Effect of the Factor V Leiden Mutation on the Clinical Expression of Severe Hemophilia A

Targeted exome analysis in patients with rare bleeding disorders: data from the Rare Bleeding Disorders in the Netherlands study

Background

Rare coagulation factor deficiencies and disorders of fibrinolysis (defined as rare bleeding disorders [RBDs]) present with a heterogeneous bleeding phenotype, and bleeding severity is difficult to predict.

Objectives

Describe underlying rare genetic variants in the Dutch RBD population and investigate the relationship between genotype, laboratory phenotype, and clinical phenotype.

Methods

The Rare Bleeding Disorders in the Netherlands is a cross-sectional, nationwide study conducted between October 1, 2017, and November 30, 2019. Bleeding scores and blood samples were collected during a single study visit. Coagulation factor levels were measured centrally, and targeted exome analysis was performed on 156 genes involved in thrombosis and hemostasis. Pathogenicity was assigned according to the Association for Clinical Genetic Science guidelines.

Results

Rare genetic variants specific to the diagnosed RBD were found in 132 of 156 patients (85%). Of the 214 rare genetic variants identified, 57% (n = 123) were clearly pathogenic, 19% (n = 40) were likely pathogenic, and 24% (n = 51) were variants of unknown significance. No explanatory genetic variants were found in patients with plasminogen activator inhibitor type 1 deficiency or hyperfibrinolysis. A correlation existed between factor activity levels and the presence of a genetic variant in the corresponding gene in patients with rare coagulation factor deficiencies and alpha-2-antiplasmin deficiency. Co-occurrence of multiple genetic variants was present in a quarter of patients, but effect on phenotype remains unclear.

Conclusion

Targeted exome analysis may offer advantages over single-gene analysis, emphasized by a number of combined deficiencies in this study. Further studies are required to determine the role of co-occurring hemostasis gene variants on the bleeding phenotype in RBDs.

Emicizumab-mediated hemostatic function assessed by thrombin generation assay in an in vitro model of factor VIII-depleted thrombophilia plasma

Patients with hemophilia A (PwHA) may have concurrent deficiency of representative anticoagulant proteins, protein (P)C, PS, and antithrombin (AT), which reduces bleeding frequency. However, emicizumab-driven hemostasis in PwHA with such thrombophilic potential remains unclarified. This study investigated the influence of natural anticoagulants on emicizumab-driven coagulation in HA model plasma. Various concentrations of PS and AT were added to PS-deficient plasma and AT-deficient plasma in the presence of anti-FVIII antibody (FVIIIAb; 10BU/mL). PC-deficient plasma was mixed with normal plasma at various concentrations in the presence of FVIIIAb. Emicizumab (50 µg/mL) was added to these thrombophilic HA model plasmas, prior to tissue factor/ellagic acid-triggered thrombin generation assays. Co-presence of emicizumab increased peak thrombin values (PeakTh) dependent on PS, AT, and PC concentrations. Maximum coagulation potentials in the PS-reduced HA model plasmas remained normal in the presence of emicizumab. PeakTh were close to normal in the presence of 50%AT irrespective of emicizumab, but were higher than normal in the presence of 25%AT. Addition of recombinant FVIIa (corresponding to an administered dose of 90 μg/kg) enhanced coagulation potential to normal levels. Our findings provide novel information on hemostatic regulation in emicizumab-treated PwHA with a possible thrombophilic disposition.

Insights into the Molecular Genetic of Hemophilia A and Hemophilia B: The Relevance of Genetic Testing in Routine Clinical Practice

Hemophilia A and hemophilia B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of coagulation FVIII or FIX activity levels, which is determined by the type of the pathogenic variants in the genes encoding the two factors (F8 and F9, respectively). Molecular genetic analysis is widely applied in inherited bleeding disorders. The outcome of genetic analysis allows genetic counseling of affected families and helps find a link between the genotype and the phenotype. Genetic analysis in hemophilia has tremendously improved in the last decades. Many new techniques and modifications as well as analysis softwares became available, which made the genetic analysis and interpretation of the data faster and more accurate. Advances in genetic variant detection strategies facilitate identification of the causal variants in up to 97% of patients. In this review, we discuss the milestones in genetic analysis of hemophilia and highlight the importance of identification of the causative genetic variants for genetic counseling and particularly for the interpretation of the clinical presentation of hemophilia patients.

Thromboembolic Disease in Haemophilic Patients Undergoing Major Orthopaedic Surgery: Is Thromboprophylaxis Mandatory?

Haemophilia is a rare genetic disorder, that results from various degrees of deficiency of coagulation factor VIII (haemophilia A), or factor IX (haemophilia B), with an X-linked transmission. The patients affected are in the majority of cases males (who inherit the affected X-chromosome from the maternal side), with rare cases of females with haemophilia (FVIII or FIX < 40 IU/dL), situations in which both X-chromosomes are affected, or one is affected, and the other one is inactive (known as carrier). The hypocoagulable state due to the deficiency of clotting factors, manifests as an excessive, recurrent tendency to bleeding, which positively correlates with plasmatic levels. Severe haemophilia results in hemarthrosis, although recent data have shown that moderate or even mild disease can lead to joint bleeding. Recurrent episodes of haemorrhages, usually affecting large joints such as knees, elbows, or ankles, lead to joint remodelling and subsequent haemophilic arthropathy, which may require arthroplasty as a last therapeutic option. Orthopaedic patients have the highest risk among all for deep vein thrombosis (DVT) and venous thromboembolism (VTE) with morbid and potentially fatal consequences. While for the rest of the population thromboprophylaxis in orthopaedic surgery is efficient, relatively safe, and widely used, for patients with haemophilia who are considered to have a low thromboembolic risk, there is great controversy. The great heterogeneity of this particular population, and the lack of clinical trials, with only case reports or observational studies, makes thromboprophylaxis in major orthopaedic surgery a tool to be used by every clinician based on experience and case particularities. This review aims to briefly summarise the latest clinical data and to offer an insight into the current recommendations that readers would find useful in daily practice.

Thromboelastography and thrombin generation assessments for pediatric severe hemophilia A patients are highly variable and not predictive of clinical phenotypes

Background

Severe hemophilia A (SHA) patients vary in severity of bleeding, arthropathy, and requirements for replacement factor VIII (FVIII). Baseline hemostatic activity assays using calibrated automated thrombography (CAT) and thromboelastography (TEG) may offer insights into the physiological basis of clinical heterogeneity.

Objectives

Use CAT and TEG to measure baseline hemostatic activity in a cohort of 30 pediatric SHA patients with available clinical data. Determine effect of contact activation inhibition with corn trypsin inhibitor (CTI). Assess heterogeneity among patients for baseline hemostatic activity and examine correlations between assay results and clinical parameters including FVIII dosing regimen, von Willebrand factor level, and Pettersson arthropathy score.

Methods

SHA blood after FVIII washout was subjected to TEG, and platelet-rich (PRP) and platelet-poor plasma was used for CAT assays. Varying concentrations of tissue factor (TF) were used. Statistical analysis examined relationships between assay results, and clinical parameters.

Results

CTI treatment was required to obtain TEG and CAT results representative of baseline hemostatic activity. Weak activity was observed in assays with low TF concentrations (0.5-2 pM), and most but not all samples approached normal activity levels at high TF concentrations (10-20 pM). A significant positive correlation was observed between results of TEG and CAT-PRP assays. Correlations were not detected between hemostatic assay results and clinical parameters.

Conclusions

In vitro hemostatic assay results of samples containing platelets showed concordance. Assay results were not predictive of FVIII requirements or correlated with other clinical parameters. SHA patient heterogeneity is influenced by factors other than baseline hemostatic activity.

Heterogeneity in Bleeding Tendency and Arthropathy Development in Individuals with Hemophilia

People with hemophilia (PWH) have an increased tendency to bleed, often into their joints, causing debilitating joint disease if left untreated. To reduce the incidence of bleeding events, PWH receive prophylactic replacement therapy with recombinant factor VIII (FVIII) or FIX. Bleeding events in PWH are typically proportional to their plasma FVIII or IX levels; however, in many PWH, bleeding tendency and the likelihood of developing arthropathy often varies independently of endogenous factor levels. Consequently, many PWH suffer repeated bleeding events before correct dosing of replacement factor can be established. Diagnostic approaches to define an individual's bleeding tendency remain limited. Multiple modulators of bleeding phenotype in PWH have been proposed, including the type of disease-causing variant, age of onset of bleeding episodes, plasma modifiers of blood coagulation or clot fibrinolysis pathway activity, interindividual differences in platelet reactivity, and endothelial anticoagulant activity. In this review, we summarize current knowledge of established factors modulating bleeding tendency and discuss emerging concepts of additional biological elements that may contribute to variable bleeding tendency in PWH. Finally, we consider how variance in responses to new gene therapies may also necessitate consideration of patient-specific tailoring of treatment. Cumulatively, these studies highlight the need to reconsider the current "one size fits all" approach to treatment regimens for PWH and consider therapies guided by the bleeding phenotype of each individual PWH at the onset of therapy. Further characterization of the biological bases of bleeding heterogeneity in PWH, combined with the development of novel diagnostic assays to identify those factors that modulate bleeding risk in PWH, will be required to meet these aspirations.

A mathematical model of coagulation under flow identifies factor V as a modifier of thrombin generation in hemophilia A

BACKGROUND

The variability in bleeding patterns among individuals with hemophilia A, who have similar factor VIII (FVIII) levels, is significant and the origins are unknown.

OBJECTIVE

To use a previously validated mathematical model of flow-mediated coagulation as a screening tool to identify parameters that are most likely to enhance thrombin generation in the context of FVIII deficiency.

METHODS

We performed a global sensitivity analysis (GSA) on our mathematical model to identify potential modifiers of thrombin generation. Candidates from the GSA were confirmed by calibrated automated thrombography (CAT) and flow assays on collagen-tissue factor (TF) surfaces at a shear rate of 100 per second.

RESULTS

Simulations identified low-normal factor V (FV) (50%) as the strongest modifier, with additional thrombin enhancement when combined with high-normal prothrombin (150%). Low-normal FV levels or partial FV inhibition (60% activity) augmented thrombin generation in FVIII-inhibited or FVIII-deficient plasma in CAT. Partial FV inhibition (60%) boosted fibrin deposition in flow assays performed with whole blood from individuals with mild and moderate FVIII deficiencies. These effects were amplified by high-normal prothrombin levels in both experimental models.

CONCLUSIONS

These results show that low-normal FV levels can enhance thrombin generation in hemophilia A. Further explorations with the mathematical model suggest a potential mechanism: lowering FV reduces competition between FV and FVIII for factor Xa (FXa) on activated platelet surfaces (APS), which enhances FVIII activation and rescues thrombin generation in FVIII-deficient blood.

Paradigm shift for the treatment of hereditary haemophilia: Towards precision medicine

Patients with haemophilia A (HA) or B (HB) experience spontaneous limb- or life-threatening bleedings which are prevented by regular prophylactic intravenous infusions of the deficient coagulation factor (FVIII or FIX). Prophylaxis with subcutaneous long-acting non-factor products that improve in vivo thrombin generation is now under intensive investigation (concizumab, fitusiran) or successfully employed (emicizumab) in haemophilia patients. Both haemophilia patients with/without inhibitors take advantage of non-factor products employed alone. In those who also need bypassing agents (or FVIII concentrates) for breakthrough bleeds, thromboembolic events and/or thrombotic microangiopathy may occur. By enhancing thrombin generation, prothrombotic mutations co-segregating with FVIII/FIX gene mutations may trigger thrombotic episodes in HA patients carrying acquired thrombogenic factors (e.g. venous catheters). A thorough knowledge of individual needs increasingly contributed to improve comprehensive care and personalize treatments in haemophilia. Integrating genomics, lifestyle and environmental data is expected to be key to: 1) identify which haemophilia patients are less likely to benefit from a given intervention; 2) define optimal dosing and scheduling of bypassing agents (or FVIII) to employ in combination with non-factor products; 3) establish tests to monitor in vivo thrombin generation; 4) improve communication and deliver results to individuals. As individual outcomes will be improved and the risk of adverse events minimized, non-factor products will come into wider use within the haemophilia community, and patients will hopefully have no more risks of breakthrough bleeds. The risks of a normal life for a "former haemophilia patient" is likely to change the treatment landscape and the structure of haemophilia Centers.

Factor VIII prophylaxis effects outweigh other hemostasis contributors in predicting severe haemophilia A joint outcomes

INTRODUCTION

The Joint Outcome Study (JOS) demonstrated that previously untreated children with severe haemophilia A treated with prophylactic factor VIII (FVIII) concentrate had superior joint outcomes at age 6 years compared to those children treated episodically for bleeding. However, variation in joint outcome within each treatment arm was not well explained.

AIM

In this study, we sought to better understand variation in joint outcomes at age 6 years in participants of the JOS.

METHODS

We evaluated the influence of FVIII half-life, treatment adherence, constitutional coagulant and anticoagulant proteins, and global assays on joint outcomes (number of joint bleeds, total number of bleeds, total MRI score and joint physical exam score). Logistic regression was used to evaluate the association of variables with joint failure status on MRI, defined as presence of subchondral cyst, surface erosion or joint-space narrowing. Each parameter was also correlated with each joint outcome using Spearman correlations.

RESULTS

Prophylaxis treatment arm and FVIII trough were each found to reduce risk of joint failure on univariate logistic regression analysis. When controlling for treatment arm, FVIII trough was no longer significant, likely because of the high level of covariation between these variables. We found no consistent correlation between any laboratory assay performed and any joint outcome parameter measured.

CONCLUSION

In the JOS, the effect of prescribed prophylactic FVIII infusions on joint outcome overshadowed the contribution of treatment adherence, FVIII half-life, global assays of coagulation and constitutional coagulation proteins. (ClinicalTrials.gov number, NCT00207597).

A novel, point-of-care, whole-blood assay utilizing dielectric spectroscopy is sensitive to coagulation factor replacement therapy in haemophilia A patients

BACKGROUND

Reliable monitoring of coagulation factor replacement therapy in patients with severe haemophilia, especially those with inhibitors, is an unmet clinical need. While useful, global assays, eg thromboelastography (TEG), rotational thromboelastometry (ROTEM) and thrombin generation assay (TGA), are cumbersome to use and not widely available.

OBJECTIVE

To assess the utility of a novel, point-of-care, dielectric microsensor - ClotChip - to monitor coagulation factor replacement therapy in patients with haemophilia A, with and without inhibitors.

METHODS

The ClotChip T_peak parameter was assessed using whole-blood samples from children with severe haemophilia A, with (n = 6) and without (n = 12) inhibitors, collected pre- and postcoagulation factor replacement therapy. ROTEM, TGA and chromogenic FVIII assays were also performed. Healthy children (n = 50) served as controls.

RESULTS

ClotChip T_peak values exhibited a significant decrease for samples collected postcoagulation factor replacement therapy as compared to baseline (pretherapy) samples in patients with and without inhibitors. A difference in T_peak values was also noted at baseline among severe haemophilia A patients with inhibitors as compared to those without inhibitors. ClotChip T_peak parameter exhibited a very strong correlation with clotting time (CT) of ROTEM, endogenous thrombin potential (ETP) and peak thrombin of TGA, and FVIII clotting activity.

CONCLUSIONS

ClotChip is sensitive to coagulation factor replacement therapy in patients with severe haemophilia A, with and without inhibitors. ClotChip T_peak values correlate very well with ROTEM, TGA and FVIII assays, opening up possibilities for its use in personalized coagulation factor replacement therapy in haemophilia.

Advances in the Treatment of Hemophilia: Implications for Laboratory Testing

BACKGROUND

Until recently, clinical laboratories have monitored hemophilia treatment by measuring coagulation factors before/after infusion of human-derived or recombinant factors. Substantial changes are expected in the near future based on new therapeutic approaches that have been or are being developed.

CONTENT

Hemophilia treatment includes replacement therapy with human-derived/recombinant factors or treatment with bypassing agents for patients without or with inhibitors, respectively. Accordingly, laboratory methods for monitoring include one-stage clotting or chromogenic assays meant to measure either factor VIII/IX or global coagulation tests to measure the effect of bypassing agents. Recently, modified long-acting coagulation factors have been introduced for which discrepant results may be expected when measurement is performed with one-stage clotting or chromogenic assays. Currently, novel drugs not based on coagulation factors are under development and are being tested in clinical studies. These drugs do require new methods and therefore laboratory evaluation of hemophilia will undergo dramatic changes in the near future.

SUMMARY

From the analysis of the current practice and literature, we draw the following conclusions: (a) Thrombin generation or thromboelastometry are the logical candidate assays to monitor bypassing agents. (b) Considerable differences are expected when measuring modified long-acting coagulation factors, depending on whether one-stage or chromogenic assays are used. Although no definitive conclusions can presently be drawn, chromogenic assays are probably more suitable than one-stage clotting. (c) Novel drugs not based on coagulation factors such as emicizumab, fitusiran, or concizumab that are entering the market do require alternative methods that are not yet well established.

Modifiers of clinical phenotype in severe congenital hemophilia

Patients with inherited hemophilia A and B usually exhibit a bleeding tendency of a severity proportional to the degree of plasmatic deficiency of the coagulant activity of factor VIII (FVIII:C) and factor IX (FIX:C). Although patients with severe hemophilia (i.e., with FVIII:C and FIX:C levels <1IU/dL) are generally those with the most severe bleeding phenotype, it is common experience that a variable proportion of them experiences a milder bleeding tendency. In this review, we summarize the current knowledge on the possible mechanisms at the basis of the phenotypic heterogeneity of severe hemophilia, focusing in particular on the role of FVIII/FIX gene mutations and thrombophilic polymorphisms. Finally, the possible therapeutic implications of such modifiers will be analyzed.

Outcome of Patients with Venous Thromboembolism and Factor V Leiden or Prothrombin 20210 Carrier Mutations During the Course of Anticoagulation

BACKGROUND

Individuals with factor V Leiden or prothrombin G20210A mutations are at a higher risk to develop venous thromboembolism. However, the influence of these polymorphisms on patient outcome during anticoagulant therapy has not been consistently explored.

METHODS

We used the Registro Informatizado de Enfermedad TromboEmbólica database to compare rates of venous thromboembolism recurrence and bleeding events occurring during the anticoagulation course in factor V Leiden carriers, prothrombin mutation carriers, and noncarriers.

RESULTS

Between March 2001 and December 2015, 10,139 patients underwent thrombophilia testing. Of these, 1384 were factor V Leiden carriers, 1115 were prothrombin mutation carriers, and 7640 were noncarriers. During the anticoagulation course, 160 patients developed recurrent deep vein thrombosis and 94 patients developed pulmonary embolism (16 died); 154 patients had major bleeding (10 died), and 291 patients had nonmajor bleeding. On multivariable analysis, factor V Leiden carriers had a similar rate of venous thromboembolism recurrence (adjusted hazard ratio [HR], 1.16; 95% confidence interval [CI], 0.82-1.64), half the rate of major bleeding (adjusted HR, 0.50; 95% CI, 0.25-0.99) and a nonsignificantly lower rate of nonmajor bleeding (adjusted HR, 0.66; 95% CI, 0.43-1.01) than noncarriers. Prothrombin mutation carriers and noncarriers had a comparable rate of venous thromboembolism recurrence (adjusted HR, 1.00; 95% CI, 0.68-1.48), major bleeding (adjusted HR, 0.75; 95% CI, 0.42-1.34), and nonmajor bleeding events (adjusted HR, 1.10; 95% CI, 0.77-1.57).

CONCLUSIONS

During the anticoagulation course, factor V Leiden carriers had a similar risk for venous thromboembolism recurrence and half the risk for major bleeding compared with noncarriers. This finding may contribute to decision-making regarding anticoagulation duration in selected factor V Leiden carriers with venous thromboembolism.

Impact of Prothrombotic Risk Factors in a Cohort of Egyptian Hemophilia A Patients

INTRODUCTION

Hemophilias are a group of related bleeding disorders that show an X-linked pattern of inheritance. The clinical phenotype of severe hemophilia may vary markedly among patients as a result of many factors, including genetic prothrombotic risk factors.

OBJECTIVES

Our objective was to study the incidence of the most common prothrombotic risk factors for additive effects among Egyptian patients with hemophilia A and their impact on clinical phenotype; annual bleeding frequency and severity of hemophilic arthropathy, as well as the effect of a single variation in these patients.

METHODS

This study was carried out in 100 patients with hemophilia A. Genotyping for factor V Leiden (FVL) G1691A, prothrombin G20210A, MTHFR C677T, and A1298C mutations was conducted using a real time-polymerase chain reaction (RT-PCR) assay.

RESULTS

Our study revealed mutations in hemophilia patients as follows: prothrombin G20210A (3 %), FVL (14 %), MTHFR C677T (42 %), and A1298C (59 %). Despite a lack of statistical significance when each gene was analysed separately, heterozygosity of prothrombin G20210A or FVL was always associated with either a mild or moderate, but never a severe, clinical presentation. The lowest bleeding frequency (less than once per month) was identified among patients with two heterozygous variants irrespective of the involved genes. In addition, the incidence of hemarthrosis was significantly higher among patients with a wild genotype of the prothrombin gene and FVL, and the average number of affected joints was significantly higher among patients with wild-type prothrombin and FVL genes than among heterozygous patients.

CONCLUSION

These prothrombotic mutations have a cumulative effect in amelioration of the severity of bleeding in hemophiliacs. The most prominent effect is that of prothrombin G20210A and FVL, while MTHFR C677A and A1298C gene mutations are less conclusive.

Thrombosis in Hemophiliacs with Prothrombotic Molecular Defect

Thrombosis in hemophiliacs is a very unusual event mostly reported in patients treated with concentrates containing large quantities of activated coagulation factors. A patient with hemophilia A is reported who had an acute myocardial infarction and in whom investigation for hereditary thrombophilia showed a prothrombotic molecular defect, the G20210A prothrombin mutation.

Factors that influence the bleeding phenotype in severe hemophilic patients

Hemophilia A and B are rare, X-linked bleeding disorders resulting from a partial or total deficiency of functionally active coagulation factor VIII or factor IX, respectively. Endogenous factor levels have traditionally been used to characterize the severity of the disorder, with severe hemophilia considered as circulating levels of factor less than 1% of normal. Identifying patients with severe hemophilia is essential to effective treatment, since these patients are at highest risk of spontaneous life or limb-threatening bleeding and disability resulting from repeated joint bleeding and are most likely to benefit from prophylaxis. However, there is variability in bleeding tendency, even among patients with severe hemophilia. This article will review potential modifiers of hemophilia-associated bleeding other than endogenous factor activity, which may influence bleeding tendencies and complications in hemophilic patients considered to have severe hemophilia. These potential modifiers include physiologic factors, such as elements of the hemostatic system; pathophysiologic factors, such as hemophilic arthropathy, associated inflammation, and angiogenesis; and others, such as seasonal variation, body weight, and physical activity.

Genetic sequence analysis of inherited bleeding diseases

The genes encoding the coagulation factor proteins were among the first human genes to be characterized over 25 years ago. Since then, significant progress has been made in the translational application of this information for the 2 commonest severe inherited bleeding disorders, hemophilia A and B. For these X-linked disorders, genetic characterization of the disease-causing mutations is now incorporated into the standard of care and genetic information is used for risk stratification of treatment complications. With electronic databases detailing >2100 unique mutations for hemophilia A and >1100 mutations for hemophilia B, these diseases are among the most extensively characterized inherited diseases in humans. Experience with the genetics of the rare bleeding disorders is, as expected, less well advanced. However, here again, electronic mutation databases have been developed and provide excellent guidance for the application of genetic analysis as a confirmatory approach to diagnosis. Most recently, progress has also been made in identifying the mutant loci in a variety of inherited platelet disorders, and these findings are beginning to be applied to the genetic diagnosis of these conditions. Investigation of patients with bleeding phenotypes without a diagnosis, using genome-wide strategies, may identify novel genes not previously recognized as playing a role in hemostasis.

Hemophilia A and hemophilia B: focus on arthropathy and variables affecting bleeding severity and prophylaxis

Hemophilia A (HA) and hemophilia B (HB) are X-linked, recessive disorders. Although their clinical manifestations are essentially indistinguishable, it has been suggested that bleeding episodes in patients with HA are generally more severe and occur at higher frequency than in patients with HB. Nevertheless, considerable debate remains regarding the relative severity of HA and HB. Based on the relative risk of undergoing joint arthroplasty, it appears that patients with HA have more severe joint deterioration compared with patients with HB. Although it is difficult to speculate on the factors that might modify bleeding severity in patients with hemophilia, recent observations indicate that other coagulation proteins, such as tissue factor pathway inhibitor or polymorphisms in coagulation factor genes and genetic defects associated with hypercoagulability may account for the variability in clinical phenotype among patients with hemophilia. Numerous studies have provided evidence supporting the clinical and social benefits of administration of clotting factor in prophylaxis. However, it is still unclear why this approach is more commonly utilized in patients with HA than in those with HB.

Correlation between phenotype and genotype in a large unselected cohort of children with severe hemophilia A

Previously untreated patients with severe hemophilia A caused by F8 null mutations show a more severe phenotype than previously untreated patients with non-null mutations. The phenotypic differences are modest, and as such not likely to affect decisions regarding when and how to start prophylaxis.

Effect of Prothrombotic Mutations on Factor Consumption in Children With Hemophilia

Introduction:

In hemophilia A, factor activity usually correlates with clinical severity; however, there are patients with severe hemophilia who have bleeding less than expected.

Aim:

The aim of this study is to evaluate the impact of prothrombotic mutations on annual factor consumption in children with hemophilia.

Methods:

Factor V Leiden (FVL) G1691A, Prothrombin (PT) G20210A and methylenetetrahydrofolate reductase (MTHFR) C677T and A128C mutations were evaluated in children with moderate–severe hemophilia A (n = 51) and controls (n = 25).

Results:

None of the cases and controls carried the FVL and PT G20210A in homozygous state. There was no difference in factor consumption between carriers of FVL, PT mutations, and noncarriers. Patients who were homozygous for MTHFR C677T were found to have increased factor consumption compared to noncarriers, and this was a negative association. No decrease in factor consumption was noted in patients with hemophilia having MTHFR A1298C mutation.

Conclusion:

We could not demonstrate a significant decrease in factor concentrate consumption in children with hemophilia having prothrombotic mutations.

Factor V Leiden thrombophilia

Factor V Leiden is a genetic disorder characterized by a poor anticoagulant response to activated Protein C and an increased risk for venous thromboembolism. Deep venous thrombosis and pulmonary embolism are the most common manifestations, but thrombosis in unusual locations also occurs. The current evidence suggests that the mutation has at most a modest effect on recurrence risk after initial treatment of a first venous thromboembolism. Factor V Leiden is also associated with a 2- to 3-fold increased relative risk for pregnancy loss and possibly other obstetric complications, although the probability of a successful pregnancy outcome is high. The clinical expression of Factor V Leiden is influenced by the number of Factor V Leiden alleles, coexisting genetic and acquired thrombophilic disorders, and circumstantial risk factors. Diagnosis requires the activated Protein C resistance assay (a coagulation screening test) or DNA analysis of the F5 gene, which encodes the Factor V protein. The first acute thrombosis is treated according to standard guidelines. Decisions regarding the optimal duration of anticoagulation are based on an individualized assessment of the risks for venous thromboembolism recurrence and anticoagulant-related bleeding. In the absence of a history of thrombosis, long-term anticoagulation is not routinely recommended for asymptomatic Factor V Leiden heterozygotes, although prophylactic anticoagulation may be considered in high-risk clinical settings. In the absence of evidence that early diagnosis reduces morbidity or mortality, decisions regarding testing at-risk family members should be made on an individual basis.

Activated protein C inhibitor for correction of thrombin generation in hemophilia A blood and plasma1

BACKGROUND

Replacement therapy for hemophilic patient treatment is costly, because of the high price of pharmacologic products, and is not affordable for the majority of patients in developing countries.

OBJECTIVE

To generate and evaluate low molecular weight agents that could be useful for hemophilia treatment.

METHODS

Potential agents were generated by synthesizing specific inhibitors [6-(Lys-Lys-Thr-[homo]Arg)amino-2-(Lys[carbobenzoxy]-Lys[carbobenzoxy]-O-benzyl)naphthalenesulfonamide] (PNASN-1)] for activated protein C (APC) and tested in plasma and fresh blood from hemophilia A patients.

RESULTS

In the activated partial thromboplastin time-based APC resistance assay, PNASN-1 partially neutralized the effect of APC. In calibrated automated thrombography, PNASN-1 neutralized the effect of APC on thrombin generation in normal and congenital factor VIII-deficient plasma (FVIII:C < 1%). The addition of PNASN-1 to tissue factor-triggered (5 pm) contact pathway-inhibited fresh blood from 15 hemophilia A patients with various degrees of FVIII deficiency (FVIII:C < 1-51%) increased the maximum level of thrombin generated from 78 to 162 nm, which approached that observed in blood from a healthy individual (201 nm). PNASN-1 also caused a 47% increase in clot weight in hemophilia A blood.

CONCLUSIONS

Specific APC inhibitors compensate to a significant extent for FVIII deficiency, and could be used for hemophilia treatment.

Molecular diagnosis of haemophilia A at Centro Hospitalar de Coimbra in Portugal: study of 103 families--15 new mutations

Haemophilia A (HA), the most commonly inherited bleeding disorder, has well known phenotype heterogeneity, influenced by the type of mutation, modulating factors and development of inhibitors. Nowadays, new technologies in association with bioinformatics tools allow a better genotype/phenotype correlation. With the main objective of identifying familial carrier women and to offer prenatal diagnosis, 141 HA patients belonging to 103 families, followed or referred to the Haemophilia Centre of CHC, E.P.E., were studied. Molecular diagnosis strategy was based on HA severity: IVS22 and IVS1 inversions, direct sequencing and MLPA technique. New missense and splicing mutations were further analyzed using molecular modelling. Genotype/phenotype correlation was assessed taking into account the known modulating factors. During this study, mutations were detected in 102/103 families, carrier status was determined in 83 women and 14 prenatal diagnoses were performed. In a total of 46 different mutations identified, 15 have not been reported previously by the HAMSTeRS and HGMD. Genotype/phenotype correlation revealed two cases with a clinical picture less severe than expected by the type of mutation identified. Six patients developed inhibitors: five severe (IVS22, IVS1, large deletion) and one mild (p. Gln2265Lys). The adopted strategy allowed the identification of 99% of the molecular alterations underlying the HA phenotype (98% detection rate for severe and 100% for moderate and mild). Evaluation of genotype-phenotype correlation was complemented with structural protein modelling of newly identified missense mutations, contributing to better understanding of the disease-causing mechanisms and to deepening knowledge on protein structure-function.

Severe hemophilia with mild bleeding phenotype: molecular characterization and global coagulation profile

BACKGROUND

Patients with severe hemophilia may show very varied bleeding tendencies, and the reasons for this heterogeneous clinical expression are unclear. The factor VIII/FIX genotype is the main determinant of the residual factor activity; however, different bleeding phenotypes have also been reported in patients sharing the same mutation. Such global coagulation tests as thrombin generation assays are tools with which to investigate different coagulation profiles among severe hemophiliacs.

OBJECTIVES, PATIENTS AND METHODS

This case-control study was aimed at comprehensively evaluating the role of genotype and endogenous thrombin potential (ETP) as predictors of the clinical phenotype in severe hemophiliacs with an extremely mild bleeding tendency (cases, n = 22), in comparison with those showing a typical bleeding tendency (controls, n = 50).

RESULTS

Cases were more frequently affected by hemophilia B than by hemophilia A, and showed a lower incidence of severe FVIII/FIX gene defects (referred to as null mutations), higher FVIII and FIX antigen levels and higher ETP values in platelet-rich plasma than controls (P < 0.05). By multivariate logistic regression, only non-null mutations were confirmed as an independent predictor of a mild clinical phenotype.

CONCLUSIONS

These results indicate that non-null mutations represent the main determinant of the bleeding tendency, and that ETP measurement in platelet-rich plasma is able to identify severe hemophiliacs with a mild clinical phenotype.

Thrombin generation testing in haemophilia comprehensive care centres

SUMMARY

Haemophilia comprehensive care centres (HCCC) were first created more than 50 years ago. Their first objective was educating the patient and healthcare professionals in the management of bleeding. Today HCCCs are centres of excellence with multidisciplinary specialists, which continue to provide essential services that are continually reassessed in light of new scientific information. In addition, HCCCs make significant research contributions by studying new methods to improve the well-being of patients with haemophilia. Laboratory expertise is one of the central pillars of HCCCs with a direct impact on diagnosis and management of the haemophilia disease. Vast efforts have been made for the standardization of factor VIII (FVIII) and FIX measurements and inhibitor detection. Molecular biology has improved diagnostics and made it possible to develop new, more secure FVIII and FIX concentrates for replacement therapy. However, phenotyping of each haemophilia patient with an accurate prediction of the individual bleeding risk and also the individual response of patients to antihaemophilic treatment still remains a challenge. In the last 5 years, an expanding interest of haematologists for thrombin generation testing (TGT) reflects the need for new laboratory tools able to evaluate the overall coagulating capacity of patients. This study will review unmet laboratory needs in haemophilia and the potential applications of TGT in the management of haemophiliacs. Furthermore, technical and standardization issues of the method will be discussed.

Thrombin generation assay: a useful routine check-up tool in the management of patients with haemophilia?

Severity assessment of patients with haemophilia A (HA) is traditionally based on FVIII activity (FVIII:C). Clinical phenotype of HA patients often differs between individuals with the same FVIII:C determined with clotting and chromogenic assays. The aim of this study was to assess the influence of the FVIII:C on thrombin generation (TG) assay parameters both in vitro and ex-vivo postinfusion plasma. For in-vitro approach, influence of FVIII:C was evaluated on TG parameters in several dilutions of a normal plasma pool with commercial FVIII-depleted-plasma (FVIIIDP) and in others experiments, adding increasing amounts of different commercial FVIII concentrates (Fanhdi, Haemate-P, Hemofil-M and Kogenate Bayer) to FVIIIDP. In a series of 50 postinfusion samples, from HA patients of different severity, we assayed TG and FVIII:C (chromogenic and clotting). In vitro experiments, the 50% of maximum TG peak (TGMP) was achieved using only 5% FVIII:C and the TGMP was obtained with 40% of normal VIII:C. Impaired response compared with normal plasma was found in FVIIIDP using addition of increasing amounts of different commercial FVIII concentrates. An overall good correlation between the two FVIII assays was observed (y = 0.9115x - 0.273, r = 0.975, P < 0.001); TGMP and the Lag-Phase-Time (LPT) provided some discrepant results when compared with the total range of FVIII:C measurements. In contrast, correlations for TGMP, LPT and endogenous thrombin potential were improved in samples restricted to FVIII:C <5%. We conclude that TG parameters tentatively could be a tool to tailor the global haemostatic capacity in haemophilic patients.

Validation of a composite score for clinical severity of hemophilia

INTRODUCTION

Evaluation of modulators of the phenotypic expression of hemophilia may benefit from a scoring system that reflects several aspects of the clinical severity instead of only one dimension.

METHODS

We describe here how we constructed a composite Hemophilia Severity Score (HSS) and performed validation. The items in the HSS are annual incidence of joint bleeds, World Federation of Hemophilia Orthopedic joint score, and annual factor consumption. The latter two were adjusted for age at start of prophylaxis and body weight. Data for 100 adolescent or adult patients with hemophilia A or B in the mild, moderate or severe form without inhibitors were collected for the 1990-1999 period. We evaluated the reliability (multidimension property, test-retest) and validity (content, convergent, discriminant and known groups) of the score.

RESULTS

The HSS ranged from 0 to 0.94 and was higher in severe hemophilia A than severe hemophilia B (median 0.50 and 0.24; P = 0.031). The validation indicated that the HSS is reliable and reflective of the clinical severity of hemophilia. The presence of factor V G1691A or prothrombin G20210A polymorphisms was found in 13 patients. The clinical severity, measured as the HSS or each of the three components, appeared to be modified by prothrombin G20210A but not by FV G1691A.

CONCLUSION

The HSS is a well-defined tool that provides a comprehensive representation of the clinical severity of hemophilia in adults. It would be useful in larger studies on the assessment of modulators of the phenotypic expression of hemophilia.

The hemostatic balance revisited through the lessons of mankind evolution

Under physiologic conditions, a hemostatic balance is achieved through the effects of natural procoagulant and anticoagulant factors which, in equilibrium with each other, provide hemostasis at the sites of vascular injury. Abnormalities of these hemostasis factors can result in a tendency toward hemorrhagic or thrombotic events. In this review the influence of inherited prothrombotic risk factors--especially the more frequent factor V Leiden and prothrombin gene mutations--on normal and abnormal hemostasis is analyzed from an evolutionary point of view. The effect of inherited bleeding disorders on the development of thrombotic or atherosclerotic processes is also discussed.

Prevention of haemophilic synovitis: prophylaxis

It has been proven that early prophylactic therapy can prevent bleeding and arthropathy. Numerous retrospective non-randomized cohort studies have demonstrated that prophylaxis, if started early in life, is associated with a considerable reduction of the mean number of joint bleeds and the rate of joint deterioration. It is quite extraordinary that despite the considerable evidence base it has been considered necessary by investigators to pursue the ideal of the controlled randomized trial and expose children to the risk of cerebral bleed. This questionable ethical approach is driven by the reluctance of the 'willingness to pay' but it is important that patients are not subjected to unnecessary investigation at either the behest of the Cochrane Database or those who control the financing of haemophilia care.

Peptidomimetic inhibitors for activated protein C: implications for hemophilia management

BACKGROUND

Several clinical studies and experiments with transgenic mice have suggested that the severity of the bleeding phenotype in hemophilic patients is substantially reduced in association with impaired inactivation of factor (F) Va by activated protein C (APC) in the presence of the FV Leiden mutation. Experiments using a synthetic coagulation proteome model showed that the presence of FV Leiden significantly increased thrombin generation in the absence of FVIII or FIX.

OBJECTIVE

To test the effect of APC inhibition on thrombin generation in hemophilia.

METHODS

Prothrombinase and a synthetic coagulation proteome model of tissue factor-triggered thrombin generation were used.

RESULTS

Peptide-based APC inhibitors, which mimic the P4-P4' residues surrounding the APC cleavage site at Arg306 of FVa, were synthesized. These compounds are specific and reversible inhibitors of APC, with Ki values as low as 1-2 microM; most have insignificant affinity for FXa or thrombin. The affinity for APC is dependent upon the location and character of the protecting groups. Representatives of this group of compounds inhibit FVa inactivation by APC and prolong FVa functional activity in the prothrombinase complex. When evaluated in a synthetic coagulation proteome model, one inhibitor partially compensated for the absence of FVIII.

CONCLUSIONS

Synthetic APC inhibitors may be useful as adjuvants for hemophilia treatment.

Thrombin generation in factor VIII-depleted neonatal plasma: nearly normal because of physiologically low antithrombin and tissue factor pathway inhibitor

BACKGROUND

Bleeding in hemophilic neonates has a low incidence. A possible explanation for this could be the peculiarities of the neonatal hemostatic system, especially low levels of the inhibitors tissue factor pathway inhibitor (TFPI) and antithrombin (AT).

OBJECTIVE

We investigated the influence of an elevation of these inhibitors to adult levels on the thrombin generation (TG) in normal neonatal plasma and factor (F) VIII-depleted neonatal plasma by means of incubation with anti-FVIII-antibodies.

PATIENTS/METHODS

TG was measured after activation with low amounts of tissue factor (TF) by using Calibrated Automated Thrombography.

RESULTS

TG in FVIII-depleted neonatal plasma was nearly as high as in normal neonatal plasma. TG decreased after elevation of AT in both neonatal plasmas. After elevation of TFPI TG decreased much more in FVIII-depleted neonatal plasma than in normal neonatal plasma. After elevation of both inhibitors their synergistic effect led to a stronger decrease of TG in FVIII-depleted neonatal plasma. TG measured in plasma of one hemophilic newborn showed the same pattern as in FVIII-depleted neonatal plasma.

CONCLUSION

Our observation provides a biochemical basis for the rare bleeding in hemophilic neonates and shows the important role of the natural inhibitors in the hemostatic system of hemophilic patients.

Factor V Leiden improves in vivo hemostasis in murine hemophilia models

The role of factor V Leiden (FVL) as a modifier of the severe hemophilia phenotype is still unclear. We used mice with hemophilia A or B crossed with FVL to elucidate in vivo parameters of hemostasis. Real-time thrombus formation in the microcirculation was monitored by deposition of labeled platelets upon laser-induced endothelial injury using widefield microscopy in living animals. No thrombi formed in hemophilic A or B mice following vascular injuries. However, hemophilic mice, either heterozygous or homozygous for FVL, formed clots at all injured sites. Injection of purified activated FV into hemophilic A or B mice could mimic the in vivo effect of FVL. In contrast to these responses to a laser injury in a microvascular bed, FVL did not provide sustained hemostasis following damage of large vessels in a ferric chloride carotid artery injury model, despite of the improvement of clotting times and high circulating thrombin levels. Together these data provide evidence that FVL has the ability to improve the hemophilia A or B phenotype, but this effect is principally evident at the microcirculation level following a particular vascular injury. Our observations may partly explain the heterogeneous clinical evidence of the beneficial role of FVL in hemophilia.

Thrombin generation and phenotypic correlation in haemophilia A

The clinical phenotype of patients with haemophilia A (HA) often differs between individuals with the same factor VIII (FVIII) gene defect (e.g. within the same family) or the same coagulant activity of FVIII (FVIII:C). We proposed that because the thrombin generation assay in platelet-poor plasma of HA patients provides more information [peak thrombin concentration, endogenous thrombin potential (ETP), rate of thrombin generation and lag-time] than a clot-based FVIII assay it might provide insight into these differences. We therefore investigated the relation between the results of the thrombin generation assay and the clinical severity in nine families with HA (23 patients with different phenotypes). We also examined the contribution of prothrombotic risk factors: (FV Leiden G1691A and prothrombin G20210A), the coagulant activity of FVIII and tissue factor (5'UTR) polymorphisms. Our data detect marked differences between individuals but these did not correlate with the reported clinical phenotype. These differences were also reflected in a marked difference in response to the therapeutic amounts of FVIII. This might account for differences in amounts of treatment consumption. Reduced peak and possibly rate of thrombin generation, rather than FVIII:C or ETP appear to represent the critical defects in FVIII-deficient plasma. We suggest that the analysis of parameters in thrombin generation is a useful tool to detect bleeding tendency in HA but not to predict the modulation of the haemorrhagic tendency in patients within families. However the presence of the other factors such as vessel wall components, protein C and platelets might need to be incorporated into this system.

Variability in clinical phenotype of severe haemophilia: the role of the first joint bleed

To quantify variation in clinical phenotype of severe haemophilia we performed a single centre cohort study among 171 severe haemophilia patients. Age at first joint bleed, treatment requirement (i.e. annual clotting factor use), annual bleeding frequency and arthropathy were documented. Because treatment strategies intensified during follow-up, patients were stratified in two age groups: patients born 1968-1985 (n = 91), or 1985-2002 (n = 80). A total of 2166 patient-years of follow-up were available (median 12.0 years per patient). Age at first joint bleed ranged from 0.2 to 5.8 years. Patients who had their first joint bleed later needed less treatment and developed less arthropathy. In patients born 1968-1985 during both on-demand and prophylactic treatment, the 75th percentile of annual joint bleed frequency was consistently four times as high as the 25th percentile. In both age groups variation in annual clotting factor use between 25th and 75th percentiles was 1.4-1.5 times for prophylaxis and 3.8 times for on-demand treatment. To conclude, the onset of joint bleeding is inversely related with treatment requirement and arthropathy and may serve as an indicator of clinical phenotype. Thus, providing a starting point for aetiological research and individualization of treatment.