A Novel VWD Variant Identified in a Multi-Generational Canadian Ojibway Kindred with a Type 2B VWD Phenotypic Expression

Introduction: Type 2 VWD is caused by variants in the von Willebrand factor (VWF) gene leading to impaired function. Distinction between subtypes of Type 2 has traditionally relied on a panel of assays including VWF antigen (VWF:Ag), VWF ristocetin-cofactor activity (VWF:RCo), VWF multimers, and Factor VIII (FVIII:C). In type 2A, there is either impaired synthesis or accelerated degradation of the more adhesive VWF high molecular weight multimers (HMWMs). In type 2B, enhanced VWF-platelet interactions result in binding and removal of the HMWMs, impairing platelet adhesion. Type 2B VWD can manifest spontaneous platelet agglutination and thrombocytopenia. The inheritance patterns of Type 2A and 2B VWD are generally described to be autosomal dominant and fully penetrant. We identified a multigenerational Canadian First Nations Ojibway kindred with VWD harboring a missense variant in exon 28 (A>T transversion at nucleotide 4898), leading to a single amino acid substitution (p.Asn1633Ile). Some individuals in the kindred are heterozygous, and some homozygous, for the causative variant. Objectives: The objective of this case series are to describe the genetic basis and pattern of inheritance of this variant of VWD, and to characterize the laboratory hemostasis characteristics in the affected individuals. Methods: A retrospective case review was conducted on all affected individuals in the kindred known or suspected to harbour this variant. There were 20 individuals seen at our centre over 32 years who were included in this study. We collected clinical and laboratory data to characterize the bleeding phenotype. Results: Sixteen of the 20 individuals in the study were known or inferred to be heterozygous, and 4 were homozygous. We were able to examine laboratory hemostasis in ten individuals in the study (Table 1). The platelet count, FVIII:C and VWF:Ag levels were within or slightly above reference range for all individuals. In the heterozygous individuals, VWF:RCo was mildly reduced, VWF multimer testing showed loss of HMWMs, and ristocetin-induced platelet aggregation (RIPA) testing normal aggregation to a higher dose (1.25 mg/ml), a pattern consistent with mild Type 2A VWD (Table 1). In homozygous individuals, VWF:RCo was markedly reduced, and while RIPA was minimal with low-dose ristocetin, aggregation to the higher dose was normal despite the very low ristocetin cofactor activity in the plasma. The PFA-100 (collagen-epinephrine) closure times were markedly prolonged in the homozygous subjects and in one heterozygous subject, exceeding 300 seconds. Discussion/Conclusion: This novel VWF variant confers a laboratory phenotype consistent with type 2A VWD in the heterozygotes. Homozygotes have more severely impaired hemostatic function. The conventional hallmark of type 2B VWD (hyperresponsiveness to low-dose ristocetin) was not seen, but the fact that full aggregation was obtained in homozygotes despite ristocetin cofactor activities of only 5-6% in the plasma suggests some degree of hyperaggregability, and hence a phenotype more in keeping with Type 2B than 2A. In the future, it would be interesting to see how this missense variant affects GP1b binding to VWF, as RIPA and VWF:RCo are not entirely comparable assays. Disclosures No relevant conflicts of interest to declare.

von Willebrand factor variant D1472H has no effect in mice with humanized VWF-platelet interactions

The von Willebrand factor ristocetin cofactor activity assay (VWF:RCo) is used for diagnosis of von Willebrand disease (VWD) because of its ability to evaluate VWF binding to platelets. VWF sequence variant p.D1472H is associated with lower VWF:RCo levels in the absence of associated bleeding symptoms, indicating the VWF:RCo may not be accurate for characterizing VWF function in individuals with this variant. Thus, this study aimed to determine the implications of the variant on VWF functioning in vivo. Mice were engineered with humanized wild-type (WT*) VWF A1/A2 and VWF with the p.D1472H (1472H) variant along with humanized platelet GPIbα and bred to homozygosity. VWF antigen and VWF binding to GPIbα were measured using enzyme-linked immunosorbent assay. Gel electrophoresis was used for VWF multimer analysis. Tail bleeding assays were performed at a 3-mm defined length. Normal VWF multimers were preserved in both WT* and 1472H mice. VWF expression was normal in the WT* and 1472H mice, and VWF binding to GPIbα did not statistically differ between the groups. Additionally, tail bleeding times were similar for WT* and 1472H mice. These results show the p.D1472H variant does not impair hemostasis in mice, and support the conclusion that p.D1472H is a normal variant in humans.

The possibility to obtain reagent from platelet concentrates with long storage time for determination of von Willebrand factor ristocetin cofactor activity (vWF:RCo)

Введение. Фактор Виллебранда (ФВ) является важным компонентом системы гемостаза, и отклонение от нормы его содержания или состава вызывает развитие различных типов болезни Виллебранда. Определение ристоцетин-кофакторной активности ФВ (ФВ:РКФА) является особенно значимым при выявлении таких типов болезни Виллебранда как 2А, 2В и 2М, при которых содержание антигена ФВ находится в нормальных пределах, а ФВ:РКФА значительно снижена. Цель исследования: получение реагента для измерения ФВ:РКФА из концентратов тромбоцитов с длительным сроком хранения, обеспечивающего правильность диагностики. Материалы и методы. Функционально полноценные тромбоциты получали из донорских тромбоцитарных концентратов со сроком хранения 7–14 суток. Результаты. При создании реагента для измерений ФВ:РФКА нами был подобран метод отбора функционально полноценных донорских тромбоцитов для получения фиксированных формальдегидом клеток. На основе таких тромбоцитов был разработан реагент, позволяющий измерять ФВ:РКФА с использованием как агрегационного, так и агглютинационного метода. Выявлено соответствие результатов определения ФВ обоими методами с коэффициентом корреляции 0,96. Проведена оценка агрегационного метода измерения ФВ:РКФА по результатам участия в международной программе внешнего контроля качества UK NEQAS for Blood Coagulation (Великобритания). Заключение. Показано, что использование полученного из фиксированных тромбоцитов реагента позволяет правильно измерять ФВ:РКФА. Introduction. Von Willebrand factor (vWF) is an important component of hemostatic system and deviations from the norm of its content or composition are the cause of various types of von Willebrand disease development. Determination of ristocetin-cofactor activity of vWF (vWF:RCo) is particularly important for identifying 2A, 2B and 2M types of von Willebrand disease, in which the content of vWF antigen is within the normal range, and vWF:RCo signifi cantly reduced. Aim: to obtain a reagent for the measurement of vWF:RCo from platelet concentrates with a long shelf life, providing correct diagnostics. Materials and methods. Fully functional platelets were obtained from donor platelet concentrates with a shelf life of 7–14 days. Results. We discovered the method for selection of fully functional donor platelets to produce formaldehyde-fi xed cells. On the basis of these platelets we developed a reagent that allows to measure vWF:RCo using both aggregation and agglutination methods. The appropriateness was found between the results of vWF determination by both methods with a correlation coeffi cient 0.96. The aggregation method of measuring vWF:RCo was evaluated by a result of participation in the international program of external quality control UK NEQAS for Blood Coagulation (United Kingdom). Conclusion. It is shown that the use of a reagent obtained from fi xed platelets allows for the correct measurement of vWF:RCo.

Successful Management of Pregnancy with Severe Von Willebrand Disease in a Jehovah's Witness with Recombinant Von Willebrand Factor

Background: Von Willebrand disease (vWD) is the most common inherited bleeding disorder with a reported prevalence of 1% in epidemiological studies and symptomatic prevalence of 1 in 10,000. Pregnancy in vWD is associated with increased bleeding risk particularly postpartum hemorrhage. Treatment options include desmopressin acetate (DDAVP), plasma derived factor concentrates and antifibrinolytic agents. Human Recombinant von Willebrand factor (vWF) (Vonvendi®) has been approved in the United States for on demand treatment and perioperative management of adults with vWD. It has been shown to maintain sustained levels of VWF activity but requires co-administration with FVIII to achieve adequate FVIII levels. Recombinant VWF is an option for patients who refuse blood for religious reasons. Case: Here we describe a 39 year old patient in her third pregnancy who is a Jehovah's Witness. Consent was obtained from the patient for this report. She was initially diagnosed with von Willebrand`s disease at the age of six, when she had hematuria. At the age of 11, with menarche, she had significant menorrhagia resulting in symptomatic anemia, a reduction in her hemoglobin concentration to 44 g/L, requiring uterine artery embolization. She was placed on an oral contraceptive pill for menorrhagia. She used DDAVP for trauma induced injury. Her first pregnancy resulted in spontaneous abortion. She required a D&C and DDAVP was used. Prior to delivery of the second pregnancy DDAVP was used but she had postpartum hemorrhage, requiring additional dosing of DDAVP and uterine artery embolization. In the current pregnancy, aPTT was 36.4 seconds with normal PT and platelet count and blood group O. At 15 weeks' gestational age, VWF antigen (ACL TOP 700 -IL HemosIL) was 0.11 units/ml (normal range for blood group O 0.45-1.5 unit/ml), ristocetin cofactor (ACL TOP 700 -IL HemosIL), 0.09 units/ml (normal range 0.48-2.0 units/ml for blood group O), and FVIII level (Sysmex CS5100 -Dade Actin FS) 0.09 units/ml (normal range 0.58-1.9 units/ml). Factor levels at 23 weeks' gestation 1 hour following DDAVP were FVIII 1.05 units/ml, VWF antigen 0.5 units/ mL, and ristocetin cofactor 0.52 units/ml. She was willing to accept recombinant factor concentrates only. Results: She had an elective admission for induction of labor at 37 weeks but proceeded to Cesarean Section due to non-progression of labor. Her PTT on admission was 40 seconds with VWF antigen of 0.11 units/ml, VWF activity < 0.07 units/ml and FVIII 0.13 units/ml. The Table describes her levels following the administration of recombinant vWF. She was administered Vonvendi® on a planned dose of 40 IU/kg Xynta® and rFVIII 30 IU/kg to increase factor levels to more than 50%; 60-min following infusions vWF : RCo was 0.64 U/ml with FVIII 0.79 U/ml. The Cesarean section was performed under spinal anesthesia without complications. Tranexamic acid was used intravenously before the delivery of the neonate and continued for first two days and then changed to oral dose. Target levels were achieved over the 5 days after delivery with the current regimen. She experienced a transient hypersensitivity reaction with urticaria and dyspepsia after the third dose of Vonvendi®. She did not have significant bleeding. Her hemoglobin concentration remained stable at 120 g/L throughout her inpatient stay. The neonate did not have bleeding with delivery but was found to have VWF antigen of 0.11 U /ml, VWF activity of 0.07 U/ml and FVIII of 0.16 U/ml. Genetic analysis of the mutation associated with her vWD is in progress. Conclusion: The use of rvWF and rVIII resulted in adequate hemostasis peripartum. Further prospective data are required to reaffirm the safety and dosing of rvWF for peripartum management of patients with vWD who require intervention. Disclosures Kazi: Shire: Other: Vonvendi was provided by Shire.

Extended Storage of Thawed Cryoprecipitate: Responsible and Rational Use of a Scarce Resource

Background Cryoprecipitate (cryo) is a frozen plasma derivative consisting of fibrinogen, factor (F) XIII, FVIII and von Willebrand factor (vWF), and was originally intended to replace FVIII in hemophilia. Today, cryo is primarily used as fibrinogen replacement in acquired coagulopathy related to trauma, obstetric hemorrhage, and DIC. Due to the lability of FVIII, guidelines mandate that cryo be given within 6 hours of thawing. Fibrinogen is much more stable; however, and these time constraints may unnecessarily contribute to delayed product utilization and increased waste. Viscoelastic assays are increasingly used to assess coagulopathy and may be better indicators of global coagulation function than standard coagulation assays. Here we evaluated the performance of thawed, refrigerated cryoprecipitate over extended storage times. Methods Cryo (six donor pools, n=8) was purchased from South Texas Blood and Tissue, thawed on first day of testing, and stored in aliquots refrigerated at 4°C for up to 35 days. Assays were performed in 37°C rewarmed product at baseline post-thaw and at 4, 24, and 72h, and then weekly to 35 days. Assays for factor levels were conducted in cryo diluted 1:10 in PBS and using a hematology analyzer (Stago) for fibrinogen and FVIII or by ristocetin cofactor assay (RCo) for vWF (Siemens). Coagulation and thrombin generation of stored cryo was tested in ROTEM and Calibrated Automated Thrombogram (CAT) by mixing cryo with frozen aliquots of cryo-poor plasma. A massive transfusion protocol (MTP) was simulated by combining cryo with red cells, fresh frozen plasma, and fresh apheresis platelets (1:1:1:1 ratio); this simulation was tested for coagulation with ROTEM and for vWF-mediated fluorescent-labeled platelet adhesion to collagen in a microfluidics flow system (Bioflux). Results In simulated MTP, global coagulation function as measured by EXTEM and FIBTEM G-values from ROTEM were above normal reference ranges for whole blood for the entire 35d period (EXTEM smallest median G=13592 dyn/cm2, ref. range=4800-12250; FIBTEM smallest median G=2041, ref. range=495-1667). There was a slight decline in G value over storage duration, but it was not statistically significant (Fig 1). Lysis index at 30 min (LI30) in the EXTEM of simulated MTP did not statistically deviate over time (Fig 2). The MTP FIBTEM A10 value, shown to be correlated with fibrinogen concentration, remains high over 35 days, with only some values on D35 dropping into the normal range (Fig 3; means at D0=35.75mm and D35=26.63; ref. range=9-24). A10 and G were highly correlated (r=.812, p=.008). FVIII activity in cryo declined from 9-fold above average plasma levels over 35 days to approximately 25% of its starting activity. Surprisingly, the drop in FVIII was not correlated with clotting time (CT) in the EXTEM (r=-.335, p=.739), and CT was either faster than or within normal references ranges for whole blood at all time points (Fig 4; slowest median CT=49.5s, ref. range=42-72). The change in CT was correlated with measured peak thrombin levels (Fig 5; r=-.883, p=.002), although FVIII was not correlated with peak thrombin generation (r=.403, p=.282). vWF activity of cryo initially increased as has been previously reported but declined to baseline level by D7 and further through D35. vWF activity was correlated with the rate of platelet adhesion to a collagen surface under arterial flow (Fig 6; r=.677, p=.045). Discussion Cryo is mainly used in resuscitation of severe hemorrhage in MTP. It contributes to hemostasis by providing vWF to support platelet adhesion and primary hemostasis, FVIII to augment thrombin generation, and fibrinogen as clot substrate. Standard coagulation assays such as PT and aPTT or isolated factor activity assays are inadequate for evaluating the contribution of cryo to global MTP performance. The data presented here, derived from multiple functional tests including ROTEM, CAT, ristocetin cofactor assay, and Bioflux, show that thawed cryoprecipitate stored at 4°C is functionally viable for up to 35 days; as part of a massive transfusion protocol. It supports clot strength, thrombin generation, and platelet adhesion. Adoption of an extended shelf life for thawed cryo would reduce waste and increase availability for treatment of hemorrhage. Disclosures No relevant conflicts of interest to declare.

Management of Type 2B von Willebrand Disease during Pregnancy

Type 2B von Willebrand disease is a rare bleeding condition resulting in thrombocytopenia and a reduction in large VWF multimers. It usually has an autosomal dominant pattern of inheritance. We report the management of a patient with type 2B von Willebrand disease, whose diagnosis was confirmed by demonstration of a R1306W mutation, through her first pregnancy. The patient's von Willebrand factor (VWF) antigen and VWF ristocetin cofactor levels rose throughout pregnancy, with an associated drop in the platelet count. The patient was successfully managed through labour to a surgical delivery with VWF concentrate, platelet transfusions and tranexamic acid. The patient delivered a male baby who was found to have inherited type 2B von Willebrand disease and had a significant cephalhaematoma at delivery. The baby was managed with VWF concentrate and platelet transfusions and made a full recovery. There is a lack of evidence to guide the best management of pregnant patients with type 2B von Willebrand disease. We adopted a pragmatic management plan, in keeping with other published case reports. To the best of our knowledge, this is the first case report in which the child was found to have inherited type 2B von Willebrand disease and encountered bleeding problems, making this case unique amongst the published literature.

Common bleeding disorders affecting individuals with Hereditary Hemorrhagic Telangiectasia

Purpose: Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant disorder affecting vasculature in different organ systems; seen at a rate of approximately 1:5000 in North America. Complications, with significant increases in health service utilization, arise from bleeding and shunts, and are particularly problematic in the lung and liver. Although these patients tend to chronically bleed from the GI tract and nasal cavities, a single bleed from arterio-venous malformations in the lungs or brain can have serious health implications and may be fatal. Bleeding due to vascular wall fragility in HHT patients can be further complicated with a concomitant bleeding disorder. Methods: The proportion of adult patients seen in the Edmonton HHT center with a concomitant bleeding disorder, as assessed by blood test results for Factor VIII and related factors (Ristocetin Cofactor), Factor IX and Factor XI, was determined in a retrospective, single centre study. Results: Of 77 individuals with HHT, four had below normal values of von Willebrand Factor, Ristocetin Cofactor or Factor VIII. Two patients had laboratory parameters diagnostic of a bleeding disorder, accounting for 2.6% of confirmed HHT subjects. These results indicate that establishing screening for bleeding disorders in HHT centers is important in managing bleeding symptomatology. Conclusions: In individuals with HHT, the presence of a second bleeding disorder can have significant clinical implications on patient management and health care utilizations. This paper highlights areas that need to be reviewed with respect to best practice protocols for the management of HHT patients.