasma inhibitor to ristocetin cofactor activity was detected. In each case this was localized to the IgG fraction of plasma. In addition, VIII:C activity was found to be associated with the IgG fraction of patients' plasma and altered mobility of VIII:C was detected on Laurell immunoelectrophoresis. Furthermore, plasma from all four patients and the IgG fraction therefrom resulted in a dissociation of normal VIII:C into two components separable by gel-filtration on Sepharose 6B. Finally the circulating half-life of the three factor VIII activities was found to be markedly reduced in the patients with acquired von Willebrand's disease. We conclude that in the patients studied the coagulation defect was related to the presence of a circulating inhibitor to the factor VIII complex and that this inhibitor was associated with the IgG fraction of plasma.

Fast migrating protein, immunochemically related to human factor VIII, studied by crossed immunoelectrophoresis in agarose

A fast migrating protein (FMP) was detected by agarose radio-crossed immunoelectrophoresis, in addition to factor VIII antigen (VIII:RAg), using antiserum to human factor VIII (FVIII). FMP had partial immunochemical identity with FVIII, migrated as an alpha-protein, and was distinct from alpha-2 macroglobulin, fibronectin or IgM. FMP was precipitated by concanavalin A and was separable from the bulk of VIII:RAg by ammonium sulphate fractionation. A significant amount of FMP was seen in normal serum (n = 12), plasma from patients with: (a) disseminated intravascular coagulation (n = 12) and (b) severe haemophilia A (n = 6). Trace amounts of FMP were observed in plasma from normal donors (n = 12), but neither VIII:ARg nor FMP was detectable in the plasma or serum from patients with severe von Willebrand's disease (n = 3). Freshly prepared cryoprecipitate contained trace amounts of FMP, similar to normal plasma, but increased levels were observed in antihaemophilic factor concentrates prepared for patient use. Significant levels of FMP were also seen in cryoprecipitate after storage at 4 degrees C for 7 d and this generation of FMP was diminished by the addition of protease inhibitors. The presence of significant levels of FMP in situations where proteolytic enzymes may be activated and inhibition of its generation by protease inhibitors, suggest that this protein is produced by proteolytic action of enzyme(s) on the FVIII molecule.

Pseudo-von Willebrand's disease. An intrinsic platelet defect with aggregation by unmodified human factor VIII/von Willebrand factor and enhanced adsorption of its high-molecular-weight multimers

Four members (from four generations) of a family with a mild bleeding disorder and intermittent thrombocytopenia had decreased plasma levels of properties related to factor VIII/von Willebrand factor (FVIII/VWF), an absence of high-molecular-weight forms of FVIII/VWF in the plasma (but normal multimeric structure in the platelets), and increased ristocetin-induced platelet aggregation, as in Type IIB von Willebrand's disease. However, unlike the abnormality in FVIII/VWF in Type IIB disease, the basic defect in this family was in their platelets, which absorbed FVIII/VWF high-molecular-weight multimers at lower concentrations of ristocetin than did normal platelets. In addition, either in platelet-rich plasma or suspended in buffer, their platelets were aggregated by unmodified normal human FVIII/VWF without ristocetin. Since the abnormalities of plasma FVIII/VWF in this family may be secondary to the platelet abnormalities, the term "pseudo-von Willbrand's disease" may be suitably descriptive of their disorder.

Factor VIII-related antigen pre-peak on crossed immunoelectrophoresis: a non-random phenomenon

The incidence of a "pre-peak" over the well on crossed immunoelectrophoresis of factor VIII-related antigen (VIIIR:Ag) was found to be not significantly different in groups of hemophilia carriers and non-carrier women. Only 10% of hemophiliacs more than three days post-transfusion exhibited the feature. Upon transfusion 5 out of 6 hemophiliacs showed a transient appearance of the pre-peak. It was also present during pregnancy in 6 of 8 normal women, 2 hemophilia carriers and two von Willebrand's patients. The pre-peak pattern was quite reproducible both in the same sample tested on different days and in different samples from the same subject. The pre-peak material shows a line of treatment of plasma and by cryoprecipitation.

von Willebrand syndromes and mitral-valve prolapse; linked mesenchymal dysplasias

We searched for mitral-valve prolapse by two-dimensional echocardiography in 15 patients with von Willebrand syndromes to test the hypothesis that this bleeding disorder is actually a mesenchymal dysplasia that resembles the heritable disorders of connective tissue. This valvular abnormality was found in nine (60 per cent) of these patients, as compared with four (13.3 per cent) of 30 sex-matched and age-matched healthy controls. This difference was statistically significant (P less than 0.01). The association between these two disorders encourages a search for mitral-valve prolapse in persons with a von Willebrand syndrome. The complex of a von Willebrand syndrome and mitral-valve prolapse may be an example of a newly recognized category of related coagulation and cardiovascular disorders.

Von Willebrand disease associated with familial thrombocytopenia and increased ristocetin-induced platelet aggregation

Two cases of von Willebrand disease (vWD) associated with familial thrombocytopenia were reported. The proband (daughter) and her father showed thrombocytopenia with large platelets and decreased von Willebrand factor activity (VIIIR:WF). Factor VIII procoagulant activity (VIII:C) and factor VIII-related antigen (VIIIR:AG) were normal, but both patients revealed an increased ristocetin-induced platelet aggregation and a qualitative abnormality of the factor VIII protein, which was characterized by fast electrophoretic mobility of VIIIR:AG and an abnormal elution of factor VIII-related activities on Sepharose 2B. DDAVP was hemostatically effective even in this thrombocytopenic patient undergoing a dental extraction.

New methods in coagulation

Recent advances in the elucidation of the molecular biochemistry of the coagulation proteins have provided the foundation for the development of synthetic substrates. These substrates are oligopeptide with either a chromophore or fluorophore group attached to the C-terminal end. They may be used in the laboratory to assay for a number of the serine proteases involved in either coagulation or fibrinolysis. Also, by suitably modifying the assay system, the various inhibitors can be quantitated. These substrates promise to revolutionize the coagulation laboratory allowing for more precise quantitation of trace enzymes and also improved standardization and precision of coagulation assays. In addition to these substrates, the introduction of a number of immunologic procedures into the diagnostic laboratory have been of major importance in elucidating the heterogeneity of hereditary coagulation defects. By correlating the immunologic assays, coagulation assays and clinical picture, a number of subgroups of hereditary deficiencies have been identified. Also, the immunologic assays have provided a means for identifying the carrier state of hemophilia A and have significantly contributed to the improved diagnosis of von Willebrand's disease. The use of ristocetin cofactor assays, when used in conjunction with the Factor VIII antigens, have enable the laboratory to more accurately diagnose the majority of patients with von Willebrand's disease. Ristocetin cofactor may be assayed utilizing either formalin fixed or washed platelets and recently a snake venom has been introduced to assay for this particular aspect of the Factor VIII complex. Platelet specific proteins (i.e., platelet factor 4 and beta-thromboglobulin) may be assayed utilizing either radioimmunoassays or in the case of platelet factor 4 modified coagulation assays. These proteins provide evidence of in vivo platelet activation and hopefully may, in the future, be correlated with platelet kinetics.

Structural analysis of factor VIII antigen in von Willebrand disease

The Factor VIII antigen molecules in the plasma of patients with classical type 1 and variant type 2A von Willebrand disease were compared to the Factor VIII antigen molecules in normal plasma. Factor VIII antigen was isolated from plasma by solid-phase immunoprecipitation and analyzed by NaDodSO4/polyacrylamide gel electrophoresis; the stained Factor VIII antigen bands were removed, radioiodinated, and subjected to tryptic digestion. Computerized analysis of autoradiographs revealed that the two-dimensional peptide maps of the different Factor VIII antigens were remarkably similar. The results suggest that the Factor VIII antigen molecules in these two forms of von Willebrand disease are probably identical to the Factor VIII antigen molecules present in normal plasma. It is thus likely that the differences observed in plasma Factor VIII antigen in classical and variant von Willebrand disease are not due to qualitatively abnormal molecules but rather represent quantitative shifts in the metabolism of normal Factor VIII antigen molecules.

Patterns of factor-VIII related antigen on crossed immunoelectrophoresis and large pore polyacrylamide gel-crossed immunoelectrophoresis in von Willebrand's disease

Plasma samples from patients with various types of von Willebrand's disease were subdivided into six patterns according to the electrophoretic mobility and shape of VIIIR: Ag on crossed immunoelectrophoresis (CIE): pattern 1 no precipitation are, pattern 2 normal mobility with low arc, arc, pattern 3 intermediate mobility with low arc, pattern 4 faster anodal mobility with low arc, pattern 5 normal mobility with normal are height, pattern 6 faster anodal mobility with normal are height. Of 62 patients, 14 had pattern 1, 6 pattern 2, 16 pattern 3, 12 pattern 4, 9 pattern 5, and 5 pattern 6. Large pore polyacrylamide-agarose gel-crossed immunoelectrophoresis (PAAG-CIE) of crude factor VIII fraction from cryoprecipitate revealed no arcs in patients with pattern 1, three arcs of reduced height in the patients with patterns 2 and 3, four arcs very similar to normal control in patients with pattern 5, and two arcs with fast anodal migration in the patients with patterns 4 and 6. Crude factor VIII fractions from normal cryosupernatant showed one low fast anodally migrating arc corresponding to the fourth arc of normal cryoprecipitate. No peak was seen in patients with pattern 1, and one low fast anodal arc similar to normal control was present in the patients with patterns 2, 3, 4, 5 and 6.

Factor VII and fibrinolytic response to deamino-8-D-argenine vasopressin in normal subjects and dissociate response in some patients with haemophilia and von Willebrand's disease

Deamino-8-D-argenine vasopressin (DDAVP) was given by intravenous infusion to normal subjects, haemophiliacs and patients with von Willebrand's disease (vWd) and the factor VIII and plasminogen activator response was studied. In normal subjects and most patients with mild haemophilia and mild (intermediate) von Willebrand's disease there was an increase in plasminogen activator and all factor VIII related activities. In patients with mild vWd the prolonged bleeding time was shortened by DDAVP despite only a modest rise in factor VIII related Ristocetin cofactor activity (VIIIR:RiCoF). Sub-groups of patients have been characterized in whom atypical responses was observed. In two brothers with clinically severe haemophilia, but with 5--6 u/dl procoagulant factor VIII (VIIIC), there was an increase in VIIIC but no rise of the corresponding antigen, suggesting increased release of an antigenically abnormal poorly functioning molecule. A patient with intermediate vWd was studied in whom neither DDAVP, adrenaline infusion, nor venous occlusion resulted in an increase in either plasminogen activator or factor VIII related antigen (VIIRAg), although there was a significant increase in VIIIC. In a further patient with severe vWd, DDAVP failed to elicit any plasminogen activator or VIII response. The results obtained from these two patients suggested that in some individuals the presumed endothelial cell abnormality in vWd may be more extensive than a defect in VIIIRAg synthesis. Sub-groups of patients have been identified for whom treatment with factor VIII concentrates would be more appropriate than DDAVP prior to minor surgery.

Variant von Willebrand's disease: characterization of two subtypes by analysis of multimeric composition of factor VIII/von Willebrand factor in plasma and platelets

We have examined the multimeric composition of factor VIII/von Willebrand factor in plasma and platelet lysates by means of sodium dodecyl sulfate agarose electrophoresis followed by staining with (125)I-labeled affinity-purified antibody. In normal plasma and platelet lysates, factor VIII/von Willebrand factor displayed 10 distinct multimers that ranged in apparent molecular weight from 0.86 to 9.9 x 10(6). The molecular weight difference between adjacent bands was 0.8-1.1 x 10(6). Larger material, not resolved into discrete bands, was also present with an average M(r) of 14.5 x 10(6). Though the dimer (apparent M(r) = 0.48 x 10(6)) and the monomer (apparent M(r) = 0.28 x 10(6)) generated by reduction of disulfide bonds were readily identified in this system, they were not detected in normal plasma or platelets. No differences were observed between fresh plasma prepared without anticoagulant and fresh or frozen plasma anticoagulated with either citrate or heparin. "Variant" (type II) von Willebrand's disease could be divided into two subtypes. In subtype IIA, factor VIII/von Willebrand factor in plasma consisted predominantly of the five smaller multimers with traces of the sixth and seventh (M(r) up to 4.5 x 10(6)). In subtype IIB, all these multimers were easily detected and, in addition, bands of intermediate size (M(r) = 8.5 x 10(6) and smaller) were present. In contrast, the multimeric composition of IIB platelet factor VIII/von Willebrand factor was identical to normal, whereas in subtype IIA the larger multimers were absent from platelets as well as from plasma. In subtype IIB, binding of factor VIII/von Willebrand factor to platelets occurred at lower concentrations of ristocetin than required for normal and multimers of smaller size than in normal bound. On the contrary, in subtype IIA, binding was minimal, as was true of normal factor VIII/von Willebrand factor of equivalent size. Thus, physical as well as functional differences in the two subtypes of variant von Willebrand's disease described suggest that different pathogenetic mechanisms underlie the factor VIII/von Willebrand factor abnormalities in these patients.

Heightened interaction between platelets and factor VIII/von Willebrand factor in a new subtype of von Willebrand's disease

The form of von Willebrand's disease characterized by a qualitative abnormality of Factor VIII/von Willebrand factor (FVIII/vWF) in plasma has been designated as Type II. We have now identified 20 persons from five families whose qualitatively abnormal FVIII/vWF shows heightened responsiveness to ristocetin. We have classified this form of the disease as Type IIB and reclassified as Type IIA the form previously described as Type II, in which the interaction of the abnormal FVIII/vWF with platelets is decreased or absent in the presence of ristocetin. The enhanced reactivity of FVIII/vWF in Type IIB was evident in studies of ristocetin-induced platelet agglutination and of binding of FVIII/vWF to platelets in the presence of ristocetin. In both Type IIA and IIB, crossed immunoelectrophoresis of plasma FVIII/vWF demonstrated similar absence of the larger, less anodic forms. These findings suggest that ristocetin-mediated interactions between platelets and FVIII/vWF do not accurately reflect the "bleeding-time" (von Willebrand factor) defect in this newly described subtype of von Willebrand's disease.

Von Willebrand disease with an increased ristocetin-induced platelet aggregation and a qualitative abnormality of the factor VIII protein

Two cases of von Willebrand disease (VWD) that revelaed an increased ristocetin-induced platelet aggregation (RIPA) and a qualitative abnormality of the factor VIII protein are reported. The threshold concentration of ristocetin giving a 30% increase in light transmission was 0.5 mg/ml in the proband and 0.4 mg/ml in her father (normal: 1.16 +/- SD 0.18 mg/ml) although both patients showed reduced plasma von Willebrand factor activity (VIIIR:WF). In both patients, the amount of factor VIII related antigen (VIIIR:AG) in their platelets were normal, but an increased binding affinity of platelets to plasma factor VIII was demonstrated. The qualitative abnormality of the factor VIII protein was characterized by an increasead anodal migration of VIIIR:AG in crossed immunoelectrophoresis (CIE), a delayed elution pattern as demonstrated by gel filtration on Sepharose 2B, and a decreased precipitation with concanavalin A (Con A). The response to DDAVP was also investigated.

The factor VIII abnormality in severe von Willebrand's disease

We attempted to characterize the small amounts of factor VIII-related antigen detectable in the severe recessive form of von Willebrand's disease with newly developed radioimmunoprecipitin techniques and radiocrossed immunoelectrophoresis. Previous studies have failed to demonstrate factor VIII-related antigen in most patients tested even with the highly sensitive immunoradiometric assays. Using the newer techniques, we found antigen in the plasma of six of eight patients with severe von Willebrand's disease from different kindreds. Qualitative abnormalities of the trace quantities of factor VIII-related antigen were demonstrated in five of the patients, with absence or relative decrease of the larger, less anodal forms. In addition, five distinct patterns were observed, each suggesting a different molecular abnormality. Heterozygous parents had normal to moderately decreased factor VIII-related antigen, with normal crossed immunoelectrophoretic patterns. This study suggests that severe von Willebrand's disease is a heterogeneous syndrome with various underlying molecular defects.

Studies on factor VIII-related protein. III. Size distribution and carbohydrate content of human and bovine factor VIII

Human and bovine factor VIII were isolated from cryoprecipitate of fresh frozen plasma by gel filtration on Sepharose CL-2B. The elution diagrams and SDS-agarose electrophoretic analysis of eluted fractions show no significant differences in the size-distribution of factor VIII aggregates between the two species. Agarose gels were stained for carbohydrate by two methods: (1) the dansyl hydrazine reaction following oxidation with periodic acid and (2) staining with fluorescein-labeled concanavalin A. Results of both procedures indicate that in human factor VIII neither the size distribution nor its ristocetin cofactor activity are related to carbohydrate content. Bovine factor VIII contains slightly less sugar than the human preparation as judged from the relative dansyl hydrazine staining intensities. In contrast to human factor VIII, the binding affinity for concanavalin A of bovine factor VIII was gradually decreased with increasing aggregate size. This finding suggests an impaired accessibility of reactive sugar residues in large aggregates of bovine factor VIII.