Inhibitor development is the major treatment complication in children with severe hemophilia A. It is not clear whether the risk of inhibitors is higher with recombinant factor VIII or with ...plasma-derived factor VIII. We used multivariate analysis to compare 2 cohorts of previously untreated patients (PUPs) with severe hemophilia A: 62 patients treated with the same brand of high-purity plasma-derived FVIII (pFVIII) containing von Willebrand factor (VWF) and 86 patients treated with full-length recombinant FVIII (rFVIII). In addition to the usual end points (all inhibitors, high inhibitors), we also examined a third end point (high inhibitors and/or immune tolerance induction). The risk of inhibitor development was higher in patients treated with rFVIII than in patients treated with pFVIII, regardless of other risk factors (F8 genotype; nonwhite origin; history of inhibitors in patients with a family history of hemophilia; age at first FVIII infusion). The adjusted relative risk (RRa) for inhibitor development with rFVIII versus pFVIII was 2.4 (all inhibitors), 2.6 (high inhibitors), and 3.2 (high inhibitors and/or immune tolerance induction), respectively, depending on the end point (above). The pathophysiology of this large effect must be understood in order to improve the characteristics of recombinant products and to reduce the incidence of inhibitors to FVIII.
Inhibitors in haemophilia are a serious complication that may render usual replacement therapy ineffective. The risk is greatest in previously untreated children with severe haemophilia A. The role ...of replacement factor VIII in this group is an important issue.
Until now, few clinical studies have correctly taken into account the variety of cofactors involved in inhibitor development: genetic (familial antecedents, ethnicity, F8 and immune response genotypes), and environmental cofactors (age at first infusion, prophylaxis and intensity of treatment). This is a prerequisite to correctly evaluating the putative role of the type of factor replacement. Prospective cohort studies are therefore urgently needed. Depending on the expected inhibitor risk in the reference group, the intensity of the relationship between risk factor and endpoint, the duration of patient follow up, and the design of the study (balanced or unbalanced groups), cohorts including 200-500 previously untreated children should be sufficient to demonstrate an increased intensity of risk of about 2 or more with one product compared with another.
Aside from clinical studies, fundamental research is essential to test the multiple hypotheses that could explain a difference in inhibitor risk between the currently available factor VIII concentrates in order to develop less immunogenic factor VIII.
Fifteen previously untreated patients (Pups) with severe haemophilia B (factor IX activity < or = 2 U/dl) only treated with one brand of plasma-derived high purity factor IX concentrate (FIX LFB) ...were studied. Age at first injection varied from 1 to 137 months and follow-up since this first injection from 21 to 86 months (median: 35). Cumulative exposure days (CED) were from 4 to over 100 (median: 26). Among these 15 Pups only one developed an inhibitor. Mutation analysis performed in all patients showed total gene deletion in the patient with inhibitor, partial gene deletion in another one, and missense mutations in 9 families. Mutation was not found in one patient. Actually, according to the data already published, only two patients were at high risk for inhibitor development in our population. Our study, although rather small, confirms the previously reported low incidence of inhibitors in haemophilia B. Large studies on incidence of FIX inhibitors are indeed difficult to perform, due to both the overall small number of severe haemophilia B patients and the low incidence of FIX inhibitors. Consequently, the impact of bias, such as prevalence of different types of gene defects in a given population, is major. Therefore, any study, dealing with incidence of FIX inhibitors in severe haemophilia B should report, for each patient, the type of gene defect.
Glanzmann's thrombasthenia (GT) is a rare congenital bleeding disorder caused by deficiency or dysfunction of platelet surface glycoprotein (GP) IIb/IIIa receptor. Platelet transfusion is the ...standard treatment for bleeding that remains non-responsive to conservative measures, and for surgical coverage. Platelet transfusions, however, may result in the development of antibodies to GPIIb/IIIa and/or human leukocyte antigen (HLA), rendering further transfusions ineffective. Recombinant human activated factor VII (rFVIIa; NovoSeven/Niastase Canada, Novo Nordisk, Bagsvaerd, Denmark) has documented efficacy in GT patients, and is approved in the European Union for the treatment of GT patients with platelet antibodies and platelet refractoriness. However, there are insufficient data to determine the optimal rFVIIa regimen (eg, for major surgery) or to allow thorough safety evaluation (eg, thrombotic risk). A post-marketing, prospective, observational, multinational registry has been developed to collect data on the efficacy and safety of rFVIIa in the treatment and prevention of bleeding in GT patients with platelet antibodies or platelet refractoriness. Patients treated with other hemostatic agents or rFVIIa to avoid the development of antibodies against GPIIb/IIIa will also be reported. Standardized data will be collected using a customized internet-based (www.glanzmann-reg.org) data collection tool. Data collection will begin in 2005 and continue for up to 6 years. Patients of all ages from any country are eligible for inclusion.
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