Von Willebrand Factor

July 12, 2003
14:00 to 18:00
Hall 11
The International Convention Center, Birmingham

Chairman:  R. Montgomery, USA
Co-chairs:  G. Castaman, Italy; D. Lillicrap, Canada; J. Eikenboom, The Netherlands;
A. B. Federici, Italy; A. Goodeve, UK; P. A. Kouides, USA;
C. Mazurier, France; F. Rodeghiero, Italy

Summary of VWF Subcommittee Approvals and Working Parties
  1. The Subcommittee unanimously approved the FVIII VWF standard proposed by A. Hubbard and the IBSC.  
  2. The working Party study of intra laboratory assay standardization of the ADAMTS13 protease.  All but 2 centers have completed their assays and we expect a final report at the next SSC Meeting.  (P.M. Mannucci, Chair)
  3. The working party on diagnosis of VWD and variant VWD is in active progress and should be able to send lyophilized patient plasmas to study centers this fall and expects to have accomplished this by next SSC Meeting.  (A. Federici, Chair)
  4. The working party on response to DDAVP has developed a web site and will be operational soon.  (A. Federici, Chair)
  5. Approved a new working party to re-examine the current adequacy of VWD classification as a 10 year follow-up to the VWF Subcommittee’s current classification.  A formal report is expected by the next SSC Meeting.   (J.E. Sadler, Chair)
  6. Approved a Joint Working Party with the Platelet Immunology Subcommittee to develop a registry of type 2B VWD and Platelet-type VWD because of their association with thrombocytopenia.  (Jim Bussel, New York)
Issues Identified as Requiring Further Study or Standardization
  1. Type 1 VWD as a discrete disease or disorder versus VWF as a continuous risk factor and how this should be approached internationally.
  2. Standard characterization of VWF concentrates and the importance of multimer size in clinical efficacy. (Work in progress, U. Budde and C. Mazurier)
  3. Definition of genetic modifiers that affect hemorrhagic expression in type 1 VWD.
  4. Further identification and understanding about FVIII levels in treatment products and the impact on thrombosis with VWF concentrate administration.  (Work in progress, P.M. Mannucci)
  5. Potential for standardization of the VWF:RCo assay with recombinant, well-defined ELISA assays.
  6. Consideration of PFA or other shear-related endpoint assays and their use a replacements for bleeding times in clinical evaluation and clinical efficacy of treatment.
The VWF Subcommittee was attended by about 375 attendees at the first session and 275 participants for the second session.  They actively participated in the discussion of the various talks provided by the program.  This is the final VWF Subcommittee meeting under R. Montgomery as Chair.  The following represents the minutes of the program.


Multinational/Epidemiological Study Updates   Anne Goodeve, United Kingdom

Dr Goodeve presented the current ISTH VWF SSC electronic database. The database replaced the original version, maintained in the USA, during 2002. All data from the original was transferred. The database now lists 291 mutations, 72% of which are missense. These are located throughout the VWF gene from exons 3-52, the majority (55%) are in the A domains. The database also lists 143 polymorphisms. Both mutation and polymorphism listings can be queried. The large sequence resource section has complete human genomic and cDNA, many other species cDNA and alignments between cDNA and amino acid sequence for human and mouse, and for human gene-pseudogene. Additionally the database has example multimer gels, information for patients, A1 and A3 domain molecular models and recommended nomenclature for mutations and polymorphisms and for VWF and its activities.

Dr Goodeve then presented a brief update on the progress of the collaborative European study Molecular and clinical markers for the diagnosis and management of type 1 VWD. 154 families comprising 743 family members plus 1143 normal individuals were recruited into the study. Mean levels of VWF:Ag and VWF:RCo in index cases and in affected family members were approx 42 and 40 IU/dl respectively, compared to close to 100 IU/dl in unaffected family members and controls. Multimer analysis in 101 families indicated that 51 had a pattern consistent with type 1 VWD, 28 had a 2A (IIE) pattern and 8 had a 2M pattern. 2 index cases had reduced VWF:FVIIIB consistent with 2N VWD and 4 index cases had a heterozygous pattern. Mutation analysis initiated in 150 index cases has identified 100 candidate mutations to date in 83 individuals. 71% are missense mutations, splicing errors, small insertion and deletions, nonsense mutations and 5’UTR changes were also identified in small numbers of patients. The study aims to provide a comprehensive analysis of patients diagnosed with type 1 VWD and to make recommendations for future enhanced diagnosis.

Working Party Updates  Claudine Mazurier, France

A. Federici (coordinator with K. Friedman) presented an update of the Working Party on VWD diagnosis. The main achievements since SSC Boston July 2002 are: 1) Financial support from several companies (Account name = ISTH) to cover the costs, 2) Data of the pilot study on the comparison of VWF:Ag, VWF:CB, VWF:RCo levels and VWF multimers  before and after lyophilization of a small plasma volume from 2 (type 2A and 2B) VWD patients , 3) London Ethical Committee approval for plasmapheresis (600 ml from 6 VWD patients and 2 controls). Enrolment of 30 labs (30 or 40 % in developing countries) is open. The list of participating labs is foreseen to be available by the 15th September 2003 and the lyophilized samples by 15th January 2004.

A. Federici (coordinator with C. Lee and S. Lethagen) reported on the Working Party on desmopressin (DDAVP) in the management of VWD. The prospective observational study is organized on behalf of ISTH-SSC on VWF and AICE (Italian Association of Hemophilia Centers) to evaluate worldwide the clinical efficacy of DDAVP in type 1 and 2 VWD patients. The enrolment started in Milan on May 15th 2003. The files for inclusion of centers and the final CRF version  will be available on the www.ddavp-invwd.it web site.


Diagnostic Testing of VWF  David Lillicrap, Canada

In the first session relating to diagnostic testing for VWD, Tony Hubbard presented details of the new 5th International Plasma Standard for FVIII/VWF.  This plasma has been collected from a pool of 22 normal donors and after immediate freezing has been aliquoted into 5,500 ampoules.  The 5th International Plasma Standard has a FVIII:C value of 0.68 U/mL, VWF:Ag of 0.91 U/mL, VWF:RCo of 0.78 U/mL and a VWF:CB of 0.94 U/mL.  The multimer profile of the Standard is normal.  The 5th International Plasma Standard received unanimous approval from the sub-committee.

Connie Miller presented data from studies in African Americans highlighting ethnic differences in VWF indices and in platelet function.  In the first of two presentations relating to mulitmeric analysis of VWF, Ulrich Budde described a comparative quantitative study of multimer testing performed in his laboratory and that of Claudine Mazurier.  Although the ranking of samples for their HMW mulitmeric content was the same in both laboratories, the absolute values for HMW mulitmeric content was significantly different.  Dr. Budde has proposed a prospective study of this issue in 15 laboratories.  Dr. Trong next described a novel method for multimer analysis involving electrophoretic quasi-elastic light scattering.  This methodology can currently provide a quantitative assessment of multimer size that has a 3-fold resolution improvement over current gel-based electrophoresis and has the potential of providing results from a plasma sample in 20 seconds.

Presentations from Drs. Federici, Favaloro and Seitz provided more information concerning the utility of the collagen binding assay in VWD testing.  There is growing evidence to indicate that this test would provide a complement to the VWF:RCo and multimer analysis in evaluating type 2 VWD variants.  Finally, Hans Deckmyn described a novel GpIb binding assay for VWF in which the GpIb fragment is provided by plasma glycocalicin.  With intra- and inter-assay CVs of <10% and a sensitivity of 0.0005 U/mL this assay appears to have significant promise as an alternative to the VWF:RCo assay.  

Potpourri Session  Giancarlo Castaman, Italy

G. Castaman presented the ad interim results with PFA-100 evaluation in the European study MCMDM-VWD1. So far, data from 263 members of 96 families with type 1 VWD recruited in 9 different EU Centers were available. By analysing the data with  ROC methodology, it appears that probably PFA system is able to identify a significant greater proportion of patients with type 1 VWD in comparison with bleeding time. ADP and Epinephrine cartridges were similarly effective to this purpose. C. Hayward presented the Hamilton experience with PFA-100 in the screening of inherited bleeding disorders. The system was superior to BT in diagnosing VWD, but it appeared to have low specificity and sensitivity in some platelet disorders. Furthermore, clinicians feel further testing would be required, regardless of CT results. Cost is also an important issue. D. Nugent presented data on PFA-100 system in the USA. The system is used to screen not only for inherited coagulation or platelet disorders, but also for monitoring effective inhibition of platelet function with antiplatelet agents in some clinical situations. Probably, a refinement of the more appropriate use of the system appears necessary. A. Tripodi presented the methodology for a multicenter study for the standardization of ADAMTS 13 assay. A preliminary survey on the methodology used in several laboratories showed a large heterogeneity of the methods used. First results are anticipated to be availbale for the next SSC meeting. P.M.Mannucci reported an additional case of venous thromboembolism in an older VWD patient treated with VIII/VWF concentrate during high-risk surgery without anti-thrombotic prophylaxis. Very high FVIII:C levels were attained during the post-operative period, despite a RiCof of 100 %. D. Bowen presented results on the relationships between blood group and VWF proteolysis in plasma. Blood group O shows enhanced proteolysis, while A and AB groups showed reduced time-course proteolytic pattern. The Tyr1584Cys change in VWF seems to be associated  with an increased susceptibility to proteolytic attack by ADAMTS 13.


VWD – A disease or a risk factor Jeroen Eikenboom, Netherlands, Chair

In this session the clinical significance and appropriate management of low VWF levels were discussed. Evan Sadler proposed a two-tiered approach, dividing subjects into a small group with "VWD type 1" and a much larger group with "low VWF." The diagnosis of VWD type 1 would apply to patients with exceptionally low VWF levels who are likely to experience significant bleeding symptoms and frequently have mutations in the VWF gene. The category of low VWF would apply to persons with modest decreases in VWF level that may associate coincidentally with bleeding, and in whom a genetic basis for the low VWF level usually cannot be identified. This risk management strategy would be analogous to that applied already to risk factors for cardiovascular disease. Implementation of such a strategy will require more data on the relationship between VWF level and the risk of bleeding in specific clinical settings. Francesco Rodeghiero argued that VWD type 1 is a clinically relevant diagnosis when based on family investigation. The high prevalence (up to 10-20 %) of isolated, often trivial, very mild bleeding symptoms in normal population together with a 2.5 % prevalence of low VWF level by definition predicts that about 0.5 % (20 % X 2.5 %) of such cases in normal population could be detected by chance. However, this situation is not representative of the average patient referred to a specialized center (reasonably less than 1 % of  normal). In this case, the rate of false positivity by chance falls below 1 / 4,000. For a definite diagnosis, family investigation is required. We propose that appropriate selection of patients on the basis of personal and/or familial history for laboratory diagnosis of VWD is crucial for producing a clinically relevant and useful diagnosis.

Diagnosis/classification issues  Augusto Federici, Italy

Enigmas in VWD diagnosis was presented by U, Budde  He reported that by using his sensitive mulitmeric assay more type 2 defects can be identified among previously type 1 VWD: a large number of 2A especially with the subtype 2A/IIE are present.  Issues to be addressed: 1b/2A; 1/2M.  VWF gene linkage with low VWF levels was presented by J. Eikemboom. He described the results of recent published studies in VWD Italian and British families and he showed that linkage cannot be demonstrated in all of them. European and Canadian studies ongoing can provide additional information.  Genetic Modifiers of VWD was presented by J. Di Paola. He described his methodology to apply specific platelet polymorphisms in different racial population.  T. Kunicki presented his recent data on platelet SNPs in a group of 15 well characterized families with type 1 VWD enrolled in Milan, as a part of the families of the European Study MCMDM-1VWD. Some of these SNPs seem to correlate with the bleeding score.  At the end of the session A.B. Federici proposed the WP on VWD classification with the aims to update the previous classification by J.E. Sadler. J.E. Sadler agreed to chair this WP together with the Chairman and Co-Chairmen of this SSC on VWF

Clinical Assessment Tools and Treatment Issues  Peter Kouides, USA

Drs. Castaman, Miller, and Kouides summarized their work with clinical data assessment forms.  In light of the on-going discussion/topic in this SSC of von Willebrand factor as a risk factor for bleeding as opposed to a being a marker of disease, this session was convened in order to clarify, establish and address the future development of clinical tools in assessing the degree and risk of bleeding. An international perspective was presented beginning with a study of VWD families presented by Dr. Alberto Tosetto of bleeding symptoms in obligatory Type 1 carriers and affected Type 1 patients; surprisingly cutaneous bleeding proved to be the most discriminatory symptom followed by dental related bleeding then surgical related bleeding; equally surprising was the relative low sensitivity of menorrhagia. Studies are on-going in validating algorithms for diagnosis and management of VWD based on this analysis. Dr. Connie Miller then presented the data from the Centers for Disease Control in the study of 102 women registered at Hemophilia Treatment Centers in the US. Four bleeding symptoms were more prevalent in the VWD patient than controls: heavy menstrual bleeding, bleeding after minor injuries, bleeding after surgery and excessive gum bleeding. Based on this a predictive tool has also been developed and is undergoing validation as is a similar predictive tool (based on multi-regression analysis incorporating age, history of anemia, history of dental or surgical related bleeding, decreased quality of life during menses) from studies in Rochester NY USA presented by Dr. Kouides. Dr. Kouides also presented data from Rochester NY, CDC Atlanta and Royal Free London on bleeding symptoms in menorrhagia patients. It was emphasized that there is a need to pool data of symptoms from the various VWD menorrhagia prevalence studies worldwide in correlating those symptoms with the measurement of menstrual flow and the VWF level in predicting menorrhagia risk in relation to the VWF level.  Dr. Michiels reviewed correlation of response to DDAVP based on the VWF:Ag/VWF:RCo ratios in confirming further the diagnosis of VWD. Labeling of VWF concentrates was also reviewed with the point made that there is need of further study not necessarily of laboratory parameters after infusion of VWF containing concentrates but of clinical efficacy. Dr. Kessler made several recommendations for clinical efficacy of VWF concentrates: use a central laboratory independent of industry, need for back-up samples, importance of mulitmeric analysis over surrogate tests, inclusion of genotype in response  analysis, screening for hypercoaguable states if positive family history and need for accurate surgical assessment., Lastly, Dr. Bussell presented a joint proposal on behalf of the Platelet subcommittee on a study of Type 2B VWD in accruing further clinical data such as the severity of symptoms and treatment data such a the safety of DDAVP.

Revised and submitted 7-27-03
Robert R. Montgomery, Chair