Safety and efficacy of damoctocog alfa pegol prophylaxis in patients with severe haemophilia A: Results of an interventional, post-marketing study.

INTRODUCTION: Damoctocog alfa pegol (BAY 94-9027, Jivi® ) is an approved extended half-life factor VIII (FVIII) for treatment of previously treated patients with haemophilia A aged ≥12 years. We report the final results of an interventional, post-marketing study of damoctocog alfa pegol prophylaxis in patients with severe haemophilia A. METHODS: In this open-label, interventional, post-marketing, phase 4 trial (NCT04085458), previously FVIII-treated patients with severe haemophilia A aged ≥18 years received damoctocog alfa pegol for ≥100 exposure days (EDs). Patients initially received 45 IU/kg every 5 days (recommended) or 40 IU/kg twice-weekly. At Visit 3, patients' doses could be increased, or treatment frequency adapted. The primary endpoint was FVIII inhibitor development (titre ≥.6 Bethesda units). Secondary endpoints included anti-polyethylene glycol (PEG) antibody development, treatment-emergent adverse events (AEs) and annualized bleeding rate (ABR). RESULTS: Overall, 36 patients were enrolled; 32 patients received treatment, of whom, 27 completed the study. No patients developed FVIII inhibitors; three tested transiently positive for low-titre anti-PEG antibodies without clinical relevance. Three patients reported study-drug-related AEs of mild or moderate intensity. Two patients discontinued the study due to AEs. No deaths occurred. Most patients (70%) were treated with E5D/E7D regimens. The median (Q1;Q3) total ABR (N = 30) was 3.0 (.0;9.0) pre-study and 1.8 (.7;5.9) during the study. CONCLUSION: Damoctocog alfa pegol individualized prophylaxis regimens were well-tolerated with no immunogenicity concerns. ABRs improved following the switch from pre-study prophylaxis to damoctocog alfa pegol prophylaxis. These results support the favourable safety and efficacy profile of damoctocog alfa pegol prophylaxis.

The value-based healthcare approach to haemophilia: Development of outcome measures for the evaluation of care of people with haemophilia.

INTRODUCTION: Considering the advances in haemophilia management and treatment observed in the last decades, a new set of value-based outcome indicators is needed to assess the quality of care and the impact of these medical innovations. AIM: The Value-Based Healthcare in Haemophilia project aimed to define a set of clinical outcome indicators (COIs) and patient-reported outcome indicators (PROIs) to assess quality of care in haemophilia in high-income countries with a value-based approach to inform and guide the decision-making process. METHODS: A Value-based healthcare approach based on the available literature, current guidelines and the involvement of a multidisciplinary group of experts was applied to generate a set of indicators to assess the quality of care of haemophilia. RESULTS: A final list of three COIs and five PROIs was created and validated. The identified COIs focus on two domains: musculoskeletal health and function, and safety. The identified PROIs cover five domains: bleeding frequency, pain, mobility and physical activities, Health-Related Quality of Life and satisfaction. Finally, two composite outcomes, one based on COIs, and one based on PROIs, were proposed as synthetic outcome indicators of quality of care. CONCLUSION: The presented standard set of health outcome indicators provides the basis for harmonised longitudinal and cross-sectional monitoring and comparison. The implementation of this value-based approach would enable a more robust assessment of quality of care in haemophilia, within a framework of continuous treatment improvements with potential added value for patients. Moreover, proposed COIs and PROIs should be reviewed and updated routinely.

Pattern of use and clinical outcomes with rIX-FP in pediatric/adolescent patients with haemophilia B in Italy: Results from IDEAL real-world study.

OBJECTIVES: To evaluate pattern of use and clinical outcomes in pediatric/adolescent patients enrolled in the IDEAL study. METHODS: This post-hoc analysis of IDEAL retrospective-prospective observational study focused on patients <18 years, 100% on prophylaxis during the entire observation period. RESULTS: Thirteen subjects (median age 10.0 years; 61.5% ≤ 11 years) were analyzed. The infusion frequency changed from 2/week in 84.6% (N = 11) of patients with previous rFIX, to less than 1/weekly in 76.9% (N = 9) with rIX-FP and the annualized number of infusions reduced of 57% (p = .002), from a mean ± SD of 95.1 ± 22.77 to 40.4 ± 6.79, respectively. Annualized mean consumption decreased of about 56% (p = .001), from 3748.4 ± 1155.40 IU/kg with previous rFIX, to 1656.8 ± 456.63 IU/kg of rIX-FP. Mean FIX trough level changed from 3.0% ± 1.98% to 10.92% ± 3.6%. Low mean Annualized Bleeding Rate was maintained across all prophylaxis regimens (0.8 ± 1.69 vs. 0.3 ± 0.89) and zero bleeding patients moved from 69.2% (N = 9) with previous rFIX to 84.6% (N = 11) with rIX-FP (p = .63). Two adverse events, none related to rIX-FP, occurred in two patients. No inhibitors development was reported. CONCLUSIONS: The results in this pediatric/adolescent subgroup support rIX-FP prophylaxis may reduce infusion frequency, while providing high FIX trough levels, stable annualized bleeding rate and a good safety profile.

Laying the foundations for gene therapy in Italy for patients with haemophilia A: A Delphi consensus study.

INTRODUCTION: Current treatment for haemophilia A involves factor VIII replacement or non-replacement (emicizumab) therapies, neither of which permanently normalise factor VIII levels. Gene therapy using adeno-associated viral (AAV) vectors is an emerging long-term treatment strategy for people with severe haemophilia A (PwSHA) that is likely to be available for clinical use in the near future. AIM: This article proposes practical guidelines for the assessment, treatment, and follow-up of potential PwSHA candidates for AAV-based gene therapy. METHOD: Using the Delphi method, a working group of Italian stakeholders with expertise in and knowledge of the care of adults with haemophilia A analysed literature for AAV-based gene therapy and drafted a list of statements that were circulated to a panel of Italian peers. During two rounds of voting, panel members voted on their agreement with each statement to reach a consensus. RESULTS: The Delphi process yielded 40 statements regarding haemophilia A gene therapy, across five topics: (1) organisational model; (2) multidisciplinary team; (3) patient engagement; (4) laboratory surveillance; and (5) patient follow-up and gene therapy outcomes. The consensus was reached for all 40 statements, with the second round of voting needed for five statements. CONCLUSION: Use of the hub-and-spoke organisational model and multidisciplinary teams are expected to optimise patient selection for gene therapy, as well as the management of dosing and patient follow-up, patient engagement, laboratory surveillance, and patient expectations regarding outcomes. This approach should allow the benefits of AAV-based gene therapy for haemophilia A to be maximised.

IDEAL study: A real-world assessment of pattern of use and clinical outcomes with recombinant coagulation factor IX albumin fusion protein (rIX-FP) in patients with haemophilia B in Italy.

INTRODUCTION: Factor IX replacement therapy is used for treatment and prophylaxis of bleeding in haemophilia B. rIX-FP is an extended half-life albumin-fusion protein, which, in clinical studies, has demonstrated prolonged dosing intervals up to 21 days for routine prophylaxis, providing therapeutic benefit. AIMS: To describe dosing frequency and consumption (primary endpoint), efficacy and safety of rIX-FP treatment during routine clinical practice in Italy. METHODS: Patients with moderate/severe haemophilia B on prophylaxis with rIX-FP for ≥6 months, were enrolled in this observational study from October 2017 to February 2019 and followed-up for 2 years. Descriptive analysis included prospective and retrospective data (12 months prior to switching to rIX-FP). RESULTS: Data were collected from 59 male patients (median age 30.1 years) enrolled by 23 Italian centres. Of them, 50 were on prophylaxis during the entire observation period and completed the study. The infusion frequency changed from 2-3 times/week in 86.0% of patients with previous treatment, to less than once a week in 84.0% of patients treated with rIX-FP at the 2nd-year follow-up. The annual number of infusions decreased by about 70%, whereas the mean FIX activity trough level increased from 3.8% to 14.4% (mean > 10% in all the infusion regimens). Median Annualised Bleeding Rate of .0 was achieved across all prophylaxis regimens. Subjects with zero bleedings increased from 66.0% to 78.0% with rIX-FP. CONCLUSION: Treatment with rIX-FP reduced infusion frequency, while providing higher FIX trough levels with substantial benefit in terms of annualised bleeding rate and a good safety profile.

Personalized Prophylaxis with myPKFiTCE: A Real-World Cost-Effectiveness Analysis in Haemophilia A Patients.

Background and Objectives: This study aimed to assess the effectiveness and costs associated with pharmacokinetics-driven (PK) prophylaxis based on the myPKFiT® device in patients affected by hemophilia A (HA) in Italy. Materials and Methods: An observational retrospective study was conducted in three Italian hemophilia centers. All patients with moderate or severe HA, aged ≥ 18 years, capable of having PK estimated using the myPKFiT device, and who had had a clinical visit between 1 November 2019 and 31 March 2022 were included. Differences in clinical, treatment, health resources, and cost data were assessed comparing post-PK prophylaxis with pre-PK. The incremental cost-effectiveness ratio (ICER) was estimated as cost (EUR) per bleed avoided. Results: The study enrolled 13 patients with HA. The mean annual bleeding rate decreased by -1.45 (-63.80%, p = 0.0055) after the use of myPKFiT®. Overall, the consumption of FVIII IU increased by 1.73% during follow-up compared to the period prior the use of the myPKFiT. Prophylaxis based on the myPKFiT resulted in an ICER of EUR 5099.89 per bleed avoided. Conclusions: The results of our study support the idea that the use of PK data in clinical practice can be associated with an improvement in the management of patients, as well as clinical outcomes, with a reasonable increase in costs.

The Arrival of Gene Therapy for Patients with Hemophilia A.

Historically, the standard of care for hemophilia A has been intravenous administration of exogenous factor VIII (FVIII), either as prophylaxis or episodically. The development of emicizumab, a humanized bispecific monoclonal antibody mimicking activated FVIII, was a subsequent advance in treatment. However, both exogenous FVIII and emicizumab require repeated and lifelong administration, negatively impacting patient quality of life. A recent breakthrough has been the development of gene therapy. This allows a single intravenous treatment that could result in long-term expression of FVIII, maintenance of steady-state plasma concentrations, and minimization (or possibly elimination) of bleeding episodes for the recipient's lifetime. Several gene therapies have been assessed in clinical trials, with positive outcomes. Valoctocogene roxaparvovec (an adeno-associated viral 5-based therapy encoding human B domain-deleted FVIII) is expected to be the first approved gene therapy in European countries, including Italy, in 2022. Some novel challenges exist including refining patient selection criteria, managing patient expectations, further elucidation of the durability and variability of transgene expression and long-term safety, and the development of standardized 'hub and spoke' centers to optimize and monitor this innovative treatment. Gene therapy represents a paradigm shift, and may become a new reference standard for treating patients with hemophilia A.

ABO Blood Group and Inhibitor Risk in Severe Hemophilia A Patients: A Study from the Italian Association of Hemophilia Centers.

Considering the profound influence exerted by the ABO blood group system on hemostasis, mainly through the von Willebrand factor and factor VIII (FVIII) complex, we have conducted a study evaluating the possible role of blood type on the risk of inhibitor development in hemophilia A. A total of 287 consecutive Caucasian patients with severe hemophilia A (202 without FVIII inhibitors and 85 with FVIII inhibitors) followed at seven Italian Hemophilia Treatment Centers belonging to the Italian Association of Hemophilia Centers (AICE) were included in the study. A higher prevalence of O blood group was detected in patients without inhibitors as compared in inhibitor patients (55 vs. 30.6%; p < 0.001). Among the other variables analyzed (age, F8 mutation, type and intensity of treatment and treatment regimen), F8 mutation class (high-risk vs. low-risk), and treatment regimen (on-demand vs. prophylaxis) were significantly correlated with inhibitor development. However, on a multivariate analysis, only the effects of F8 mutation and ABO blood type were independent of other covariates, being that non-O blood type is associated with a 2.89-fold increased risk of inhibitor development. In conclusion, our study supports the protective effect of O blood type on inhibitor risk in severely affected hemophilia A patients.

Diagnosis and management of cerebral venous sinus thrombosis in children: a single-center retrospective analysis.

PURPOSE: Cerebral venous thrombosis (CVT) is a rare disease in children, characterized by partial or total occlusion of blood flow in the cerebral venous system. The aim of this study is to describe clinical presentation, neuroimaging features, therapeutic management, and outcome of children with CVT. METHODS: We retrospectively analyzed the data, including clinical manifestations, laboratory data, neurological findings, and treatment of children with radiologically confirmed CVT, admitted between January 2010 and March 2020 to our hospital. Cases of CVT complicating brain surgery were excluded. RESULTS: We enrolled 24 children with CVT. Infection was the main etiology (58.3%), followed by trauma in 16.7% of cases. In the remaining 25% of cases, the cause was identified only in one patient presenting a thrombophilic factor. The most frequent site of thrombosis was the superficial venous system (86.8%), with multiple localizations disclosed in 79% of patients. All children received anticoagulant therapy with low molecular weight heparin (LMWH). One patient died for systemic complications of an underlying disease. No patient developed hemorrhagic events during the therapy, lasting from 35 to 360 days (mean 86 days). In all but one surviving patients (22 out of 24), recanalization of the sinus was observed at AngioMRI performed during follow-up. No neurological complications of CVT were recorded (mean follow-up: 1.5 year). CONCLUSIONS: CVT may present with subtle and unspecific clinical manifestations in children. High level of suspicion should be kept in trauma and sinusitis. Anticoagulation treatment is safe and effective and should be promptly started to improve outcome.

Does chronic oral anticoagulation reduce in-hospital mortality among COVID-19 older patients?

BACKGROUND: Patients hospitalized with COVID-19 experienced an increased risk of venous thromboembolism. AIMS: To evaluate the effect of chronic oral anticoagulation (OAC) therapy, both with vitamin K antagonists (VKAs) or direct oral anticoagulants (DOACs), on prognosis of COVID-19 older patients. METHODS: Single-center prospective study conducted in the Emergency Department (ED) of a teaching hospital, referral center for COVID-19 in central Italy. We evaluated all the patients ≥ 65 years, consecutively admitted to our ED for confirmed COVID-19. We compared the clinical outcome of those who were on chronic OAC at ED admission with those who did not, using a propensity score matched paired cohort of controls. The primary study endpoint was all-cause in-hospital death. Patients were matched for age, sex, clinical comorbidities, and clinical severity at presentation (based on NEWS ≥ 6). Study parameters were assessed for association to all-cause in-hospital death by a multivariate Cox regression analysis to identify independent risk factor for survival. RESULTS: Although overall mortality was slightly higher for anticoagulated patients compared to controls (63.3% vs 43.5%, p = 0.012), the multivariate adjusted hazard ratio (HR) for death was not significant (HR = 1.56 [0.78-3.12]; p = 0.208). Both DOACs (HR 1.46 [0.73-2.92]; p = 0.283) and VKAs (HR 1.14 [0.48-2.73]; p = 0.761) alone did not affect overall survival in our cohort. CONCLUSIONS: Among older patients hospitalized for COVID-19, chronic OAC therapy was not associated with a reduced risk of in-hospital death. Moreover, our data suggest similar outcome both for patients on VKAs or in patients on DOACs.

Carbamazepine interaction with direct oral anticoagulants: help from the laboratory for the personalized management of oral anticoagulant therapy.

Current guidelines recommend caution in prescribing concomitant use of direct-acting oral anticoagulants (DOACs) and antiepileptic drugs due to drug-drug interactions leading to potential risk of DOACs subtherapeutic concentration and treatment failure. Herein we report a significant interaction between carbamazepine (CZP) and apixaban, causing subtherapeutic concentration of the drug in a patient with atrial fibrillation who had a transient ischemic attack (TIA) episode. Another anti-Xa DOAC, edoxaban, administered to the patient after TIA occurrence did not show significant interaction with CZP. In addition to confirm that cautions should be used when antiepileptic and DOACs are concomitantly prescribed, the present case also demonstrates that, in the management of certain subsets of patients who need anticoagulant treatment, measurement of DOAC plasma concentration can help guide a personalized management and avoid adverse clinical outcomes.

Molecular dynamics characterization of five pathogenic Factor X mutants associated with decreased catalytic activity.

Factor X (FX) is one of the major players in the blood coagulation cascade. Upon activation to FXa, it converts prothrombin to thrombin, which in turn converts fibrinogen into fibrin (blood clots). FXa deficiency causes hemostasis defects, such as intracranial bleeding, hemathrosis, and gastrointestinal blood loss. Herein, we have analyzed a pool of pathogenic mutations, located in the FXa catalytic domain and directly associated with defects in enzyme catalytic activity. Using chymotrypsinogen numbering, they correspond to D102N, T135M, V160A, G184S, and G197D. Molecular dynamics simulations were performed for 1.68 µs on the wild-type and mutated forms of FXa. Overall, our analysis shows that four of the five mutants considered, D102N, T135M, V160A, and G184S, have rigidities higher than those of the wild type, in terms of both overall protein motion and, specifically, subpocket S4 flexibility, while S1 is rather insensitive to the mutation. This acquired rigidity can clearly impact the substrate recognition of the mutants.

Perceived challenges and attitudes to regimen and product selection from Italian haemophilia treaters: the 2013 AICE survey.

Despite great advances in haemophilia care in the last 20 years, a number of questions on haemophilia therapy remain unanswered. These debated issues primarily involve the choice of the product type (plasma-derived vs. recombinant) for patients with different characteristics: specifically, if they were infected by blood-borne virus infections, and if they bear high or low risk of inhibitor development. In addition, the most appropriate treatment regimen in non-inhibitor and inhibitor patients compel physicians operating at the haemophilia treatment centres (HTCs) to take important therapeutic decisions, which are often based on their personal clinical experience rather than on evidence-based recommendations from published literature data. To know the opinion on the most controversial aspects in haemophilia care of Italian expert physicians, who are responsible for common clinical practice and therapeutic decisions, we have conducted a survey among the Directors of HTCs affiliated to the Italian Association of Haemophilia Centres (AICE). A questionnaire, consisting of 19 questions covering the most important topics related to haemophilia treatment, was sent to the Directors of all 52 Italian HTCs. Forty Directors out of 52 (76.9%) responded, accounting for the large majority of HTCs affiliated to the AICE throughout Italy. The results of this survey provide for the first time a picture of the attitudes towards clotting factor concentrate use and product selection of clinicians working at Italian HTCs.

Design organization and clinical processes around patient characteristics: Evidence from a multiple case study of Hemophilia.

Background: There is growing evidence of the relevance of designing organization of care around patient characteristics; this is especially true in the case of complex chronic diseases.Purpose: The goal of the paper - that focuses on the analysis of the clinical condition hemophilia in three different centers - is to address two different research questions:1. How can we define, within the same clinical condition, different patient profiles homogeneous in terms of intensity of service required (e.g. number of visits or diagnostics)? 2. What are the conditions to re-organize care around these patient profiles in a multidisciplinary and coordinated manner?Research design: The authors have used a multiple case study approach combining both qualitative and quantitative methodologies; in particularly the semi-structured interviews and the direct observation were aimed to map the process in order to come up with an estimate of the cost of the full cycle of care.Study sample: The research methodology has been applied consistently in three different centers. The selection of the structures has been based on two main different criteria: (i) high standards regarding both organizational and clinical aspects and (ii) willingness from management, nurses and physicians to provide data.Results: The study clearly shows that different patient profiles - within the same clinical condition - trigger a different set of diagnostic and therapeutic activities. It is, thus, important considering patient characteristics in the development and implementation of clinical pathways and this will imply relevant differences in terms of organizational and economic impact.Conclusions: These process-based analyses are very much critical especially if we want to move to a bundled and integrated payment system but, as shown by this study itself, require a lot of time and efforts since our healthcare information systems are still fragmented and vertically designed.

Von Willebrand factor hyperactivity affects the outcome of lower limb revascularization in subjects with type 2 diabetes mellitus complicated by diabetic foot vasculopathy: An observational pilot study.

Aim of this study is to evaluate any differences in VWF antigen, VWF activity and ADAMTS-13 activity before and after successful and non-successful Percutaneous Transluminal Angioplasty (PTA) in subjects with type 2 diabetes (T2DM) complicated by Chronic limb-threatening ischemia (CLTI) in diabetic foot vasculopathy. METHODS: In this prospective observational pilot study, we enrolled 35 T2DM subjects who underwent lower limb PTA. Transcutaneous oximetry was performed in all patients before and 6 weeks after PTA. The change in oxygen partial pressure (TcpO2) before and after PTA was expressed as TcpO2-delta (ΔTcpO2). VWF antigen, VWF activity and ADAMTS-13 activity were measured before and 6 weeks after PTA; changes were expressed as delta and ratio from baseline. RESULTS: Subjects with ∆TcpO2 < 15 mmHg presented higher ΔVWF activity (p = 0.050) and lower ADAMTS-13 activity ratio (p = 0.080). Subjects with ∆TcpO2 < 30 mmHg showed lower ADAMTS-13 activity Δ and ratio (p = 0.028). CONCLUSIONS: VWF antigen levels and VWF activity may potentially affect PTA outcome. Higher levels of VWF could derive from VWF release as consequence of PTA-induced mechanical endothelial damage and/or oxidative stress-induced modifications of VWF structure with impairment of VWF-ADAMTS13 interactions.

Liver-related aspects of valoctocogene roxaparvovec gene therapy for hemophilia A: expert guidance for clinical practice.

Adeno-associated virus (AAV)-based gene therapy (valoctocogene roxaparvovec) is an attractive treatment for hemophilia A. Careful clinical management is required to minimize the risk of hepatotoxicity, including assessment of baseline liver condition to determine treatment eligibility and monitoring liver function after gene therapy. This article describes recommendations (developed by a group of hemophilia experts) on hepatic function monitoring before and after gene therapy. To prevent harmful liver-related effects, gene therapy is contraindicated in patients with uncontrolled liver infections, autoimmune hepatitis, liver stiffness ≥8 kPa or cirrhosis. Before using gene therapy in patients with liver steatosis or other liver disorders, the risk of liver damage should be considered using a highly individualized approach. Treatment is not recommended in patients with abnormal liver enzymes, including alanine aminotransferase (ALT) at any level above the upper limit of normal (ULN). Therefore, pre-treatment assessment of liver health should include laboratory tests, abdominal ultrasound and liver stiffness measurements by transient elastography (TE). In the first year after therapy, ALT levels should be monitored 1-2 times/week to detect elevations ≥1.5 × ULN, which may require immunosuppressant therapy. Patients with ALT elevation should receive prednisone 60 mg/day for 2 weeks, followed by stepwise tapering when ALT returns to baseline. ALT monitoring should continue long-term (every 3-6 months), along with abdominal ultrasound (every 6 months) and TE (yearly) evaluations. When patients with good liver health are selected for treatment and closely monitored thereafter, ALT elevations can be promptly treated and are expected to resolve without long-term hepatic sequelae.

Real-World Efficacy and Safety of Plasma-Derived Von Willebrand Factor-Containing Factor VIII Concentrates in Patients With Von Willebrand Disease in Italy.

Plasma-derived von Willebrand factor-containing factor VIII concentrates (pd-VWF/FVIII-C) are the mainstay of treatment in von Willebrand disease (VWD). Real-world data on efficacy and safety of these pd-VWF/FVIII-C are required. To retrospectively evaluate the efficacy and safety of pd-VWF/FVIII-C (Fanhdi® and Alphanate®, Grifols) in clinical practice in Italy. A multicentric, observational, retrospective study at 10 Italian centers was conducted. Eligible patients diagnosed with inherited VWD (ISTH criteria) were treated with either Fanhdi® or Alphanate® for bleeding episodes, prevention of surgical bleeding and secondary long-term prophylaxis (SLTP) according to clinical practice with medical records collected from January 2007 to December 2019. Efficacy/safety of pd-VWF/FVIII-C was assessed according to FDA-agreed objective criteria following regulatory procedures. Fifty-seven patients (M/F: 21/36) were enrolled in the study with the following VWD types: VWD1 (n = 29, 52%), VWD2A (n = 10, 18%), VWD2B (n = 7, 12%), VWD2M (n = 2, 4%), VWD2N (n = 1, 2%), VWD2 unclassified (n = 1, 2%), and VWD3 (n = 7, 12%). These pd-VWF/FVIII-C were used to manage 58 bleeding episodes (n = 24 patients), 100 surgeries (n = 47 patients), and 7 SLTP (n = 6 patients). Global clinical efficacy with these pd-VWF/FVIII-C was reported to be excellent/good in 85% of bleeding episodes, 98% of surgeries, and 100% of SLTP. As far as safety, no adverse-drug-related episodes, immunogenic or thrombotic events were reported. This study confirmed that Fanhdi® and Alphanate® were effective and safe in the management of bleeding episodes, the prevention of bleeding during surgeries and for SLTP in Italian patients with inherited VWD.

An integrated multitool analysis contributes elements to interpreting unclassified factor IX missense variants associated with hemophilia B.

BACKGROUND: Dissection of genotype-phenotype relationships in hemophilia B (HB) is particularly relevant for challenging (mild HB) or for HB-associated but unclassified factor (F)IX missense variants. OBJECTIVE: To contribute elements to interpret unclassified HB-associated FIX missense variants by a multiple-level approach upon identification of a reported, but uncharacterized, FIX missense variant associated with mild HB. METHODS: Molecular modeling of wild-type and V92A FIX variants, expression studies in HEK293 cells with evaluation of protein (ELISA, western blotting) and activity (activated partial thromboplastin time-based/chromogenic assays) levels after recombinant expression, and multiple prediction tools. RESULTS: The F9(NM_000133.4):c.275T>C (p.V92A) variant was found in a mild HB patient (antigen, 45.4 U/dL; coagulant activity, 23.6 IU/dL; specific activity, 0.52). Newly generated molecular models showed alterations in Gla/EGF1-EGF2 domain conformation impacting Ca++ affinity and protein-protein interactions with activated factor XI (FXIa). Multitool analysis indicated a moderate impact on protein structure/function of the valine-to-alanine substitution, in accordance with patient and modeling data. Expression studies on the V92A variant showed a specific activity (0.49 ± 0.07; wild-type, 1.0 ± 0.1) recapitulating that of the natural variant, and pointed toward a moderate activation impairment as the main determinant underlying the p.V92A defect. The validated multitool approach, integrated with evidence-based data, was challenged on a panel (n = 9) of unclassified FIX missense variants, which resulted in inferred protein (secretion/function) outputs and HB severity. CONCLUSION: The rational integration of multitool and multiparameter analyses contributed elements to interpret genotype/phenotype relationships of unclassified FIX missense variants, with implications for diagnosis, management, and treatment of HB patients, and potentially translatable into other human disorders.