Hemophilia B (Factor IX Deficiency)

Outcome measures analysis following total knee arthroplasty in patients with severe haemophilic arthropathy of the knee

Total knee arthroplasty (TKA) has been the gold standard for treating severe haemophilic arthropathy of the knee when all conservative measures fail. However, performing a TKA in patients with haemophilic arthropathy is difficult due to severe joint deformity and destruction, and poor bone quality. The aim of the present study was to evaluate the short-term results of TKA in the treatment of knee haemophilic arthropathy in a tertiary referral centre, with an emphasis on health-related quality of life and knee function. A prospective study was conducted that included 19 male patients with end-stage haemophilic knee arthropathy who underwent TKA in a tertiary referral centre. Clinical outcome and health-related quality of life were assessed by the Western Ontario and McMaster Universities Arthritis (WOMAC) index and the Short Form-36 (SF-36) both pre-operatively and at 1-year post-operatively. The mean age of the patients was 50.37±7.63 years (range, 40-65 years). Pre-operative health-related quality of life was impaired in all patients in all SF-36 domains but was markedly improved after TKA. Knee function in all dimensions (pain, stiffness and physical function), as measured by the WOMAC questionnaire, significantly improved after TKA. Pre-operative pain, stiffness and function, along with total WOMAC score, were strongly and negatively correlated with pre-operative SF-36. Overall, the present study indicated a significant improvement in quality of life and clinical outcome after TKA in patients with advanced haemophilic arthropathy. More studies with longer follow-up periods in a larger population are needed to fully elucidate the mid- and long-term values of TKA in haemophilic patients.

Six-Year, Real-World Use of Prophylaxis with Recombinant Factor IX-Albumin Fusion Protein (rIX-FP) in Persons with Hemophilia B: A Single-Center Retrospective-Prospective Study

Background: Extended half-life (EHL) factor IX (FIX) concentrates allow for prophylaxis with prolonged dosing intervals and high bleeding protection in persons with hemophilia B. Long-term real-world studies are lacking. Methods: In a retrospective-prospective study, the six-year use of prophylaxis with the EHL recombinant FIX-albumin fusion protein (rIX-FP) was analyzed, comparing outcomes with previous standard half-life (SHL) FIX in patients already on prophylaxis. Results: Prophylaxis with rIX-FP was prescribed in 15 patients (10 severe, 5 moderate; follow-up: 57 ± 17 months). Based on a pharmacokinetic assessment and clinical needs, the first regimen was 47 ± 7 IU/Kg every 9 ± 2 days. All but one patient remained on rIX-FP prophylaxis, adjusting infusion frequency and/or dose; the last prescribed frequency was ≥10 days in 10/13 patients, being reduced in seven and increased in four vs. the first regimen. The weekly FIX dose was unchanged; FIX trough levels were >5% in all patients. The annual infusion number and FIX IU/Kg significantly decreased (~60%) in eight patients previously on SHL FIX prophylaxis, with similar concentrate costs. Very low bleeding rates (most traumatic bleeds and the last quartile of the infusion interval), improved orthopedic and pain scores, unchanged HEAD-US scores and problem joints, and high treatment adherence (>90%) and satisfaction were registered. Conclusions: Personalized, carefully adjusted rIX-FP regimens contribute to the diffusion and optimization of prophylaxis in persons with severe and moderate hemophilia B, with long-term favorable bleeding, joint, and patient-reported outcomes.

Factor IX administration in the skin primes inhibitor formation and sensitizes hemophilia B mice to systemic factor IX administration

Background

Factor IX inhibitor formation is the most serious complication of replacement therapy for the bleeding disorder hemophilia B, exacerbated by severe allergic reactions occurring in up to 60% of patients with inhibitors. Low success rates of immune tolerance induction therapy in hemophilia B necessitate the search for novel immune tolerance therapies. Skin-associated lymphoid tissues have been successfully targeted in allergen-specific immunotherapy.

Objectives

We aimed to develop a prophylactic immune tolerance protocol based on intradermal administration of FIX that would prevent inhibitor formation and/or anaphylaxis in response to replacement therapy.

Methods

We measured FIX inhibitor, anti-FIX immunoglobulin G1, and immunoglobulin E titers using the Bethesda assay and enzyme-linked immunosorbent assay after 4 weeks of twice-weekly intradermal FIX or FIX-Fc administration followed by 5 to 6 weeks of weekly systemic FIX injections in C3H/HeJ hemophilia B mice. We also measured skin antigen-presenting, follicular helper T, and germinal center B cell frequencies in skin-draining lymph nodes after a single or repeat intradermal FIX administration.

Results

Intradermal administration enhanced FIX inhibitor formation in response to systemic administration. We further found that intradermal administration alone triggers inhibitor formation, even at a low dose of 0.4 IU/kg, which is 100-fold lower than the intravenous dose of 40 IU/kg typically required to induce inhibitor development in hemophilia B mice. Also, intradermal administration triggered germinal center formation in skin-draining lymph nodes and sensitized mice to systemic administration. Factor IX-Fc fusion protein did not modulate inhibitor formation.

Conclusion

Intradermal FIX administration is highly immunogenic, suggesting that the skin compartment is not amenable to immune tolerance induction or therapeutic delivery of clotting factors.

Magnesium Deficiency and Cardiometabolic Disease

Magnesium (Mg²⁺) has many physiological functions within the body. These include important roles in maintaining cardiovascular functioning, where it contributes to the regulation of cardiac excitation-contraction coupling, endothelial functioning and haemostasis. The haemostatic roles of Mg²⁺ impact upon both the protein and cellular arms of coagulation. In this review, we examine how Mg²⁺ homeostasis is maintained within the body and highlight the various molecular roles attributed to Mg²⁺ in the cardiovascular system. In addition, we describe how nutritional and/or disease-associated magnesium deficiency, seen in some metabolic conditions, has the potential to influence cardiac and vascular outcomes. Finally, we also examine the potential for magnesium supplements to be employed in the prevention and treatment of cardiovascular disorders and in the management of cardiometabolic health.

Molecular pathogenesis of a novel Met394Thr variant causing hemophilia B

BACKGROUND

Hemophilia B (HB), a rare bleeding disorder, shows X-linked recessive inheritance and is caused by heterogeneous variants in the FIX gene (F9) encoding coagulation factor IX (FIX). This study aimed to investigate the molecular pathogenesis of a novel Met394Thr variant causing HB.

METHODS

We used Sanger sequencing to analyze F9 sequence variants in members of a Chinese family with moderate HB. Subsequently, we performed in vitro experiments on the identified novel FIX-Met394Thr variant. In addition, we performed bioinformatics analysis of the novel variant.

RESULTS

We identified a novel missense variant (c.1181T>C, p.Met394Thr) in a Chinese family with moderate HB in the proband. The proband's mother and grandmother were carriers for the variant. The identified FIX-Met394Thr variant did not affect the transcription of F9 and the synthesis and secretion of FIX protein. The variant may, therefore, affect the physiological function of FIX protein by disrupting its spatial conformation. In addition, another variant (c.88+75A>G) in intron 1 of F9 was identified in the grandmother, which may also affect FIX protein function.

CONCLUSION

We identified FIX-Met394Thr as a novel causative variant of HB. Further understanding of the molecular pathogenesis underlying FIX deficiency may guide novel strategies for precision HB therapy.

The Molecular Basis of FIX Deficiency in Hemophilia B

Coagulation factor IX (FIX) is a vitamin K dependent protein and its deficiency causes hemophilia B, an X-linked recessive bleeding disorder. More than 1000 mutations in the F9 gene have been identified in hemophilia B patients. Here, we systematically summarize the structural and functional characteristics of FIX and the pathogenic mechanisms of the mutations that have been identified to date. The mechanisms of FIX deficiency are diverse in these mutations. Deletions, insertions, duplications, and indels generally lead to severe hemophilia B. Those in the exon regions generate either frame shift or inframe mutations, and those in the introns usually cause aberrant splicing. Regarding point mutations, the bleeding phenotypes vary from severe to mild in hemophilia B patients. Generally speaking, point mutations in the F9 promoter region result in hemophilia B Leyden, and those in the introns cause aberrant splicing. Point mutations in the coding sequence can be missense, nonsense, or silent mutations. Nonsense mutations generate truncated FIX that usually loses function, causing severe hemophilia B. Silent mutations may lead to aberrant splicing or affect FIX translation. The mechanisms of missense mutation, however, have not been fully understood. They lead to FIX deficiency, often by affecting FIX’s translation, protein folding, protein stability, posttranslational modifications, activation to FIXa, or the ability to form functional Xase complex. Understanding the molecular mechanisms of FIX deficiency will provide significant insight for patient diagnosis and treatment.