Summary.  von Willebrand disease (VWD) is a commonly encountered inherited bleeding disorder affecting both males and females, causing mucous membrane and skin bleeding symptoms, and bleeding with surgical or other haemostatic challenges. VWD may be disproportionately symptomatic in women of child‐bearing age. It may also occur less frequently as an acquired disorder (acquired von Willebrand syndrome). VWD is caused by deficiency or dysfunction of von Willebrand factor (VWF), a plasma protein that mediates platelet haemostatic function and stabilizes blood coagulation factor VIII. The pathophysiology, classification, diagnosis and management of VWD are relatively complex, but understanding them is important for proper diagnosis and management of patients with VWD. These evidence‐based guidelines for diagnosis and management of VWD from the National Heart, Lung, and Blood Institute (NHLBI) Expert Panel (USA) review relevant publications, summarize current understanding of VWD pathophysiology and classification, and present consensus diagnostic and management recommendations based on analysis of the literature and expert opinion. They also suggest an approach for clinical and laboratory evaluation of individuals with bleeding symptoms, history of bleeding or conditions associated with increased bleeding risk. This document summarizes needs for further research in VWF, VWD and bleeding disorders, including clinical research to obtain more objective information about bleeding symptoms, advancements in diagnostic and therapeutic tools, and enhancement in the education and training of clinicians and scientists in bleeding and thrombotic disorders. The NHLBI Web site (http://www.nhlbi.nih.gov/guidelines/vwd) has a more detailed document, a synopsis of these recommendations, and patient education information.

No abstract

Platelet alpha-granules constitute the major rapidly releasable reservoir of thrombospondin-1 in higher animals. Although some fragments and peptides derived from thrombospondin-1 stimulate or inhibit platelet aggregation, its physiologic function in platelets has remained elusive. We now show that endogenous thrombospondin-1 is necessary for platelet aggregation in vitro in the presence of physiologic levels of nitric oxide (NO). Exogenous NO or elevation of cGMP delays thrombin-induced platelet aggregation under high shear and static conditions, and exogenous thrombospondin-1 reverses this delay. Thrombospondin-1-null murine platelets fail to aggregate in response to thrombin in the presence of exogenous NO or 8Br-cGMP. At physiologic concentrations of the NO synthase substrate arginine, thrombospondin-1-null platelets have elevated basal cGMP. Ligation of CD36 or CD47 is sufficient to block NO-induced cGMP accumulation and mimic the effect of thrombospondin-1 on aggregation. Exogenous thrombospondin-1 also reverses the suppression by NO of alphaIIb/beta3 integrin-mediated platelet adhesion on immobilized fibrinogen, mediated in part by increased GTP loading of Rap1. Thrombospondin-1 also inhibits cGMP-mediated activation of cGMP-dependent protein kinase and thereby prevents phosphorylation of VASP. Thus, release of thrombospondin-1 from alpha-granules during activation provides positive feedback to promote efficient platelet aggregation and adhesion by overcoming the antithrombotic activity of physiologic NO.

Patients infected with HIV have an unexpectedly high occurrence of osteonecrosis of the hip. Although screening asymptomatic patients is not warranted, HIV-infected patients with persistent groin or hip pain should be evaluated for this debilitating complication.

We constructed a first-generation adenovirus vector (AVC3FIX5) that we used to assess the rhesus macaque as a nonhuman primate model for preclinical testing of hemophilia B gene therapy vectors. Although we succeeded in our primary objective of demonstrating expression of human factor IX we encountered numerous toxic side effects that proved to be dose limiting. Following intravenous administration of AVC3FIX5 at doses of 3.4 x 10(11) vector particles/kg to 3.8 x 10(12) vector particles/kg, the animals in our study developed antibodies against human factor IX, and dose-dependent elevations of enzymes specific for liver, muscle, and lung injury. In addition, these animals showed dose-dependent prolongation of clotting times as well as acute, dose-dependent decreases in platelet counts and concomitant elevation of fibrinogen and von Willebrand factor. These abnormalities may be caused by the direct toxic effects of the adenovirus vector itself, or may result indirectly from the accompanying acute inflammatory response marked by elevations in IL-6, a key regulator of the acute inflammatory response. The rhesus macaque may be a useful animal model in which to evaluate mechanisms of adenovirus toxicities that have been encountered during clinical gene therapy trials.

Von Willebrand factor (VWF) mediates blood platelet adhesion and accumulation at sites of blood vessel injury, and also carries coagulation factor VIII (FVIII) that is important for generating procoagulant activity. Von Willebrand disease (VWD), the most common inherited bleeding disorder, affects males and females, and reflects deficiency or defects of VWF that may also cause decreased FVIII. It may also occur less commonly as an acquired disorder (acquired von Willebrand syndrome). This article briefly summarizes selected features of the March 2008 evidence-based clinical and laboratory diagnostic recommendations from the National Heart, Lung, and Blood Institute (NHLBI) Expert Panel for assessment for VWD or other bleeding disorders or risks. Management of VWD is also addressed in the NHLBI guidelines, but is not summarized here. The VWD guidelines are available at the NHLBI Web site (http://www.nhlbi.nih.gov/guidelines/vwd).

HIV-infected patients are at approximately 100-fold greater risk of developing osteonecrosis than the general population. Disease progression is slower in asymptomatic patients than in symptomatic patients. Given the high frequency of total hip replacement in symptomatic patients, studies to assess preventive and treatment strategies are essential.

Turecek PL, Mannucci PM. Measurement of von Willebrand factor cleaving protease (ADAMTS-13): results of an international collaborative study involving 11 methods testing the same set of coded plasmas. J Thromb Haemost 2004; 2: 1601-09.Summary. Background: ADAMTS-13 is a von Willebrand factor (VFW)-cleaving protease. Its congenital or acquired deficiency is associated with thrombotic thrombocytopenic purpura (TTP) and more rarely with the hemolytic uremic syndrome. We report on a survey evaluating 11 methods for ADAMTS-13 measurement performed in different labs. Design: Two plasmas, one normal and one from a patient with familial TTP, were mixed at the co-ordinating center to prepare 6 plasmas with 0%, 10%, 20%, 40%, 80% and 100% ADAMTS-13 levels. Each plasma was aliquoted and assembled into sets of 60 (coded from 1 to 60), each containing 10 copies of the original 6 plasmas. Plasmas were frozen and shipped in dry ice to 10 labs with a common frozen reference plasma. Laboratories were asked to measure ADAMTS-13 with their methods. Results were sent to the coordinating center for statistical analysis. Results: Of the 10 methods performed under static conditions 9 were quantitative and one was semiquantitative. One method performed under flow conditions evaluated the extent of cleavage of endothelial cell-derived ultralarge VWF string-like structures and expressed results as deficient, normal, or borderline. Linearity (expected-vs-observed levels), assessed as the squared correlation coefficient, ranged from 0.98 to 0.39. Reproducibility, expressed as the coefficient of variation for repeated measurements, ranged from <10% to 83%. The majority of methods were able to discriminate between different ADAMTS-13 levels. The majority were able to detect the plasma with 0% level and some of them to discriminate between 0% and 10%. Overall the best performance was observed for three methods measuring cleaved VWF by ristocetin cofactor, collagen binding, and immunoblotting of degraded multimers of VWF substrate, respectively. The poor interlaboratory agreement of results was hardly affected by the use of the common standard. The method performed under flow conditions identified the plasmas with 0%, 10%, 20% and 40% activity as deficient in 7, 5, 1 and 3 of the 10 replicate measurements. The plasmas with 80% and 100% were identified as normal in all of the 10 replicate measurements. Conclusions: The survey shows varied performance, but supports an optimistic view about the reliability of current methods for ADAMTS-13.