Mutation analysis of Swedish haemophilia B families – high frequency of unique mutations

Prophylactic Treatment of Children with Hemophilia in Sweden

Hemophilia A/B are caused by deficiency or lack of coagulation factors VIII (FVIII) or factor IX (FIX), respectively, in plasma. A person with hemophilia develops bleeding in the joints and muscles at an early age, which, if left untreated, leads to early arthropathy. Preventive treatment can be achieved by regular (prophylactic) administration of FVIII/FIX. In 1958, this was implemented on a small scale in Sweden with FVIII in patients with severe hemophilia A, and in those with hemophilia B in 1972 when FIX became available. However, there were problems with human immunodeficiency virus and hepatitis infection from contaminated blood products. In the 1990s, recombinant FVIII and FIX concentrates were introduced. The major remaining problems then were the development of inhibitors, and the need for a venous route for the injections in very young children. High-titer inhibitors were treated by immune tolerance induction according to a modified model of the original Bonn high-dose protocol. A central venous line, i.e., Port-A-Cath, has enabled early prophylaxis in many children with poor venous access and has enabled the early start of home treatment with adequate injection frequency. Scoring systems for X-rays, magnetic resonance imaging, and function of joints were developed early in Sweden and have been widely disseminated worldwide, partly with modifications. Extended half-life products with half-life increased three to five times have been developed, which can provide superior bleed protection when dosed once-weekly and can maintain therapeutic trough levels when administered less frequently. The ultimate prophylaxis therapy in the future may be gene therapy.

Nonacog beta pegol prophylaxis in children with hemophilia B: safety, efficacy, and neurodevelopmental outcomes for up to 8 years

Background

Nonacog beta pegol (N9-GP) is an extended half-life PEGylated factor (F)IX product with established efficacy and short-term safety in persons with hemophilia B (HB). Long-term safety has been evaluated for polyethylene glycol exposure but not N9-GP.

Objectives

To assess safety, neurodevelopmental, and efficacy outcomes of children with HB receiving N9-GP prophylaxis across 2 open-label, single-arm, phase 3 studies: paradigm5 (previously treated patients [PTPs]) and paradigm6 (previously untreated patients [PUPs]) in this interim analysis.

Methods

PTPs (aged ≤12 years) and PUPs (aged <6 years) with severe/moderate (≤2% FIX level) HB were recruited to N9-GP prophylaxis (40 IU/kg once weekly) in paradigm5 and paradigm6, respectively. Safety assessments included FIX inhibitor incidence, adverse events, neurocognitive and neurologic outcomes, polyethylene glycol concentration in plasma, and medical events of special interest. Efficacy endpoints included bleeds, N9-GP hemostatic effect, and FIX consumption.

Results

Overall, 25 patients in paradigm5 and 50 patients in paradigm6 received N9-GP and were followed for up to 8 and 6 years, respectively. No inhibitory antibodies were reported in PTPs; 4 of the 50 PUPs developed inhibitors. Extensive evaluation revealed no neurocognitive or neurologic concerns with N9-GP use in children during the study period. Across both studies, few adverse events were reported as possibly related to N9-GP. High hemostatic response rate, high treatment adherence, low annualized bleeding rates, and no new target joints were reported.

Conclusion

These data provide the longest follow-up for an extended half-life FIX and confirm the long-term efficacy of N9-GP prophylaxis in children with HB with no observed neurocognitive or neurologic safety concerns.

Clinical Implications of Discrepancy between One-Stage Clotting and Chromogenic Factor IX Activity in Hemophilia B

BACKGROUND

 Discrepancy in factor IX activity (FIX:C) between one-stage assay (OSA) and chromogenic substrate assay (CSA) in patients with hemophilia B (PwHB) introduces challenges for clinical management.

AIM

 To study the differences in FIX:C using OSA and CSA in moderate and mild hemophilia B (HB), their impact on classification of severity, and correlation with genotype.

METHODS

 Single-center study including 21 genotyped and clinically characterized PwHB. FIX:C by OSA was measured using ActinFSL (Siemens) and CSA by Biophen (Hyphen). In addition, in vitro experiments with wild-type FIX were performed. Reproducibility of CSA was assessed between three European coagulation laboratories.

RESULTS

 FIX:C by CSA was consistently lower than by OSA, with 10/17 PwHB having a more severe hemophilia type by CSA. OSA displayed a more accurate description of the clinical bleeding severity, compared with CSA. A twofold difference between OSA:CSA FIX:C was present in 12/17 PwHB; all patients had genetic missense variants in the FIX serine protease domain. Discrepancy was also observed with diluted normal plasma, most significant for values below 0.10 IU/mL. Assessment of samples with low FIX:C showed excellent reproducibility of the CSA results between the laboratories.

CONCLUSION

 FIX:C was consistently higher by OSA compared with the CSA. Assessing FIX:C by CSA alone would have led to diagnosis of a more severe hemophilia type in a significant proportion of patients. Our study suggests using both OSA and CSA FIX:C together with genotyping to classify HB severity and provide essential information for clinical management.

An updated interactive database for 1692 genetic variants in coagulation factor IX provides detailed insights into hemophilia B

BACKGROUND

Genetic variants in coagulation factor IX (FIX) are associated with hemophilia B, a rare bleeding disease. F9 variants are widespread across the gene and were summarized in our FIX variant database introduced in 2013.

OBJECTIVES

We aimed to rationalize the molecular basis for 598 new F9 variants and 1645 new clinical cases, totaling 1692 F9 variants and 5358 related patient cases.

METHODS

New F9 variants were identified from publications and online resources, and compiled into a MySQL database for comparison with the human FIXa protein structure.

RESULTS

The new total of 1692 F9 variants correspond to 406 (88%) of the 461 FIX residues and now include 70 additional residues. They comprise 945 unique point variants, 281 deletions, 352 polymorphisms, 63 insertions, and 51 others. Most FIX variants were point variants, although their proportion (56%) has reduced compared to 2013 (73%); at the same time, the proportion of polymorphisms has increased from 5% to 21%. The 764 unique mild severity variants in the mature protein with known phenotypes include 74 (9.7%) quantitative type I variants and 116 (15.2%) predominantly qualitative type II variants. The remaining 574 variants types are unspecified. Inhibitors are associated with 152 hemophilia B cases out of 5358 patients (2.8%), an increase of 93 from the previous database.

CONCLUSION

The even distribution of the F9 variants revealed few mutational hotspots, and most variants were associated with small perturbations in the FIX protein structure. The updated database will assist clinicians and researchers in assessing treatments for patients with hemophilia B.

Results of genetic analysis of 11 341 participants enrolled in the My Life, Our Future hemophilia genotyping initiative in the United States

BACKGROUND

Hemophilia A (HA) and hemophilia B (HB) are rare inherited bleeding disorders. Although causative genetic variants are clinically relevant, in 2012 only 20% of US patients had been genotyped.

OBJECTIVES

My Life, Our Future (MLOF) was a multisector cross-sectional US initiative to improve our understanding of hemophilia through widespread genotyping.

METHODS

Subjects and potential genetic carriers were enrolled at US hemophilia treatment centers (HTCs). Bloodworks performed genotyping and returned results to providers. Clinical data were abstracted from the American Thrombosis and Hemostasis Network dataset. Community education was provided by the National Hemophilia Foundation.

RESULTS

From 2013 to 2017, 107 HTCs enrolled 11 341 subjects (68.8% male, 31.2% female) for testing for HA (n = 8976), HB (n = 2358), HA/HB (n = 3), and hemophilia not otherwise specified (n = 4). Variants were detected in most male patients (98.2%% HA, 98.1% HB). 1914 unique variants were found (1482 F8, 431 F9); 744 were novel (610 F8, 134 F9). Inhibitor data were available for 6986 subjects (5583 HA; 1403 HB). In severe HA, genotypes with the highest inhibitor rates were large deletions (77/80), complex intron 22 inversions (9/17), and no variant found (7/14). In severe HB, the highest rates were large deletions (24/42). Inhibitors were reported in 27.3% of Black versus 16.2% of White patients.

CONCLUSIONS

The findings of MLOF are reported, the largest hemophilia genotyping project performed to date. The results support the need for comprehensive genetic approaches in hemophilia. This effort has contributed significantly towards better understanding variation in the F8 and F9 genes in hemophilia and risks of inhibitor formation.

Adeno-associated virus-mediated expression of activated factor V (FVa) for hemophilia phenotypic correction

Adeno-associated virus (AAV) gene therapy has been successfully applied in hemophilia patients excluding patients with inhibitors. During the coagulation pathway, activated factor V (FVa) functions downstream as a cofactor of activated factor X (FXa) to amplify thrombin generation. We hypothesize that the expression of FVa via gene therapy can improve hemostasis of both factor IX and FVIII deficiencies, regardless of clotting factor inhibitor. A human FVa (hFVa) expression cassette was constructed, and AAV8 vectors encoding hFVa (AAV8/TTR-hFVa) were intravenously administrated into mice with hemophilia A and B with or without FVIII inhibitors. Hemostasis, including hFVa level, activated partial thromboplastin time (aPTT), tail clip, and the saphenous vein bleeding assay (SVBA), was evaluated. In hemophilia B mice, a dose of 4 × 1013 vg/kg AAV8/TTR-hFVa vectors achieved a complete phenotypic correction over 28 weeks. In hemophilia A mice, hemostasis improvement was also achieved, regardless of FVIII inhibitor development. In vivo hemostasis efficacy was confirmed by tail clip and SVBA. Interestingly, while minimal shortening of aPTT was observed at a lower dose of AAV8 vectors, hemostasis improvement was still achieved via in vivo bleeding assays. Collectively, FVa-based AAV gene therapy shows promise for hemostasis correction in hemophilia, regardless of inhibitor development and no potential risk for thrombosis.

Factor IX antibodies and tolerance in hemophilia B in the Nordic countries - The impact of F9 variants and complications

INTRODUCTION

The development of inhibitory antibodies (inhibitors) in persons with hemophilia B (PwHB) causes significant morbidity. Data on the impact of the F9 variant and immune tolerance induction (ITI) outcome are limited. The aim of this study was to investigate the presence of neutralizing and non-neutralizing antibodies (NNA) in severe hemophilia B (HB) and to evaluate ITI outcome and complications in relation to the pathogenic F9 variant.

MATERIALS AND METHODS

Persons with severe HB in the Nordic countries were enrolled and information on F9 variants, inhibitors, ITI and complications were collected. Analyses of anti-FIX antibodies with a fluorescence-immunoassay (xFLI) and an ELISA method were conducted.

RESULTS

Seventy-nine PwHB were enrolled. Null variants were seen in 33 (42 %) PwHB and 12 (15 %) had a current or former inhibitor. Eleven (92 %) of the inhibitor patients had experienced allergic manifestations and three (25 %) nephrotic syndrome. Of 10 PwHB with at least one ITI attempt, eight (80 %) were considered tolerant at enrolment. Immunosuppression was included in seven of eight successful or partially successful attempts. Five PwHB had at least one ITI failure before a successful or partially successful ITI. No NNA could be identified.

CONCLUSION

A high proportion of severe F9 gene defects among persons with severe HB in the Nordic countries may explain the observed relatively high prevalence of inhibitors. ITI success was independent of the F9 variant and attained despite allergic manifestations and previous ITI failures. Inclusion of immunosuppression tentatively enhances the chances of ITI success. No NNA were observed.

Inhibitor incidence in an unselected cohort of previously untreated patients with severe haemophilia B: a PedNet study

The incidence of factor IX (FIX) inhibitors in severe hemophilia B (SHB) is not well defined. Frequencies of 3-5% have been reported but most studies to date have been small, including patients with different severities, and without prospective follow up for inhibitor incidence. The study objective was to investigate the inhibitor incidence in patients with SHB followed up for to 500 exposure days (ED), the frequency of allergic reactions, and the relationship with genotypes. Consecutive previously untreated patients (PUP) with SHB enrolled into the PedNet cohort were included. Detailed data was collected for the first 50 ED, followed by the annual collection of the inhibitor status and allergic re-actions. The presence of inhibitors was defined by at least two consecutive positive samples. Additionally, data on FIX gene mutation was collected. One hundred and fifty-four PUP with SHB were included; 75% were followed up until 75 ED, and 43% until 500 ED. Inhibitors developed in 14 patients (seven high-titer). The median number of ED at inhibitor manifestation was 11 (interquartile range [IQR]: 6.5-36.5). The cumulative inhibitor incidence was 9.3% (95% Confidence Interval [CI]: 4.4-14.1) at 75 ED, and 10.2% (95% CI: 5.1-15.3) at 500 ED. Allergic reactions occurred in four (28.6%) inhibitor patients. Missense mutations were most frequent (46.8%) overall but not associated with inhibitors. Nonsense mutations and deletions with large structural changes comprised all mutations among inhibitor patients and were associated with an inhibitor risk of 26.9% and 33.3%, respectively. In an unselected, well-defined cohort of PUP with SHB, the cumulative inhibitor incidence was 10.2% at 500 ED. Nonsense mutations and large deletions were strongly associated with the risk of inhibitor development. The ‘PedNet Registry’ is registered at clinicaltrials.gov; identifier: NCT02979119.

Nonacog beta pegol (N9-GP) in hemophilia B: First report on safety and efficacy in previously untreated and minimally treated patients

BACKGROUND/OBJECTIVE

We report the first analysis of an extended half-life recombinant factor IX, nonacog beta pegol (N9-GP), in previously untreated patients (PUPs) and minimally treated patients with hemophilia B.

METHODS

Paradigm 6 (Safety and Efficacy of Nonacog Beta Pegol [N9-GP] in Previously Untreated Patients With Haemophilia B) is a multicenter, open-label, single-arm, phase 3 trial. Main inclusion criteria were males aged < 6 years, with hemophilia B with factor IX (FIX) activity ≤ 2%, who were previously untreated or with ≤ 3 exposure days (EDs) to FIX-containing products. Patients received N9-GP 40 IU/kg once weekly (prophylaxis) or individualized dosing (preprophylaxis). Bleeds were treated with N9-GP 40 IU/kg (80 IU/kg if severe). The primary end point was incidence of anti-FIX inhibitory antibodies (inhibitors). Secondary end points included safety outcomes and annualized bleeding rate (ABR).

RESULTS

At data cutoff (August 31, 2018), 38 patients had been screened, and 37 had received N9-GP (median age, 1.0 years [range, 0-4]). Total in-trial EDs amounted to 2833, representing ~ 65 patient-years. Two (6.1%) of 33 "at-risk" patients (patients with ≥ 10 EDs plus patients who developed inhibitors) developed high-titer inhibitors and were withdrawn. No other safety concerns, including thromboembolic events, were identified. In the prophylaxis group (n = 28), 67.9% were bleed free; all bleeds (n = 15) were treated with one N9-GP injection; and overall, spontaneous, and traumatic ABRs were low (median ABRs of 0.0, 0.0, and 0.0, respectively; modeled mean ABRs of 0.31, 0.08, and 0.23, respectively). Estimated mean FIX trough activity was 15.0%.

CONCLUSION

We report an inhibitor incidence of 6.1%, which is within the expected range for PUPs with hemophilia B. No other safety concerns were identified; moreover, N9-GP provided effective hemostatic coverage.

Molecular characterization of hemophilia B patients in Colombia

BACKGROUND

Hemophilia B (HB) is a coagulation disorder with an X-linked recessive inheritance pattern, caused by plasma FIX deficiency. In Colombia, HB is considered a rare and high-cost disease, with 362 males reported in 2017.

METHODS

Here, we characterized 20 HB apparently unrelated families by PCR amplification and Sanger sequencing.

RESULTS

Fourteen unique variants were identified: seven missense, three nonsense, one variant in the 3' UTR region, two large deletions >50 bp, and one intronic substitution that affects splicing c.520+13A>G that was present in 7/20 patients (35%). All these variants have been previously reported in the literature, except for exons 3 and 4, deletions, present in one patient. The genotype-phenotype association correlates with the reported in the literature, with the exception of one patient.

CONCLUSION

This molecular analysis allowed us to establish the causal variant of HB in 100% of patients, to provide the appropriate genetic counseling to each of the families, and to propose a more cost-effective carrier analysis. Here, we reported the first variants in Colombian population with Hemophilia B, finding a new variant and one intron recurrent variant present in 35% of patients.

Prevention and Management of Bleeding Episodes in Children with Hemophilia

Regular prophylactic treatment with factor VIII (FVIII) and factor IX (FIX) concentrates in hemophilia A and B, respectively, is introduced in early infancy and has resulted in dramatic improvement of the conditions. Recombinant FVIII and FIX concentrates have been available for > 25 years and have been modified and refined through the years; however, unfortunately frequent intravenous administrations are still necessary. The half-lives of these products have now been extended (EHL) by fusion with albumin, the Fc-portion of IgG, or by being PEGylated. This has been very successful for EHL-FIX, with 3-5 times longer half-life, and to a lesser degree for EHL-FVIII with a half-life extension of only 1.5 times the conventional products. New treatment principles using FVIII mimetics or monoclonal antibodies that rebalance the pro- and anti-coagulation system by interfering with production of anti-thrombin or tissue factor pathway inhibitor have the benefits of long-lasting activity, subcutaneous administration, and being useful in patients both with and without neutralizing antibodies. As the ultimate treatment, recent progress has also been made with gene therapy of both hemophilia A and B.

Navigating Speed Bumps on the Innovation Highway in Hemophilia Therapeutics

The unprecedented emergence of novel therapeutics for both hemophilia A and B during the last half decade has been accompanied by the promise of even more extraordinary progress in ameliorative and curative strategies for both disorders. Paradoxically, the speed of innovation has created new dilemmas for persons with hemophilia and their physicians with respect to optimizing individual choices from the expanding menu of standard and novel therapies and approaches to symptom or risk reduction, and ultimately, to normalizing the hemophilia phenotype. Among the most disruptive new approaches, challenges remain in the form of the adverse reactions that have been observed with nonfactor therapies, as well as in the uncertain long-term safety profile of potentially curative gene therapy. Together, these challenges have generated uncertainty as to how to adopt novel therapies and treatment strategies across a diverse patient population, creating speed bumps on the hemophilia innovation highway. It is from this perspective that this article discusses the current state of gene therapy and bleeding prophylaxis for hemophilia A and B, as well as prevention and treatment of the factor VIII inhibitor phenotype in hemophilia A. It further posits that these speed bumps may provide important clues to the mechanistic understanding of both symptom manifestation and resilience within the hemophilia phenotype, as well as opportunities to reconsider and reconfigure the current paradigms for symptom prediction and individualized therapeutic decision making.

Mutation Spectrum and Genotype-Phenotype Analyses in a Pakistani Cohort With Hemophilia B

This study aimed to (1) identify F9 genetic alterations in patients with hemophilia B (HB) of Pakistani origin and (2) determine the genotype-phenotype relationships in these patients. Diagnosed cases of HB were identified through registries at designated tertiary health-care centers across the country. Consenting patients were enrolled into the study. The factor IX (FIX) coagulation activity (FIX:C) and key clinical features were recorded. Direct sequencing of F9 was carried out in all patients. All the variants identified were analyzed for functional consequences employing in silico analysis tools. Accession numbers from National Center of Biotechnology Information ClinVar database were retrieved for the novel variants. Genotype-FIX:C relationships were determined followed by FIX:C clinical phenotype assessment. A total of 52 patients with HB from 36 unrelated families were identified, which mainly comprised patients with moderate HB (n = 35; 67.3%). Among these, 35 patients from 22 unrelated families could be contacted and enrolled into the study. Missense variants were the most frequent (58.8%), followed by nonsense variants (17.6%). A missense, a short insertion, and a nonsense novel variants in exon 2, 6, and 7, respectively, were also identified. The disease manifested FIX:C heterogeneity in relation to the corresponding mutation in a significant number of cases. Clinical phenotype heterogeneity was also observed in relation to FIX:C-based severity assessment. We concluded that the registered FIX-deficient population of Pakistan mainly comprises moderate HB. F9 mutation spectrum in Pakistani patients with HB is heterogeneous. The HB population of Pakistan manifests a significant amount of genotype-FIX:C and FIX:C-clinical phenotype heterogeneities.