The Clinical Genetics of Hemophilia B (Factor IX Deficiency)

The genetic analysis of eight families with hemophilia B in Mongolia: Identification of two novel mutation

BACKGROUND

This study aimed to conduct molecular diagnostics among individuals with hemophilia B (HB) and carriers of hemophilia in Mongolia.

METHODS

Eight patients (six severe, two mild) with HB and their 12 female relatives were enrolled from eight families. Sanger sequence was performed for mutation identification. The questionnaire survey was conducted to evaluate carrier symptoms in female relatives.

RESULTS

Two families had a history of HB. A total of five different variants (c.223C > T; c.344A > G; c.464G > C; c.187_188del; and c.1314_1314delA) were identified in six patients with severe HB. Of these, two (c.187_188del and c.1314_1314delA) were novel. No variant in the entire F9 was found in two patients with mild HB. Nonsense c.223C > T (p.Arg75*) mutation was detected in two unrelated patients. Carrier testing identified five mothers as carriers, while one younger sister was a non-carrier. The carrier status of six female relatives of the two mild patients remained undetermined. By questionnaire survey, only one of the five genetically identified carriers displayed noticeable symptoms of being a carrier.

CONCLUSION

The novel variants c.187_188del and c.1314_1314delA can cause severe hemophilia B. This study did not observe a significant association between symptoms and carrier status in the five carriers.

Joint deficiency of coagulation factors VII and IX: a case report

The diagnostic and therapeutic approach for an unusual clinical situation is presented. Twenty-three-year-old female patient is evaluated for hematuria and metrorrhagia. She reported irregular follow-up with hematology because of bleeding in childhood. She has also been receiving factor VII for 2 years, denying hospitalizations because of bleeding. Laboratory reported hb: 5.2 g/dl; platelets: 234 000/mm 3 ; PT: 100 s; PTT: 112 s, fibrinogen: 90 mg/dl without other alterations. Abdominal ultrasound reported uterine myoma, urinalysis was pathological. The gynecology indicated oral progesterone. She started antibiotic therapy, transfusion of red-blood cells, plasma, and cryoprecipitates and subsequently reported: factor VII: 2%, IX: 1% and VIII: 70%. She received factor VII-recombinant (rFVII), achieving resolution of bleeding. She was prescribed prophylactic rFVII and hematology monitoring. Readmission due to acute abdomen with Hb 5 g/dl, prolonged prothrombin time (PT)/partial thromboplastin time (PTT) and abdominal tomography reported hemoperitoneum. She received rFVII and required laparotomy and left oophorectomy. Then readmission to metrorrhagia, hb6 g/dl, prolonged PT/PTT and factor VII-IX of two coagulation factors were reported, without reports found in the literature consulted.

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.

Fidanacogene Elaparvovec: First Approval

Fidanacogene elaparvovec (PrBEQVEZ™) is an adeno-associated viral (AAV) vector-based gene therapy developed by Spark Therapeutics (a subsidiary of Roche) and Pfizer (under a license from Spark Therapeutics) for the treatment of haemophilia B. In December 2023, fidanacogene elaparvovec received its first approval for the treatment of adults (aged ≥ 18 years) with moderately severe to severe haemophilia B (congenital factor IX deficiency) who are negative for neutralizing antibodies to variant AAV serotype Rh74 (AAVRh74var). Fidanacogene elaparvovec is under regulatory review in the USA and the European Union and clinical studies are ongoing in multiple countries. This article summarizes the milestones in the development of fidanacogene elaparvovec leading to this first approval for moderately severe to severe (factor IX activity ≤ 2%) haemophilia B who are negative for neutralizing antibodies to AAVRh74var.

Spontaneous postoperative bleeding after periodontal procedure: An alarming sign of bleeding disorder

The prevalence of inherited bleeding disorders (BDs) is low in the general population (10-20 per 100,000 individuals), particularly hemophilia B cases, which may remain undiagnosed for a very long time until exposed to some surgical procedure. The dental professional must be aware of the possibility that patients with no previous history of abnormal bleeding may manifest their first bleeding episode in the dental office. Particularly as periodontists, we often encounter patients with bleeding gums and severe bleeding complications may precipitate while performing routine periodontal procedures. Hence, we must have a thorough knowledge of BDs and their management in challenging hemorrhagic situations. Management of such patients necessitates a multidisciplinary approach by involving the patient's hematologist and advanced laboratory facilities. The present case report is an attempt to discuss the diagnosis and management of a bleeding episode that occurred post periodontal flap surgery in an undiagnosed hemophilia B patient.

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.

Acquired Hemophilia A in a Female: A Case Report

INTRODUCTION: Coagulation factor deficit is a very uncommon hemostatic condition in which a single component or numerous factors are lacking. Hereditary coagulation factor defects are autosomal recessive, meaning that they can affect both men and women. However, hemophilia A, caused by lack of clotting factor VIII (FVIII), is an X-linked condition. Acquired hemophilia A (AHA) is a bleeding disorder caused by autoantibodies to FVIII. It should be distinguished from congenital hemophilia, an inherited disorder caused by a mutation in the FVIII gene. Here, we report the first known case in Indonesia, a 24-year-old female diagnosed with AHA. CASE PRESENTATION: A 24-year-old woman was referred to our facility for prolonged epistaxis. She had no previous history of extended menstrual flow or frequent epistaxis episodes, and there was no history of epistaxis or prolonged bleeding in her family. Bleeding time and prothrombin time were both normal, but time to activate partial thromboplastin was longer. The patient was diagnosed with AHA after von Willebrand disease (VWD) was ruled out. DISCUSSION: In some rare situations, females can be affected by X-linked illnesses such as hemophilia A and B. This may be due to a carrier mother or affected father, skewed X chromosome inactivation, Turner syndrome, inhibitory antibodies (acquired hemophilia), or a random mutation on the active X chromosome. In such instances, treatment is challenging. The usual treatment of choice is recombinant coagulation factors. CONCLUSION: Although VWD is the most frequent hereditary bleeding problem in females, other rare disorders such as AHA may be implicated. Clinicians should be aware of this when faced with patients that lack a history of bleeding disorders. Furthermore, AHA should be considered as a differential diagnosis in every female patient suffering from hemorrhage. Therefore, a comprehensive diagnostic approach is needed.

Investigation of the Bleeding Tendency in Sudanese Female Carriers of Hemophilia B

Background. Hemophilia (HB) is an X-linked, recessive bleeding disorder characterized by the deficiency or absence of the coagulation factor IX. Usually, females are carriers of the trait, while males are affected. FIX deficiency leads to uncontrollable bleeding events, and the severity is dependent on the levels of the clotting factor. The objective of this research was to measure the prevalence of bleeding tendency in Sudanese carriers of HB. Materials and Methods. In this cross-sectional study, 88 Sudanese carriers of HB participated. The activated partial thromboplastin time test (APTT) and FIX test were performed for each carrier. The frequencies of DNA polymorphism and FIX-linked restriction fragments BamHI, HhaI, and MnII were also assessed. The study was conducted in Khartoum, Sudan, during the period from 2015 to 2017. Results. The study showed that 55 (62.5%) HB carriers were from the Laban village in the White Nile State, and all of them were members of the Shinkheb tribe. The mean age of the study population was 26.3 years. Among the carriers, 57 (64.7%) had abnormal coagulation profiles. The mean value of the APTT level among carriers was significantly increased ( $P$ value: 0.000), while the mean concentration of the FIX levels among the carriers was significantly decreased ( $P$ value: 0.000). The study also showed a negative correlation between PTT and F assay with $P$ value of 0.000 and $R$ value of 0.578. Conclusion. The APTT is high in most carriers and the FIX assay level is low in most carriers. Most carriers had no symptoms and were not bleeding. The Shinkheb tribe is the most ethnic tribe carrying HB (62.5%). HhaII is more informative for carrier detection than others, but it is of significant value if both (MnII and HhaII) were performed in parallel. In Sudanese, BamHI was informative but MnII and HhaII were best in the mutation detection and for prenatal diagnosis.

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.