Recessively inherited coagulation disorders

The molecular basis of factor V and VIII procofactor activation

Activation of precursor proteins by specific and limited proteolysis is a hallmark of the hemostatic process. The homologous coagulation factors (F)V and FVIII circulate in an inactive, quiescent state in blood. In this so-called procofactor state, these proteins have little, if any procoagulant activity and do not participate to any significant degree in their respective macromolecular enzymatic complexes. Thrombin is considered a key physiological activator, cleaving select peptide bonds in FV and FVIII which ultimately leads to appropriate structural changes that impart cofactor function. As the active cofactors (FVa and FVIIIa) have an enormous impact on thrombin and FXa generation, maintaining FV and FVIII as inactive procofactors undoubtedly plays an important regulatory role that has likely evolved to maintain normal hemostasis. Over the past three decades there has been widespread interest in studying the proteolytic events that lead to the activation of these proteins. While a great deal has been learned, mechanistic explanations as to how bond cleavage facilitates conversion to the active cofactor species remain incompletely understood. However, recent advances have been made detailing how thrombin recognizes FV and FVIII and also how the FV B-domain plays a dominant role in maintaining the procofactor state. Here we review our current understanding of the molecular process of procofactor activation with a particular emphasis on FV.

A novel missense mutation causing abnormal LMAN1 in a Japanese patient with combined deficiency of factor V and factor VIII

Combined deficiency of coagulation factor V (FV) and factor VIII (FVIII) (F5F8D) is an inherited bleeding disorder characterized by a reduction in plasma concentrations of FV and FVIII. F5F8D is genetically linked to mutations in either LMAN1 or MCFD2. Here, we investigated the molecular basis of F5F8D in a Japanese patient, and identified a novel missense mutation (p.Trp67Ser, c.200G>C) in the LMAN1, but no mutation in the MCFD2. The amount of LMAN1 in Epstein-Barr virus-immortalized lymphoblasts from the patient was found to be almost the same as that in cells from a normal individual. Interestingly, an anti-MCFD2 antibody did not co-immunoprecipitate the mutant LMAN1 with MCFD2 in lymphoblasts from the patient, suggesting the affinity of MCFD2 for the mutant LMAN1 is weak or abolished by the binding of the anti-MCFD2 antibody. In addition, a Myc/6xHis-tagged recombinant form of wild-type LMAN1 could bind to D-mannose, but that of the mutant could not. The p.Trp67Ser mutation was located in the carbohydrate recognition domain (CRD), which is thought to participate in the selective binding of LMAN1 to the D-mannose of glycoproteins as well as the EF-motif of MCFD2. Taken together, it was suggested that the p.Trp67Ser mutation might affect the molecular chaperone function of LMAN1, impairing affinity for D-mannose as well as for MCFD2, which may be responsible for F5F8D in the patient. This is the first report of F5F8D caused by a qualitative defect of LMAN1 due to a missense mutation in LMAN1. Am. J. Hematol. 2009. (c) 2009 Wiley-Liss, Inc.

Treatment of congenital fibrinogen deficiency: overview and recent findings

Afibrinogenemia is a rare bleeding disorder with an estimated prevalence of 1:1,000,000. It is an autosomal recessive disease resulting from mutations in any of the 3 genes that encode the 3 polypeptide chains of fibrinogen and are located on the long arm of chromosome 4. Spontaneous bleeding, bleeding after minor trauma and excessive bleeding during interventional procedures are the principal manifestations. We review the management of afibrinogenemia. Replacement therapy is the mainstay of treatment of bleeding episodes in these patients and plasma-derived fibrinogen concentrate is the agent of choice. Cryoprecipitate and fresh frozen plasma are alternative treatments that should be used only when fibrinogen concentrate is not available. Secondary prophylactic treatment may be considered after life-threatening bleeding whereas primary prophylactic treatment is not currently recommended. We also discuss alternative treatment options and the management of surgery, pregnancy and thrombosis in these patients. The development of new tests to identify higher risk patients and of safer replacement therapy will improve the management of afibrinogenemia in the future.

Rare inherited disorders of fibrinogen

Fibrinogen, a hexameric glycoprotein encoded by three genes - FGA, FGB, FGG - clustered on chromosome 4q is involved in the final steps of coagulation as a precursor of fibrin monomers required for the formation of the haemostatic plug. Inherited disorders of fibrinogen abnormalities are rare and not as well clinically characterized as some other inherited bleeding disorders. To characterize the clinical manifestations, molecular defects and treatment modalities of these rare disorders, a Medline search from January 1966 to September 2007 for these disorders reported in large studies and registries was undertaken. Inherited fibrinogen disorders can manifest as quantitative defects (afibrinogenemia and hypofibrinogenemia) or qualitative defects (dysfibrinogenemia). Quantitative fibrinogen deficiencies may result from mutations affecting fibrinogen synthesis, or processing while qualitative defects are caused by mutations causing abnormal polymerization, defective cross-linking or defective assembly of the fibrinolytic system. Clinical manifestations vary from being asymptomatic to developing catastrophic life-threatening bleeds or thromboembolic events. Management of bleeds includes use of purified plasma-derived concentrates, cryoprecipitate or fresh frozen plasma. Use of some of these products carries risks of viral transmission, antibody development and thromboembolic events. Establishment of registries in Iran, Italy and North America has fostered a better understanding of these disorders with an attempt to explore molecular defects. Rare Bleeding Disorder Registries developed through the United States and international efforts hopefully will encourage development and licensure of safer, effective products.

[Appropriate laboratory investigation in women with menorrhagia]

Inherited bleeding disorders are potentially causes of menorrhagia and must be investigated if no specific cause is identified. The reported prevalence of inherited bleeding disorders is high in women with menorrhagia compared to the general population. The most frequent disorders reported are von Willebrand's disease and Factor XI deficiency. Menorrhagia is, also, a frequent finding in women with congenital bleeding disorders. Morever, menorrhagia represents the major cause of iron-deficiency anemia among women of reproductive age. Primary evaluation for an underlying disorder of hemostasis in a woman wih menorrhagia is a focused history for familiy and personal history of bleeding symptoms and a complete blood cell count. This will rule out thrombocytopenic bleeding and also assesses for the degree, if any, of anemia. Those women with a positive screen and normal platelet count should be evaluated with laboratory investigation including prothrombin time, activated partial thromboplastin time, factor VIII, VWF ristocetin cofactor and antigen. If initial hemostasis testing above is normal, then further hemostasis testing can be considered, especially in terms of platelet aggregation, in a multidisciplinary clinic.

Major differences in bleeding symptoms between factor VII deficiency and hemophilia B

SUMMARY BACKGROUND

The autosomally-inherited factor VII (FVII) deficiency and X-linked hemophilia B offer an attractive model to investigate whether reduced levels of FVII and FIX, acting in the initiation and amplification of coagulation respectively, influence hemostasis to a different extent in relation to age and bleeding site.

METHODS

Hemophilia B patients (n = 296) and FVII-deficient males (n = 109) were compared for FVII/FIX clotting activity, F7/F9 genotypes and clinical phenotypes in a retrospective, multi-centre, cohort study.

RESULTS

Major clinical differences between diseases were observed. Bleeding occurred earlier in hemophilia B (median age 2.0 years, IR 0.9-5.0) than in FVII deficiency (5.2 years, IR 1.9-15.5) and the bleeding-free survival in FVII deficiency was similar to that observed in 'mild' hemophilia B (P = 0.96). The most frequent disease-presenting symptoms in hemophilia B (hematomas and oral bleeding) differed from those in FVII deficiency (epistaxis and central nervous system bleeding). Differences were confirmed by analysis of FVII-deficient women.

CONCLUSIONS

Our data support the notion that low FVII levels sustain hemostasis better than similarly reduced FIX levels. On the other hand, minute amounts of FVII, differently to FIX, are needed to prevent fatal bleeding, as indicated by the rarity of null mutations and the associated life-threatening symptoms in FVII deficiency, which contributes towards shaping clinical differences between diseases in the lowest factor level range. Differences between diseases are only partially explained by mutational patterns and could pertain to the specific roles of FVII and FIX in coagulation phases and to vascular bed-specific components.

Prophylaxis of bleeding episodes and surgical interventions in patients with rare inherited coagulation disorders

Rare inherited coagulation disorders (RICD) represent a group of inherited deficiencies of clotting factors characterized by a low prevalence in the general population (usually around 1:1,000,000 inhabitants) and, in severe cases (homozygous or compound heterozygotes), by the invariable occurrence of bleeding after invasive procedures if not adequately treated. Furthermore, spontaneous or post-traumatic severe bleeding may occur, as usually observed in patients with haemophilia, although less frequently. The clinical picture of patients with RICD may, however, be complicated by particular situations not encountered in haemophiliacs, such as gynaecological bleeding. The availability of virally-inactivated plasma-derived concentrates of the missing factors, apart from factor V, has rendered surgery and prophylaxis more feasible in these disorders, thus reducing the risk of life-threatening episodes and significantly improving the quality of life of affected patients. The goal for the future is to render this treatment accessible to all patients with these disorders, also to those living in developing countries.

National and international registries of rare bleeding disorders

Rare bleeding disorders (RBDs) are autosomal recessive disorders, representing 3-5% of all the inherited deficiencies of coagulation factors. Their frequency in the general population ranges from 1:500,000 to 1:2 millions. In countries with a high rate of consanguineous marriages RBDs occur more frequently, representing a significant clinical and social problem. Patients affected by RBDs have a wide spectrum of clinical symptoms that vary from a mild or moderate bleeding tendency to potentially serious or life-threatening haemorrhages. Current treatment is based on both replacement therapy and non-transfusional treatment. However, despite the existence of several concentrates, there is no Factor V concentrate available for the treatment of Factor V deficiency, yet. In 2004, to improve the understanding of RBDs prevalence, diagnosis and treatments, the Rare Bleeding Disorders database (RBDD, www.rbdd.org) was developed. The RBDD project allowed the collection of epidemiological information on 3,230 patients from 66 Centres scattered all over the world. Epidemiological data can also be derived from the annual survey of the World Federation of Hemophilia (www.wfh.org) and from other existing national registries. However, these data are not homogenous and global surveys provide a non-real picture of the distribution of RBDs, as about 50% of data refers to European patients. Hence, we focused on Europe and, thanks to a European project (EN-RBD), we set up a network of 10 Treatment Centres to develop a homogeneous communication tool for inserting, managing and viewing information on RBD patients (www.rbdd.eu). This on-line database resulted to be a powerful tool to improve the quality of data collection. Preliminary results showed that a homogeneous and harmonized data collection using a unique model will help to have more accurate data for statistical analysis.

The spectrum of inherited bleeding disorders in pediatrics

Inherited bleeding disorders (IBDs) are caused by quantitative and qualitative alterations of either platelets or plasma proteins involved in coagulation and fibrinolysis. Hemophilias are the most frequent IBDs; however, accumulated data from various studies reported that von Willebrand disease (VWD) is the most common cause of IBD, with an increased incidence of platelet function defects, mostly due to the increased rate of consanguinity in some communities. VWD is an inherited disorder of homeostasis due to quantitative or qualitative defect of von Willebrand factor. Data on its epidemiology and impact in developing countries are limited. The objective of this study was to assess the local prevalence of some IBD and establish the clinical and historical variables that are predictive for those bleeding disorders in pediatrics. The study involved 43 children with various bleeding manifestations and 15 age- and sex-matched controls, recruited from the Pediatrics Hematology Clinic at the National Research Centre, Sausan Mubarek children's hospital in Cairo, Egypt and the King Abdulaziz University Hospital, Jeddah, Kingdom of Saudi Arabia. Hematological profile included platelet counts and function, prothrombin time, partial thromboplastin time, factor VIII antigen and its activity, factor IX antigen and its activity, von Willebrand factor and its activity assayed with multimeric analysis. A total of 12 (27.9%) children had VWD, 11 (25.5%) had hemophilia A, three (7%) had hemophilia B, seven (16.3%) had platelet dysfunction and 10 (23.3%) had bleeding with undiagnosed cause. Two of the VWD cases had type I, three had type II, four had type III and one case appeared to have type IIM and another to have IIB VWD. Bruising and epistaxis were the main symptoms in all children with VWD The majority of platelet dysfunction disorders were diagnosed as Glanzmann's thrombasthenia. VWD and Glanzmann's thrombasthenia should be considered not uncommon causes of IBDs in children in Egypt and Kingdom of Saudi Arabia. Routine hematological screening should be mandatory in children with positive family history of bruising and bleeding as a predictor for IBD.

Laboratory testing for fibrinogen abnormalities

Fibrinogen is essential for the formation of a fibrin clot. Acquired and congenital disorders of fibrinogen may result in decreased concentration or altered function of fibrinogen, often leading to an increased risk of bleeding. Routine coagulation testing and specialized laboratory investigations can guide diagnosis in patients suspected of having a fibrinogen abnormality. This article summarizes the types of laboratory assays that are used to assess fibrinogen disorders, and key abnormalities found in different types of fibrinogen disorders.

Factor VII deficiency: clinical manifestation of 717 subjects from Europe and Latin America with mutations in the factor 7 gene

The congenital FVII deficiency (FVIID) is a rare haemorrhagic disorder with an autosomal recessive pattern of inheritance. Data on phenotype and the genotype from 717 subjects in Central Europe (six countries), Latin America (Costa Rica, Venezuela) and United States, enrolled in the Greifswald Registry of FVII Deficiency were analysed. We detected 131 different mutations in 73 homozygous, 145 compound heterozygous and 499 heterozygous subjects. Regional differences were observed in the mutation pattern and the clinical profile of the evaluated patients. Seventy-one per cent of homozygous and 50% of compound heterozygous subjects were symptomatic. The clinical manifestations of the homozygous subjects were characterized by intracranial haemorrhage (2%), gastrointestinal bleeding (17%), haemarthrosis (13%), epistaxis (58%), gum bleeding (38%), easy bruising (37%), haematoma (15%), haematuria (10%) and menorrhagia (19 of 26 females, 73%). The clinical variability and genotype-phenotype correlation was evaluated in the homozygous subjects. The pattern of bleeding symptoms among compound heterozygous patients was severe and similar to that of the homozygous patients. The large-scale analysis of 499 heterozygous subjects shows that 93 (19%) presented with spontaneous bleeding symptoms such as haemarthrosis (4%), epistaxis (54%), gum bleeding (14%), easy bruising (38%), haematoma (23%), haematuria (5%) and menorrhagia (19 of 45 females; 42%). The severe haemorrhages - intracranial and gastrointestinal - were not reported in heterozygous subjects. The clinical variability and the regional differences in the mutation pattern are discussed regarding care and treatment.

Pharmacokinetics and pharmacodynamics of a new highly secured fibrinogen concentrate

BACKGROUND

Inherited afibrinogenemia is a rare autosomal recessive disorder characterized by the absence or trace amounts of plasma fibrinogen inducing varying bleeding tendencies. Little is known about the pharmacokinetics of plasma-derived fibrinogen concentrates used in the treatment of afibrinogenemic patients.

OBJECTIVE

This open, prospective, multicenter study assessed the pharmacokinetic and pharmacodynamic profiles of FIBRINOGENE T1 (FGT1; LFB, Les Ulis, France), a human fibrinogen concentrate treated with three specific biological safety steps.

PATIENTS/METHODS

Five adult patients with congenital afibrinogenemia received a single infusion of 0.06 g kg(-1) of FGT1. Plasma samples drawn up to day 14 were assayed for fibrinogen antigen and activity and for coagulation parameters in a central laboratory.

RESULTS

Fibrinogen antigen and activity were similar and highly correlated, with very low between-patient variability for pharmacokinetic parameters. Fibrinogen levels increased rapidly and significantly, with a mean plasma concentration of 1.39 g L(-1) being achieved 1 h after the end of the infusion, leading to almost complete in vivo recovery (94%). The mean half-life was 3.4 days, with slow linear elimination, and the distribution was mainly restricted to the vascular compartment. Coagulation parameters were normalized after the infusion and during the following 6-10 days. FGT1 was well tolerated overall.

CONCLUSIONS

FGT1 behaves like natural functional fibrinogen, and its pharmacokinetic properties are in line with those expected from a fibrinogen concentrate. Our findings suggest that FGT1 can restore efficient hemostasis in afibrinogenemic patients, and predict good clinical efficacy.

Maxillary hemophilic pseudotumor in a patient with mild hemophilia A

Hemophilic pseudotumors are rare, but well known complications of severe hemophilia A, which most frequently develops at the femur, tibia, pelvic bones, iliac bones, or rarely in the cranium or gnathic bones. This report describes a case of hemophilic pseudotumor of the maxillary alveolar ridge that occurred in a boy with mild hemophilia A (14% factor VIII activity). The lesion, which presented as an alveolar mucosal swelling, responded well to enucleation, curettage, and intralesional fibrin glue injection.

Genetic counseling in southern Iran: consanguinity and reason for referral

Population based genetic counseling that promotes public health goals is an appropriate health care service. The genetic counseling center in Shiraz, southern Iran serves most of the clients in the region. During a 4-year period, 2,686 couples presented for genetic counseling. Data files revealed that 85% had consanguineous relationships (1.5% double first cousin, 74% first cousin, 8% second cousin, 1.5% beyond second cousin). Most prevalent reasons for referral were premarital counseling (80%), with 89% consanguinity, followed by preconception (12%), postnatal (7%), and prenatal counseling (1%). The most common abnormalities in probands or relatives were intellectual and developmental disabilities, hearing loss/impairment, and neuromuscular dystrophies. Family history of medical problem(s) and/or consanguinity was the main indication for referral in nearly every family. Premarital consanguinity poses unique challenges and opportunities. There is considerable opportunity for genetic counseling and education for couples in this population. The tradition of consanguinity, which is likely to persist in Iran, requires multidisciplinary agreement regarding the appropriate process of genetic counseling. Effective genetic counseling in Iran hinges on inclusion of data from genetic counseling services in national genomic and epidemiologic research programs.

Vitamin K-induced modification of coagulation phenotype in VKORC1 homozygous deficiency

BACKGROUND

Combined vitamin K-dependent clotting factor (VKCF) deficiency type 2 (VKCFD2) is a rare bleeding disorder caused by mutated vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) gene.

METHODS AND RESULTS

An Italian patient with moderate to severe bleeding tendency was genotyped, and found to be homozygous for the unique VKORC1 mutation (Arg98Trp) so far detected in VKCFD2. The activity levels of VKCFs were differentially reduced, and inversely related to the previously estimated affinity of procoagulant factor propeptides for the gamma-carboxylase. The normal (factor IX) or reduced antigen levels (other VKCFs) produced a gradient in specific activities. Vitamin K supplementations resulted in reproducible, fast and sustained normalization of PT and APTT. At 24 h the activity/antigen ratios of VKCFs were close to normal, and activity levels were completely (factor VII and IX), virtually (prothrombin, factor X and protein C) or partially (protein S) restored. Thrombin generation assays showed a markedly shortened lag time. The time to peak observed at low tissue factor concentration, potentially mimicking the physiological trigger and able to highlight the effect of reduced protein S levels, was shorter than that in pooled normal plasma. At 72 h the thrombin generation times were normal, and the decrease in activity of procoagulant VKCFs was inversely related to their half-life in plasma. The improved coagulation phenotype permitted the uneventful clinical course after invasive diagnostic procedures.

CONCLUSIONS

Modification of coagulation phenotypes in VKCFD2 after vitamin K supplementation was clinically beneficial, and provided valuable patterns of factor specific biosynthesis, half-life and decay.

Mutations in the MCFD2 gene are predominant among patients with hereditary combined FV and FVIII deficiency (F5F8D) in India

Combined FV and FVIII deficiency (F5F8D) is a rare (1:1.000.000) autosomal recessive disorder caused by a defect in the LMAN1 or MCFD2 genes, encoding for a FV and FVIII cargo receptor complex. We report the phenotype and genotype analyses in nine unrelated Indian patients with low FV and FVIII coagulant activity [FV:C, range: 5.6-22.4% and FVIII:C, range: 8.3-27.1%]. Four homozygous mutations, including two frame shift, one missense and one splice site, were identified in all the nine patients. Three of them, a 72-bp deletion in LMAN1 (c.813_822 + 62del72, p.K272fs), a 35-bp deletion in MCFD2 (c.210_244del35) and a missence mutation in MCFD2 (p.D122V), identified in four patients, were novel mutations. A previously reported c.149 + 5G > A transition in MCFD2 was identified in the remaining five patients. Haplotype analysis of MCFD2 gene in patients with p.E71fs and c.149 + 5G > A defects suggested an independent origin of both these mutations. The identification of two common mutations (p.E71fs, c.149 + 5G > A) in MCFD2 gene in seven of nine patients, particularly the c.149 + 5G > A (55,6% of patients), suggests that this gene could be the first to be analysed during the genetic diagnosis of F5F8D in this population. This is the first report describing the molecular analysis of a consistent number of F5F8D patients of South Indian origin, a population with a high frequency of such recessive bleeding disorders.

Thrombosis and bleeding disorders outside Western countries

The rapidly developing countries of Asia are witnessing substantial progress in the awareness of bleeding and thrombotic disorders as important health care problems. It has been thought for a long time that venous thromboembolism is very rare in Asia. Recent large studies that involved the majority of Asian countries demonstrated that this is not true, so that the practice of not using thromboprophylaxis in high-risk medical and surgical cases should be abandoned. The management of hemophilia and allied coagulation disorders has also dramatically improved in several Asian countries, due to the increased availability of blood products for replacement therapy coupled with the leadership role exerted by a few charismatic physicians, particularly in India and Thailand. As to the future, countries such as China and India have the capacity and expertise in biotechnology to consider the production of recombinant factors and gene transfer as the best strategies to tackle the management of persons with hemophilia in these densely populated and huge countries.

Treatment of urgent bleeding in von Willebrand disease

von Willebrand factor (VWF) is a complex plasma protein that promotes platelet adhesion to the subendothelial matrix of injured blood vessels and provides stability to factor VIII in the circulation. von Willebrand disease (VWD) is a haemorrhagic disorder of highly variable severity caused by qualitative and quantitative abnormalities of VWF. The approach to treating urgent bleeding in patients with VWD is dependent on an accurate diagnosis of the patient's type of VWD and knowledge of the expected responses to treatment modalities. These include administration of desmopressin (DDAVP), a vasopressin analogue that promotes the release of VWF and factor VIII (FVIII) from storage sites, and replacement therapy with a viral-inactivated concentrate containing normal VWF and FVIII. Monitoring of an individual's response in the non-bleeding state is required to determine the response to desmopressin that may be achieved and to determine the individual pharmacokinetics of infused VWF and FVIII. In this article, specific approaches to the choice of treatment modalities, calculation of dosages, monitoring of therapy, possible side effects and complications of the treatment of the various types of VWD will be discussed.

Hematopoietic stem cell transplantation for Hodgkin's disease in a patient with dysfibrinogenemia and thrombosis

INTRODUCTION

Dysfibrinogenemia is a disorder of fibrinogen structure and is associated with a functional abnormality. Since fibrinogen is a key component of both the procoagulant and fibrinolytic pathways, defects in fibrinogen function can be associated with increased risk for both hemorrhage and thrombosis. Management of patients with dysfibrinogenemia and a thrombotic tendency usually involves long-term anticoagulation.

CASE

A 36-year-old male with relapsed nodular sclerosing Hodgkin's was found to have a prolonged prothrombin time, low fibrinogen activity and a normal fibrinogen antigen during evaluation for a hematopoietic peripheral blood stem cell transplant. His past medical history was significant for an acute myocardial infarction and two episodes of acute pancreatitis. His father had dysfibrinogenemia complicated by multiple thrombotic episodes. A trans-esophageal echocardiogram revealed two thrombi, one each in the superior vena cava and the descending aorta. He was treated with enoxaparin and received peripheral blood stem cell transplantation. An effort was made to maintain his fibrinogen activity levels at 200 mg/dL using cryoprecipitate. A month following the transplant he developed a new thrombus in the right internal jugular vein, while on enoxaparin and he was started on argatroban and cryoprecipitate followed by fondaparinux. A repeat echocardiogram six weeks later demonstrated that the burden of thrombus both in the right atrium and descending aorta was significantly lower.

DISCUSSION

This is the first case report of a patient with dysfibrinogenemia undergoing peripheral blood stem cell transplantation. Conventional anticoagulant therapy and cryoprecipitate seem to be a reasonable management strategy to prevent thrombosis in a patient with dysfibrinogenemia and a thrombophilic tendency. Secondly, fondaparinux can be used in cases of failure of therapy with low molecular weight heparins and may actually be superior to low molecular weight heparins, especially in patients with dysfibrinogenemia.

Intracellular evaluation of ER targeting elucidates a mild form of inherited coagulation deficiency

Missense mutations reduce protein levels through several molecular mechanisms. Among them, altered targeting to endoplasmic reticulum (ER) and its relationship with clinical phenotypes in patients have been poorly investigated. To address this point, we studied the prepeptide mutations (L-48P, L-42P) associated with mild deficiency of factor VII (FVII), the serine-protease triggering blood coagulation. Mutations were introduced into the native FVII to evaluate secreted and intracellular protein levels, and into a chimeric FVII-GFP to study ER targeting in living cells. In conditioned medium from stably or transiently transfected cells, expression levels of the -48PFVII (9% and 55%, respectively) and particularly those of the -42PFVII (2% and 12%) were decreased compared with those of WtFVII, indicating the causative nature of mutations. Markedly reduced protein levels were observed in cell organelles for -48PFVII (10.5 +/- 4.9 ng/mL; Wt-FVII, 130 +/- 43.4 ng/mL) and -42PFVII (approximately 5 ng/mL), thus suggesting impaired ER targeting. Fluorescence of the -48PFVII-GFP and -42PFVII-GFP was diffuse, covered the nucleus, and declined upon plasma membrane permeabilization with digitonin, which demonstrated mislocalization of variants in the cytosol. Noticeably, the residual fluorescence of -48PFVII-GFP (10%) and -42PFVII-GFP (20%) in organelles was fairly compatible with FVII levels in patients' plasma. The studies with the native and chimeric proteins indicated that both prepeptide mutations were associated with residual expression of normal FVII, which explained the mild form of FVII deficiency in patients. This approach, extendable to other coagulation serine proteases, clearly contributed to elucidate the relationship of genotype with plasma and clinical phenotype.

Severe prothrombin deficiency caused by prothrombin-Edmonton (R-4Q) combined with a previously undetected deletion

BACKGROUND

During infancy, a male patient experienced several life-threatening bleeding episodes. Standard coagulation tests revealed that the patient's plasma prothrombin activity was 8%, while his father's and mother's levels were 74% and 62%, respectively.

OBJECTIVES

A molecular genetic approach was used to determine the molecular basis of prothrombin deficiency within the family.

PATIENT/METHODS

Prothrombin genomic DNA fragments were amplified by using the polymerase chain reaction (PCR). In addition, liver cDNA fragments were amplified from the patient by using reverse transcription (RT) and PCR. The nucleotide sequences of the DNA fragments were determined.

RESULTS

A novel, heterozygous point mutation (g.1755 G > A, named prothrombin-Edmonton) was detected in the patient and his mother, resulting in the mutation of Arg-4 in the prothrombin propeptide to Gln (R-4Q). RT-PCR analysis of the patient's liver sample demonstrated the presence of two mRNA transcripts that differed by the presence or absence of exon 11. Real-time PCR analysis on genomic DNA and cDNA confirmed a deletion (g.10435_10809del) in the paternal allele.

CONCLUSIONS

The patient has a maternally-inherited point mutation (R-4Q) and a paternally-inherited deletion. By analogy with the previously reported factor IX San Dimas, the R-4Q mutation probably causes under-carboxylation of prothrombin and poor cleavage of the propeptide in the hepatocyte. The deletion probably results in a polypeptide that lacks 50 amino acids from the protease domain; this is likely to impair folding, secretion, stability and/or activity of the truncated prothrombin. The two mutations combine to give the prothrombin deficiency observed in the patient.

The molecular basis of quantitative fibrinogen disorders

Hereditary fibrinogen disorders include type I deficiencies (afibrinogenemia and hypofibrinogenemia, i.e. quantitative defects), with low or unmeasurable levels of immunoreactive protein; and type II deficiencies (dysfibrinogenemia and hypodysfibrinogenemia, i.e. qualitative defects), showing normal or altered antigen levels associated with reduced coagulant activity. While dysfibrinogenemias are in most cases autosomal dominant disorders, type I deficiencies are generally inherited as autosomal recessive traits. Patients affected by congenital afibrinogenemia or severe hypofibrinogenemia may experience bleeding manifestations varying from mild to severe. This review focuses on the genetic bases of type I fibrinogen deficiencies, which are invariantly represented by mutations within the three fibrinogen genes (FGA, FGB, and FGG) coding for the three polypeptide chains Aalpha, Bbeta, and gamma. From the inspection of the mutational spectrum of these disorders, some conclusions can be drawn: (i) genetic defects are scattered throughout the three fibrinogen genes, with only few sites appearing to represent relative mutational hot spots; (ii) several different types of genetic lesions and pathogenic mechanisms have been described in affected individuals (including gross deletions, point mutations causing premature termination codons, missense mutations affecting fibrinogen assembly/secretion, and uniparental isodisomy associated with a large deletion); (iii) the possibility to express recombinant fibrinogen mutants in eukaryotic cells is rapidly shedding light into the molecular mechanisms responsible for physiologic and pathologic properties of the molecule; (iv) though mutation analysis of the fibrinogen cluster does not yield precise information for predicting genotype/phenotype correlations, it still provides a valuable tool for diagnosis confirmation, identification of potential carriers, and prenatal diagnosis.

Factor X deficiency: clinical manifestation of 102 subjects from Europe and Latin America with mutations in the factor 10 gene

Inherited factor X deficiency (FXD) is a rare (1:1,000,000) recessive bleeding disorder. The clinical and laboratory phenotypes of FXD are poorly correlated and few regional studies on the genotype and the clinical manifestations of FXD are known. To understand the association between clinical manifestations and causative genotype, detailed evaluation of bleeding pattern in a high number of patients is needed. This international study analysed the phenotype and genotype of 102 subjects from Central Europe (Germany, Poland and Slovakia) and Latin America (Costa Rica and Venezuela) with causative mutations in the F10 gene, via sequencing. Twenty-eight homozygous, seven compound-heterozygous and 67 heterozygous FXD subjects were characterized. Twenty-nine different causative mutations, including 15 novel mutations, were analysed. Spontaneous bleeding symptoms in 42 symptomatic individuals (26 homozygous, seven compound heterozygous and nine heterozygous) comprised easy bruising (55%), haematoma (43%), epistaxis (36%), haemarthrosis (33%), intracranial haemorrhage (ICH; 21%), and gastrointestinal (GI) haemorrhage (12%). The manifestation of bleeding symptoms in 9 of 67 (13%) symptomatic heterozygous subjects is described. The bleeding patterns of the enrolled patients showed differences that are associated with the types of F10 mutation, and the corresponding genotypes. The homozygous patients were evaluated for genotype-phenotype correlation. The results suggested that ICH seems to be associated with the F10 mutation Gly380Arg, and possibly with the mutations IVS7-1G>A and Tyr163delAT. A tentative association of other mutations to severe symptoms such as haemarthrosis and GI haemorrhage is reported. The severity of FXD, the genotype-phenotype association, and the results of regional studies are discussed.

Use of recombinant factor VIIa prior to lumbar puncture in pediatric patients with acute leukemia

The persistence of abnormal coagulation test results after standard treatment with fresh frozen plasma (FFP) poses significant problems in children with acute leukemia requiring a diagnostic lumbar puncture and intrathecal chemotherapy. We report the prophylactic use of a single dose of 90 microg/kg recombinant activated factor VII (rFVIIa) in three children and the rapid correction of abnormal coagulation test results previously not corrected by FFP. Administration of rFVIIa was useful in avoiding a delay of diagnostic lumbar punctures and intrathecal chemotherapy. Hemorrhagic complications and adverse effects of rFVIIa were not observed. Prospective evaluation of this indication and dose appears warranted. (c) 2005 Wiley-Liss, Inc.

Rare bleeding disorders

Deficiencies of coagulation factors other than factor VIII and factor IX (afibrinogenemia, FII, FV, FV+FVIII, FVII, FX, FXI, FXIII) that cause bleeding disorders (RBDs) are inherited as autosomal recessive traits and are rare, with prevalences in the general population varying between 1 in 500,000 and 1 in 2 million for the homozygous forms. As a consequence of the rarity of these deficiencies, the type and severity of bleeding symptoms, the underlying molecular defects, and the actual management of bleeding episodes are not as well established as for hemophilia A and B. The study of the genetic basis of these disorders could represent an important tool for prevention through prenatal diagnosis. Treatment of patients with RBDs during bleeding episodes or surgery is a challenge because of the lack of experience and the paucity of data. For some deficiency factor concentrates are still non available and severe complications can occur. These complications can be minimized by assessment of risks of bleeding and thrombosis, use of haemostatic means other than blood components or no therapy at all. The RBDs pose a problem for guideline writers because there are no suitable clinical trials to supply good evidence for how these people are best treated. The lack of adequate information on clinical manifestations, treatment and genetic basis of RBDs could be improved by the collection of data in an International Database (http://www.rbdd.org), linkable to others previously published. This could be a useful tool to fill the gap between clinical data and clinical practice. This article reviews the genetic basis of RBDs, problems and complications of treatment, problems in the preparation of suitable guidelines for treatment and the future perspectives of the International Registry on RBDs.