The first report of a multi‐exon duplication in the F9 gene causative of severe haemophilia B
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Haemophilia B
General hospital
Haemophilia A and B are relatively rare, X-linked inherited bleeding disorders which are life-threatening to patients unless treated by regular injections of factors VIII or IX, respectively. Gene therapy offers the prospect of a cure for the disease, thus potentially freeing patients from the existing regimens of regular intravenous injection of proteins and the risks of infection by contaminating viruses. Although, in theory, gene therapy is very attractive to patients and clinicians, in practice, preclinical experiments in animal models suggests that it may be difficult to obtain adequate therapeutic levels of either factors VIII or IX for long periods of time in patients unless improved methods can be devised. Progress in the preclinical studies is more encouraging with haemophilia B than with haemophilia A. Clinical trials for haemophilia B patients have started in China.
Haemophilia B
Factor IX
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Haemophilia is an X-linked inherited clotting disorder with a prevalence of 1 per 5000 men. A deficiency of clotting factor VIII (FVIII; haemophilia A) or IX (FIX; haemophilia B) causes haemophilia patients to suffer from spontaneous bleeding and excessive blood-loss following surgery or trauma. Prophylactic administration of a factor VIII- or factor IX-concentrate is the standard treatment for children with severe haemophilia. Women who are carriers of the F8 or F9 gene mutation can have a lowered plasma concentration of factor VIII or IX, and thus suffer from a mild form of haemophilia. Drugs that have a negative influence on blood clotting, such as NSAIDs, can lead to life-threatening bleeding in haemophilia patients. One of the main complications of haemophilia treatment is the formation of inhibiting antibodies that inactivate FVIII or FIX. Haemophilia patients should be treated by a multidisciplinary team in a hospital with a haemophilia treatment centre.
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Clotting factor
Factor IX
Blood clotting
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The incidence of living haemophiliacs in Sweden (total population 8.1 millions) is about 1:15,000 males and about 1:30,000 of the entire population. The number of haemophiliacs born in Sweden in 5-year periods between 1931-1975 (June) has remained almost unchanged. The total number of haemophilia families in Sweden is 284 (77% haemophilia A, 23% haemophila B) with altogether 557 (436 with A and 121 with B) living haemophiliacs. Of the haemophilia A patients 40% have severe, 18% moderate, and 42% mild, haemophilia. The distribution of the haemophilia B patients is about the same. Inhibitors have been demonstrated in 8% of the patients with severe haemophilia A and in 10% of those with severe haemophilia B. There are 2 main Haemophilia Centres (Stockholm, Malmö) to which haemophiliacs from the whole of Sweden are admitted for diagnosis, follow-up and treatment for severe bleedings, joint defects and surgery. Minor bleedings are treated at local hospitals in cooperation with the Haemophilia Centres. The concentrates available for treatment in haemophilia A are human fraction I-0 (AHF-Kabi), cryoprecipitate, Antihaemophilic Factor (Hyland 4) and Kryobulin (Immuno, Wien). AHF-Kabi is the most commonly used preparation. The concentrates available for treatment in haemophilia B are Preconativ (Kabi) and Prothromplex (Immuno). Suffcient amounts of concentrates are available. In Sweden 3.2 million units of factor VIII and 1.0 millino units of factor IX are given per year. Treatment is free of charge. Only 5 patients receive domiciliary treatment, but since 1958 we in Sweden have practised prophylactic treatment of boys (4-18 years old) with severe haemophilia A. At about 5-10 days interval they receive AHF in amounts sufficient to raise the AHF level to 40-50%. This regimen has reduced severe haemophilia to moderate. The joint score is identical with that found in moderate haemophilia in the same age groups. For treatment of patients with haemophilia A and haemophilia B complicated by inhibitors we have used a large dose of antigen (factor VIII or factor IX) combined with cyclophosphamide. In most cases this treatment produced satisfactory haemostasis for 5 to 30 days and prevented the secondary antibody rise.
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Cryoprecipitate
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Haemophilia B
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Summary. Frequent evaluation of haemophilia treatment is necessary to improve patient care. The 2010 Practice Patterns Survey (PPS) investigated current trends in haemophilia treatment in the United States, as reported by nurses. The aim was to document practice patterns for haemophilia A and haemophilia B Survey questionnaires were sent to nurses at haemophilia treatment centres (HTCs) across the United States. Seventy‐one of 126 HTCs (56%) responded to the survey. Factor dosage across treatment modalities ranged from 20 to 50 IU kg ‐1 for severe haemophilia A. Dosage for severe haemophilia B was more variable (<40 to >100 IU kg ‐1 ). On‐demand dosing regimens were inconsistent for haemophilia A and more so for haemophilia B. Rates of adherence to prescribed treatment were similar for both haemophilia types (∼80%). The main barrier to adherence was identified as inconvenience. More bleeding episodes occurred in adults (16.6 bleeding episodes per year) with severe haemophilia A than in younger patients (11.3 bleeding episodes per year) before switching patients to prophylaxis. For both haemophilia types, most patients who switched from prophylaxis to on‐demand treatment were aged 13–24 years; these patients also had the lowest adherence (60–71%). More paediatric patients with severe haemophilia A and inhibitors (53%) received prophylactic bypassing therapy than their haemophilia B counterparts (38%). Adults with severe haemophilia A faced challenges in relation to co‐morbidities and long‐term care. This PPS provides insights into previously unexplored aspects of haemophilia care that will serve to increase awareness and promote discussion of current issues affecting haemophilia patient care.
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Summary. This survey provides new information on the severity of factor IX deficiencies among patients being treated for haemophilia B and on the prevalence of factor IX inhibitors in this population. A questionnaire was sent to 150 haemophilia treatment centres in the United States and Canada. 82 centres responded and provided data on 1967 patients with haemophilia B. 37% of these patients had severe haemophilia B (<1% of the normal level of factor IX), 33% had moderate haemophilia B (1–5% of the normal level of factor IX), and 30% had mild haemophilia B (>5% of the normal level of factor IX). Only 29 (1.5%) of the patients had factor IX inhibitors; 28 of these patients (96.6%) had severe haemophilia B, and one of these patients (3.4%) had moderate haemophilia B. Factor IX inhibitor titres were 0.6–1 Bethesda unit (BU) in seven patients, > 1–5 BU in four patients, > 5–10 BU in one patient, and > 10 BU in 17 patients. Factor IX inhibitors are much less common in patients with haemophilia B than in patients with haemophilia A.
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Summary. Prophylaxis is standard of care for boys with severe haemophilia A. Indications for prophylaxis in adulthood, non‐severe haemophilia A, haemophilia B and haemophilia with inhibitors are less well defined. This survey, conducted in 2006, aimed to describe prophylaxis use in patients of all ages and severities with haemophilia A or haemophilia B in Canada. Data on 2663 individuals (2161 haemophilia A; 502 haemophilia B), including 78 inhibitor‐positive patients, were returned by 22/25 Canadian haemophilia treatment centres. This represented 98% of the Canadian haemophilia population. Frequency of prophylaxis use, defined as infusion of factor VIII/IX concentrate at least once weekly for ≥45 weeks of the year, was highest in individuals with severe haemophilia A (69%). It was lower in individuals with severe haemophilia B (32%), moderate haemophilia A (18%) or B (5%) and mild haemophilia A (1%) or B (1%). Among individuals with severe haemophilia A, the frequency of prophylaxis use was 84% in children (≤18 years) and 55% in adults (>18 years). Thirteen per cent of inhibitor‐positive individuals were receiving prophylaxis with bypassing agents. Comparison with data obtained from a 2002 Canadian survey showed a greater use of prophylaxis in children ≤5 years of age with severe haemophilia A (73% vs. 49%). Prophylaxis is no longer confined to children with severe haemophilia A, but is used in a significant proportion of adults with severe haemophilia A and individuals with severe haemophilia B or moderate haemophilia A. Prophylaxis is being started earlier in boys with severe haemophilia A.
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Whilst the global prevalence of haemophilia B is less than that of haemophilia A, rapid and remarkable innovations have been made in the development of haemophilia B therapies in the last decade. The most recent developments are the evolution of extended half-life haemophilia B replacement therapies which are designed to reduce the treatment burden associated with prophylactic infusion of factor IX (FIX) to prevent bleeding in haemophilia B participants. Clinical development programmes have culminated in the completion of three phase III studies on extended half-life (EHL) recombinant FIX (rFIX) products and subsequent approval and registration of these in many countries around the world. Current data from the three EHL rFIX clinical studies indicate that these products have acceptable safety profiles with no allergic reactions, thromboembolic phenomena or neutralizing antibodies when given to previously treated adolescent and adults for the prevention of bleeds, for the treatment of bleeds and in the perisurgical haemostasis use. Studies in previously untreated paediatric participants are currently ongoing. The EHL rFIX products have the potential impact to reduce the treatment burden associated with prophylactic infusion of replacement FIX, to treat and prevent bleeds in participants with haemophilia B and to improve the participant’s health-related quality of life. The impact of EHL rFIX is likely to be modified by current development of other haemophilia B therapy such as antitissue factor pathway inhibitors and haemophilia B gene therapy. In this review, we aim to provide an update on the safety and efficacy data from the three EHL rFIX clinical studies and to consider their roles in the face of novel haemophilia B therapy currently evolving.
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Factor IX
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Haemophilia B
Clotting factor
Factor IX
Arthropathy
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