Procedural outcomes in children with mild type 1 von Willebrand disease.

Background: In patients with mild type 1 von Willebrand disease (VWD), treatment guidelines suggest individualization of surgical management. However, these conditional recommendations are based on very low-certainty evidence due to limited data on surgical outcomes in this population. Objectives: To characterize procedural bleeding prophylaxis strategies and outcomes in children with mild type 1 VWD. Methods: This is a retrospective cohort study that included patients aged between 0 and 21 years with mild type 1 VWD (defined as von Willebrand factor antigen and/or an activity of 30-50 IU/dL) who underwent a procedure from July 1, 2017, to July 1, 2022. Demographic, surgical, medication, and bleeding data were collected by manual chart review. Results: A total of 161 procedures were performed in 108 patients. The population was primarily female (75%), White (77.8%), and non-Hispanic (79.6%). Median age was 15.8 years (IQR, 8.2-17.6). Fifty-nine surgeries were classified as major, 66 as minor, and 36 as dental. For most procedures, patients received only antifibrinolytics for bleeding prophylaxis (n = 128, 79.5%); desmopressin was used in 17 (10.6%) procedures, and von Willebrand factor concentrate was used in 12 (7.5%) procedures. Bleeding complications occurred in 8 (5.0%) procedures: these included 1 major, 4 clinically relevant nonmajor, and 3 minor bleeding events. No patient required blood transfusion or an additional procedure to achieve hemostasis. Most bleeding complications were seen following intrauterine device (IUD) placement (5/8). Nearly 30% of patients who underwent IUD placement reported bleeding. Conclusion: Pediatric patients with mild type 1 VWD can safely undergo procedures using a tailored approach. Bleeding complications were uncommon, with the majority following IUD placement.

Haemophilia in the era of novel therapies: Where do inhibitors feature in the new landscape?

INTRODUCTION: The advent of therapeutic recombinant factor VIII (FVIII) and factor IX (FIX) protein infusions revolutionized the care of persons with haemophilia in the 1990s. It kicked off an era with the increasing use of prophylactic factor infusions for patients and transformed conversations around the ideal trough activity levels as well as the ultimate goals in tailored, individualized care. Our knowledge surrounding the immunologic basis of inhibitor development and treatment derives from a time when patients were receiving frequent factor infusions and focused on immune tolerance induction following inhibitor development. DISCUSSION: More recently, care was revolutionized again in haemophilia A with the approval of emicizumab, a bispecific antibody mimicking activated FVIII function, to prevent bleeding. The use of emicizumab prophylaxis has resulted in a significantly slower accumulation of factor exposure days and continued effective prophylaxis in the case of inhibitor development. While emicizumab is effective at reducing the frequency of bleeding events in patients with haemophilia A, management of breakthrough bleeds, trauma, and surgeries still requires additional treatment. Ensuring that FVIII is a therapeutic option, particularly for life-threatening bleeding events and major surgeries is critical to optimizing the care of persons with haemophilia A. Other novel non-factor concentrate therapies, including rebalancing agents, will dramatically change the landscape for persons with haemophilia B with inhibitors. CONCLUSION: This review discusses the changing landscape regarding the timing of inhibitor development and management strategies after inhibitor development, stressing the importance of education across the community to continue to vigilantly monitor for inhibitors and be prepared to treat persons with inhibitors.

Evaluating the clinical validity of genes related to hemostasis and thrombosis using the Clinical Genome Resource gene curation framework.

BACKGROUND: Inherited bleeding, thrombotic, and platelet disorders (BTPDs) are a heterogeneous set of diseases, many of which are very rare globally. Over the past 5 decades, the genetic basis of some of these disorders has been identified, and recently, high-throughput sequencing has become the primary means of identifying disease-causing genetic variants. OBJECTIVES: Knowledge of the clinical validity of a gene-disease relationship is essential to provide an accurate diagnosis based on results of diagnostic gene panel tests and inform the construction of such panels. The Scientific and Standardization Committee for Genetics in Thrombosis and Hemostasis undertook a curation process for selecting 96 TIER1 genes for BTPDs. The purpose of the process was to evaluate the evidence supporting each gene-disease relationship and provide an expert-reviewed classification for the clinical validity of genes associated with BTPDs. METHODS: The Clinical Genome Resource (ClinGen) Hemostasis/Thrombosis Gene Curation Expert Panel assessed the strength of evidence for TIER1 genes using the semiquantitative ClinGen gene-disease clinical validity framework. ClinGen Lumping and Splitting guidelines were used to determine the appropriate disease entity or entities for each gene, and 101 gene-disease relationships were identified for curation. RESULTS: The final outcome included 68 Definitive (67%), 26 Moderate (26%), and 7 Limited (7%) classifications. The summary of each curation is available on the ClinGen website. CONCLUSION: Expert-reviewed assignment of gene-disease relationships by the ClinGen Hemostasis/Thrombosis Gene Curation Expert Panel facilitates accurate molecular diagnoses of BTPDs by clinicians and diagnostic laboratories. These curation efforts can allow genetic testing to focus on genes with a validated role in disease.

Successful Perioperative Management of Orthotopic Cardiac Transplantation in a Pediatric Patient With Concurrent Congenital von Willebrand Disease and Acquired von Willebrand Syndrome Using Recombinant von Willebrand Factor.

Von Willebrand disease (VWD) is the most common bleeding disorder and reportedly affects 1:1,000 of the world's population. There are three subtypes of VWD characterized by a quantitative defect (types 1 and 3 VWD) or a qualitative defect (type 2 VWD). Type 1 VWD results in a partial deficiency of von Willebrand factor (VWF) and affects approximately 75% of individuals with VWD, whereas type 3 VWD results in a severe or complete deficiency of VWF. Individuals with type 2 VWD subtypes (types 2A, 2B, 2M, and 2N VWD) express a dysfunctional VWF protein that has impaired interactions with platelets or factor VIII. The majority of individuals with VWD have mild type 1 VWD and occasionally require bolus infusions of VWF for severe bleeding or major surgery. A subset of patients, especially those with type 2A or 3 VWD, may require more frequent VWF replacement or prophylaxis for refractory bleeding or bleeding prevention, respectively. Acquired von Willebrand syndrome (AVWS) is a rare bleeding disorder that primarily occurs as a result of an underlying disease or other pathologic mechanism. Cases of AVWS associated with heart valve defects, left ventricular assist devices, or congenital cardiac disease result from high shear stress in the circulation that induces VWF unfolding and subsequent proteolysis of high-molecular-weight multimers by ADAMTS-13. In rare instances, plasma-derived factor VIII-containing VWF concentrates have been administered to individuals with AVWS for persistent or challenging bleeding events. In this case report, the hemostatic challenges and the perioperative management of cardiac transplantation surgery using a novel recombinant VWF product in a pediatric patient diagnosed with AVWS concomitant with congenital type 1 VWD are described. Written informed consent was obtained from the patient's mother for this case report. The diagnosis of congenital VWD remains a challenge because of multiple potential modifiers that can alter VWF laboratory results. Concurrent conditions, such as congenital heart disease and the rare secondary condition of AVWS, in addition to congenital VWD, can further affect interpretation of coagulation studies. This can result in delays in diagnosis, increase severity of the bleeding phenotype, and complicate hemostatic management in individuals at risk for bleeding and thrombosis. A multidisciplinary approach, including anesthesiologists, cardiologists, cardiovascular surgeons, hematologists, and pharmacists, is critical to achieving optimal patient outcomes, as highlighted in this case report. As diagnostic capabilities and understanding of VWD broaden, future studies evaluating alternative treatment approaches for individuals with various types of VWD would be of great benefit to the medical community.

F5-Atlanta: A novel mutation in F5 associated with enhanced East Texas splicing and FV-short production.

BACKGROUND: Elucidating the molecular pathogenesis underlying East Texas bleeding disorder (ET) led to the discovery of alternatively spliced F5 transcripts harboring large deletions within exon 13. These alternatively spliced transcripts produce a shortened form of coagulation factor V (FV) in which a large portion of its B-domain is deleted. These FV isoforms bind tissue factor pathway inhibitor alpha (TFPIα) with high affinity, prolonging its circulatory half-life and enhancing its anticoagulant effects. While two missense pathogenic variants highlighted this alternative splicing event, similar internally deleted FV proteins are found in healthy controls. OBJECTIVE: We identified a novel heterozygous 832 base pair deletion within F5 exon 13, termed F5-Atlanta (F5-ATL), in a patient with severe bleeding. Our objective is to investigate the effect of this deletion on F5 and FV expression. METHODS & RESULTS: Assessment of patient plasma revealed markedly elevated levels of total and free TFPI and a FV isoform similar in size to the FV-short described in ET. Sequencing analyses of cDNA revealed the presence of a transcript alternatively spliced using the ET splice sites, thereby removing the F5-ATL deletion. This alternative splicing pattern was recapitulated by heterologous expression in mammalian cells. CONCLUSIONS: These findings support a mechanistic model consisting of cis-acting regulatory sequences encoded within F5 exon 13 that control alternative splicing at the ET splice sites and thereby regulate circulating FV-short and TFPIα levels.

Use of plasma-derived factor X concentrate in neonates and infants with congenital factor X deficiency.

BACKGROUND: Congenital factor X deficiency (FXD) is a rare bleeding disorder that often presents with severe bleeding in the neonatal period. Long-term prophylaxis with infusions of FX-containing products is recommended in patients with FXD and a personal or family history of severe bleeding. A plasma-derived FX concentrate (pdFX) is approved for on-demand and prophylactic therapy in adults and children with FXD. The safety and efficacy of pdFX has been demonstrated in patients <12 years of age, yet limited data exist regarding its use in infants. PATIENTS/METHODS: This retrospective case series details clinical experience using pdFX in four neonates with moderate and severe FXD across four institutions. RESULTS AND CONCLUSIONS: All four patients presented in the first week of life with severe bleeding. Following treatment of the acute bleed, prophylactic pdFX was initiated at an average of 29 days of life and a dose of 69 IU/kg every 48 hours. Incremental recovery (IR) in three infants averaged 1.42 IU/dL per IU/kg (min-max: 1.06-1.67 IU/dL per IU/kg). One patient experienced thrombotic complications in the setting of sepsis. After a median follow-up of 26.5 months, no patient has experienced breakthrough bleeding episodes. Our study supports the use of pdFX in neonates and infants and suggests that higher pdFX dosing of 70 to 80 IU/kg every 48 hours based on the smallest available vial size is feasible. Because of variability in IR, close monitoring of FX activity should be used to guide dosing in this age group.

Immune tolerance induction in paediatric patients with haemophilia A and inhibitors receiving emicizumab prophylaxis.

INTRODUCTION: The formation of neutralizing antifactor VIII (fVIII) antibodies, called inhibitors, is the most common complication in modern haemophilia A care. Novel non-factor replacement therapies, such as emicizumab, have sought to address the limitations of bypassing agents for bleeding management in patients with inhibitors. However, immune tolerance induction (ITI) remains the primary method for eradicating inhibitors and restoring the hemostatic response to fVIII. AIM: The aim of this study was to review a case series of paediatric patients with haemophilia A and inhibitors who have received ITI for inhibitor eradication concomitantly with emicizumab prophylaxis for bleeding prevention. METHODS: Single institution retrospective chart review of paediatric patients with severe haemophilia A receiving ITI and emicizumab. RESULTS: Seven patients were included in this cohort. Six patients used three different recombinant fVIII products at 100 IU/kg three times per week, and one patient used a plasma-derived fVIII product at an initial dose of 50 IU/kg three times per week. Three patients achieved a negative inhibitor titre <0.6 Chromogenic Bethesda Units per mL (CBU/mL), and two patients achieved a normal fVIII recovery ≥66%. There were nine bleeding events in four patients, but no thrombotic events. All patients remained on ITI and emicizumab. CONCLUSION: Immune tolerance induction while on emicizumab prophylaxis is a feasible approach in paediatric haemophilia A patients with inhibitors. This is the first report of the concomitant use of ITI in patients receiving emicizumab prophylaxis described as the 'Atlanta Protocol'.

Role of motif III in catalysis by acetyl-CoA synthetase.

The acyl-adenylate-forming enzyme superfamily, consisting of acyl- and aryl-CoA synthetases, the adenylation domain of the nonribosomal peptide synthetases, and luciferase, has three signature motifs (I-III) and ten conserved core motifs (A1-A10), some of which overlap the signature motifs. The consensus sequence for signature motif III (core motif A7) in acetyl-CoA synthetase is Y-X-S/T/A-G-D, with an invariant fifth position, highly conserved first and fourth positions, and variable second and third positions. Kinetic studies of enzyme variants revealed that an alteration at any position resulted in a strong decrease in the catalytic rate, although the most deleterious effects were observed when the first or fifth positions were changed. Structural modeling suggests that the highly conserved Tyr in the first position plays a key role in active site architecture through interaction with a highly conserved active-site Gln, and the invariant Asp in the fifth position plays a critical role in ATP binding and catalysis through interaction with the 2'- and 3'-OH groups of the ribose moiety. Interactions between these Asp and ATP are observed in all structures available for members of the superfamily, consistent with a critical role in substrate binding and catalysis for this invariant residue.