Different clinical phenotype in triplets with haemophilia A.

Although many patients with haemophilia may have exactly the same residual clotting factor level, the clinical disease phenotype may vary greatly. This variation may be related to different genetic mutations responsible for haemophilia, environmental influences and co-inheritance of polymorphisms affecting the coagulation system. The study of siblings with haemophilia offers the opportunity to examine additional factors, other than genetic mutation and environment that may impact on the clinical phenotype of haemophilia.

The mutational spectrum of type 1 von Willebrand disease: Results from a Canadian cohort study.

In order to evaluate the changes within the VWF gene that might contribute to the pathogenesis of type 1 von Willebrand disease (VWD), a large multicenter Canadian study was undertaken. We present data from the sequence analysis of the VWF gene in 123 type 1 VWD index cases and their families. We have identified putative mutations within the VWF gene in 63% (n = 78) of index cases, leaving 37% (n = 45) with no identified changes.

Adenovirus-induced thrombocytopenia: the role of von Willebrand factor and P-selectin in mediating accelerated platelet clearance.

Thrombocytopenia has been consistently reported following the administration of adenoviral gene transfer vectors. The mechanism underlying this phenomenon is currently unknown. In this study, we have assessed the influence of von Willebrand Factor (VWF) and P-selectin on the clearance of platelets following adenovirus administration.

The role of immunomodulation in the management of factor VIII inhibitors.

Approximately 25% of persons with hemophilia A will have their treatment complicated by the development of anti-FVIII inhibitory antibodies. This adverse event requires the use of alternative hemostatic agents to treat bleeding and the consideration of a protocol to generate immunological tolerance to FVIII. The pathogenetic factors contributing to FVIII inhibitor generation include both patient- and concentrate-related characteristics.

Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand Factor.

von Willebrand disease (VWD) is a bleeding disorder caused by inherited defects in the concentration, structure, or function of von Willebrand factor (VWF). VWD is classified into three primary categories. Type 1 includes partial quantitative deficiency, type 2 includes qualitative defects, and type 3 includes virtually complete deficiency of VWF.

DNA microarray analysis for the detection of mutations in hemophilia A.

Background: Congenital deficiency of factor (F) VIII results in the inherited X-linked bleeding disorder hemophilia A. More than 900 different mutations are reported in the hemophilia A mutation database with the largest number of mutations being single nucleotide substitutions distributed throughout the gene. Complicating the molecular characterization of this disease is the complexity of the F8 gene, the mutational heterogeneity, and technical limitations of the current mutation detection techniques.

Genetic testing for von Willebrand disease: the Canadian experience.

Von Willebrand disease (vWD) is the most common inherited bleeding disorder in humans, but its diagnosis, using clinical criteria and phenotypic hemostasis test results, can be problematic. Since the cloning of the von Willebrand factor ( VWF) gene in the mid-1980s, a significant amount of information has been gathered with respect to the molecular pathology responsible for this trait. The extent of this information, along with major advances in genetic technology, has now made the integration of genetic testing for vWD a feasible option in some instances.

Induction of partial immune tolerance to factor VIII through prior mucosal exposure to the factor VIII C2 domain.

Background: The development of anti-factor VIII (FVIII) neutralizing antibodies (inhibitors) is a significant obstacle to FVIII replacement therapy.

Objective: As mucosal administration of an antigen may induce immune tolerance we have evaluated the efficacy of mucosal antigen exposure to achieve tolerance to FVIII.

Methods: We investigated the effects of oral and nasal administration of the purified FVIII C2 domain (FVIII-C2) to FVIII-deficient BALB/c mice prior to FVIII protein challenge.

Inhibitor development in hemophiliacs: the roles of genetic versus environmental factors.

Approximately 5 to 7% of patients with hemophilia A have inhibitory antibodies to factor (F) VIII, which increases to approximately 13% in patients with severe disease. The strongest determinant of the risk of inhibitor development identified is the type of mutation in the FVIII gene that gives rise to the disease. However, accumulating evidence clearly indicates that other genetic factors (e.

Tailored prophylaxis in severe hemophilia A: interim results from the first 5 years of the Canadian Hemophilia Primary Prophylaxis Study.

Background: Prophylactic treatment for severe hemophilia A is likely to be more effective than treatment when bleeding occurs, however, prophylaxis is costly. We studied an inception cohort of 25 boys using a tailored prophylaxis approach to see if clotting factor use could be reduced with acceptable outcomes.

Methods: Ten Canadian centers enrolled subjects in this 5-year study.

Laboratory issues in bleeding disorders.

The clinical history of the patient and of his/her relatives is the most important tool for making correct diagnosis of inherited or acquired bleeding disorders. Several attempts have been made by clinicians to evaluate the sensitivity and specificity of bleeding symptoms. Specific and detailed questionnaires have been designed to quantify the bleeding tendency of patients with von Willebrand's disease (VWD) and a bleeding score has been calculated.

Cellular and genetic therapies for haemophilia.

Haemophilia continues to be a prime target for a variety of gene and cell-based therapies. Pre-clinical successes in both mouse and dog models of the disease have been documented with a variety of approaches over the past decade, and there have now been six small clinical trials of gene transfer in haemophilia. To date, the only significant adverse events documented in these trials have been related to host immune responses, indicating that immunologic barriers continue to represent the major obstacle to achieving success of gene transfer in humans.

Ethical issues in haemophilia.

Ethical issues surrounding both the lack of global access to care as well as the implementation of advancing technologies, continue to challenge the international haemophilia community. Haemophilia is not given the priority it deserves in most developing countries. Given the heavy burdens of sickness and disease and severe resource constraints, it may not be possible to provide effective treatment to all who suffer from the various 'orphan' diseases.

Genetic linkage and association analysis in type 1 von Willebrand disease: results from the Canadian type 1 VWD study.

Background: von Willebrand disease (VWD) is the most common bleeding disorder known in humans, with type 1 VWD representing the majority of cases. Unlike the other variant forms of VWD, type 1 disease represents a complex genetic trait, influenced by both genetic and environmental factors.

Aim: To evaluate the contribution of the von Willebrand factor (VWF) and ABO blood group loci to the type 1 VWD phenotype, and to assess the potential for locus heterogeneity in this condition, we have performed genetic linkage and association studies on a large, unselected type 1 VWD population.

Multiyear therapeutic benefit of AAV serotypes 2, 6, and 8 delivering factor VIII to hemophilia A mice and dogs.

Hemophilia A, a deficiency of functional coagulation factor VIII (FVIII), is treated via protein replacement therapy. Restoring 1% to 5% of normal blood FVIII activity prevents spontaneous bleeding, making the disease an attractive gene therapy target. Previously, we have demonstrated short-term activity of a liver-specific AAV2 vector expressing canine B-domain-deleted FVIII (cFVIII) in a hemophilia canine model.

The value of genetic testing for type 2B Von Willebrand disease.

Von Willebrand disease (VWD) is an inherited bleeding disorder that may be associated with significant morbidity, but is often a diagnostic challenge. While an appropriate clinical bleeding history suggests the condition, current laboratory screening investigations lack the sensitivity and specificity to confirm the diagnosis in many cases. Recently, much work has gone into characterizing the genetic mutations associated with the various subtypes of VWD.

Efficient lentiviral transduction and improved engraftment of human bone marrow mesenchymal cells.

Human bone marrow (BM) mesenchymal stem/progenitor cells are potentially attractive targets for ex vivo gene therapy. The potential of lentiviral vectors for transducing BM mesenchymal cells was examined using a self-inactivating vector that expressed the green fluorescent protein (GFP) from an internal cytomegalovirus (CMV) promoter. This vector was compared with oncoretroviral vectors expressing GFP from the CMV promoter or a modified long-terminal repeat that had been optimized for long-term expression in stem cells.

Aminoglycoside suppression of nonsense mutations in severe hemophilia.

Aminoglycoside antibiotics exhibit their bactericidal effect by interfering with normal ribosomal activity. In this pilot study, we have evaluated the effect of the aminoglycoside antibiotic gentamicin on the factor VIII (FVIII) and IX levels of severe hemophiliacs with known nonsense mutations. Five patients were enrolled and each patient was given 3 consecutive days of gentamicin at a dose of 7 mg/kg intravenously every 24 hours.

Can activated recombinant factor VII be used to postpone the exposure of infants to factor VIII until after 2 years of age?

Two retrospective studies have suggested that exposure to factor VIII (FVIII) in early infancy is associated with an increased risk of FVIII inhibitor development. We prospectively studied 11 infants who needed replacement therapy for bleeding episodes before the age of 2 years. They received activated recombinant factor VII (rFVIIa) concentrate on demand, with the intention of postponing their first exposure to FVIII after 2 years of age.

Identification and functional characterization of a novel 27-bp deletion in the macroglycopeptide-coding region of the GPIBA gene resulting in platelet-type von Willebrand disease.

Interaction between the platelet glycoprotein Ibalpha (GPIbalpha) receptor and its adhesive ligand von Willebrand factor (VWF) has a critical role in the process of hemostasis. Platelet-type von Willebrand disease (PT-VWD) is a rare bleeding disorder that results from gain-of-function mutations in the GPIBA gene. We studied this gene from 5 members of a previously unreported family with a PT-VWD phenotype.

Cell type-specific regulation of von Willebrand factor expression by the E4BP4 transcriptional repressor.

Mechanisms of tissue-restricted patterns of von Willebrand factor (VWF) expression involve activators and repressors that limit expression to endothelial cells and megakaryocytes. The relative transcriptional activity of the proximal VWF promoter was assessed in VWF-producing and -nonproducing cells, and promoter activity was highest in endothelial cells followed by megakaryocytes. Only basal VWF promoter activity was seen in nonendothelial cells.

Heterogeneity of the immune response to adenovirus-mediated factor VIII gene therapy in different inbred hemophilic mouse strains.

Background: The development of anti-factor VIII (FVIII) antibodies (inhibitors) is a critical concern when considering gene therapy as a potential treatment modality for hemophilia A. We used a hemophilia A mouse model bred on different genetic backgrounds to explore genetically controlled differences in the immune response to FVIII gene therapy.

Methods: C57BL/6 FVIII knockout (C57-FVIIIKO) mice were bred with normal BALB/c (BAL) mice, to generate a recombinant congenic BAL-FVIIIKO model of hemophilia A.