SCIENTIFIC SUBCOMMITTEE SESSION
6 July 2007 Palexpo, Geneva, Switzerland  

von Willebrand Factor

Chair: D. Lillicrap (Canada)
Co-Chairs: T. Abshire ( USA), G. Castaman (Italy), J. DiPaola (USA), J. Eikenboom (The Netherlands), E. Favaloro (Australia), A. Federici (Italy), A. Goodeve (UK), B. Lämmle (Switzerland), R. Schneppenheim (Germany)

335 people in attendence

Working Group on VWF assays in the diagnosis of VWD (Christine Lee, UK)

Plasmapheresis of 6 patients with different types of VWD. Prospective study involving 32 laboratories worldwide. Laboratories from 17 countries participated. Laboratories reported a median 6 correct diagnoses. 16 laboratories could perform all of VWF tests. The Lyophilized plasma samples collected for this study maintained their multimeric patterns. All 5 assays are required for optimal diagnostic evaluation. The more tests performed the better. At low levels of VWF the RCo:Ag ratio is problematic.

VWF collagen binding assays (Emmanuel Favaloro, Australia)

A number of laboratories performed VWF:CB in the recent prospective assessment of diagnostic tests for VWD. Discussed the relative merits of the VWF:CB in the VWD diagnostic samples. Bovine and equine tendon material is preferred (type 1 collagen). Can give results that are more sensitive than the VFW:RCo. Discussion of the potential of alternative forms of collagen.

VWF propeptide (Bob Montgomery, USA: Jan van Mourik, Netherlands)

The VWF propeptide can identify patients with accelerated clearance of VWF. Should the measurement of the VWF:pp and the VWFpp/VWFAg be standardized? Prior assessment of the VWF:pp with other existing ISTH and WHO standards for VWF has shown good consistency. The pp:Ag ratio is also consistent. There is an influence of the ABO blood group on the pp:Ag ratio. There is a need to involve more laboratories to extend the assessment of the VWF:pp assay. We need to agree upon the accepted nomenclature for the VWF:pp. Measurement of the VWF:pp and VWF:Ag also allow assessment of endothelial cell perturbation. The respective half-lives of the VWF:pp and VWF:Ag are 2.5 and 12 hrs. The assays of VWF:Ag and VWF:pp can be used to diagnose acquired VWD where VWF is cleared prematurely from the plasma. The plasma level of VWF:pp is 5.5 nmol/L.

VWF Standards (Tony Hubbard, UK)

The current VWF plasma standard is the 5 th WHO FVIII/VWF plasma standard (202/150 established in 2003). 700 ampoules of this standard are distributed each year. There is a need to replace this plasma standard by end of 2009. The 1 st WHO VWF concentrate standard (00/514) was established in 2001. There have been problematic discrepancies using collagen binding assays with the VWF concentrate standard. Collagen binding assays are very sensitive to the HMW multimers. It is important to correlate concentrate and plasma units for diagnosis and therapeutic purposes. The requirement of the highest MW VWF multimers is still uncertain in therapy. Proposal for a 2nd VWF concentrate with a lack of HMW multimers to try to address the issue of the collagen binding assay discrepancies.

Standardization of VWF propeptide using SSC Lot#3 standard. It is proposed that this initially be undertaken by a small number of laboratories – 5/6 labs. Future international assessment of the VWF:pp standardization. There are currently also two different assays that have been developed in the laboratories of Drs. Montgomery and Van Mourik. There appear to be some pre-analytical factors that will alter the assay results. Working groups need to be established for propeptide measurement and for the use of collagen binding assays in standardizing VWF concentrates. The committee voted in favor of the formation of these working groups.

Acquired von Willebrand Syndrome - aVWS (Augusto Federici, Italy)

There was an initial discussion of the diagnostic background and the associated diseases and the assays needed to make the diagnosis. There is a need for better assays to identify anti-VWF autoantibodies. A working group is already in place to evaluate this diagnosis. An online registry has been established for Acquired VWS. 3 centers have enrolled 12 patients into the online registry. There is an interest in using the registry for assessment of the frequency of aVWS. MGUS and ET were the most frequent accompanying conditions. Also need to assess incidence of aVWS in association with anti-phospholipid syndrome. Finally, there is a need to evaluate novel therapies for aVWS.

ADAMTS13 assays ( Koichi Kokame, Japan)

There was a discusion of the various ADAMTS13 assay methodologies that have been developed. All are difficult to use in the clinical laboratory. An international interlaboratory study has been performed and reported but there still needs to be advances for the reliability of this test. There was a description of the VWF 73mer substrate assay using a 73mer peptide sequence around the ADAMTS13 cleavage site. This assay incorporates a FRET readout and is a single step assay. In a large population study, women had higher levels of ADAMTS13 than males. The cause of this variance is as yet unexplained.

ADAMTS13 resistance (Reinhard Schneppenheim, Germany)

The effect of variation of the VWF substrate on ADAMTS cleavage was discussed, with a consideration of the concept of a more resistant VWF molecule. Sequence variation in the A1 region has been shown to produce ADAMTS13 resistance. Type 2B rVWF appears to be ADAMTS13 resistant. In some type 2B mutants this ADAMTS13 resistance is profound. The type 2B New York/Malmo variant is ADAMTS13 resistant. There is a possibility that this could also enhance VWF clearance. This phenotype should be considered in TTP patients in whom ADAMTS13 deficiency is not present. In these patients, A1 domain VWF sequencing should be performed.

TTP - ADAMTS13 mutation registries (Johanna Kremer Hovinga and Bernhard Laemmle, Switzerland and Yoshihiro Fujimura, Japan)

There was a description of the Berne and Japanese experiences with Upshaw-Schulman Syndrome and other forms of thrombotic microangiopathy. Both presenters summarized the clinical experience they had documented. There is now an extensive molecular genetic experience with this condition. There is a proposal for an international registry to improve international awareness, to improve genotype-phenotype correlations and to learn more about the natural history of TTP. Beware the re-reporting of the same patients in the literature. Some patients are studied repeatedly. The committee voted in favor of establishing an international TTP registry. There was further discussion of thrombotic microangiopathic pathologies in 783 patients from Japan. There had been extensive investigation to evaluate the causative pathologies in these cases. Note that acquired TTP can occur in children. The outcome of these cases is poor. Diagnosis is not easy and sometimes wrong.

Standardized Bleeding scores (Francesco Rodegheiro, Italy and Paula James, Canada)

There was a review of the history of bleeding scores by the SSC and other bodies. There have been previous publications on this issue from the SSC. There is already a bleeding score questionnaire available at the VWF ISTH website. Ideal features of a bleeding score were described. There is no current ‘gold standard” for mild bleeding in particular. The aim of this initiative is to improve diagnosis, treatment and communication about bleeding within the community. In Canada, the original Vicenza survey was condensed to be able to administer this in 5-10 mins. This maintains a -1 to +4 scoring system and has positive scores of >+3 in males and >+5 in females. Data on >230 subjects was presented from 3 ongoing studies to assess the application of this bleeding score. There was a proposal for the establishment of a joint working group (with the pediatric SSC) to develop guidelines for a quantitative bleeding score. The committee voted in favor of this proposal.

Report on DDAVP study in VWD ( Giancarlo Castaman, Italy/Stefan Lethargan, Denmark)

The initial part of this international prospective study has been completed. 245 patients have been enrolled. The study will continue as the enrolled patients are followed with therapeutic administration of DDAVP. There are all types of VWD enrolled in the study

Report on Prophylaxis in VWD (Tom Abshire, USA and Eric Berntorp, Sweden)

This is a prospective international multicenter study. Central data collection center will occur in the USA and there is a central laboratory site in Sweden. The study will evaluate the effects of prophylactic therapy on joint bleeding, mucosal bleeding, epistasis and menorrhagia. This is a prospective non-randomized study. Any licensed VWF product can be used for the prophylactic therapy. The treatment strategy will involve a dose-escalation approach. Dose escalation will be carried out based on defined bleeding events. IRB review currently in progress at several centers. Enrolment will start later in 2007.

Report on type 3 VWD Registry (Augusto Federici, Italy and Paul Giangrande, UK)

There is need for a much better estimate of the prevalence of severe type 3 VWD. We also have no idea of how many of these patients have anti-VWF antibody development. In some of these antibody +ve patients episodes of anaphylaxis have been reported with the infusion of VWF concentrate. There is a significant need for a standardized anti-VWF antibody assay. Proposal for a multicenter, multinational study involving both developed and developing countries. This will involve an outreach study in which larger expert centers will assist smaller centers in the diagnosis and therapy of this condition. There is an aim to enroll approximately 500 patients for analysis.

VWF mutation and polymorphism database (Anne Goodeve, UK and Dan Hampshire, UK)

A summary was provided of the updated web-based VWF mutation database. There has been a recent significant increase in the reporting of VWD mutations. These include all types of VWD. Mutations are found across the VWF gene and involve all types of mutation. Some new categories of sequence variation have been added to the database. There was a call for the submission of newly acquired data.

VWD type 2B and Platelet type VWD Registry ( Maha Othman, Canada)

There was a description of the background of the problem. The clinical implications of the two diagnoses was highlighted. There is no idea what the frequency is for PT-VWD. Discrimination can be done with phenotypic studies or by genotype. A proposal was made for a new international registry for PT-VWD. The committee voted to support the establishment of this registry.