Mutational Profiles of F8 and F9 in a Cohort of Haemophilia A and Haemophilia B Patients in the Multi-ethnic Malaysian Population

F8/F9 variants in the population-based PedNet Registry cohort compared with locus-specific genetic databases of the European Association for Haemophilia and Allied Disorders and the Centers for Disease Control and Prevention Hemophilia A or Hemophilia B Mutation Project

Background

Hemophilia A and B are caused by variants in the factor (F) VIII or FIX gene. Selective reporting may influence the distribution of variants reported in genetic databases.

Objectives

To compare the spectrum of F8 and F9 variants in an international population-based pediatric cohort (PedNet Registry) with the spectrum found in the European Association for Haemophilia and Allied Disorders (EAHAD) and the Centers for Disease Control and Prevention Hemophilia A or Hemophilia B Mutation Project (CHAMP/CHBMP) databases.

Methods

All patients registered in the PedNet Registry on January 1, 2021 were included in this study. As comparators, data from patients with severe hemophilia included in the CHAMP/CHBMP registry (US center data) and EAHAD were used.

Results

Genetic information was available for 1941 patients. Intron 22 inversion was present in 52% of patients with severe hemophilia A; frameshift (36%), missense (28%), and nonsense (20%) were the most frequent variants in patients with severe hemophilia A who were inversion-negative. The most frequent variants in severe hemophilia B were missense (48%). In nonsevere disease, most variants were missense variants (moderate hemophilia A: 91%; mild hemophilia A: 95%, moderate and mild hemophilia B: 86% each). Comparison with the databases demonstrated a higher proportion of missense variants associated with severe hemophilia B in EAHAD (68%) than in PedNet (48%) and CHBMP (46%).

Conclusion

The PedNet population-based cohort provides an alternative to the established databases, which collect data by selective reporting, as it is a well-maintained database covering the full spectrum of pathogenic F8 and F9 variants, and indicates the number of patients affected by each particular variant.

Mutation analysis and characterisation of F9 gene in haemophilia- B population of India

Background

Hemophilia B (HB) is an X-linked bleeding disorder resulting from coagulation factor IX defects. Over 3,000 pathogenic, HB-associated mutations in the F9 gene have been identified. We aimed to investigate the role of F9 variants in 150 HB patients using sequencing technology.

Methods

F9 gene sequences were amplified from peripheral blood-derived DNA and sequenced on an Applied Biosystems (ABI) 3500 Sanger sequencing platform. Functional and structural predictions of mutant FIX were analyzed.

Results

Among 150 HB patients, 102 (68%), 30 (20%), and 18 (12%) suffered from severe, moderate, and mild HB, respectively. Genetic analysis identified 16 mutations, including 3 novel mutations. Nine mutations (7 missense and 2 stop-gain) were found to be pathogenic. Only 3 mutations (c.127C>T, c.470G>A, and c.1070G>A) were associated with different severities. While 2 mutations were associated with mild HB cases (c.304C>T and c.580A>G), 2 (c.195G>A and c.1385A>G) and 3 mutations (c.223C>T, c.1187G>A, and c.1232G>A) resulted in moderate and severe disease, respectively. Additionally, 1 mutation each was associated with mild-moderate (c.*1110A>G) and mild-severe HB disease (c.197A>T), 4 mutations were associated with moderate-severe HB cases (c.314A>G, c.198A>T, c.676C>T, and c.1094C>A). FIX concentrations were lower in the mutated group (5.5±2.5% vs. 8.0±2.5%). Novel p.E66D and p.S365 mutations were predicted to be pathogenic based on changes in FIX structure and function.

Conclusion

Novel single nucleotide polymorphisms (SNPs) largely contributed to the pathogenesis of HB. Our study strongly suggests that population-based genetic screening will be particularly helpful to identify risk prediction and carrier detection tools for Indian HB patients.

Molecular study of a large cohort of 109 haemophilia patients from Cuba using a gene panel with next generation sequencing-based technology

INTRODUCTION

In several countries, molecular diagnosis of haemophilia A (HA) and B (HB) is hampered by a lack of resources for DNA analysis. The advent of next-generation sequencing (NGS) has enabled gene analysis at a reasonable cost.

AIM

Describe a collaboration between Cuban and Spanish researchers to identify candidate variants and investigate the molecular epidemiology of 106 Cuban haemophilia patients using NGS.

PATIENTS/METHODS

The molecular analysis protocol included well-established LR-PCR procedures to detect F8 inversions, NGS with a 30-gene panel to sequence F8 and F9, and multiplex ligation-dependent probe amplification to identify large structural variants.

RESULTS

One-hundred and thirty-one candidate variants were identified along F8, F9, and VWF; 72 were unique and 28 (39%) had not been previously recorded. Putative variants were identified in 105/106 patients. Molecular characterization enabled confirmation and reclassification of: 90 HA (85%), 15 HB (14%), and one type 2N VWD (1%). Null variants leading to non-production of FVIII or FIX were common in severe HA (64%), moderate HA (74%), and severe HB (60%), whereas missense variants were frequent in mild HA (57%) and moderate or mild HB (83%). Additional variants in VWF were identified in 16 patients.

CONCLUSION

This is the first description of the molecular epidemiology of HA and HB in Cuba. Variants identified in index cases will be of value for local implementation of familial studies and prenatal diagnosis using the molecular approaches available in Cuba. The results of this protocolled genetic study improved the accuracy of the clinical diagnosis and will facilitate management of these patients.

The severe spontaneous bleeding phenotype in a novel hemophilia A rat model is rescued by platelet FVIII expression

Previous studies have shown that platelet-specific factor VIII (FVIII) expression (2bF8) restores hemostasis and induces immune tolerance in hemophilia A (HA) mice even with preexisting inhibitors. Here we investigated for the first time whether platelet FVIII expression can prevent severe spontaneous bleeding in rat HA, a model mimicking the frequent spontaneous bleeding in patients with severe HA. A novel FVIII-/- rat model in a Dahl inbred background (Dahl-FVIII-/-) with nearly the entire rat FVIII gene inverted was created by using a CRISPR/Cas9 strategy. There was no detectable FVIII in plasma. Spontaneous bleeding in the soft tissue, muscles, or joints occurred in 100% of FVIII-/- rats. Sixty-one percent developed anti-FVIII inhibitors after ≥2 doses of recombinant human FVIII infusion. However, when 2bF8 transgene was crossed into the FVIII-/- background, none of the resulting 2bF8tg+FVIII-/- rats (with platelet FVIII levels of 28.26 ± 7.69 mU/108 platelets and undetectable plasma FVIII) ever had spontaneous bleeding. When 2bF8tg bone marrow (BM) was transplanted into FVIII-/- rats, only 1 of 7 recipients had a bruise at the early stage of BM reconstitution, but no other spontaneous bleeding was observed during the study period. To confirm that the bleeding diathesis in FVIII-/- rats was ameliorated after platelet FVIII expression, rotational thromboelastometry and whole-blood thrombin generation assay were performed. All parameters in 2bF8tg BM transplantation recipients were significantly improved compared with FVIII-/- control rats. Of note, neither detectable levels of plasma FVIII nor anti-FVIII inhibitors were detected in 2bF8tg BM transplantation recipients. Thus, platelet-specific FVIII expression can efficiently prevent severe spontaneous bleeding in FVIII-/- rats with no anti-FVIII antibody development.

Minimal Essential Human Factor VIII Alterations Enhance Secretion and Gene Therapy Efficiency

One important limitation for achieving therapeutic expression of human factor VIII (FVIII) in hemophilia A gene therapy is inefficient secretion of the FVIII protein. Substitution of five amino acids in the A1 domain of human FVIII with the corresponding porcine FVIII residues generated a secretion-enhanced human FVIII variant termed B-domain-deleted (BDD)-FVIII-X5 that resulted in 8-fold higher FVIII activity levels in the supernatant of an in vitro cell-based assay system than seen with unmodified human BDD-FVIII. Analysis of purified recombinant BDD-FVIII-X5 and BDD-FVIII revealed similar specific activities for both proteins, indicating that the effect of the X5 alteration is confined to increased FVIII secretion. Intravenous delivery in FVIII-deficient mice of liver-targeted adeno-associated virus (AAV) vectors designed to express BDD-FVIII-X5 or BDD-FVIII achieved substantially higher plasma FVIII activity levels for BDD-FVIII-X5, even when highly efficient codon-optimized F8 nucleotide sequences were employed. A comprehensive immunogenicity assessment using in vitro stimulation assays and various in vivo preclinical models of hemophilia A demonstrated that the BDD-FVIII-X5 variant does not exhibit an increased immunogenicity risk compared to BDD-FVIII. In conclusion, BDD-FVIII-X5 is an effective FVIII variant molecule that can be further developed for use in gene- and protein-based therapeutics for patients with hemophilia A.