Plasma of patients with Upshaw-Schulman syndrome, a congenital deficiency of von Willebrand factor-cleaving protease activity, enhances the aggregation of normal platelets under high shear stress

Upshaw-Schulman syndrome (USS) is an autosomal recessive disorder characterized by repeated episodes of chronic thrombocytopenia and microangiopathic haemolytic anaemia (MAHA) that responds dramatically to infusions of fresh frozen plasma (FFP). Recent studies have provided consistent evidence that USS is a congenital deficiency of plasma von Willebrand factor-cleaving protease (VWF-CPase) activity and, therefore, unusually large VWF multimers (UL-VWFMs) are present in the plasma. However, the molecular mechanism of the clinical symptoms of USS is not well understood. We studied the relationship between UL-VWFMs and thrombocytopenia in two USS patients by analysing platelet aggregation using a mixture of the patient's plasma and normal washed platelets under high shear stress. Our results clearly showed a remarkably enhanced high shear stress-induced platelet aggregation (H-SIPA) by the patient's plasma. At 24 h after FFP infusion (approximately equal to 10 ml/kg body weight), the enhanced H-SIPA became almost completely normalized but, 2 d later, it began to return to the preinfusion level. These results were in accordance with the change in VWFM patterns. The specific effects of enhanced H-SIPA on VWF, platelet glycoprotein Ib and endogenous ADP released from platelets upon stimulation were confirmed using reagents that specifically inhibit their respective functions. Our present results clearly indicate that thrombocytopenia in USS patients is caused by a combination of the presence of UL-VWFMs, platelets and high shear stress generated in the microcirculation.     

Von Willebrand factor--cleaving protease activity in congenital thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is characterized by microangiopathic haemolytic anaemia (MAHA), thrombocytopenia, fluctuating neurological impairment, renal dysfunction and fever. Both acquired and congenital forms are recognized. Recurrent episodes, which may be predictable (occurring every 21-28 d), are seen in congenital disease and may be treated by infusion with fresh-frozen plasma (FFP). Congenital TTP has recently been associated with deficiency of a novel von Willebrand factor (VWF)-cleaving protease. To investigate whether residual protease activity dictates clinical manifestations, we determined protease activity in three patients with congenital TTP of varying severity. Intrinsic VWF-cleaving protease activity of a range of plasma-derived products was also assessed as one patient had been successfully maintained for many years, initially using an intermediate-purity factor VIII concentrate (Kryobulin) and then cryoprecipitate. All three patients had a severe absolute deficiency of VWF-cleaving protease activity (< 3%) up to 5 months after clinical symptoms. Three relatives were also found to have a mild reduction in protease activity (25-50%). Nevertheless, the intrinsic VWF-cleaving protease activity of plasma-derived products correlated with their clinical efficacy: significant (100%) protease activity was found in FFP, cryosupernatant, solvent-detergent-treated plasma, cryoprecipitate and Kryobulin. Two clinically ineffective factor VIII products (Fahndi and Haemate P) possessed only low protease activity (6.25% and 12.5% respectively). Although this suggests that VWF-cleaving protease activity is central to the pathogenesis of congenital TTP, either small differences in protease activity below 3% or hitherto unknown factors have a profound influence on clinical phenotype. The possible use of factor VIII concentrates in the treatment of this condition also warrants further investigation.     

Does cryosupernatant plasma improve outcome in thrombotic thrombocytopenic purpura? No answer yet

A randomized prospective trial compared cryosupernatant plasma (CSP) to fresh frozen plasma (FFP) for treatment of thrombotic thrombocytopenic purpura (TTP). A total of 236 patients were required: 28 patients were treated with CSP and 24 with FFP within 30 months. There were no differences in survival at 1 month. By day 9, 17 of 26 patients with CSP and 18 of 24 with FFP had a platelet count >100 x 10(9)/l. At entry, von Willebrand factor (VWF) multimers were normal in all patients (range 1.1-3.95 IU/ml). ADAMTS-13 levels showed large variations ranging from 10% to 100% activity. At entry, no individual had <5% VWF cleaving protease. By day 9 (end of cycle), 89% (FFP) and 67% (CSP) had levels >50% of the controls. At 6 months some patients showed inhibitors to the enzyme in spite of adequate or normal platelet counts. The data from this study do not show an apparent advantage to the use of CSP in TTP. A large number of patients will be required to determine appropriate replacement therapy. We were not able to find a statistically significant relationship between the low level of protease activity at presentation of TTP and response.     

ADAMTS13 content in plasma‐derived factor VIII/von Willebrand factor concentrates

Thrombotic thrombocytopenic purpura (TTP) is a microangiopathy syndrome caused by a congenital or acquired deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor (VWF) and thus prevents the formation of platelet‐rich thrombi in the microcirculation. TTP can be fatal if not appropriately and timely treated with the infusion of fresh frozen plasma (FFP) or exchange plasmapheresis, that reverse the process of microangiopathy by removing anti‐ADAMTS13 autoantibodies and replacing functional ADAMTS13. The treatment of TTP with FFP is not free from risks and must be administered in hospitals or clinics, owing to the substantial amount of plasma volume infused or exchanged and the frequent need of catheter application. Moreover, most FFPs are not subjected to treatments to remove or inactivate blood‐borne infectious agents. A number of recent reports indicate that certain plasma‐derived VWF‐factor VIII (FVIII) concentrates are clinically effective in the treatment of congenital TTP. In this study, we measured ADAMTS13 levels in various plasma‐derived VWF‐FVIII concentrates, showing that Koate^®‐DVI (Grifols), contained relatively high amounts of ADAMTS13 and that Alphanate^® (Grifols) was the closest other product in terms of protease content. Koate^®‐DVI contains, on average (five lots tested), 0.091 ± 0.007 Units of ADAMTS13 activity per IU of FVIII. On the basis of this analysis and other reports of VWF‐FVIII concentrate utilization in congenital TTP, potential dosing, and future clinical developments are discussed. Am. J. Hematol. 88:895–898, 2013. © 2013 Wiley Periodicals, Inc.     

Plasma levels of von Willebrand factor regulate ADAMTS-13, its major cleaving protease

ADAMTS-13, the metalloprotease that disposes physiologically of the most thrombogenic multimers of von Willebrand factor (VWF), tends to be low in plasma when VWF is high. We evaluated the behaviour of these two proteins in naturally occurring, experimental and clinical situations associated with VWF levels spanning from undetectable to supranormal. ADAMTS-13 was approximately 10% higher (and VWF 35% lower) in 65 healthy individuals of blood group O than in 65 individuals of groups A, B and AB. Thirty-three patients with type 3 von Willebrand disease (VWD) with undetectable plasma VWF had approximately 35% higher levels of ADAMTS-13 than a comparable group of healthy individuals with normal VWF. When VWF was raised to supranormal levels by desmopressin (DDAVP) in 10 healthy volunteers, ADAMTS-13 decreased by approximately 20%, with no change of the protease in three patients with severe VWD who had no post-DDAVP VWF rise. When VWF was raised from very low to normal levels by the infusion of VWF-containing plasma concentrates in four patients with type 3 VWD and one with type 1 VWD plasma, ADAMTS-13 decreased in parallel. These data show that throughout a large spectrum of plasma VWF levels there is a negative association between this protein and the activity of its major cleaving protease.     

Cryoprecipitate prepared from plasma virally inactivated by the solvent detergent method

There remains a small risk of viral transmission from single-donor blood components such as fresh frozen plasma (FFP) and cryoprecipitate which have not been subjected to a viral inactivation procedure. It is now possible to subject pooled FFP to viral inactivation by the solvent detergent (SD) treatment method, but with some loss of coagulation factors. To establish whether cryoprecipitate prepared from SD plasma would be suitable for the treatment of hypofibrinogenaemia and von Willebrand's disease (VWD), control and SD cryoprecipitate were assayed for factor VIII, von Willebrand factor (VWF) and fibrinogen content. In SD cryoprecipitate, levels of VWF activity and antigen were only 36% and 37% of control values respectively, whereas fibrinogen was 72%. The highest molecular weight multimers of VWF:Ag were absent from both SD plasma and SD cryoprecipitate. SD cryoprecipitate would thus be unsuitable for treating VWD, but would provide an alternative to untreated individual donor units of cryoprecipitate for the treatment of hypofibrinogenaemic states.     

Changes in von Willebrand factor-cleaving protease (ADAMTS13) activity after infusion of desmopressin

von Willebrand factor-cleaving protease (ADAMTS13) cleaves von Willebrand factor (VWF) and regulates its physiologic function. To investigate the relation between ADAMTS13 activity and VWF, we compared ADAMTS13 activity with the VWF-related parameters VWF antigen (VWF:Ag), VWF collagen-binding activity (VWF:CBA), VWF-propeptide, proVWF, and VWF multimeric composition in 10 healthy volunteers and 3 patients with type 1 von Willebrand disease before and after infusing 0.3 microg/kg desmopressin. The VWF-related parameters in the volunteers increased 60 minutes after start of infusion by 3.7-fold for VWF:Ag, 7.2-fold for propeptide, and 2.2-fold for VWF:CBA. Unusually large VWF multimers and traces of proVWF appeared. The ADAMTS13 activity decreased to about half the initial value. After 24 hours values returned to baseline. Patients with type 1 von Willebrand disease showed similar results. We conclude that the inverse correlation between ADAMTS13 and VWF-related parameters suggests a consumption of ADAMTS13 after the desmopressin-induced release of higher multimers of VWF.     

Cryosupernatant as replacement fluid for plasma exchange in thrombotic thrombocytopenic purpura

The current established treatment of thrombotic thrombocytopenic purpura (TTP) is plasma exchange with fresh frozen plasma (FFP). With this treatment, there is a 49% response after seven exchanges and a 78% survival at 1 month. Although the exact cause of TTP is unknown, the presence of von Willebrand factor (VWF) multimers has been implicated in the disease. Accordingly, it has been suggested that cryosupernatant (plasma from which cryoprecipitate has been removed), which is relatively deficient in VWF multimers, might be an effective replacement fluid during plasma exchange.
Patients from six centres were treated by plasma exchange with cryosupernatant. 18 patients who had failed a first course (average 7.7 exchanges) of plasma exchange with FFP, received a further seven exchanges with cryosupernatant. Subsequently, 40 previously untreated patients were exchanged with cryosupernatant.
Of the 18 previously treated patients, 11 responded (defined as an increase in platelet count to >150 × 10⁹/l and no neurological events) after seven exchanges and 15 (83%) of the patients were alive at 1 month. The response rate in the 40 previously untreated patients was 75% at the end of seven exchanges and 95% of the patients were alive at 1 month. These values are significantly different ( P <0.05) from those reported in our earlier study and in other patients concurrently treated at the same centres with FFP when cryosupernatant was not available.
Some patients who have failed to respond to plasma exchange with FFP replacement will respond to further exchange with cryosupernatant. Cryosupernatant replacement may be more effective as first-line treatment of TTP than FFP.     

von Willebrand factor-cleaving protease inhibitor in a patient with human immunodeficiency syndrome-associated thrombotic thrombocytopenic purpura

Antibodies that inhibit von Willebrand Factor (VWF)-cleaving protease activity occur in patients with acute thrombotic thrombocytopenic purpura (TTP) and often persist in the chronic phase. A deficiency of this protease is likely to be responsible for the generation of ultrahigh VWF multimers and influence the formation of intra-arterial platelet aggregates that result in microangiopathic haemolytic anaemia, thrombocytopenia and end in organ failure. This report demonstrates complete deficiency of VWF-cleaving protease and the presence of a concentration-dependent IgG1 inhibitor in the plasma of a patient with acquired immunodeficiency syndrome (AIDS). These data may contribute to understanding the pathophysiology of human immunodeficiency syndrome (HIV)-related TTP.     

Prophylactic fresh frozen plasma may prevent development of hepatic VOD after stem cell transplantation via ADAMTS13-mediated restoration of von Willebrand factor plasma levels

We initially conducted a multicenter, randomized trial (n=43), and subsequently a questionnaire study (n=209) of participating hospitals, to evaluate whether infused fresh frozen plasma (FFP) could prevent the occurrence of hepatic veno-occlusive disease (VOD) after stem cell transplantation (SCT). Forty-three patients were divided into two groups: 23 receiving FFP infusions and 20 not receiving it. VOD developed in three patients not receiving FFP. Plasma von Willebrand factor (VWF) antigen levels were lower at days 0, 7 and 28 after SCT in patients receiving FFP than in those not receiving it, whereas plasma ADAMTS13 activity (ADAMTS13:AC) did not differ between them. Plasma VWF multimer (VWFM) was demonstrated to be defective in the high approximately intermediate VWFM during the early post-SCT phase, but there was a significant increase in high VWFM just before VOD onset. This suggests that a relative enzyme-to-substrate (ADAMTS13/high-VWFM) imbalance is involved in the pathogenesis of VOD. To strengthen this hypothesis, the incidence of VOD was apparently lower in patients receiving FFP infusions than in those not receiving it (0/23 vs 3/20) in the randomized trial. Further, the results combined with the subsequent questionnaire study (0/36 vs 11/173) clearly showed the incidence to be statistically significant (0/59 vs 14/193, P=0.033).     

Evaluation of solvent/detergent-treated plasma in patients with a prolonged prothrombin time

OBJECTIVES: To compare the laboratory and clinical outcome of patients who received solvent/detergent-treated plasma (SDP) and fresh-frozen plasma (FFP). METHODS: A randomized, double-blinded study to assess the ability of SDP and FFP to reduce a prolonged prothrombin time (PT) to 相似文献   

Middle cerebral arterial thrombosis in a patient with hypofibrinogenemia, 5 days after rFVIIa and FFP infusion.

A 13-year-old female patient is presented who had hypofibrinogenemia diagnosed as von Willebrand disease at 5 years of age at another hospital. She was admitted to the department of pediatric hematology with a severe headache, vomiting, and progressive right flaccid hemiplegia and lethargy. Contrast-enhanced computed tomography scan showed subdural hematoma in posterior parietal region of the brain and impending cerebellar herniation. She was given fresh-frozen plasma (FFP) and then activated factor VII (rFVIIa), 80 microg/kg was infused for replacement of von Willebrand factor. The subdural hematoma was emergently drained. The results of coagulation tests before infusion of FFP and rFVIIa revealed hypofibrinogenemia, and FFP was given every 48 hours. The patient recovered dramatically in a few days. Five days after rFVIIa infusion, a magnetic resonance angiography-proven right middle cerebral arterial thrombosis developed. It is an interesting point of discussion whether the middle cerebral arterial thrombosis was provoked as a consequence of rFVIIa and FFP infusion.     

Pharmacokinetics of von Willebrand factor and factor VIIIC in patients with severe von Willebrand disease (type 3 VWD): estimation of the rate of factor VIIIC synthesis

Nine patients (10 infusions) with a confirmed diagnosis of type 3 VWD were infused with von Willebrand factor (human), a preparation of von Willebrand factor (VWF) with a very low factor VIII content. Each patient was infused with one dose of approximately 50 or 100 iu ristocetin cofactor activity (VWF:RiCoF) per kg body weight. Bleeding times were performed during the 24 h period after infusion. Plasma samples were obtained over the 96 h period after infusion and were analysed for factor VIII coagulant activity (FVIIIC), VWF:RiCoF, von Willebrand factor antigen (VWF:Ag), and multimers. The FVIIIC data were analysed by non-linear least-squares analysis assuming constant FVIIIC 'synthesis' and exponential decay. The VWF data were fitted for exponential decay. The average decay rates for FVIIIC, VWF:RiCoF and VWF:Ag were 0.041, 0.061 and 0.056 respectively. The average calculated 'synthesis' rate for FVIIIC was 6.4 u/dl/h. The synthesis of FVIIIC was slightly faster and the decay slightly slower following the infusion of 100 iu VWF:RiCoF/kg than of 50 iu VWF:RiCoF/kg. Correction of the bleeding time was strongly dose dependent. At 4 h post infusion the median bleeding time was 9 min following a dose of 50 iu VWF:RiCoF/kg versus 3 min with a dose of 100 iu VWF:RiCoF/kg. There was no decrease in the bleeding time until the level of VWF:Ag or VWF:RiCoF reached >100 u/dl.     

Decreased levels of von Willebrand factor-cleaving protease in coronary heart disease and thrombotic thrombocytopenic purpura: study of a simplified method for assaying the enzyme activity based on ristocetin-induced platelet aggregation

The haemostatic activity of von Willebrand Factor (VWF) is dependent on VWF multimer stability. Fragments, arising from the proteolytic cleavage of the multimers by VWF-cleaving protease, are ineffective in initiating platelet aggregation. We designed a simple method to determine the protease activity, which was expressed as the reduction in the level of ristocetin-induced platelet aggregation between the inactive enzyme and the enzyme when activated by the addition of calcium. Samples from senior women (n = 14) with chronic coronary heart disease (CHD), age-matched control subjects (n = 15) and young healthy individuals (n = 13), as well as patients with either thrombotic thrombocytopenic purpura (TTP) (n = 2) or von Willebrand disease type 2A (VWD-2A) (n = 2), were examined. The lower protease activity observed in the CHD group, compared with the control subjects, indicated that the increased levels of VWF found in CHD relate to impaired enzyme function. The assessment of TTP patients reconfirmed the reduced protease activity previously observed in this disorder. In VWD-2A, normal enzyme function was observed, suggesting that there is an increased sensitivity of the mutated VWF protein to the protease, rather than an increase in the activity or quantity of the enzyme involved in pathogenesis. In summary, the present simplified method efficiently determines VWF protease activity and is suitable for use in laboratories where platelet aggregation analyses can be performed.     

Plasma therapy in thrombotic thrombocytopenic purpura: review of the literature and the Bern experience in a subgroup of patients with severe acquired ADAMTS-13 deficiency

Based on clinical studies daily plasma exchange (PE) has become the first-choice therapy for thrombotic thrombocytopenic purpura (TTP) since 1991. Recent findings may explain its effectiveness, which particularly may include supply of ADAMTS-13 and removal of anti-ADAMTS-13 autoantibodies and unusually large von Willebrand factor (VWF) multimers. The most preferable PE regimens as well as replacement fluids are discussed and treatment-related adverse reactions are summarized. Proposals for a potential reduction of their frequency and for improvement of treatment efficiency are given. These suggestions are partially based on the experience of our institution in adult patients with severe ADAMTS-13 deficiency (<5% activity), and include (1) continuous calcium-gluconate infusion during PE in order to reduce citrate-related adverse reactions; (2) the evaluation of solvent/detergent-treated (S/D) plasma as replacement fluid in order to reduce adverse events due to fresh frozen plasma (FFP); (3) the evaluation of immunoadsorption in order to increase procedural efficiency in autoantibody removal; and (4) the substitution of ADAMTS-13 by means of recombinant drug instead of plasma.     

Two newborn-onset patients of Upshaw–Schulman syndrome with distinct subsequent clinical courses

Upshaw–Schulman syndrome (USS) is caused by a congenital deficit in ADAMTS13 activity owing to genetic mutations. USS is characterized by severe neonatal jaundice with a negative Coombs test and repeated childhood episodes of thrombocytopenia reversible by fresh frozen plasma (FFP) infusions. We present two patients with USS, both of whom underwent exchange blood transfusions as newborns, although the disease subsequently developed along different clinical courses. USS-CC5 initially received a diagnosis of neonatal jaundice due to fetomaternal ABO incompatibility with an indirect positive Coombs test, which masked the diagnosis of USS. Before prophylactic FFP infusions were initiated, USS-CC5 had chronic thrombocytopenia. In contrast, thrombocytopenia developed in USS-HH4 only in response to infections and spontaneously normalized without FFP infusions. Analyses of the ADAMTS13 genes in USS-CC5 and USS-HH4 revealed compound heterozygotes of p.R398C/p.Q723K and p.Q449X/p.Q1374Sfs, respectively. Analysis of von Willebrand factor (VWF) multimers in plasma samples taken from both patients in remission showed single symmetrical multimer bands, which differ from the triplet structure of bands observed in normal samples. These data suggested that plasma VWF multimers in the patients had not been proteolytically modified. Our results indicate the presence of a previously unknown regulatory mechanism for VWF-dependent high-shear stress-induced platelet aggregation.     

Assays of von Willebrand factor-cleaving protease: a test for diagnosis of familial and acquired thrombotic thrombocytopenic purpura

Endothelial cells secrete von Willebrand factor (vWF) multimers that are larger than those found in the circulating plasma. These very large multimeric forms of vWF, capable of spontaneously binding to and agglutinating the blood platelets under conditions of high fluid shear rate, are degraded by a specific metalloprotease cleaving the peptide bond 842Tyr-843Met of the vWF subunit. The vWF-cleaving protease was found to be deficient in patients with familial thrombotic thrombocytopenic purpura (TTP). The acute events in these patients can be successfully treated and prophylactically prevented by repletion of the missing protease using fresh frozen plasma (FFP). In another, apparently more common, form of TTP, the protease deficiency is due to inhibiting circulating antibodies directed against the vWF-cleaving protease. Therapy of these patients should include immunosuppressive treatment in addition to plasma exchange and replacement with FFP. Normal activity of vWF-cleaving protease was established in patients with a clinically similar disorder: hemolytic-uremic syndrome (HUS). The level of vWF-cleaving protease activity is thus a laboratory parameter that provides important information for the differential diagnosis and treatment of patients with TTP/HUS. Several assays of vWF-cleaving protease have been described and are summarized here.     

Dissociation between the level of von Willebrand factor-cleaving protease activity and disease in a patient with congenital thrombotic thrombocytopenic purpura

Decreased von Willebrand factor (VWF)-cleaving protease activity (<5%) has been implicated in patients with congenital thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (Upshaw-Schulman syndrome) and associated with mutations within the ADAMTS13 gene. In this report, we describe longitudinal studies in a patient with congenital TTP who ultimately developed end-stage renal failure and required plasma therapy from infancy. The patient was deficient in plasma high molecular weight (HMW)-VWF multimers during acute disease but had increased amounts of the HMW-VWF multimers during periods of remission. DNA analysis of this patient detected homozygosity for the R692C mutation on exon 17 of the ADAMTS13 gene, previously linked to congenital TTP. The level of VWF-cleaving protease activity in the patient was remarkably low (<5%) throughout her disease, even after she entered complete remission. However, despite no improvement in the level of VWF-cleaving protease activity, this patient had complete resolution of disease following splenectomy and commencing hemodialysis, without need for ongoing plasma therapy. The patient has remained in remission for over 4 years. These observations suggest that there are other factors in conjunction with severe deficiency of VWF protease activity that participate in the platelet-mediated thrombotic complications and other disease manifestations of congenital TTP. In addition, it is possible that splenectomy could be an effective treatment option for some patients with severe, congenital TTP.     

Repeated infusions of VWF/FVIII concentrate: impact of VWF:FVIII ratio on FVIII trough and peak levels in a rabbit model

Summary. The ratio of von Willebrand factor (VWF) to FVIII differs among available VWF/FVIII concentrates. Repeated infusions of concentrates with a low VWF:FVIII ratio may expose patients with von Willebrand disease to supranormal FVIII levels. The aim of this study was to determine the effects of repeated infusions with two VWF/FVIII concentrates differing in VWF:FVIII ratio on attained FVIII trough and peak levels as well as other pharmacokinetic parameters. Rabbits were randomized to receive multiple 150 IU kg⁻¹ VWF:RCo infusions at 4 h intervals with VWF/FVIII concentrates of a high (Haemate^® P/Humate‐P^®) or low (Wilate^®) VWF:FVIII ratio. Trough plasma FVIII and VWF levels were measured after each infusion. Pharmacokinetic analysis was performed using samples collected frequently after infusion. Mean FVIII trough level after the first Wilate infusion was 50.6 IU dL⁻¹ with a 95% confidence interval (CI) of 43.1–58.2 IU dL⁻¹, compared with 31.8 IU dL⁻¹ (CI, 24.4–39.1 IU dL⁻¹) for Haemate P (P < 0.001). Trough levels progressively increased over the 24 h treatment period in both groups. After the final infusion, mean trough FVIII remained significantly higher (P = 0.002) in recipients of Wilate. Mean peak FVIII concentration after infusion was 67% higher in the Wilate group (167 vs. 100 IU dL⁻¹, respectively; P = 0.002). Mean cumulative exposure to FVIII, as measured by area under the curve, was 84% greater in Wilate‐treated animals. Half‐life did not differ between the two concentrates. Animal model data suggest that exposure to elevated FVIII levels can be reduced through use of VWF/FVIII concentrates with higher VWF:FVIII ratios.     

Von Willebrand factor and ADAMTS13 in arterial thrombosis: a systematic review and meta-analysis

Von Willebrand Factor (VWF) plays an important role in hemostasis by mediating platelet adhesion and aggregation. Ultralarge VWF multimers are cleaved by ADAMTS13 in smaller, less procoagulant forms. An association between high VWF levels and cardiovascular disease has frequently been reported, and more recently also an association has been observed between low ADAMTS13 levels and arterial thrombosis. We reviewed the current literature and performed meta-analyses on the relationship between both VWF and ADAMTS13 with arterial thrombosis. Most studies showed an association between high VWF levels and arterial thrombosis. It remains unclear whether ADAMTS13 is a causal independent risk factor because the association between low ADAMTS13 and arterial thrombosis is so far only shown in case-control studies. Prospective studies are awaited. A causal role for ADAMTS13 is supported by mice studies of cerebral infarction where the infusion of recombinant human ADAMTS13 reduced the infarct size.