Variant Of Von Willebrand Disease Research Articles

Different organization of von Willebrand factor oligomers in type-2A and -2B von Willebrand disease variants: effects of DDAVP infusion and protease inhibitors.

Plasma von Willebrand factor (vWf) displays a complex pattern of repeating multimers, whose heterogeneous size distribution seems to depend on the proteolytic cleavage of the constituent vWf subunit. Smaller vWf multimers are thought to derive by proteolytic cleavage of the larger forms. To clarify the relationship between large multimer representation and the structure of small vWf oligomers, DDAVP was infused in patients with type-2A and -2B von Willebrand disease (vWd) variants which lack circulating high vWf forms. Before infusion, high-resolution multimer analysis demonstrated a more pronounced representation of the satellite bands of each oligomer, mainly concerning fast-moving components, especially in type 2B vWd. After DDAVP, in type-2A vWd each oligomer displayed a different organization depending on whether restoration of large vWf multimers occurred. The lack of large vWf multimer restoration, as shown in citrated samples, was associated with the fast band being significantly more represented than the slower, and almost similar to the central component. In contrast, when the high-molecular-weight vWf forms were restored, as occurred in the samples collected in the presence of protease inhibitors, the relative representation of the fast- and slow-moving bands was similar to that of normal samples. In type-2B vWd, regardless of the anticoagulant used, DDAVP infusion did not restore large vWf multimers, and each oligomer displayed a significant increase in both the central band and fast-moving satellite, the fast being even more highly represented. These findings suggest that, regardless of the origin, the disappearance of large circulating multimers in type-2A and -2B vWd induces an increased representation of the fast-moving satellite of the low-molecular-weight multimers. Moreover, the time course of large and low/intermediate multimer decrease and increase provides a further demonstration that low vWf multimers derive from the larger ones, and that mainly the fast-moving band of the oligomer is involved.

Different organization of von Willebrand factor oligomers in type-2A and -2B von Willebrand disease variants: effects of DDAVP infusion and protease inhibitors

Different organization of von Willebrand factor oligomers in type-2A and -2B von Willebrand disease variants: effects of DDAVP infusion and protease inhibitors

Discrepancy between IIA phenotype and IIB genotype in a patient with a variant of von Willebrand disease

Type IIA and IIB von Willebrand disease (vWD) result from qualitative abnormalities of von Willebrand factor (vWF) characterized by an absence in plasma of high molecular weight vWF multimers and an abnormal reactivity of vWF towards platelet glycoprotein (GP) Ib, which is decreased in type IIA and increased in type IIB. In this report, we describe the case of a patient having a IIA vWD phenotype associated with an intermittent thrombocytopenia atypical in this subtype but observed in type IIB vWD. The patient plasma vWF showed an absence of high molecular weight and intermediate multimers and had a decreased binding capacity to GPIb. The affinity of botrocetin was normal for plasma vWF from the propositus. Analysis of the propositus vWF gene showed the presence of a substitution Val 551 to Phe of the mature vWF subunit. This mutation is localized within a 509-695 disulphide loop of the vWF that plays an important role in the binding to GPIb and is where most of the molecular defects described so far were associated with type-IIB vWD. We have reproduced the Val 551 Phe substitution onto the vWF cDNA, expressed it in COS-7 cells, and performed structural and functional analysis of the mutant recombinant protein (rvWFPhe 551). The rvWFPhe 551 had a normal multimeric structure and showed the capacity to spontaneously interact with GPIb. Botrocetin had a decreased affinity for rvWFPhe 551. In conclusion, the Val 551 Phe mutation modifies the affinity of vWF for platelet GPIb, as does a type IIB mutation, and may be responsible for the thrombocytopenia of the patient and the clearance of the high molecular weight and intermediate-sized multimers of vWF from the plasma. The study of the rvWFPhe 551 has confirmed the discrepancy between the IIA phenotype and the IIB genotype of the patient.

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

AbstractA 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.

Von Willebrand factor mutation enhancing interaction with platelets in patients with normal multimeric structure.

Variant von Willebrand disease designated as type I New York or type Malmö is characterized by enhanced ristocetin-induced platelet agglutination with normal von Willebrand factor multimeric distribution in plasma. We have studied four such patients belonging to three unrelated families and found in all of them a unique cytosine-to-thymine transition changing the codon for Pro503 (CCG) to Leu (CTG). In three patients the mutant allele also had a silent mutation in the codon for Ser500 (TCG-->TCA). Both nucleotide changes are present in the von Willebrand factor pseudogene; however, the characterization of distinctive markers where the gene and pseudogene differ, as well as the examination of amplified cDNA derived from platelet mRNA, confirmed that the abnormality occurs in the von Willebrand factor gene of the patients. Moreover, recombinant expression of the isolated glycoprotein Ib-binding domain of von Willebrand factor provided direct evidence that the Pro503-->Leu mutation is responsible for enhanced platelet reactivity to lower ristocetin concentrations. These results define a new structural element affecting the affinity of von Willebrand factor for glycoprotein Ib and establish the molecular basis of a variant form of von Willebrand disease.

Therapy of von Willebrand disease.

Impressive progress has been made in the treatment of von Willebrand disease. Desmopressin is the drug of choice for mild to moderate type I von Willebrand disease patients in whom adequate hemostatic levels of vWF activity can be achieved. Cryoprecipitate from random donors is no longer an optimal choice because of the risk of transfusion-associated viral infections. In special circumstances, cryoprecipitate from a very small donor pool, particularly if obtained following desmopressin stimulation, remains an attractive alternative because these donors can be intensively screened. This therapy may also be somewhat less expensive than commercial concentrates. Virally attenuated commercial concentrates containing intact vWF multimers are currently the treatment of choice to achieve high levels of vWF for moderate to severe von Willebrand disease and for patients with variants of von Willebrand disease that cannot be adequately treated with desmopressin or for whom desmopressin is contraindicated. It is hoped that concentrates of vWF specifically designed for treatment of von Willebrand disease will prove to be safe and efficacious. Standardized assays of vWF in concentrates need to be established. Although, the optimal treatment product has not been produced, several of the more recently developed products have structures that more closely resemble intact normal plasma vWF and appear promising.

The Mutation Arg (53) → Trp Causes von Willebrand Disease Normandy by Abolishing Binding to Factor VIII. Studies With Recombinant von Willebrand Factor

Abstract von Willebrand factor (vWF) and factor VIII (FVIII) circulate in plasma as a noncovalently linked protein complex. The FVIII/vWF interaction is required for the stabilization of procoagulant FVIII activity. Recently, we reported a new variant of von Willebrand disease (vWD) tentatively named “Normandy,” characterized by plasma vWF that appears to be structurally and functionally normal except that it does not bind FVIII. Three patients from one family were found to be homozygous for a C----T transition at codon 816 converting Arg 53 to Trp in the mature vWF subunit. To firmly establish a causal relationship between this missense mutation and vWD Normandy phenotype, we have characterized the corresponding recombinant mutant vWF(R53W). Expressed in COS-7 cells or CHO cell lines, normal vWF and vWF(R53W) were processed and formed multimers with equal efficiency. However, vWF(R53W) exhibited the same defect in FVIII binding as did plasma vWF from patients with vWD Normandy, confirming that this mutation is responsible for the vWD Normandy phenotype. These results illustrate the importance of Arg 53 of the mature vWF subunit for the binding of FVIII to vWF, and identify an amino acid residue within a disulfide loop not previously known to be involved in this interaction.

A new variant of von willebrand disease (type II I) with a normal degree of proteolytic cleavage of von Willebrand factor

A variant of type II von Willebrand disease (vWd) is described in a young woman and her mother with severe lifelong bleeding histories. On electrophoresis with low-resolution agarose gels the plasma of the proband lacked large and intermediate-size multimers of von Willebrand factor (vWF) but the platelet multimeric structure was normal. On high-resolution gels, smaller multimers could be resolved into a broader central band and four satellite bands, which were much fainter than in normal plasma. In the proband plasma, the relative concentrations of proteolytic fragments of the vWF subunit were within the normal laboratory range. Since this variant of vWd appears to differ from those reported hitherto, the designation of type II I is proposed.

The mutation Arg (53)----Trp causes von Willebrand disease Normandy by abolishing binding to factor VIII. Studies with recombinant von Willebrand factor

von Willebrand factor (vWF) and factor VIII (FVIII) circulate in plasma as a noncovalently linked protein complex. The FVIII/vWF interaction is required for the stabilization of procoagulant FVIII activity. Recently, we reported a new variant of von Willebrand disease (vWD) tentatively named "Normandy," characterized by plasma vWF that appears to be structurally and functionally normal except that it does not bind FVIII. Three patients from one family were found to be homozygous for a C----T transition at codon 816 converting Arg 53 to Trp in the mature vWF subunit. To firmly establish a causal relationship between this missense mutation and vWD Normandy phenotype, we have characterized the corresponding recombinant mutant vWF(R53W). Expressed in COS-7 cells or CHO cell lines, normal vWF and vWF(R53W) were processed and formed multimers with equal efficiency. However, vWF(R53W) exhibited the same defect in FVIII binding as did plasma vWF from patients with vWD Normandy, confirming that this mutation is responsible for the vWD Normandy phenotype. These results illustrate the importance of Arg 53 of the mature vWF subunit for the binding of FVIII to vWF, and identify an amino acid residue within a disulfide loop not previously known to be involved in this interaction.

Abnormal binding of factor VIII is linked with the substitution of glutamine for arginine 91 in von Willebrand factor in a variant form of von Willebrand disease.

von Willebrand factor (vWf) is a multimeric plasma glycoprotein that functions in hemostasis as the initiator of platelet adhesion to damaged blood vessels and as the carrier of Factor VIII (FVIII). Montgomery et al. (Montgomery, R.R., Hathaway, W.E., Johnson, J., Jacobsen, L., and Muntean, W. (1982) Blood 60, 201-207) reported a variant of von Willebrand disease characterized by the abnormal interaction between FVIII and a defective vWf. To identify the molecular basis of this abnormal interaction, we isolated platelet RNA from members of one of the affected families and determined the nucleotide sequence of the FVIII-binding domain encoded by the vWf mRNA. A single G to A transition at nucleotide 2561 was linked with disease expression and results in the substitution of Gln for Arg91 in mature vWf. A restriction fragment containing this mutation was introduced into a full-length vWf expression vector, and both wild type and mutant vWf were expressed in COS-7 cells. In a solid-phase binding assay, expressed vWf was captured with anti-vWf monoclonal antibody AVW1 and then incubated with 6.25-400 milliunits of recombinant FVIII. After washing, vWf-bound FVIII activity was determined with a chromogenic assay. Mutant vWf showed reduced binding of FVIII compared with wild type, suggesting that the substitution of Gln for Arg91 is the likely basis for the abnormal vWf/FVIII interaction in this von Willebrand disease variant.

Identification of two point mutations in the von Willebrand factor gene of three families with the ‘Normandy’variant of von Willebrand disease

Plasma von Willebrand factor (vWf) is a multi-domain multimerized glycoprotein which has a dual role in haemostasis: it promotes platelet adhesion to subendothelium and is the carrier of blood coagulation factor VIII (FVIII). We previously characterized a functional defect of vWf, limited to its ability to bind FVIII, in two families whose affected members have the same phenotype that mimics mild haemophilia A and was tentatively named von Willebrand's disease (vWD) 'Normandy'. A homozygous point mutation C----T converting Thr 28 to Met in mature vWf subunit was identified in one of these patients who was born of third-cousin parents. In the present studies we report two unrelated new cases of vWD 'Normandy' and characterize, using the analysis of the vWf gene intron 40 region containing a variable number of tandem repeats, the recessive inheritance of the disease in two affected families without known consanguinity. Exons 18-24 of the vWf gene encoding for the first 311 amino acids of mature vWf subunit were amplified by the polymerase chain reaction method and sequenced. Two new missense mutations, both corresponding to a C----T transition and predicting respectively an Arg 53----Trp and an Arg 91----Gln substitution, were characterized. The three patients from family 1 were homozygous for the first-mentioned mutation while the patient from family 3 was homozygous for the second. The patient from family 2 was found a compound heterozygote for the two mutations. None of the two point mutations reported, both destroying a MspI restriction site, could be detected in DNA from 50 normal controls screened by restriction endonuclease analysis. Our data show that different mutations may be found in patients with the 'Normandy' phenotype. The mutations characterized so far are all localized on the N-terminal region of mature vWf subunit, within or near the major FVIII binding domain, and some of them occur within the epitope of monoclonal antibodies inhibiting the vWf/FVIII interaction. These observations suggest a causal relationship between these mutations and the vWD 'Normandy' phenotype.

Molecular characterization of a unique von Willebrand disease variant. A novel mutation affecting von Willebrand factor/factor VIII interaction

von Willebrand factor (vWF) plays a central role in blood coagulation, mediating the adhesion of the initial platelet plug to the subendothelium, and serving as the carrier for factor VIII (FVIII) in the circulation. In previous studies, we have mapped the epitope for an anti-vWF monoclonal antibody which inhibits the interaction between FVIII and vWF to a region spanning Thr78 to Thr96 of the mature protein (Bahou, W.F., Ginsburg, D., Sikkink, R., Litwiller, R., and Fass, D. N. (1989) J. Clin. Invest. 84, 56-61). We now report the identification of a mutation within this region of vWF that results in decreased FVIII binding. Sequence analysis of polymerase chain reaction amplified platelet vWF mRNA from a von Willebrand disease (vWD) patient with a disproportionately low FVIII level identified a single nucleotide substitution (G----A), resulting in the conversion of Arg91----Gln. Recombinant vWF carrying this substitution showed decreased binding to FVIII compared with wild-type vWF or vWF carrying a polymorphic substitution in the same region (Arg89----Gln). These observations suggest a critical role for Arg91 in the interaction of vWF with FVIII and identify the molecular mechanism for a variant of vWD associated with unusually low FVIII levels.

The "Normandy" variant of von Willebrand disease: characterization of a point mutation in the von Willebrand factor gene

We previously reported a functional defect of von Willebrand factor (vWF) in a new variant of von Willebrand disease (vWD) tentatively named vWD “Normandy.” The present work has attempted to characterize the molecular abnormality of this vWF that fails to bind factor VIII (FVIII). The immunopurified vWF from normal and patient's plasma were digested by trypsin and the resulting peptides were compared. The electrophoresis of ““vWF Normandy” showed a shift in the band corresponding to a polypeptide from amino acid 1 to 272. Consequently, we performed the molecular analysis of the portion of the vWF gene of this patient encoding this amino acid sequence. Exons 18–24 were amplified by the use of polymerase chain reaction and their nucleotide sequences corresponding to 1.8 kb were determined. Our analysis showed a point mutation C to T at codon 791, resulting in the substitution of Methionine for Threonine at position 28 of the mature vWF subunit. Because this nucleotide substitution destroyed a Mae II restriction site, this mutation was conveniently sought in various individual DNAs. The patterns obtained were consistent with the homozygous and heterozygous state of this mutation in the patient and in her son, respectively, and with its absence in 28 normal individuals. We conclude that Threonine at position 28 in plasma vWF may be crucial for the conformation and FVIII-binding capacity of its cystine-rich N- terminal domain.

The “Normandy” Variant of von Willebrand Disease: Characterization of a Point Mutation in the von Willebrand Factor Gene

We previously reported a functional defect of von Willebrand factor (vWF) in a new variant of von Willebrand disease (vWD) tentatively named vWD "Normandy." The present work has attempted to characterize the molecular abnormality of this vWF that fails to bind factor VIII (FVIII). The immunopurified vWF from normal and patient's plasma were digested by trypsin and the resulting peptides were compared. The electrophoresis of "vWF Normandy" showed a shift in the band corresponding to a polypeptide from amino acid 1 to 272. Consequently, we performed the molecular analysis of the portion of the vWF gene of this patient encoding this amino acid sequence. Exons 18-24 were amplified by the use of polymerase chain reaction and their nucleotide sequences corresponding to 1.8 kb were determined. Our analysis showed a point mutation C to T at codon 791, resulting in the substitution of Methionine for Threonine at position 28 of the mature vWF subunit. Because this nucleotide substitution destroyed a Mae II restriction site, this mutation was conveniently sought in various individual DNAs. The patterns obtained were consistent with the homozygous and heterozygous state of this mutation in the patient and in her son, respectively, and with its absence in 28 normal individuals. We conclude that Threonine at position 28 in plasma vWF may be crucial for the conformation and FVIII-binding capacity of its cystine-rich N-terminal domain.

Molecular basis of von Willebrand disease type IIB. Candidate mutations cluster in one disulfide loop between proposed platelet glycoprotein Ib binding sequences.

Many variants of von Willebrand disease (vWD) with qualitatively abnormal von Willebrand factor (vWF) are recognized. In vWD type IIB, the abnormal protein displays enhanced affinity for a platelet vWF receptor, the glycoprotein Ib-IX complex. 14 patients from 7 unrelated families with vWD type IIB were studied to determine the molecular basis for this phenotype. Specific oligonucleotide primers were used to amplify portions of vWF exon 28 encoding a domain that interacts with the platelet glycoprotein Ib-IX complex. Candidate missense mutations were identified for all 14 patients by DNA sequencing, allele specific oligonucleotide hybridization, and restriction endonuclease digestion. These sequence changes occur in an 11 amino acid segment within a single disulfide loop bounded by Cys(509) and Cys(695). All of these sequence changes are C----T transitions within CG dinucleotides. Six patients from two unrelated families were heterozygous for the encoded sequence Arg(543)----Trp. Seven patients from four unrelated families were heterozygous for the encoded sequence Arg(545)----Cys; this sequence change appears to have occurred independently three times, once as a new spontaneous mutation. One patient with apparently sporadic vWD type IIB was heterozygous for the encoded sequence Val(553)----Met, and this appears to be a new mutation. None of these sequence changes was found in 100 normal alleles. These findings suggest that vWD type IIB may be caused by relatively few distinct mutations, that these mutations may cluster within a specific region of one disulfide loop in vWF domain A1, and that this region can modulate the affinity of vWF for the platelet glycoprotein Ib-IX complex.

A de novo and heterozygous gene deletion causing a variant of von Willebrand disease

An abnormal von Willebrand factor (vWF) gene restriction pattern has been found in a patient with von Willebrand disease. Because this gene alteration is not present in his parents or in 50 normal and 25 affected subjects, and the restriction fragment length polymorphism haplotypes are inherited normally in the patient's family, we suggest that a de novo mutation is present. Bands with reduced intensity and additional fragments, observed in several restriction digests, hybridize with noncontiguous copy DNA (cDNA) portions, thus indicating the presence of a heterozygous gene deletion. The deletion removes a genomic region containing at least codons 1147 through 1854 and corresponding to the D3-A3 homologous protein domains. The extent of the vWF pseudogene on chromosome 22 is roughly similar to that of the deleted area. However, the pseudogenic nature of the deletion is excluded by the mapping of bands with reduced intensity in the patient to the true vWF gene. The vWF antigen levels are one fourth of normal and ristocetin cofactor activity is severely impaired. The reduction of high molecular weight multimers in plasma and platelets and the altered triplet morphology are compatible with the presence of a dominant variant of type II von Willebrand disease.

New variant of von Willebrand disease with defective binding to factor VIII

A new variant of von Willebrand disease (vWD) was identified by a new analytic method which characterizes the ability of plasma von Willebrand Factor (vWF) to bind to purified factor VIII (F.VIII). vWF was isolated from small amounts of plasma by immunoadsorption with a selected monoclonal antibody to vWF previously coated onto wells of microtitration plates. Plasma F.VIII was removed from immobilized vWF by washing with 0.4 mol/L CaCl2; purified F.VIII was then added to the well. The amount of bound F.VIII was estimated directly in the wells by a chromogenic assay and immobilized vWF was estimated by an immunologic a pool of normal plasma, ten control individuals, 13 with hemophilia A and five with type I vWD. In all cases, the dose-response curves were linear and the slopes of the regression lines were essentially the same. The method was then applied to investigate the binding of vWF to F.VIII in two vWD patients (sister and brother) who demonstrated significantly lower activity of F.VIII than of vWF. The first patient, with a long history of epistaxis, bruising, and hematomas, showed a slightly prolonged bleeding time (10 minutes); 15% VIII:C and 39% of vWF:Ag and vWFRCo. Her brother, who has a bleeding syndrome but no hematomas, showed similar data (bleeding time 9 minutes, 20% VIII:C, 53% vWF:Ag and vWFRCo). Similar levels of F.VIII were observed in the two propositi by four different methods (one- and two-stage clotting and chromogenic and immunologic assays). Sodium dodecyl sulfate (SDS) 1.4% agarose gel electrophoresis showed that all multimers of vWF were present in both patients. vWF binding to F.VIII was markedly decreased in the two propositi. The abnormal binding of vWF to F.VIII was not corrected during pregnancy or after infusion of 1-deamino (8-D- arginine) vasopressin despite an increase in vWF levels. The qualitative abnormality of vWF in both patients was associated with a subtle alteration of the multimeric structure by SDS 3% agarose gel electrophoresis in which the two central subbands of the quintuplet of individual oligomers were undetectable or poorly visible. SDS- polyacrylamide gel electrophoresis under reducing conditions demonstrated a single band of 275 Kd in the plasma of both patients, and there was no evidence of a second band corresponding to pro-vWF, the precursor of the mature vWF subunit, suggesting that proteolytic processing of vWF was normal.

New Variant of von Willebrand Disease With Defective Binding to Factor VIII

A new variant of von Willebrand disease (vWD) was identified by a new analytic method which characterizes the ability of plasma von Willebrand Factor (vWF) to bind to purified factor VIII (F.VIII). vWF was isolated from small amounts of plasma by immunoadsorption with a selected monoclonal antibody to vWF previously coated onto wells of microtitration plates. Plasma F.VIII was removed from immobilized vWF by washing with 0.4 mol/L CaCl2; purified F.VIII was then added to the well. The amount of bound F.VIII was estimated directly in the wells by a chromogenic assay and immobilized vWF was estimated by an immunologic a pool of normal plasma, ten control individuals, 13 with hemophilia A and five with type I vWD. In all cases, the dose-response curves were linear and the slopes of the regression lines were essentially the same. The method was then applied to investigate the binding of vWF to F.VIII in two vWD patients (sister and brother) who demonstrated significantly lower activity of F.VIII than of vWF. The first patient, with a long history of epistaxis, bruising, and hematomas, showed a slightly prolonged bleeding time (10 minutes); 15% VIII:C and 39% of vWF:Ag and vWFRCo. Her brother, who has a bleeding syndrome but no hematomas, showed similar data (bleeding time 9 minutes, 20% VIII:C, 53% vWF:Ag and vWFRCo). Similar levels of F.VIII were observed in the two propositi by four different methods (one- and two-stage clotting and chromogenic and immunologic assays). Sodium dodecyl sulfate (SDS) 1.4% agarose gel electrophoresis showed that all multimers of vWF were present in both patients. vWF binding to F.VIII was markedly decreased in the two propositi. The abnormal binding of vWF to F.VIII was not corrected during pregnancy or after infusion of 1-deamino (8-D-arginine) vasopressin despite an increase in vWF levels. The qualitative abnormality of vWF in both patients was associated with a subtle alteration of the multimeric structure by SDS 3% agarose gel electrophoresis in which the two central subbands of the quintuplet of individual oligomers were undetectable or poorly visible. SDS-polyacrylamide gel electrophoresis under reducing conditions demonstrated a single band of 275 Kd in the plasma of both patients, and there was no evidence of a second band corresponding to pro-vWF, the precursor of the mature vWF subunit, suggesting that proteolytic processing of vWF was normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Von Willebrand Disease “Vicenza” With Larger-Than-Normal (Supranormal) von Willebrand Factor Multimers

When normal volunteers or patients with type I von Willebrand disease (VWD) are given desmopressin (DDAVP), a set of larger-than-normal (supranormal) von Willebrand factor (VWF) multimers, similar to those present in VWF-containing cells such as platelets megakaryocytes and endothelial cells, appear transiently in postinfusion plasma. In two kindreds with mild lifelong bleeding symptoms transmitted as an autosomal dominant trait, all ten symptomatic members (but none of the five asymptomatic members) had a supranormal multimeric structure for plasma VWF, apparently identical to that seen for postdesmopressin normal plasma. Plasma factor VIII coagulant activity (VIII:C), VWF antigen (VWF:Ag), ristocetin-induced platelet agglutination, and ristocetin cofactor (RiCof) activity were low. Platelet VWF:Ag and RiCof levels (tested for three patients only) were normal. Bleeding times were normal or slightly prolonged. The patients' platelet multimeric structure was the same as that for normal platelets. After desmopressin infusion the plasma VWF multimeric structure remained supranormal as for preinfusion plasma, with VIII:C VWF:Ag and RiCof increasing markedly over baseline values and disappearing at a normal rate. Examination of the VWF subunit composition from three of these patients indicated that proteolytic processing of their VWF did not differ from normal. This study describes the first variant of VWD with a supranormal multimeric structure.

Von Willebrand disease "Vicenza" with larger-than-normal (supranormal) von Willebrand factor multimers

When normal volunteers or patients with type I von Willebrand disease (VWD) are given desmopressin (DDAVP), a set of larger-than-normal (supranormal) von Willebrand factor (VWF) multimers, similar to those present in VWF-containing cells such as platelets megakaryocytes and endothelial cells, appear transiently in postinfusion plasma. In two kindreds with mild lifelong bleeding symptoms transmitted as an autosomal dominant trait, all ten symptomatic members (but none of the five asymptomatic members) had a supranormal multimeric structure for plasma VWF, apparently identical to that seen for postdesmopressin normal plasma. Plasma factor VIII coagulant activity (VIII:C), VWF antigen (VWF:Ag), ristocetin-induced platelet agglutination, and ristocetin cofactor (RiCof) activity were low. Platelet VWF:Ag and RiCof levels (tested for three patients only) were normal. Bleeding times were normal or slightly prolonged. The patients' platelet multimeric structure was the same as that for normal platelets. After desmopressin infusion the plasma VWF multimeric structure remained supranormal as for preinfusion plasma, with VIII:C VWF:Ag and RiCof increasing markedly over baseline values and disappearing at a normal rate. Examination of the VWF subunit composition from three of these patients indicated that proteolytic processing of their VWF did not differ from normal. This study describes the first variant of VWD with a supranormal multimeric structure.