Von Willebrand factor multimer patterns in von Willebrand's disease

Von Willebrand Factor Multimer Analysis and Classification: A Comprehensive Review and Updates

Von Willebrand factor (VWF) is a multimeric glycoprotein with essential roles in primary hemostasis. Patients with von Willebrand disease (VWD), due to quantitative and/or qualitative defects of VWF usually experience mucocutaneous bleeding. Based on the laboratory results of VWF antigen, various VWF activities, factor VIII activity, and VWF multimer patterns, VWD can be categorized as type 1, 2, and 3 VWD. VWF multimer analysis by either manual or semi-automated electrophoresis and immunoblotting is a critical part of the laboratory testing to differentiate type 1, type 2 VWD, and subtypes of type 1 or 2 VWD. The multimer distribution patterns can also help to understand the underlying molecular mechanism of VWF synthesis, multimerization, and clearance defects in VWD. This review will cover VWF synthesis, multimerization, secretion, VWF multimer analysis, and VWF multimer interpretation of various types and subtypes of VWD.

Frequency of different types of von Willebrand's disease in the GDR

The frequency of different types of von Willebrand's disease (vWD) was studied in the southern part of the GDR and during investigations of relatives of already diagnosed patients. Among 111 patients diagnosed, vWD was found to be type I in 85 cases, type II in 13 cases and severe recessive type in 13 cases. The patients with type I belonged to 46 different families. Two families with type II had the II A variant and another a variant similar to II C. No patients with type II B were diagnosed. The incidence of severe recessive vWD was estimated to be lower than in Sweden but higher than in Italy and France.

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

BACKGROUND

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

OBJECTIVE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Von Willebrand disease

von Willebrand disease is a common inherited bleeding disorder and many cases are diagnosed in childhood. It has a negative impact on the quality of life of affected individuals; therefore, it is important that the condition be recognized and diagnosed. This article reviews the pathophysiology of the condition, the current classification scheme, and the available treatments, highlighting issues specific to the pediatric population.

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.

Acute abdominal pain caused by a spontaneous intramyometrial hematoma in type III von Willebrand disease

OBJECTIVES

To discuss the clinical picture, differential diagnosis and management of a pediatric patient with von Willebrand disease (vWD) presenting with severe abdominal pain caused by an intramyometrial hematoma.

METHODS

A 17-year-old girl with type III vWD was admitted to the emergency department with a complaint of severe lower abdominal pain different from her usual dysmenorrhea. She had no history of trauma to the pelvic region or any sexual intercourse. Transabdominal ultrasonography and magnetic resonance imaging revealed an intramyometrial hematoma in anterofundal region of uterus.

RESULTS

A favorable clinical outcome was obtained through a treatment with factor VIII concentrates containing von Willebrand factor which resulted in complete resolution of the sonographic findings within 3 weeks.

CONCLUSIONS

Intramyometrial hematoma can be an unusual cause of severe abdominal pain in patients with vWD applying to emergency departments. Especially in adolescence years, when transvaginal sonography could not be performed, transabdominal ultrasonography and magnetic resonance imaging are useful tools for the diagnosis.

New approach of the treatment of von Willebrand’s disease during pregnancy

AIM

The aim of the study was to analyze the effectiveness of the application of DDAVP (desmopressin) and Hemate P with cryoprecipitate pre- and postpartum in patients with von Willebrand disease.

METHODS

We monitored 32 patients with von Willebrand disease during the study period 1993-2003. DDAVP was applied in the 36th/37th week of gestation and cryoprecipitate and fresh frozen plasma were applied 1 day before and 3 days after delivery. DDAVP treatment continued for 4 weeks. Factor VIII (Hemate P) at the day of delivery

RESULTS

No complications occurred in the studied population.

CONCLUSION

Precipitation of DDAVP, Hemate P, and cryoprecipitate may help in the treatment of pregnant women with von Willebrand disease.

Guidelines for the diagnosis and management of von Willebrand disease in Italy

von Willebrand disease (vWD) is a bleeding disorder caused by quantitative (type 1 and 3) or qualitative (type 2) defects of von Willebrand factor (vWF). The molecular basis of type 2 and 3 vWD are now known and those of type 1 vWD are being understood. Phenotypic diagnosis is based on the measurements of plasma and platelet vWF, of the ability of vWF to interact with platelet receptors and the analysis of the multimeric structure of vWF. Due to the heterogeneity of vWF defects and the variables that interfere with vWF levels, a correct diagnosis of types and subtypes may sometimes be difficult but is very important for therapy. The aim of treatment is to correct the dual defects of haemostasis, i.e. abnormal intrinsic coagulation expressed by low levels of factor VIII (FVIII) and abnormal platelet adhesion. Desmopressin is the treatment of choice in patients with type 1 vWD, who account for approximately 70% of cases, because it corrects FVIII-vWF levels and the prolonged bleeding time (BT) in the majority of these patients. In type 3 and in severe forms of type 1 and 2 vWD patients, desmopressin is not effective and it is necessary to resort to plasma concentrates containing FVIII and vWF. Treated with virucidal methods, these concentrates are effective and safe, but they cannot always correct BT defect. Platelet concentrates or desmopressin can be used as adjunctive treatments when poor correction of BT after plasma concentrate treatment is associated with continued bleeding.

Advances in the genetics and treatment of von Willebrand disease

von Willebrand disease (VWD) is a bleeding disorder caused by quantitative (type 1 and 3) or qualitative (type 2) defects of von Willebrand factor (VWF). The mechanisms of most inherited VWD types have been recently elucidated by genetic and molecular diagnosis, but the phenotypic tests based on measurements of plasma and platelet VWF, the ability of VWF to interact with its platelet receptor, and the analysis of the multimeric composition of VWF are always essential to identify patients with different VWD subtypes. The aim of treatment is to correct the dual defects of hemostasis, ie, abnormal coagulation expressed by low levels of factor VIII (FVIII) and abnormal platelet adhesion expressed by prolonged bleeding time (BT). Desmopressin is the treatment of choice in most patients with type 1 and type 2 VWD, who account for 60 to 70% of cases. In type 3 and in some severe forms of type 1 and type 2 VWD, desmopressin is not effective, and it is necessary to resort to plasma concentrates containing FVIII and VWF. Treated with virucidal methods, these concentrates are effective and currently safe, but they do not always correct the BT defect. Platelet concentrates or desmopressin can be used as adjunctive treatments when poor correction of the BT after concentrates is associated with continued bleeding.

The molecular biology of von Willebrand disease

von Willebrand disease (VWD) is a common autosomally inherited bleeding disorder associated with mucosal or trauma-related bleeding in affected individuals. VWD results from either a quantitative or qualitative deficiency of von Willebrand factor (VWF)--a glycoprotein with essential roles in primary haemostasis and as a carrier of coagulation factor VIII (FVIII) in the circulation. In recent years the identification of mutations in the VWF gene in patients with VWD has improved our understanding of the structure and function of the VWF protein, and has illustrated the importance of specific regions of VWF for its interaction with other components of the vasculature. The underlying genetic lesions and associated molecular pathology have been identified in many cases of type 2A, type 2B, type 2M, type 2N and type 3 VWD. However in the most common variant, type 1 VWD, the causative molecular defect is unknown in the large majority of cases. In the absence of an understanding of the molecular pathology underlying type 1 VWD, precise diagnosis and classification of this common disorder remains problematic.

Congenital von Willebrand disease type I: definition, phenotypes, clinical and laboratory assessment

Von Willebrand disease, with a prevalence of about 1% in the general population, is the most frequent inherited bleeding disorder. Among the major subtypes, type I von Willebrand disease represents by far the more prevalent category (about 70%) and includes cases with a partial deficiency of plasma von Willebrand factor and no evidence of qualitative defects. The clinical expression as well as the laboratory phenotype of the disorder and its penetrance are greatly variable. The diagnosis usually requires the presence of autosomally inherited bleeding history co-segregating with a low von Willebrand factor level. The influence of several genetic and acquired conditions on the level of von Willebrand factor is however, widely appreciated and represents the major obstacle in correctly identifying von Willebrand disease as the cause of a bleeding diathesis in several families. The molecular genetics of the minority of cases showing high penetrance and expressivity of the phenotype are unravelling, but for the large majority of milder cases, the molecular basis is still unknown. We present a practical approach to diagnosis, based on scientific evidence and direct experience. The implications of the diagnosis of von Willebrand disease for the patient's quality of life are also considered.

A molecular approach to the classification of von Willebrand disease

The marked heterogeneity of von Willebrand disease was already recognized by von Willebrand in 1926. The accumulating knowledge of the different clinical phenotypes and the pathophysiological basis of the disease was translated into a classification that differentiated between quantitative and qualitative defects by means of quantitative and functional parameters and by analysing the electrophoretic pattern of von Willebrand factor multimers. The increasing number of different von Willebrand disease phenotypes required a revision of the nomenclature at a time when only a few types of von Willebrand disease had already been analysed at the molecular level. Consequently, the molecular data played only a minor role in the revised classification. Given the pronounced, even intra-individual, variation in the manifestation of von Willebrand disease and the diagnostic difficulties caused by a non-standardized methodology, it is clear that biochemical methods alone are insufficient for a clear classification. The advent of molecular techniques provided the opportunity for genotype-phenotype studies that recently helped to elucidate or confirm not only the important functions of von Willebrand factor and the steps of its post-translational processing, but also many disease-causing defects. The reproducible correlation between certain phenotypes and particular mutations can now be used for a molecular approach towards a final classification of von Willebrand disease, equally useful for the clinician and for research requirements.

The mechanism of pore assembly for a cholesterol-dependent cytolysin: formation of a large prepore complex precedes the insertion of the transmembrane beta-hairpins

Perfringolysin O (PFO) is a member of the cholesterol-dependent cytolysin (CDC) family of membrane-penetrating toxins. The CDCs form large homooligomers (estimated to be comprised of up to 50 CDC monomers) that are responsible for generating a large pore in cholesterol-containing membranes of eukaryotic cells. The assembly of the PFO cytolytic complex was examined to determine whether it forms an oligomeric prepore complex on the membrane prior to the insertion of its membrane-spanning beta-sheet. A PFO oligomeric complex was formed on liposomes at both 4 degrees C and 37 degrees C and shown by SDS-agarose gel electrophoresis to be comprised of a large, comparatively homogeneous complex instead of a distribution of oligomer sizes. At low temperature, the processes of oligomerization and membrane insertion could be resolved, and PFO was found to form an oligomer without significant membrane insertion of its beta-hairpins. Furthermore, PFO was found to increase the ion conductivity through a planar bilayer by large and discrete stepwise changes in conductance that are consistent with the insertion of a preassembled pore complex into the bilayer. The combined results of these analyses strongly support the hypothesis that PFO forms a large oligomeric prepore complex on the membrane surface prior to the insertion of its transmembrane beta-sheet.

The molecular basis of von Willebrand disease

von Willebrand disease (VWD) is a clinically heterogeneous bleeding disorder that reflects a wide array of defects. Quantitative subtypes of the disorder, including types 1 and 3 VWD, result in bleeding due to reduced levels of circulating von Willebrand factor (VWF) protein. Qualitative subtypes, defined as type 2 VWD, act through altered VWF function. A range of molecular defects are responsible for many of these subtypes, including missense, nonsense, splicing, insertion, and deletion mutations, resulting in either dominant or recessive inheritance. While many mutations correspond to selected variants, the basis for variation in expression and the imperfect correlations between genotype and phenotype remain to be understood.

Effective periodontal treatment in a patient with type IIA von Willebrand's disease: report of a case

von Willebrand's disease (vWD) is one of the most common hereditary hemorrhagic disorders. A mild to moderate deficiency of factor VIII and von Willebrand factor (vWf) often is associated with gingival bleeding. In this case report, the periodontal treatment of a patient with vWD is described. A 45-year-old woman with type IIA vWD was referred for periodontal therapy because of an episode of gingival hemorrhage and percussion pain of teeth #18 and #47. The periodontal findings included probing depths ranging from 2 to 6 mm, horizontal bone loss, and Class II furcation involvement of tooth #46. After consultation with a hematologist, apically positioned flap surgery and hemisection were performed on tooth #46 following completion of oral hygiene instruction, scaling and root planing, and endodontic therapy. The patient was given 500 units of factor VIII including vWf multimer 30 minutes before surgery. After healing of the periodontal tissue, prosthodontic treatment was undertaken on the posterior mandibular sextants. At follow-up, the probing depths ranged from 2 to 3 mm, and gingival bleeding on probing was minimal. The patient's children all had vWD. They had mild to moderate periodontitis with probing depths ranging from 2 to 5 mm and gingival bleeding on probing. With the combined efforts of the periodontist and hematologist, effective periodontal treatment can be provided to patients with von Willebrand's disease.

A new candidate mutation (N528S) within the von Willebrand factor propeptide identified in a Japanese patient with phenotype IIC of von Willebrand disease

Phenotype IIC of von Willebrand disease (vWD) is a subtype of type 2A vWD characterized by recessive inheritance and an impaired multimerization of von Willebrand factor (vWF) molecules beyond dimers. The 5 patients with phenotype IIC whose vWF gene defect has been characterized so far are either homozygous or double heterozygotes for mutations localized in exons 11, 12, 14 or 15. We report here the identification of a new candidate mutation in a previously described Japanese patient affected with phenotype IIC vWD. The propositus is homozygous for the A1833G nucleotide substitution, in exon 14 of vWF gene, responsible for the N528S mutation within the vWF propeptide. This finding is in agreement with the consanguineous origin of the propositus, whose parents are first cousins. Six patients' relatives who are asymptomatic were studied and found heterozygous for the N528S mutation. The screening of the whole vWF gene, either by SSCP or sequencing, did not reveal any other deleterious sequence alteration in the patient. Furthermore, the N528S nonconservative substitution identified is located in the vWF propeptide region, where the other phenotype IIC mutations described so far are clustered. The N528S candidate mutation characterized is, therefore, most probably responsible for the multimerization defect of vWF observed in this patient.

von Willebrand disease

Considerable progress has been made in characterizing the specific molecular defects responsible for the heterogeneous disorder known as von Willebrand disease (VWD). A large number of molecular defects have been identified and precise characterization may now be possible in the majority of type 2A, type 2B, type 2N, and potentially also type 3 VWD cases. However, the most common variant, type 1 VWD, still remains a major challenge. Continued progress in this area will improve our understanding of the pathogenesis of VWD and lead to more rapid and precise diagnosis and classification for this common disorder. The problems of incomplete VWD penetrance and poor diagnostic sensitivity and accuracy for the currently available clinical laboratory tests provide strong incentives for the development of DNA-based diagnostics. In addition, prenatal diagnosis is now possible either at the level of single point mutations (for some subtypes) or by RFLP analysis (assuming linkage to the von Willebrand factor [VWF] gene) and will probably be applied with increasing frequency for VWD type 3 (17, 133, 175). Understanding the molecular basis of VWD also has important implications for VWF structure and function and is helping to define critical binding domains within the VWF molecule. Insights gained from these studies may eventually lead to improved therapeutic approaches not only for VWD, but also for a variety of other genetic and acquired hemorrhagic and thrombotic disorders.

Von Willebrand's disease

von Willebrand's disease (vWD) arises from abnormalities in von Willebrand factor (vWF), an adhesive glycoprotein uniquely involved in key aspects of both primary and secondary hemostasis. The current classification distinguishes disorders arising from partial (type 1) or complete (type 3) deficiencies and from qualitative defects (type 2). Type 2 vWD is further divided into four subtypes (A, B, N, and M), reflecting distinct classes of functional abnormalities. Mis-sense mutations account for most of type 2 vWD, whereas major disruptions in the vWF gene produce type 3 variants. The molecular basis of type 1 vWD is largely undefined. The laboratory diagnosis of vWD and its several variants is made on the basis of immunologic and functional studies of vWF, factor VIII levels, and specialized electrophoretic analysis (multimer gels). The mainstay of therapy for most patients with vWD in desmopressin, a pharmacologic agent that stimulates the release of endogenous pools of vWF. Cryoprecipitate and selected factor VIII concentrates are useful sources of exogenous vWF for the treatment of patients unresponsive to this desmopressin.

Pathogenesis, clinical picture and treatment of von Willebrand's disease

Von Willebrand's disease is probably the most common congenital bleeding disorder, with a prevalence close to 1% in some epidemiological studies. The disease is caused by a quantitative deficiency or a qualitative defect of the von Willebrand factor, which is a multimeric glycoprotein consisting of subunits of 2050 amino acids. The size of multimers ranges from approximately 500 kDa to 20 MDa. Each subunit consist of repeated domain structures. Several functional domains have been identified which can bind such structures as platelet receptors glycoprotein Ib or IIb/IIIA, heparin, collagen or factor VIII. The von Willebrand factor has two main functions in haemostasis, to promote normal platelet adhesion and to be a carrier protein for factor VIII. Von Willebrand's disease is divided into three major types and several subtypes depending on the quantity and quality of the von Willebrand factor in plasma and platelets. A new classification has recently been proposed. Typical symptoms are mucosal bleeding, easy bruising and increased bleeding tendency in connection with tooth extractions and other invasive procedures. Severe cases may have joint bleeding and other haemophilia-like bleeding. Desmopressin is the treatment of choice in mild cases, whereas more severe cases need treatment with factor VIII concentrates.

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.

The role of platelet von Willebrand factor in platelet adhesion and thrombus formation: a study of 34 patients with various subtypes of type I von Willebrand disease

In order to investigate the respective role of plasma and platelet von Willebrand factor (vWF) in mediating platelet adhesion and thrombus formation, we performed ex vivo perfusion studies with native blood from patients with various subtypes of type I von Willebrand disease (vWD). We studied 34 patients with type I vWD (19 'platelet normal', five 'platelet low', two 'platelet discordant', eight 'Vicenza'). Parallel studies were carried out on nine patients with severe vWD (type III). At high shear rate (2600 s-1) we found that the defect in platelet-vessel wall interactions in patients having a normal platelet vWF content ('platelet normal' and 'Vicenza') involved thrombus formation, whereas platelet adhesion was normal. At this high shear rate, platelet adhesion and thrombus volume were significantly decreased in patients with subtypes 'platelet low' and 'platelet discordant', i.e. when platelet vWF is either low or dysfunctional. These results indicate that platelet vWF may substitute for plasma vWF to promote platelet adhesion, emphasizing the important role of platelet vWF. They also confirm the role of vWF in thrombus formation at high shear rate because an abnormal thrombus volume was observed in all patients, even when platelet adhesion was normal.

Substitution of cysteine for phenylalanine 751 in mature von Willebrand factor is a novel candidate mutation in a family with type IIA von Willebrand disease

Type IIA is a variant form of von Willebrand disease (vWD) characterized by the absence of von Willebrand factor (vWF) high molecular weight multimers in plasma. Most of the candidate missense mutations potentially responsible for type IIA vWD have been found clustered within a short segment of vWF, lying between Gly742 and Glu875 of the mature subunit. The present work reports a single heterozygous T-->G transversion in eight patients from a large type IIA vWD family, resulting in the substitution Phe751-->Cys. The absence of this mutation in 100 normal vWF genes as well as the lack, in these patients, of any other abnormality within the whole exon 28 encoding amino acids 463-921 of mature vWF, provide a strong support that this non-conservative mutation may be at the origin of the disease in this family. The presence of an additional cysteine at position 751 may induce a conformational change of the vWF subunit affecting either its 'in vivo' sensitivity to proteolytic cleavage or, more likely, its intracellular transport as suggested by the abnormal multimeric pattern of platelet vWF observed in these patients.

von Willebrand disease family studies: comparison of three methods of analysis of the von Willebrand factor gene polymorphism related to a variable number tandem repeat sequence in intron 40

A region with a variable number of tandem ATCT repeats (VNTR) has previously been localized within intron 40 of the von Willebrand factor (vWF) gene. In the present report we describe the use of this polymorphism as a genetic marker to study the inheritance pattern in five families affected with various types of von Willebrand disease (vWD): types I, IIA, IIB, IIC and the newly characterized variant with totally defective FVIII binding. Three means of investigation previously reported, all using polymerase chain reaction (PCR) amplification of this vWF gene region, were compared in terms of informativeness. The two direct single-step procedures analysing only partial sequences of the VNTR region turned out to be less informative (three studies informative out of five) than the third method characterizing the variability of the whole VNTR sequence. This latter approach, based on the analysis of the Alu I restriction pattern of the VNTR region, was informative in all the families investigated, therefore avoiding the need to combine it with other genetic marker studies for efficient gene tracking. In conclusion, this two-step (PCR and digestion) method is the most informative for the characterization of the inheritance of the different subtypes of vWD and for the prenatal diagnosis of its severe forms.

Genetic and blood coagulation characterization of "Swedish" families with von Willebrand's disease types I and III: new aspects of heredity

Twenty-five patients with von Willebrand's disease (vWD) type III were analysed with regard to blood coagulation variables and possible deletions. Nine of the probands and their families were further investigated with DNA linkage analyses. Different patterns of heredity can be suggested in our families with vWD type III, on the basis of blood coagulation analyses. The findings suggest homozygosity in five families and the possibility of compound heterozygosity or a new mutation in the proband in three families. The linkage analyses confirm the results of the coagulation analyses. The segregation of the von Willebrand factor (vWF) gene can be followed in the families, and carrier diagnosis can be made in several of the probands' relatives. The possibility of large deletions in the vWF gene of the probands and their parents was investigated with probes representing the whole vWF cDNA. No deletions were found.

A study of von Willebrand's disease in Jordan

This work reports on the results of a 9-year study of von Willebrand's disease and its subtypes in Jordan, a country with a predominantly Arab population. There were a total of 65 patients in 32 families. Detailed study of 61 patients including von Willebrand factor multimers was done for the purpose of subtyping them. Type I and variants were seen in 36 patients (59%). Type II A and variants with decreased ristocetin response accounted for seven patients (11.5%), while 11 (18%) were of type II B. The severe type (type III) accounted for seven patients (11.5%). Von Willebrand's disease was the second most commonly seen inherited bleeding disorder after hemophilia A. It is concluded that although the observed frequency of von Willebrand's disease in this study in Jordan is lower than that in Europe and the USA, the true prevalence cannot be ascertained since many of the mild cases presumably were missed because of referral patterns. Type I and its variants was the most common type found, but the observed frequency of types II B and III was more than that reported in Europeans and Americans.

On laboratory problems in diagnosing mild von Willebrand's disease

By providing some examples of variations in the levels of von Willebrand factor antigen (vWF:Ag), ristocetin cofactor, and Factor VIII during one month, the authors wish to emphasize the difficulty of diagnosing mild forms of von Willebrand's disease (vWD), especially type I. In three of 15 normal female volunteers the vWF:Ag levels, on some sampling occasions, were so low (0.25-0.30 IU/mL, normal greater than 0.50 IU/mL) that the diagnosis of vWD type I might be made while on other occasions normal levels were obtained. The coefficients of variation (CV) for vWF:Ag in these three women were 12%, 25%, and 43%. However, CVs of similar magnitude were also observed for "non-diseased" males and females. The ratio F VIII/vWF:Ag also varied greatly. In the three women with suspected vWD it was 36%, 15%, and 34%. A representative level for the entire cycle of vWF:Ag and ristocetin cofactor seems to have been obtained in the follicular phase and therefore it is suggested that in order to make the diagnosis of vWD type I, at least in females, blood samples should be taken in this phase.

Structure and function of von Willebrand factor: relationship to von Willebrand's disease

This review summarizes the current knowledge of the structure and function of von Willebrand factor and of the pathophysiologic features, diagnosis, classification, and treatment of von Willebrand's disease, the most common congenital bleeding disorder in humans. Specific regions of the von Willebrand factor subunit that are of functional importance have been identified. The structure of these functional domains of von Willebrand factor, as known to date, is described. A classification of von Willebrand's disease, based on the definition of structural and functional abnormalities of the molecule and initial characterization of genetic mutations, is discussed. With more precise characterization of molecular abnormalities, more selective therapeutic intervention for specific subtypes of von Willebrand's disease should eventuate.

Studies on an unusual von Willebrand's variant--type IID

We describe a man and his daughter from a large New Zealand family with the extremely rare variant von Willebrand's (VW) disease type IID. These two patients had a severe bleeding history following minor surgery and displayed easy bruising. However, routine laboratory screening tests and factor VIII studies were essentially normal except for slightly reduced ristocetin cofactor activity and prolonged skin bleeding times. Although lacking higher molecular weight forms of VW antigen in common with VW type II's the patients' multimer patterns were clearly different from types IIA and IIB. Instead of showing the characteristic 'triplet' pattern in each multimer band the patients gave a single prominent band with faint satellite bands different in mobility to those in normals. Von Willebrand factor from the patients' platelets gave a similar abnormal pattern. DDAVP failed to correct the bleeding time in either patient and multimer analysis confirmed that there was no increase in the higher molecular weight VWF antigen.

von Willebrand factor and its disorders: an overview of recent molecular studies

von Willebrand factor (vWF) is a plasma protein with multiple functions in haemostasis. The vWF gene, located on chromosome 12p2.1, encodes a primary gene product of 2813 amino acids. Post-translational modification, assembly and secretion of vWF are highly complex. The pro vWF promoter is covalently linked by intermolecular disulphide bonds to form a dimer of MW approximately 440 kDa. This then polymerises to form multimers ranging in MW from 1-20 x 10(6). Simultaneously the pro piece of vWF is cleaved, releasing a 741 amino acid peptide known as vW Ag II from the polymerised protomers. Two distinct secretion pathways are found in the endothelial cell, a regulated pathway with storage in Weibl-Palade bodies and a constitutive pathway. Platelets store vWF in their alpha-granules. Mature vWF participates in platelet adhesion, spreading and aggregation and is a carrier of factor VIII, protecting the latter from degradation. Disorders of vWF are highly diverse. At least 20 subtypes of von Willebrand's disease have been described to date, based on features of the vWF present in or absent from patients plasma and platelets. Some patients have reduced amounts of apparently normal vWF whilst others have clearly abnormal vWF with aberrant structure and function. Rare patients virtually or completely lack vWF. The genetic and structural basis of some of these abnormalities is just beginning to emerge. This article outlines the molecular biology and physiology of vWF, and reviews some recent progress on the molecular pathology and genetics of von Willebrand's disease.

Response to desmopressin in type IID von Willebrand's disease

Dominant transmission of a variant of von Willebrand's disease (vWD) with aberrant polymerization of von Willebrand factor (vWF) has been identified in a Scottish family. Multimer analysis of plasma vWF from the propositus and her father revealed an identical pattern to that previously reported in families designated as type IID vWD. There is loss of the larger multimers and presence of an intermediate subsidiary band not seen in normal subjects or other vWD variants. Platelet/vWF interaction induced by ristocetin is not enhanced in these cases and the platelet vWF shows the same aberrant multimer pattern as plasma vWF. DDAVP infusion in two affected members of the Scottish family and in one of the index cases produced a rise in plasma vWF antigen and factor VIII. Higher molecular weight vWF multimers appeared transiently after infusion of desmopressin (1-deamino-8-D-arginine vasopressin, abbreviated DDAVP) coincident with shortening of the bleeding time. The platelet counts did not change after the DDAVP infusions. DDAVP should be considered for management of bleeding in this variant of von Willebrand's disease.

von Willebrand factor and platelet function

vWF is an adhesive protein that binds to two distinct platelet glycoproteins, GP Ib and GP IIb-IIa complex. Its interaction with GP Ib is primarily responsible for platelet adhesion to the subendothelium. The current model is that vWF binds to collagen and/or another component of the subendothelium, after which a conformational change in the vWF molecule exposes the GP Ib binding site. This interaction may not only promote the initial attachment of platelets to the subendothelium but also play a role in thrombus formation through exposure of GP IIb-IIIa to which vWF and fibrinogen can bind. The second important function of vWF is to be a carrier for F. VIII, protecting it from degradation and playing a role in its activation by thrombin. Circulating vWF has a complex multimeric structure that ranges in Mrs from 0.5 to 20 x 10(6) Daltons. The basic subunit has a Mr of 270 kDa. Amino acid sequencing of vWF demonstrated that the basic subunit or mature vWF is made up of 2050 amino acids. Molecular cloning of the vWF cDNA revealed that the primary transcript consists of 8900 base pairs that encode for 2813 amino acids, including a 22 amino acid signal peptide and a propolypeptide of 741 amino acids, called vWF antigen II. Recent studies on the expression of recombinant vWF molecules indicate that the propolypeptide is involved in the multimerization of vWF. The domains on the vWF molecule involved in the interactions of vWF with GP Ib, GP IIb-IIIa, collagen, F. VIII and heparin have been localized to varying extents. It is anticipated that peptide analysis and recombinant DNA techniques, such as in vitro mutagenesis, will further define the structural requirements of these binding domains. vWF is synthesized in a cell-specific manner by endothelial cells and megakaryocytes. It undergoes a complex intracellular biosynthesis involving transcription of a 200 kb gene, splicing out more than 42 introns, translation of a 8900 bp mRNA, glycosylation, disulphide bond formation, sulphatation, multimerization and proteolytic cleavage. The molecule can be secreted in a constitutive or regulated manner upon perturbation of the endothelial cells with physiological and non-physiological secretagogues. The mechanisms that control the synthesis of vWF should be an exciting area of further research. vWD is probably the most common of all congenital disorders of haemostasis. It is an extremely heterogeneous syndrome involving quantitative or qualitative disorders of vWF.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical effectiveness of desmopressin in a case of acquired von Willebrand's syndrome associated with benign monoclonal gammopathy

A case of acquired von Willebrand's syndrome (avWs) secondary to benign monoclonal gammopathy, is described, in which desmopressin (DDAVP) has proven effective repeatedly in preventing bleeding after tooth extraction. The laboratory pattern was similar to that of congenital type IA von Willebrand's disease. After DDAVP, prolonged bleeding time and factor VIII/von Willebrand factor activities were normalized. The disappearance rate of the elicited activities was similar to that observed in patients with congenital disease. This report adds to the scarce data concerning the haemostatic effectiveness of DDAVP in avWs and suggests that this agent might also be used in controlling or preventing bleeding in patients with the acquired disease, selected on the basis of their biological responsiveness to a test-infusion.

Type IB von Willebrand's disease and pregnancy: comparison of analytical methods of von Willebrand factor for classification of von Willebrand's disease subtypes

The clinical course and changes in von Willebrand factor (vWf), factor VIII and bleeding time during pregnancy are described in a patient with type IB von Willebrand's disease (vWD) in whom all vWf multimers were present in plasma with relatively reduced content of the high-molecular-weight multimers. At term, ristocetin cofactor was elevated to some extent (from the baseline value of 5 U/dl to 23 U/dl), but never normalized and below the level of vWf antigen (49 U/dl). Bleeding time remained prolonged. In addition, abnormal distribution in the multimer size of plasma vWf was never corrected. These findings contrast with favorable responses during pregnancy reported in type IA individuals. The patient was infused during labor with 400 ml of fresh frozen plasma, and blood loss was approximately 800 ml. Analytical techniques of vWf by crossed immunoelectrophoresis, gel filtration on Sepharose 2B and SDS-agarose gel electrophoresis for the classification of vWD subtypes were compared. Multimer analysis by SDS-agarose gel electrophoresis was needed for differentiation of type IB from type IIA vWD.

Hyper-responsiveness to DDAVP for patients with type I von Willebrand's disease and normal intra-platelet von Willebrand factor

Desmopressin (DDAVP) has gained wide acceptance as the drug of first choice in the treatment or prevention of haemorrhages in the majority of patients with von Willebrand's disease (vWd). However, data concerning the clinical effectiveness of DDAVP refer generally to mild vWd, with factor VIII and vW factor levels usually above 20% of normal. In 14 patients with type I vWd characterized by very low plasma levels of factor VIII coagulant activity (VIII:C) and vWf, measured as ristocetin cofactor activity (lower than 20% and 3% of normal respectively), but with a normal intraplatelet content of vWf, a test infusion of DDAVP (0.4 microgram/kg) elicited a very marked increase of VIII:C and vWf and normalized the bleeding time. All these patients subsequently underwent tooth extraction after DDAVP infusion. The incidence of bleeding was remarkably low, with only two minor late bleeding episodes easily stopped by repeating DDAVP infusion. Compared to the cases of type I vWd with unknown intraplatelet vWf content reported in the literature, this subgroup of patients had a more marked, albeit short-lived, increment of VIII:C and vWf.

Canine von Willebrand's disease. A heterogeneous group of bleeding disorders

The term "von Willebrand's disease," refers to a group of inherited bleeding disorders, all of which are caused by a deficiency of the multimeric plasma glycoprotein, von Willebrand factor. The various forms of canine von Willebrand's disease can be categorized into one of three major types: in type I canine von Willebrand's disease, all sizes of von Willebrand factor multimers can be detected in the plasma; in type II canine von Willebrand's disease, only the smaller von Willebrand factor multimers are found in the plasma (larger multimers are absent); and in type III canine von Willebrand's disease, von Willebrand factor is completely absent from the plasma or present in only trace amounts. Von Willebrand's disease is common in dogs, but some forms of the disease are so mild that they are of questionable clinical significance.

Hypothyroidism as a cause of acquired von Willebrand's disease

Three patients with bleeding tendency who met the criteria for type 1 von Willebrand's disease are described. In two patients, hypothyroidism was suspected and confirmed at presentation, and in the third hypothyroidism became apparent 4 years later. In all three, the history and clinical course after treatment with thyroxine indicated acquired von Willebrand's disease secondary to hypothyroidism. The possibility of hypothyroidism should be considered in patients presenting with von Willebrand's disease.

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.