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Keywords:

  • mutation analysis;
  • type 1;
  • von Willebrand disease;
  • von Willebrand factor

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

Summary  Since its first description in 1926, the precise nature and indeed significance of von Willebrand factor (VWD) in the area of human bleeding has been unsure and often controversial. The recognition of VWD as a distinct entity in blood and the cloning of the von Willebrand factor (VWF) gene in the 1980s encouraged both phenotypic and genotypic studies, culminating in 1994 with the recognition, by the VWF subcommittee of the Scientific and Standardization Committee (SSC) of International Society of Thrombosis and Haemostasy (ISTH), of three types of VWD, characterized by severe plasma VWF deficiency (type 3), functionally deficient plasma VWF (type 2) and reduced (below normal) levels of plasma VWF, which is functionally essentially normal (type 1; 70% of all cases). Since then, whereas gene analysis has recognized VWF gene (VWF) mutations in most individuals with type 3 and type 2 disease, the latter mutations correlating well with recognized functional domains within the VWF protein, few mutations have been reported in cases with type 1 VWD. This led to speculation that other factors, particularly ABO blood group, may be primarily responsible for the majority of such patients, perhaps combined with a generic bleeding tendency throughout the normal population. Recent large studies in Europe and Canada have considerably clarified this situation, revealing that the majority of type 1 VWD is associated with mutations within VWF. The role of these mutations in the aetiology of the disease opens up new approaches to the study of the diagnosis and treatment of the condition. Conversely, the lack of a change in the VWF gene in many recruited families will lead to enhanced efforts to identify non-VWF gene causes both at the genetic and epigenetic level.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

von Willebrand factor (VWD) is the commonest bleeding disorder in man and is generally believed to be caused by defects in the von Willebrand factor (VWF) (VWF) gene. In 1994, diagnostic criteria for the classification of VWD were published by the VWF subcommittee of the ISTH SSC based essentially on phenotypic data [1]. This classification has recently been reconsidered by the same group and adapted to reflect more recent observations [2]. In essence, VWD is no longer defined as being restricted to patients with mutations in the VWF gene and type 1 disease is recognized to include some patients where subtle changes in plasma VWF multimer profile can be seen compared with normal, but where these changes do not appear to affect its function.

The complexity of the VWF gene (52 exons covering 178 kb of DNA on chromosome 12 and the presence of a partial pseudogene on chromosome 22) has until recently focused mutation analysis on those cases where functional defects (type 2 VWD) were suspected or severe deficiency was seen (type 3 VWD). These are generally the clinically more severe forms of the disease and therefore genetic diagnosis can be important in family-based diagnosis and even prenatal diagnosis. Type 1 VWD, caused by a reduction of essentially normal plasma VWF is difficult to diagnose in many cases where plasma levels of VWF are close to or overlap with the normal range. Indeed, there is a body of opinion that believes that mild cases of type 1 VWD may well be a result of the chance association of a VWF level at the lower end of the normal range and a mild bleeding tendency [2].

Until recently, mutation analysis in type 1 VWD had been rarely reported and was restricted to the most severe forms of the disease. Mutations within the VWF D3 domain at C1149R, C1130 F and T1156 M [3–6] have been identified in dominant type 1 VWD where plasma levels of VWF are around 10 IU dL−1. In vitro expression studies have shown decreased cellular secretion and the in vivo response to desmopressin also reduced, suggesting that increased clearance also adds to the observed phenotype. VWD Vicenza (R1205H) [7] is an extreme example of type 1 VWD caused by increased plasma VWF clearance. The presence of ultra-large forms of circulating plasma VWF in some patients with this form of VWD is believed to reflect a dramatically increased clearance that contributes to a reduced time when the VWF can be proteolyzed by ADAMTS-13.

Since 2005, one international and two national multi-centre studies on type 1 VWD have been reported [8–10]. All had essentially the same aim: to examine the genetic basis of type 1 VWD by analysis of the VWF gene in clinically affected patients and to relate this to the patient’s phenotype, bleeding history and response to treatment. The two largest studies across Europe [8] and Canada [9] are the most comprehensive ever reported and will be examined in some detail below. Although recruitment criteria were different, the overall conclusions are surprisingly similar, clearly showing that the majority of patients had mutations within their VWF gene.

Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

This study was supported by the European Community under the Fifth Framework Programme (QLG1-CT-2000-00 387) and involved 12 partners from nine EU countries. A comprehensive report of the main genotype/phenotype data has recently been published [8]. Recruitment criteria were based on a previous historical diagnosis of type 1 VWD together with at least one further affected family member (AFM) and unaffected family members (UFM). In all, 154 index cases (IC) were recruited, of whom four were later rejected (two with clear type 3 VWD, and two where essential assays could not be completed). Additionally, approximately 100 matched healthy controls were recruited at each participating centre. Very detailed phenotypic and genotypic analyses were performed locally, centrally and at centres where expertise in a particular assay was recognized [8]. Of particular significance to this study was the central performance of plasma VWF multimer analysis by Budde and colleagues in Hamburg, Germany, using highly sensitive methods not generally used worldwide [11]. Overall median levels of VWF:Ag and VWF:RCo in ICs were as anticipated for IC (38 IU dL−1 and 35 IU dL−1 respectively). Upon analysis of the data, the clear identification in a group of most of the more severely affected ICs of subtle abnormalities in multimer profile (57 of 150 IC) led to the separate analysis of this group. Of the abnormal multimer profiles observed, two IC had typical type 2A patterns. The profiles of the remainder resembled in several respects those seen in patients previously reported with subtypes of type 2 VWD (e.g. type IIE). Overall, this group had a median VWF:Ag level of 19 IU dL−1, a ratio of VWF:RCo to VWF:Ag of 0.53, and in 95% a mutation within VWF was identified. Fifty-four per cent of these mutations involved loss or gain of a cysteine residue. In comparison, of the 93 IC with normal multimer profiles, median levels were VWF:Ag of 47 IU dL−1, VWF:RCo of 45 IU dL−1, VWF:RCo/VWF:Ag ratio of 0.96, and 55% of IC had a detectable VWF mutation. It is reasonable to suggest that at present the former group with abnormal multimer profiles detected by sensitive procedures should be considered as possible type 2 VWD. However, as discussed below, whether such cases would be detected worldwide without the sensitive multimer assay being readily available is debateable.

The mutations identified in the EU study overall consisted of 80% missense mutations and < 20% null alleles. This is very different from reported studies on type 3 VWD where mutations predicted to lead to a null allele, including nonsense mutations, and deletions predominate. Only three mutations were found in both the normal and abnormal multimer groups (above). These were the R854Q change associated with reduced VWF/FVIII binding and present in up to 1% of some populations [12], and therefore assumed to be co-inherited with a second undetermined mutation causing the defective multimer profile, the R1205H Vicenza mutation, which comprised 10 of the 124 mutations detected, and with an abnormal multimer pattern. This was a very subtle alteration, as was that seen with the third mutation, C2304Y. It should also be noted that in 18 IC from the study, more than one VWF mutation was detected. While 55% of the group with normal multimers had a VWF mutation, 45% did not. This latter group will be of particular interest for further study as it included nine families where VWD completely co-segregated with VWF, and 19 families where co-segregation was incomplete. The remaining families were non-informative.

ABO blood groups have been known for some time to influence plasma levels of VWF, with group O normal individuals having levels some 30% lower than non-O individuals [13]. In the overall EU cohort, group O was present in 38% of controls and in 67% of IC. This figure was similar in both the normal and abnormal multimer profile groups, but dramatically increased (95%) in normal multimer cases where no mutation could be found and where co-segregation was incomplete between the VWF gene and VWD (19 families).

Study 2. Canadian study on Type 1 VWD

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

The Canadian multicentre study of type 1 VWD, recently reported [9], initially recruited 194 IC from 13 clinical centres across Canada. Using a pre-agreed study definition of type 1 VWD (personal history of excessive mucocutaneous bleeding and VWF:Ag and VWF:RCo levels between 5 and 50 IU dL−1) this number was reduced to 150. Further detailed analysis revealed abnormal VWF plasma multimer patterns in 10 cases, a further 11 cases with a VWF:RCo/VWF:Ag ratio below 0.6 and five additional cases where the families appeared to have a mixture of type 3 and type 1 phenotypes. Removal of a case with type 2 N VWD left a final well-defined cohort of 123 IC. The mean VWF:RCo level within this cohort was 34 IU dL−1, with a VWF:Ag of 36 IU dL−1. Comparison of data from the EU and Canadian studies is shown in Table 1.

Table 1.   Summary of recruitment and results from the three type 1 von Willebrand disease (VWD) studies [8–10]. *IC with abnormal plasma multimers
StudyEUCanadianUK
Recruited families15419440
Selected families15012332
Normal multimers9312332
% Excluded families38*3720
Median VWF:Ag IU dL−14736N/A
Median? Mean VWF:RCo IU dL−14534N/A
% with VWF mutation556353

A range of mutations throughout VWF were observed in 78 (63%) of IC, leaving a significant group (45) without a detectable mutation. Sixty-two per cent of mutations were missense and in 21 IC more than one putative VWF mutation was identified. The data also clearly showed that the incidence of mutations was highest in IC with the lowest VWF:Ag levels (VWF:Ag < 30 IU dL−1, 75% had mutations; VWF:Ag > 30 IU dL−1, 49% had mutations).

Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

This UK Haemophilia Centre Doctors Organization study was reported recently [10]. Forty families were initially diagnosed as having type 1 VWD and after review 32 families were included as having a recorded VWF:RCo level of < 50 IU dL−1, a VWF:RCo/VWF:Ag ratio of > 0.7 and a normal plasma VWF multimer profile. A history of significant mucocutaneous bleeding and a family history of type 1 VWD were also essential. In these IC, mutations were identified in 17 (including eight with Y1584C, which the authors describe as a polymorphism). Thus, no mutations were found in 15/32 (47%) of IC. Within the 32 families, 13 showed likely co-segregation of VWD with VWF and all showed putative mutations.

Summary of the studies

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

The three studies outlined above are remarkably similar, particularly in relation to the large number of VWF mutations identified, as shown in Table 1. Despite different recruitment criteria and subsequent selection of the final cohorts, the number of IC with detected VWF mutations is remarkably similar (53% to 63%), suggesting that this picture will be repeated worldwide. The historical criteria used in the EU study with the subsequent detailed multimer analysis and identification of a ‘possible type 2 VWD’ group has allowed for a considered appraisal of this group [8]. Ninety-five per cent of this group had detectable VWF mutations, a median level of VWF:Ag (19 IU dL−1) and a reduced VWF:RCo/VWF:Ag ratio (0.53). Several of the missense mutations observed in this group have been previously described as associated with severe forms of type 1and type 2 m VWD (mutations affecting amino acids 1130, 1205, 1315 and 1374). The detection of subtle changes in the plasma VWF multimeric profile in such cases is interesting and requires further study of its significance. It is also likely that in routine practise, the multimer pattern would be reported as normal. The difference in median levels of VWF:Ag between the EU (47 IU dL−1) and Canadian (36 IU dL−1) studies (Table 1) may reflect this, where the Canadian study includes some individuals where slight multimer abnormalities are present but remain undetected. It is probable that the inclusion or exclusion of some patients in the current type 1 VWD category may well depend in the local tests available.

Other aspects of the nature of type 1 VWD have been addressed by the EU and Canadian studies. The EU study has established patient bleeding assessment using a questionnaire-based bleeding score (BS) [14]. This was based on a similar system reported by Rodeghiero and colleagues [15]. The results clearly showed that the BS was significantly higher in IC compared with affected family members, unaffected family members and controls. ABO blood group appeared to have no effect but there was a strong significant inverse relationship with plasma VWF and FVIII levels at recruitment. The quantitative analysis of bleeding by the BS methodology has clear potential in the more accurate diagnosis of type 1 VWD.

Linkage analysis was performed in both the EU [16] and Canadian [17] studies. Previous studies have suggested variable linkage within type 1 families [18,19]. The EU study concluded that in the complete cohort, type 1 VWD co-segregated completely with the VWF gene in about 70% of families. When the abnormal multimer group (group 1 above) was excluded, this was reduced to about 50%. As group 1 contained the more severe phenotypes it is clear that the linkage proportion is higher in such kindred. James and colleagues have reported from the Canadian type 1 VWD study [17] and shown that 41% of their families showed VWF gene linkage. From the smaller UK study [10], about 25% of families did not show co-segregation of VWD with the VWF gene.

The diagnosis of type 1 VWD: impact of recent studies

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

From the data now available it is possible to begin to assess the value of various laboratory and clinical assessments in the diagnosis and treatment of type 1 VWD. As discussed above, the structured BS method utilized in the EU type 1 VWD study has shown that this methodology has the clear potential for improving the accurate diagnosis of type 1 VWD [14]. The same authors have also assessed the impact of VWF plasma levels in the diagnosis of type 1 VWD using the data from the EU study [20]. They concluded that the probability of type 1 VWD was markedly increased only for patients with VWF:Ag values below 40 IU dL−1. This was shown by a positive likelihood ratio (LR) of 95.1 for VWF:Ag. Higher values between 40 and 60 IU dL−1 only marginally indicated the probability of type 1 VWD. It is also possible from the EU data to assess other laboratory measures of VWF by reference to VWF:Ag plasma levels. An example of this approach is summarized in Fig. 1, where levels of VWF:Ag are related to the presence (or absence) of a detected VWF gene mutation and the presence of an abnormal VWF multimer pattern as discussed above. Thus, for patients presenting with VWF:Ag levels < 20 IU dL−1, at least 95% have a detectable VWF gene mutation and, using sensitive methods, about 85% of these show some abnormality in plasma VWF multimer profile. For VWF:Ag levels > 50 IU dL−1, only some 48% have a putative mutation while VWF multimers are normal in 95% of cases. The presence of candidate mutations in almost 50% of this group of IC is surprising. Whereas the mutations in the < 20 IU dL−1 VWF:Ag group are highly penetrant, this is probably not the case in the higher VWF:Ag group, though more work needs to be performed. If < 40 IU dL−1 VWF:Ag is used as suggested by Tosseto et al. [20] as a discriminator for type 1 VWD, then patients with VWF:Ag below this level will have an 85% chance of having a VWF gene mutation, whereas for those with levels above 40 IU dL−1 the chance is reduced to 52%.

image

Figure 1.  Analysis of numbers of IC as a percentage within decile groups defined by VWF:Ag levels (< 20 IU dL−1 to > 50 IU dL−1). IC are defined as with (mut+) or without (mut-) a mutation and with normal (MultN) or with abnormal (MultAb) VWF plasma multimers.

Download figure to PowerPoint

This type of analysis can be extended further to include, for example, the observed response to desmopressin. Preliminary data from 77 IC treated with desmopressin as part of the EU type 1 VWD study has shown that the most dramatic increases in plasma VWF (and FVIII) are seen in patients with abnormal VWF multimers and a VWF gene mutation (perhaps best described as possible type 2 patients, see above). A mean 11.3-fold rise was observed. However, it should be noted that this group had a low baseline level of plasma VWF (< 20 IU dL−1 VWF:RCo). There was no difference between the VWF:RCo increases seen in the normal multimer patients with (3.3-fold increase) or without (2.8-fold increase) a detected VWF gene mutation. The highest responders (greater than tenfold increases) were patients with mutations at amino acids 1130 and 1205.

It will be valuable to compare the types of VWF mutations seen in the groups defined by VWF:Ag levels in relation to their effect on VWF cellular secretion, time in the circulation and function, as well as their clinical and laboratory assessed penetrance within families. In vitro expression studies and further studies on families with these mutations will be important.

Type 1 VWD or not?

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References

The studies described and reviewed here have clearly identified a significant number of cases of type 1 VWD as defined at present. However, they have also confirmed that the diagnosis of some patients, often previously diagnosed with type 1 VWD, should be reconsidered. In general, such individuals have VWF plasma levels close to or within the normal range, no VWF gene mutation identified, and there is often incomplete co-segregation within the family of VWD and the VWF gene. This group is exemplified within the EU study data by group 3 [8], where VWF gene mutations were not detected in 42 IC. The median VWF:Ag level was 49 IU dL−1 (VWF:RCo 51 IU dL−1). Eight of these families showed complete co-segregation of VWD and VWF, suggesting an unknown genetic cause either within the VWF gene locus or linked to it. In 19 families incomplete co-segregation was seen. Fifteen families were non-informative. It is interesting that blood group O was present in 63% of IC where complete co-segregation was seen but this rose to 89% in the incomplete co-segregation group. Misdiagnosis of VWD is possible within the latter group, where the role of ABO blood group appears particularly important. It may be that these patients have mild bleeding symptoms and an occasional low level of VWF by coincidence. The cause of the mild bleeding symptoms is worthy of further study and may relate to platelet receptor expression variability for example [21,22]. The reasons for the low VWF level could involve linked and non-linked genetic loci or environmental factors.

Recent studies in mice have identified four genetic loci (Mvwf1, 2, 3 and 4) that account for some 45% of the variation in mouse plasma VWF levels between strains [23]. The chromosomal location of two of these loci (Mvwf3 and Mvwf4) exhibits homology and synteny to three human chromosomal segments previously reported by the GAIT study to be linked to VWF plasma levels in normal (thrombophilic?) humans [24]. We hope that further studies will reveal those factors in more detail and, by increasing our understanding of the genetic basis of variations in human plasma VWF levels, will explain the remaining mysteries of type 1 VWD.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Study 1. Molecular and clinical markers for the diagnosis and management of type 1 VWD (MCMCM-1VWD)
  5. Study 2. Canadian study on Type 1 VWD
  6. Study 3. VWF genotype in UK patients with type 1 VWD; UKHCDO study
  7. Summary of the studies
  8. The diagnosis of type 1 VWD: impact of recent studies
  9. Type 1 VWD or not?
  10. Disclosure of Conflict of Interests
  11. References
  • 1
    Sadler JE. A revised classification of von Willebrand disease. For the Subcommittee on von Willebrand factor of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis. Thromb Haemost 1994; 71: 5205.
  • 2
    Sadler JE, Budde U, Eikenboom CJ, Favaloro EJ, Hill FGH, Holmberg L, Ingerslev J, Lee CA, Lillicrap D, Mannucci PM, Mazurier C, Meyer D, Nichols WL , Nishino M, Peake IR, Rodeghiero F, Schneppenheim R, Ruggeri ZM, Srivastava A, Mongomery RRet al. The Working Party on von Willebrand Disease Classification. Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand factor. J Thromb Haemost 2006; 4: 210314.
  • 3
    Briët E, Sadler JE. Dominant type 1 von Willebrand disease caused by mutated cysteine residues in the D3 domain of von Willebrand factor. Blood 1996; 88: 243341.
  • 4
    Bodó I, Katsumi A, Tuleu EA, Eikenboom JC, Dong Z, Sadler JE. Type 1 von Willebrand disease mutations Cys1149Arg causes intracellular retention and degradation of heterodimers: a possible general mechanism for dominant mutations of oligomeric proteins. Blood 2001; 98: 29739.
  • 5
    Tjernerg P, Vox HL, Castaman G, Bertina RM, Eikenboom JC. Dimerization and multimerization defects of von Willebrand factor due to mutated cysteine residues. J Thromb Haemost 2004; 2: 25765.
  • 6
    Lethagen S, Isaksson C, Schaedel C, Holmberg L. Von Willebrand’s disease caused by compound heterozygosity for a substitution mutation (T1156 M) in the D3 domain of the von Willebrand factor and a stop mutation (Q2470X). Thromb Haemost 2002; 88: 4216.
  • 7
    Schneppenheim R, Federici AB, Budde U, Castaman G, Drewke E, Krey S, Mannucci PM, Reisen G, Rodeghiero F, Zieger B, Zimmermann R. Von Willebrand Disease type 2 M “Vicenza” in Italian and German patients: identification of the first candidate mutation (G3864A; R1205H) in 8 families. Thromb Haemost 2000; 83: 13640.
  • 8
    Goodeve A, Eikenboom J, Castaman G, Rodeghiero F, Federici AB, Battle J, Meyer D, Mazurier C, Goudemand J, Schneppenheim R, Budde U, Ingerslev J, Habart D, Vorlova Z, Holmberg L, Lethagen S, Pasi J, Hill F, Soteh MH, Baronciani L, et al. Phenotype and genotype of a cohort of families historically diagnosed with type 1 von Willebrand disease in the European study, Molecular and Clinical Markers for the Diagnosis and Management of Type 1 von Willebrand Disease (MCMDM-1VWD). Blood 2007; 109: 11221.
  • 9
    James PD, Notley C, Hegadorn C, Leggo J, Tuttle A, Tinlin S, Brown C, Andrews C, Labelle A, Chirinian Y, O’Brien L, Othman M, Rivard G, Rapson D, Hough C, Lillicrap D. The mutational spectrum of type 1 von Willebrand disease: results from a Canadian cohort study. Blood 2007; 109: 14554.
  • 10
    Cumming A, Grundy P, Keeney S, Lester W, Enayat S, Guilliatt A, Bowen D, Pasi J, Keeling D, Hill F, Bolton-Maggs PH, Hay C, Collins P, the UK Haemophilia Centre Doctors’ Organisation. An investigation of the von Willebrand factor genotype in UK patients diagnosed to have type 1 von Willebrand disease. Thromb Haemost 2006; 96: 63041.
  • 11
    Schneppenheim R, Plendl H, Budde U. Luminography – an alternative assay for the detection of von Willebrand factor multimers. Thromb. Haemost 1988; 60: 1336.
  • 12
    Mazurier C, Goudemand J, Hilbert L, Caron C, Fressinaud E, Meyer D. Type 2 N von Willebrand disease: clinical manifestations, pathophysiology, laboratory diagnosis and molecular biology. Best Pract Res Clin Haematol 2001; 14: 33747.
  • 13
    Gill JC, Endres-Brooks J, Bauer PJ, Marks WJ, Montgomery RR. The effect of ABO blood group on the diagnosis of von Willebrand Disease. Blood 1987; 69: 16915.
  • 14
    Tosetto A, Rodeghiero F, Castaman G, Goodeve A, Federici AB, Batlle J, Meyer D, Fressinaud E, Mazurier C, Goudemand J, Eikenboom J, Schneppenheim R, Budde U, Ingerslev J, Vorlova Z, Habart D, Holmberg L, Lethagen S, Pasi J, Hill F, et al. A quantitative analysis of bleeding symptoms in type 1 von Willebrand disease: results from a multicenter European study (MCMDM-1VWD). J Thromb Haemost 2006; 4: 76673.
  • 15
    Rodeghiero F, Castaman G, Tosetto A, Batlle J, Baudo F, Cappelletti A, Casana P, De Bosch N, Eikenboom JC, Federici AB, Lethagen S, Linari S, Srivastava A. The discriminant power of bleeding history for the diagnosis of von Willebrand disease type 1: an international multicenter study. J Thromb Haemost 2005; 3: 261926.
  • 16
    Eikenboom J, Van Marion V, Putter H, Goodeve A, Rodeghiero F, Castaman G, Federici AB, Batlle J, Meyer D, Mazurier C, Goudemand J, Schneppenheim B, Budde U, Ingerslev J, Vorlova Z, Habart D, Holmberg L, Lethagen S, Pasi J, Hill F, et al. Linkage analysis in families diagnosed with type 1 von Willebrand disease in the European study, molecular and clinical markers for the diagnosis and management of type 1 VWD. J Thromb Haemost 2006; 4: 77482.
  • 17
    James PD, Paterson AD, Notley C, Cameron C, Hegadorn C, Tinlin S, Brown C, O’Brien L, Leggo J, Association of Hemophilia Clinic Directors of Canada, D Lillicrap. Genetic linkage and association analysis in type 1 von Willebrand disease: results from the Canadian Type 1 VWD Study. J Thromb Haemost 2006; 4: 78392.
  • 18
    Castaman G, Eikenboom JCJ, Bertina RM, Rodeghiero F. Inconsistency of association between type 1 von Willebrand disease phenotype and genotype in families identified in an epidemiological investigation. Thromb Haemost 1992; 82: 106570.
  • 19
    Casana O, Martinez F, Haya S, Espinos C, Aznar JA. Significant linkage and non-linkage of type 1 von Willebrand disease to the von Willebrand factor gene. Br J Haematol 2001; 115: 692700.
  • 20
    Tosetto A, Rodeghiero F, Castaman G, Bernardi M, Bertoncello K, Goodeve A, Federici AB, Battle J, Meyer D, Mazurier C, Goudemand J, Eikenboom J, Schneppenheim R, Budde U, Ingerslev J, Vorlova Z, Habart D, Holmberg L, Lethagen S, Pasi J, et al. Impact of plasma von Willebrand factor levels in the diagnosis of type 1 von Willebrand disease: results from a multicentre European study (NCMDM-1VWD). J Thromb Haemost 2007; in press.
  • 21
    Di Paola J, Federici AB, Mannucci PM, Canciani MT, Kritzik M, Kunicki TJ, Nugent D. Low platelet alpha2beta1 levels in type 1 von Willebrand disease correlate with impaired platelet function in a high shear stress system. Blood 1999; 93: 357882.
  • 22
    Kunicki TJ, Federici AB, Salomon DR, Koziol JA, Head SR, Mondala TS, Chismar JD, Baronciani L, Canciani MT, Peake IR. An association of candidate gene haplotypes and bleeding severity in von Willebrand disease (VWD) type 1 pedigrees. Blood 2004; 104: 235967.
  • 23
    Lemmerhirt HL, Broman KW, Shavit JA, Ginsburg D. Genetic regulation of plasma von Willebrand factor levels: quantitative trait loci analysis in a mouse model. J Thromb Haemost 2007; 5: 32935.
  • 24
    Souto JC, Almasy L, Soria JM, Buil A, Stone W, Lathrop M, Blanjero J, Fontcuberta J. Genome-wide linkage analysis of von Willebrand factor plasma levels: results from the GAIT project. Thromb Haemost 2003; 89: 46874.