Congenital afibrinogenemia

Dental management of a 4-year-old child with congenital afibrinogenemia-A rare case report

Congenital afibrinogenemia is a rare hematologic disorder with an estimated incidence of 1-2 per million people worldwide. It is inherited as an autosomal recessive trait and is characterized by the inability to synthesize fibrinogen. Clinical features range from minimal bleeding to catastrophic hemorrhage. Because of its rarity, there are not enough clinical guidelines in the management of oral manifestations of patients with this disorder. The following case report presents the dental management of a 4-year-old child with congenital afibrinogenemia under general anesthesia. A multidisciplinary team approach was followed to achieve full mouth rehabilitation, thus improving the overall quality of life of the patient.

Congenital Fibrinogen Deficiency in India and Role of Human Fibrinogen Concentrate

Congenital fibrinogen deficiency is an inherited disorder due to genetic mutations with diverse presentations arising from reduced fibrinogen levels (hypofibrinogenemia), absence of fibrinogen in circulation (afibrinogenemia), abnormal functioning (dysfibrinogenemia) or both reduced levels and abnormal functioning (hypodysfibrinogenemia) of fibrinogen. The decreased fibrinogen concentration in congenital fibrinogen deficiency necessitates fibrinogen replacement therapy with fresh frozen plasma, cryoprecipitate, or human fibrinogen concentrate. However, the use of fresh frozen plasma and cryoprecipitate is limited owing to their longer transfusion time, requirement of high doses, volume overload, risk of viral transmission, and other safety concerns. The availability of human fibrinogen concentrate has made it the preferred replacement alternative due to its reduced risk of viral transmission, smaller infusion volume, and accurate dosing. The hemostatic efficacy and safety of human fibrinogen concentrate in congenital fibrinogen deficiency is well established in the literature. We review the prevalence of congenital fibrinogen deficiency in India and the current role of human fibrinogen concentrate in its management.

Plasma viscosity pattern and erythrocyte aggregation in two patients with congenital afibrinogenemia

: In this case report, we examine the behavior of plasma viscosity, explored at high and low shear rates, and erythrocyte aggregation in two patients with congenital afibrinogenemia, a clinical disorder firstly described in 1920 and that has an estimated incidence of 1 : 1-200 0000. The two hemorheological parameters examined by us showed a marked decrease in both patients, in one of whom erythrocyte aggregation was even undetectable. Keeping in mind that spontaneous thrombosis (venous and arterial) has been often described in congenital afibrinogenemia, it can be hypothesized that the decrease in plasma viscosity and erythrocyte aggregation might cause a reduction of the endothelial synthesis and release of nitric oxide through the fall of the wall shear stress.

Pharmacokinetics, surrogate efficacy and safety evaluations of a new human plasma-derived fibrinogen concentrate (FIB Grifols) in adult patients with congenital afibrinogenemia

BACKGROUND AND AIMS

Congenital afibrinogenemia is a rare coagulation disorder resulting from a deficiency in fibrinogen. This study assessed the pharmacokinetics, surrogate efficacy and safety of FIB Grifols, a new human plasma-derived fibrinogen concentrate, to treat congenital afibrinogenemia.

METHODS

Eleven adult patients from a multinational, phase 1-2, prospective, open-label, single-arm, uncontrolled clinical study received a single infusion of FIB Grifols, 70 mg/kg bw. Fibrinogen pharmacokinetics (fibrinogen activity: Clauss method; antigen plasma concentrations: ELISA) and efficacy parameters were determined over 14 days after infusion. Efficacy endpoints were the mean change on plasma maximum clot firmness (MCF) on viscoelastic testing and coagulation tests 1-hour post-infusion, and correlation with fibrinogen levels throughout. Safety parameters were also assessed.

RESULTS

For the Clauss method, (mean [standard deviation]) baseline adjusted C_max was 1.99 (0.40) g/L, reached 1.76 (1.00) h after infusion, and half-life was 76.94 (20.21) h. Using ELISA, C_max after FIB Grifols infusion was 2.88 (0.86) mg/mL, with a t_max of 3.06 (2.24) h. Fibrinogen activity and antigen concentrations showed statistically significant correlation of 0.9120 (P < 0.001). Surrogate efficacy was demonstrated by a significant increase of 12.35 (3.85) mm in MCF. Prothrombin time, activated partial thromboplastin time and thrombin time, returned to normal ranges over time, indicating restoration of functionally active fibrinogen. There were no treatment-related adverse events, allergic reactions, serious adverse events, or discontinuations.

CONCLUSIONS

The pharmacokinetic profile of functionally active FIB Grifols was established, hemostasis was restored, and FIB Grifols was safe and well tolerated in fibrinogen-deficient patients.

A review of hyperfibrinolysis in cats and dogs

The fibrinolytic system is activated concurrently with coagulation; it regulates haemostasis and prevents thrombosis by restricting clot formation to the area of vascular injury and dismantling the clot as healing occurs. Dysregulation of the fibrinolytic system, which results in hyperfibrinolysis, may manifest as clinically important haemorrhage. Hyperfibrinolysis occurs in cats and dogs secondary to a variety of congenital and acquired disorders. Acquired disorders associated with hyperfibrinolysis, such as trauma, cavitary effusions, liver disease and Angiostrongylus vasorum infection, are commonly encountered in primary care practice. In addition, delayed haemorrhage reported in greyhounds following trauma and routine surgical procedures has been attributed to a hyperfibrinolytic disorder, although this has yet to be characterised. The diagnosis of hyperfibrinolysis is challenging and, until recently, has relied on techniques that are not readily available outside referral hospitals. With the recent development of point-of-care viscoelastic techniques, assessment of fibrinolysis is now possible in referral practice. This will provide the opportunity to target haemorrhage due to hyperfibrinolysis with antifibrinolytic drugs and thereby reduce associated morbidity and mortality. The fibrinolytic system and the conditions associated with increased fibrinolytic activity in cats and dogs are the focus of this review article. In addition, laboratory and point-of-care techniques for assessing hyperfibrinolysis and antifibrinolytic treatment for patients with haemorrhage are reviewed.

Clinical pharmacology, efficacy and safety study of a triple-secured fibrinogen concentrate in adults and adolescent patients with congenital fibrinogen deficiency

Essentials A novel fibrinogen concentrate was evaluated in patients with congenital fibrinogen deficiency. An open-label, phase 2-3 trial studied pharmacology, efficacy, and safety in patients >6 years. The product offers safe and effective therapy in the treatment and prophylaxis of bleeding. Data in recovery show the need of adjusted treatment and further investigation in children. SUMMARY: Background Single-factor replacement therapy is considered the most suitable treatment option for hereditary fibrinogen deficiency. A triple-secured plasma-derived human fibrinogen product was developed to increase the safety of the former fibrinogen concentrate. Objectives This non-randomized, open-label, prospective study investigated pharmacokinetics, efficacy, and safety of a novel fibrinogen concentrate (FibCLOT® /CLOTTAFACT® LFB, France) in inherited deficiency. Patients/Methods Fourteen patients ≥40 kg received fibrinogen concentrate for pharmacology and 16 ≥ 23 kg received treatment for bleeding or surgery. Each treatment was followed by a 3-week safety observation period. Key outcomes included number of infusions, dose, bleeding control, daily assessment, hemoglobin, blood loss, transfusions, and physicians' global assessment of response. Results Incremental recovery was 2.35 mg mL-1  per mg kg-1 and maximal concentration 1.41 g L-1 (geometric mean) after 0.060 g kg-1 infusion in 14 afibrinogenemic patients. Terminal half-life was 69.3 h (non-compartmental analysis). The maximum clot firmness was increased by a mean of 10.3 mm from baseline to maximal effect. Sixteen patients participated to the efficacy phase: 32 bleeding episodes were treated in 9 patients, and 15 patients underwent 38 surgical/invasive procedures. All patients achieved appropriate hemostasis: response to treatment was successful in all bleeds (95% CI, 0.89-1.00) and procedures (95% CI, 0.91-1.00). Most (94%) bleeds were controlled with a single infusion (median 0.050 g kg-1 ). Two patients experienced asymptomatic distal venous thromboses identified by systematic ultrasound. Conclusion FibCLOT® /CLOTTAFACT® showed a pharmacokinetic profile comparable to that of other fibrinogen concentrates and provides safe and clinically effective substitution therapy for fibrinogen-deficient patients.

Fibrinogen as a Pleiotropic Protein Causing Human Diseases: The Mutational Burden of Aα, Bβ, and γ Chains

Fibrinogen is a highly pleiotropic protein that is involved in the final step of the coagulation cascade, wound healing, inflammation, and angiogenesis. Heterozygous mutations in Aα, Bβ, or γ fibrinogen-chain genes (FGA, FGB, FGG) have been described as being responsible for fibrinogen deficiencies (hypofibrinogenemia, hypo-dysfibrinogenemia, dysfibrinogenemia) and for more rare conditions, such as fibrinogen storage disease and hereditary renal amyloidosis. Instead, biallelic mutations have been associated with afibrinogenemia/severe hypofibrinogenemia, i.e., the severest forms of fibrinogen deficiency, affecting approximately 1-2 cases per million people. However, the "true" prevalence for these conditions on a global scale is currently not available. Here, we defined the mutational burden of the FGA, FGB, and FGG genes, and estimated the prevalence of inherited fibrinogen disorders through a systematic analysis of exome/genome data from ~140,000 individuals belonging to the genome Aggregation Database. Our analysis showed that the world-wide prevalence for recessively-inherited fibrinogen deficiencies could be 10-fold higher than that reported so far (prevalence rates vary from 1 in 10⁶ in East Asians to 24.5 in 10⁶ in non-Finnish Europeans). The global prevalence for autosomal-dominant fibrinogen disorders was estimated to be ~11 in 1000 individuals, with heterozygous carriers present at a frequency varying from 3 every 1000 individuals in Finns, to 1-2 every 100 individuals among non-Finnish Europeans and Africans/African Americans. Our analysis also allowed for the identification of recurrent (i.e., FGG-p.Ala108Gly, FGG-Thr47Ile) or ethnic-specific mutations (e.g., FGB-p.Gly103Arg in Admixed Americans, FGG-p.Ser245Phe in Africans/African Americans).

Congenital afibrinogenemia: from etiopathogenesis to challenging clinical management

INTRODUCTION

Congenital afibrinogenemia belongs to the group of autosomal recessive bleeding disorders and represents the absolute deficiency of fibrinogen detected by an antigenic test. This can lead to severe clinical manifestations of the disorder. Therefore, it is very important to take afibrinogenemia into account in the process of the differential diagnostics of the patients.

AREAS COVERED

The authors provide a summary of currently available literature about afibrinogenemia. They collected the information from the scientific journals dedicated to thrombosis and hemostasis and searched world-wide databases. Expert commentary: The most frequent clinical manifestation of this disorder is mucosal bleeding, but musculoskeletal bleeding pattern, gynecologic and obstetric issues, spontaneous bleeding, episodes provoked by minor injury or any other intervention, and even paradoxical thromboembolic events have been published. Afibrinogenemia is the consequence of mutations of the homozygous or compound heterozygous type in gene FGA, FGB or FGG encoding fibrinogen. Pregnant women with a family history, or with a history of consanguinity ought to be properly counselled. However, primary prophylaxis of bleeding events is not suggested. The article deals with actual information about afibrinogenemia contributing to its early diagnosis and effective treatment, which in many cases requires multidisciplinary approach.

Congenital afibrinogenemia in a new born: a rare cause for bleeding

Bleeding in the neonates may be a result of thrombocytopenia, sepsis or vitamin K deficiency. Congenital bleeding disorders are a rare cause of bleeding. The umbilical cord bleed is an important clue to underlying bleeding disorders especially factor XIII deficiency and afibrinogenemia. In some laboratories, the routine workup for the bleeding neonate may not always include fibrinogen assays, which may then delay this diagnosis. We report a case of congenital afibrinogenemia in a neonate who presented with umbilical stump bleeding for its rarity and to re-emphasize the need for including fibrinogen assays while assessing a bleeding neonate.

Paradoxical bleeding and thrombosis in a patient with afibrinogenemia and fibrinogen Mumbai mutation

OBJECTIVES

Thrombosis is rarely reported in cases of afibrinogenemia and is generally associated with thrombophilia or replacement therapy. Often, it is difficult to predict whether the patients will bleed or whether they are exposed to the risk of thrombosis.

METHODS

We report a patient with afibrinogenemia who presented with complete thrombosis of right hepatic, portal, and splenic veins and who described a lifelong history of bleeding. Direct sequencing of the three fibrinogen genes was performed to identify the mutation.

RESULTS

DNA sequencing showed the presence of a homozygous for G8017A substitution in exon 8 of the fibrinogen β-chain gene, resulting in a G434D missense mutation (Fibrinogen Mumbai).

CONCLUSIONS

Presence of both bleeding and thrombotic manifestations in a patient with afibrinogenemia in the presence of other associated risk factors warrants a very careful individualized approach in the management of patients with afibrinogenemia.

[Congenital afibrinogenemia: a case report]

Afibrinogenemia is a rare autosomal recessive disease. Its clinical manifestations vary in severity, ranging from minimal bleeding to cataclysmic hemorrhage, and can begin at birth or, sometimes, later. We report a case of a female infant, 10 months of age, hospitalized in the pediatrics department because of a postvaccination hematoma. Biologic exploration found congenital afibrinogenemia. Through this case, we review the clinical features of this disease and its management.

Loss of fibrinogen in zebrafish results in symptoms consistent with human hypofibrinogenemia

Cessation of bleeding after trauma is a necessary evolutionary vertebrate adaption for survival. One of the major pathways regulating response to hemorrhage is the coagulation cascade, which ends with the cleavage of fibrinogen to form a stable clot. Patients with low or absent fibrinogen are at risk for bleeding. While much detailed information is known about fibrinogen regulation and function through studies of humans and mammalian models, bleeding risk in patients cannot always be accurately predicted purely based on fibrinogen levels, suggesting an influence of modifying factors and a need for additional genetic models. The zebrafish has orthologs to the three components of fibrinogen (fga, fgb, and fgg), but it hasn’t yet been shown that zebrafish fibrinogen functions to prevent bleeding in vivo. Here we show that zebrafish fibrinogen is incorporated into an induced thrombus, and deficiency results in hemorrhage. An Fgb-eGFP fusion protein is incorporated into a developing thrombus induced by laser injury, but causes bleeding in adult transgenic fish. Antisense morpholino knockdown results in intracranial and intramuscular hemorrhage at 3 days post fertilization. The observed phenotypes are consistent with symptoms exhibited by patients with hypo- and afibrinogenemia. These data demonstrate that zebrafish possess highly conserved orthologs of the fibrinogen chains, which function similarly to mammals through the formation of a fibrin clot.

A novel fibrinogen B beta chain frameshift mutation causes congenital afibrinogenaemia

Congenital afibrinogenaemia is a rare autosomal recessive disorder caused by various mutations within the fibrinogen genes FGA, FGB and FGG. Ins/del mutations in FGB are extremely rare. We report a patient with afibrinogenaemia who suffered from umbilical cord bleeding and repeated bleeding episodes. His plasma fibrinogen levels could not be detected using the Clauss method and immunological methods. Molecular analyses revealed homozygosity in a novel four bases insertion in codon 40 of FGB exon 2 (g. 2833_2834 ins GTTT), which resulted in a truncated 50-residue polypeptide that contained 11 exceptional abnormal residues. In the transient expression experiments, mutant fibrinogen could be detected at higher level than wild-type fibrinogen in COS-7 cell lysates but not in culture media. These results suggest that the homozygous mutation in FGB could be responsible for congenital afibrinogenaemia in this patient. This frameshift mutation could impair fibrinogen assembly and secretion without influencing the protein synthesis.

Rare and Unusual Bleeding Manifestations in Congenital Bleeding Disorders

Epistaxis, superficial and deep hematomas, hemarthrosis, gastrointestinal bleeding, hematuria represent the most frequent hemorrhagic events in congenital coagulation disorders. Occasionally, bleeding manifestations occur in unusual sites or are peculiar. A clotting defect may alter the clinical aspect of skin conditions or infections (hemorrhagic scabies or varicella). Hemobilia may occur as a complication of transjugular liver biopsy in hemophilia or Bernard-Soulier syndrome. Hemarthrosis of small joints of feet and hands occur in patients with hemophilia treated with protease inhibitors. Intramedullary hematomas of long bones have been described in α2-plasmin inhibitor or fibrinogen deficiencies. Spleen fracture with consequent hemoperitoneum has been reported in patients with fibrinogen deficiency. Rectus muscle sheath hematoma may occur in patients with factor VII (FVII)or FX deficiency. Acute or subacute intestinal obstruction may be caused by intramural wall hematomas in hemophilia and von Willebrand (vW)-disease. Physicians should always keep in mind that a congenital hemorrhagic disorder may cause bleeding in any tissue of the body and therefore alter the normal clinical features of a given disease.

Spontaneous bilateral subhyaloid hemorrhage in congenital hypofibrinogenemia

PURPOSE

The purpose of this study was to report a case of spontaneous bilateral subhyaloid hemorrhage in congenital hypofibrinogenemia.

METHODS

This is a single case report. A 14-year-old girl presented with a spontaneous bilateral decrease in vision. Her history was unremarkable. On examination, visual acuity was 20/80 in the right eye and 20/1200 in the left eye. Fundus examination showed bilateral subhyaloid hemorrhage. Clotting profile showed normal activated partial thromboplastin time and normal prothrombin time with fibrinogen decreased to 50 mg/dL (normal, 200-400 mg/dL).

RESULTS

Therapeutic cryoprecipitate infusion was administered. At 3 months, visual acuity improved to 20/20 with resolution of subhyaloid hemorrhage in both eyes.

CONCLUSION

Estimation of fibrinogen in the absence of other evaluated causes of blood dyscrasias would help with prompt diagnosis and successful management.

Hemophilia A and congenital hypofibrinogenemia: a rare association in same family

Hemophilia A is the commonest inherited coagulation defect in human beings, whereas congenital hypofibrinogenemia is a much rarer disease. Occurrence of these two inherited diseases in the same family has not been reported so far. Younger sibling of a known case of Hemophilia A presented with recurrent, spontaneously occurring echymotic spots having prolonged PT, APTT, TT and very low absolute fibrinogen level with normal factor VIII level ultimately diagnosed as a case of congenital hypofibrinogenemia.

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.

Inherited disorders of platelet alpha-granules

Platelet alpha-granules are the storage site for the internal membrane glycoprotein P-selectin and for a variety of megakaryocyte-synthesized and plasma-derived soluble proteins. Quantitative and/or qualitative abnormalities in alpha-granules are found in a number of inherited bleeding disorders, including gray platelet syndrome, alphadelta-storage pool deficiency, the Quebec platelet disorder, and in some patients with dysmegakaryopoietic thrombocytopenia. In addition, single alpha-granular protein deficiencies are seen in other bleeding disorders,including factor V deficiency, afibrinogenemia, Glanzmann's thrombasthenia, von Willebrand disease, and plasminogen-activator inhibitor-1 deficiency. The excessive bleeding that occurs in patients with inherited abnormalities of platelet alpha-granules indicates that the proteins stored within this compartment are important for normal hemostasis. The clinical and laboratory features of these different, inherited platelet storage pool disorders suggest unique molecular and biochemical defects are responsible for these conditions. However, the genetic causes of these disorders are largely unknown. This paper reviews our current knowledge of the inherited disorders of platelet alpha-granules.

Treatment of congenital fibrinogen disorders

BACKGROUND

The goal of the coagulation pathway is the conversion of fibrinogen to fibrin and formation of an insoluble clot. Although relatively rare, congenital fibrinogen disorders are interesting and pose several challenges that can serve as paradigms for many diseases. An impressive body of knowledge has accumulated recently, particularly thanks to international collaborative clinical and genetic studies allowing the molecular characterization of these disorders. However, apart from the possibility of developing safer fibrinogen concentrates and the availability of prenatal diagnosis, the basic therapeutic approach has changed little.

OBJECTIVE

We need to better understand the clinical phenotype of patients in order to administer fibrinogen preparations or other treatments more appropriately.

METHODS

We discuss current therapeutic options and others that could be available in the near future.

RESULTS/CONCLUSION

Patients with congenital fibrinogen deficiencies require better predictive tests for clinical complications and more efficient and available fibrinogen concentrates. Global hemostasis tests in combination with routine assays could help to individually tailor therapeutic protocols.

Molecular mechanisms accounting for fibrinogen deficiency: from large deletions to intracellular retention of misfolded proteins

Fibrinogen, the soluble precursor of fibrin, which is the main protein constituent of the blood clot, is synthesized in hepatocytes in the form of a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta, and gamma). Each polypeptide is encoded by a distinct gene, FGA, FGB and FGG, all three clustered in a region of 50 kb on 4q32. Congenital afibrinogenemia is characterized by the complete absence of fibrinogen. The first causative mutation for this disease was identified in Geneva in a non-consanguineous Swiss family in 1999: the four patients were homozygous for a large deletion in the fibrinogen cluster, which eliminated almost the entire FGA genomic sequence. Mutations in the fibrinogen genes may lead to deficiency of fibrinogen by several mechanisms: acting at the DNA level, at the RNA level by affecting mRNA splicing or stability, or at the protein level by affecting protein synthesis, assembly or secretion. Recent reviews have provided helpful updates for the rapidly growing number of causative mutations identified in patients with fibrinogen deficiencies, either afibrinogenemia or hypofibrinogenemia. The aim of this review is to highlight specifically the subset of mutations that allow fibrinogen chain synthesis and hexamer assembly but impair secretion. Indeed, functional studies of these mutations have shed light on the specific sequences and structures in the fibrinogen molecule involved in the quality control of fibrinogen secretion.

Mutations in the fibrinogen gene cluster accounting for congenital afibrinogenemia: an update and report of 10 novel mutations

Fibrinogen is synthesized in hepatocytes in the form of a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta, and gamma). Each polypeptide is encoded by a distinct gene, FGA, FGB, and FGG, all three clustered in a region of 50 kb on 4q31. Congenital afibrinogenemia is characterized by the complete absence of fibrinogen, the precursor of the major protein constituent of the blood clot, fibrin. Although the disease was first described in 1920, the genetic defect responsible for this disorder long remained unknown. We identified the gene and the first causative mutations for this disease in a nonconsanguineous Swiss family in 1999. Since this first report, 61 additional mutations, the majority in FGA, have been identified in patients with afibrinogenemia (in homozygosity or in compound heterozygosity) or in heterozygosity in hypofibrinogenemia, since many of these patients are in fact asymptomatic carriers of afibrinogenemia mutations. Mutations in the fibrinogen genes may lead to deficiency of fibrinogen by several mechanisms: these can act at the DNA level, at the RNA level by affecting mRNA splicing or stability, or at the protein level by affecting protein synthesis, assembly, or secretion. The expression of selected mutations has shown that mechanisms acting at all three levels play a role in the molecular basis of this disease. We report here the identification of 10 novel mutations, of which eight are localized in FGA, thus increasing the total number of causative mutations identified to 72 and confirming the relative importance of FGA in the molecular basis of fibrinogen deficiency.

Genetics of coagulation: considerations for cardiac surgery

Genetic variants in the coagulation system have been known since antiquity. Today, because of modern improvements in diagnosis and medical management, the clinician is likely to encounter a spectrum of coagulation factor deficiencies and identified polymorphic variants in the surgical population. Because perioperative hemorrhagic and thrombotic complications are potentially serious, it is important to understand the role that these defects and variants may play in predicting risk and optimizing patient management. The implications of coagulation genetics on the perioperative management of the cardiac surgery patient are reviewed.

Acute osteomyelitis in congenital hypofibrinogenemia

A 10-month-old female child presented with intermittent high grade fever, pain and diffuse swelling in the left knee joint with history of ecchymosis in different areas of the body. There was radiological features of acute osteomyelitis, low fibrinogen level and bacteremia due to the presence of coagulase positive staphylococcus aureus. The child responded nicely to the treatment for acute osteomyelitis and congenital hypofibrinogenemia. So, in congenital hypofibrinogenemia, a joint swelling might be a resultant of an acute osteomyelitis, not mere hemarthrosis.

Quality control of fibrinogen secretion in the molecular pathogenesis of congenital afibrinogenemia

Congenital afibrinogenemia is a rare bleeding disorder characterized by the absence in circulation of fibrinogen, a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta and gamma). Each polypeptide is encoded by a distinct gene, FGA, FGB and FGG, all three clustered in a region of 50 kb on 4q31. A subset of afibrinogenemia mutations has been shown to specifically impair fibrinogen secretion, but the underlying molecular mechanisms remained to be elucidated. Here, we show that truncation of the seven most C-terminal residues (R455-Q461) of the Bbeta chain specifically inhibits fibrinogen secretion. Expression of additional mutants and structural modelling suggests that neither the last six residues nor R455 is crucial per se for secretion, but prevent protein misfolding by protecting hydrophobic residues in the betaC core. Immunofluorescence and immuno-electron microscopy studies indicate that secretion-impaired mutants are retained in a pre-Golgi compartment. In addition, expression of Bbeta, gamma and angiopoietin-2 chimeric molecules demonstrated that the betaC domain prevents the secretion of single chains and complexes, whereas the gammaC domain allows their secretion. Our data provide new insight into the mechanisms accounting for the quality control of fibrinogen secretion and confirm that mutant fibrinogen retention is one of the pathological mechanisms responsible for congenital afibrinogenemia.

Efficacy and tolerability of a pasteurised human fibrinogen concentrate in patients with congenital fibrinogen deficiency

The efficacy and tolerability of a pasteurised human fibrinogen concentrate were assessed in an open, multi-centre, non-controlled retrospective study in patients with congenital fibrinogen deficiency. Haemostatic efficacy was assessed by laboratory investigation and clinical observation. The study included 12 patients (afibrinogenaemia, n = 8; hypofibrinogenaemia, n = 3; dysfibrinogenaemia combined with hypofibrinogenaemia, n = 1). Fibrinogen substitution was indicated: to stop an ongoing bleed; as prophylaxis before surgery; or for routine prophylaxis to prevent spontaneous bleeding. In total, 151 fibrinogen infusions were recorded. The median single dosage was 63.5mg/kg body weight for bleeding events or surgery and 76.9 mg/kg for prophylaxis. The median total dose per event for bleeding events or surgery was 105.6 mg/kg. Fibrinogen was administered in 26 bleeding episodes; 11 surgical operations; and 89 prophylactic infusions, of which 86 were received by one patient. The median response (n = 8) was 1.5 mg/dl per substituted mg of fibrinogen per kg body weight (0.8-2.3). The median in vivo recovery (n = 8) was 59.8% (32.5-93.9). Clinical efficacy was very good in all events with the exception of one surgical procedure, where it was moderate. No intercurrent bleeding occurred during prophylaxis. All but one infusion was well tolerated; the patient, who was administered 86 prophylactic infusions, experienced an anaphylactic reaction after the 56th infusion. In addition, one patient developed deep vein thrombosis and non-fatal pulmonary embolism with treatment for osteosynthesis after collum femoris fracture. Fibrinogen substitution could not be excluded as a contributing factor in this high-risk patient. Substitution with pasteurised human fibrinogen concentrate in patients with congenital fibrinogen deficiencies is efficient and generally well tolerated.

Expression and analysis of a split premature termination codon in FGG responsible for congenital afibrinogenemia: escape from RNA surveillance mechanisms in transfected cells

Congenital afibrinogenemia, the most severe form of fibrinogen deficiency, is characterized by the complete absence of fibrinogen. The disease is caused by mutations in 1 of the 3 fibrinogen genes FGG, FGA, and FGB, clustered on the long arm of human chromosome 4. The majority of cases are due to null mutations in the FGA gene although one would expect the 3 genes to be equally implicated. However, most patients studied so far are white, and therefore the identification of causative mutations in non-European families is necessary to establish if this finding holds true in all ethnic groups. In this study, we report the identification of a novel nonsense mutation (Arg134Xaa) in the FGG gene responsible for congenital afibrinogenemia in 10 patients from Lebanon. Expression studies in COS-7 cells demonstrated that the Arg134Xaa codon, which is encoded by adjacent exons (TG-intron 4-A) affected neither mRNA splicing nor stability, but led to the production of an unstable, severely truncated fibrinogen gamma chain that is not incorporated into a functional fibrinogen hexamer.

Congenital afibrinogenemia: intracellular retention of fibrinogen due to a novel W437G mutation in the fibrinogen Bβ-chain gene

Congenital afibrinogenemia is a rare autosomal recessive coagulation disorder characterised by hemorrhagic manifestations of variable entity and by severe plasma fibrinogen deficiency. Among the 31 afibrinogenemia-causing mutations so far reported, only 2 are missense mutations and both are located in the fibrinogen Bbeta-chain gene. Direct sequencing of the fibrinogen gene cluster in two afibrinogenemic Iranian siblings revealed a novel homozygous T>G transversion in exon 8 (nucleotide position 8025) of the fibrinogen Bbeta-chain gene. The resulting W437G missense mutation involves a highly conserved amino acid residue, located in the C-terminal globular D domain. The role of the W437G amino acid substitution on fibrinogen synthesis, folding, and secretion was assessed by in vitro expression experiments in COS-1 cells, followed by qualitative and quantitative analyses of intracellular and secreted mutant fibrinogen. Results of both pulse-chase experiments and enzyme-linked immunosorbent assays demonstrated intracellular retention of the mutant W437G fibrinogen and marked reduction of its secretion. These data, besides elucidating the pathogenetic role of the W437G mutation in afibrinogenemia, underline the importance of the Bbeta-chain D domain in fibrinogen folding and secretion.

Hemopneumothorax associated with Marfan syndrome and congenital afibrinogenemia

In patients with afibrinogenemia who require operation, prophylaxis against bleeding is important. We report the case of a 14-year-old boy with Marfan syndrome and congenital afibrinogenemia in whom hemopneumothorax developed. Video-assisted thoracoscopic surgery was performed successfully under intravenous administration of fibrinogen and with careful monitoring of plasma fibrinogen level.

The dynamics of thrombin formation

The central event of the hemostatic process is the generation of thrombin through the tissue factor pathway. This is a highly regulated, dynamic process in which thrombin itself plays many roles, positively and negatively its production and destruction. The hemostatic process is essential to normal physiology and is also the Achilles heel of our aging population. The inappropriate generation of thrombin may lead to vascular occlusion with the consequence of myocardial infarction, stroke, pulmonary embolism, or venous thrombosis. In this review, we summarize our present views regarding the tissue factor pathway by which thrombin is generated and the roles played by extrinsic and intrinsic factor Xa generating complexes in hemostasis and the roles of the stoichiometric and dynamic inhibitors that regulate thrombin generation.

Laboratory diagnosis of dysfibrinogenemia

Dysfibrinogenemia is a coagulation disorder caused by a variety of structural abnormalities in the fibrinogen molecule that result in abnormal fibrinogen function. It can be inherited or acquired. The inherited form is associated with increased risk of bleeding, thrombosis, or both in the same patient or family. Traditionally, dysfibrinogenemia is diagnosed by abnormal tests of fibrin clot formation; the thrombin time and reptilase time are the screening tests, and the fibrinogen clotting activity-antigen ratio is the confirmatory test. The inherited form is diagnosed by demonstrating similar laboratory test abnormalities in family members, and if necessary by analysis of the fibrinogen protein or fibrinogen genes in the patient. The acquired form is diagnosed by demonstrating abnormal liver function tests and by ruling out dysfibrinogenemia in family members. This article reviews the laboratory testing of dysfibrinogenemia and presents an algorithm for sequential test selection that can be used for diagnosis.

Fibrinogen stabilizes placental-maternal attachment during embryonic development in the mouse

In humans, maternal fibrinogen (Fg) is required to support pregnancies by maintaining hemostatic balance and stabilizing uteroplacental attachment at the fibrinoid layer found at the fetal-maternal junction. To examine relationships between low Fg levels and early fetal loss, a genetic model of afibrinogenemia was developed. Pregnant mice homozygous for a deletion of the Fg-gamma chain, which results in a total Fg deficiency state (FG(-/-)), aborted the fetuses at the equivalent gestational stage seen in humans. Results obtained from timed matings of FG(-/-) mice showed that vaginal bleeding was initiated as early as embryonic day (E)6 to 7, a critical stage for maternal-fetal vascular development. The condition of afibrinogenemia retarded embryo-placental development, and consistently led to abortion and maternal death at E9.75. Lack of Fg did not alter the extent or distribution pattern of other putative factors of embryo-placental attachment, including laminin, fibronectin, and Factor XIII, indicating that the presence of fibrin(ogen) is required to confer sufficient stability at the placental-decidual interface. The results of these studies demonstrate that maternal Fg plays a critical role in maintenance of pregnancy in mice, both by supporting proper development of fetal-maternal vascular communication and stabilization of embryo implantation.

Congenital afibrinogenemia: mutations leading to premature termination codons in fibrinogen A alpha-chain gene are not associated with the decay of the mutant mRNAs

Congenital afibrinogenemia is a rare coagulation disorder with autosomal recessive inheritance, characterized by the complete absence or extremely reduced levels of fibrinogen in patients' plasma and platelets. Eight afibrinogenemic probands, with very low plasma levels of immunoreactive fibrinogen were studied. Sequencing of the fibrinogen gene cluster of each proband disclosed 4 novel point mutations (1914C>G, 1193G>T, 1215delT, and 3075C>T) and 1 already reported (3192C>T). All mutations, localized within the first 4 exons of the A alpha-chain gene, were null mutations predicted to produce severely truncated A alpha-chains because of the presence of premature termination codons. Since premature termination codons are frequently known to affect the metabolism of the corresponding messenger RNAs (mRNAs), the degree of stability of each mutant mRNA was investigated. Cotransfection experiments with plasmids expressing the wild type and each of the mutant A alpha-chains, followed by RNA extraction and semiquantitative reverse-transcriptase-polymerase chain reaction analysis, demonstrated that all the identified null mutations escaped nonsense-mediated mRNA decay. Moreover, ex vivo analysis at the protein level demonstrated that the presence of each mutation was sufficient to abolish fibrinogen secretion.

Embolized ischemic lesions of toes in an afibrinogenemic patient: possible relevance to in vivo circulating thrombin

Fibrinogen plays a complex role in hemostasis, thrombosis, and vascular disease. Hyperfibrinogenemia is an independent vascular risk factor and dysfibrinogenemia can provoke thrombosis. Afibrinogenemia is usually responsible for hemorrhagic diathesis, and unexpected ischemic lesions are intriguing. We report the case of an afibrinogenemic patient, who at the age of 30 developed ischemic lesions of the feet related to severe stenosis of the iliac and hypogastric arteries. The biopsy of the iliac artery lesion showed an intense myointimal hyperplasia. We performed standard hemostatic analysis and analyzed the activation markers of platelets and coagulation factors and the kinetics of thrombin generation in the patient and in normal control plasmas treated or not with reptilase. Occlusive arterial lesions were attributed to a disruptive hematoma penetrating the vascular lumen. Thrombin concentration after calcium addition increase markedly in the afibrinogenemic patient and in defibrinated normal plasma, as compared to untreated normal plasma. Thrombin-antithrombin complexes (T-AT) were markedly enhanced while F1+2 prothrombin fragments stayed in the normal range. These results suggested activation of coagulation and in vivo circulating thrombin. Thrombin activates the platelets that secrete growth factors for smooth muscle cells and generate the intimal hyperplasia. Recurrent hemorrhage within the vessel wall might induce injury and local thrombin generation. Thrombin not trapped by the clot is available for platelet activation and smooth muscle cell migration and proliferation. The absence of a protective fibrin cap on the intima might account for intima vulnerability and embolization. Afibrinogenemia appears in this paradoxical situation as a vascular risk factor.

Recurrence phenomena after immunoglobulin therapy for snake envenomations: Part 2. Guidelines for clinical management with crotaline Fab antivenom

Recurrent local and coagulopathic effects (worsening after clinical improvement) have been described after treatment with Fab antivenom for envenomation by North American crotaline snakes. Although similar phenomena have been described previously in snakebite, few studies have examined recurrence or its management. Recurrence is consistent with known venom and antivenom kinetics and dynamics. The clinical significance of late coagulopathy after snakebite is uncertain, but clinically significant bleeding is a possibility. Prevention and treatment of recurrence with Fab antivenom require repeated dosing for at least 18 hours, with close monitoring of at-risk patients in the follow-up period. Duration of therapy depends on individual risk factors and coagulation response.

Current therapy for rare factor deficiencies

Haemophilia A and B and von Willebrand disease account for 80-85% of all inherited bleeding disorders. The other 15% are represented by deficiencies of fibrinogen, prothrombin, or factors V, VII, X, XI, or XIII. In addition, acquired factor deficiencies are seen in a variety of conditions ranging from malignancies to autoimmune disorders. The spectrum of symptoms in these conditions varies from severe and life-threatening haemorrhage to a mild bleeding diathesis. The diagnosis depends on demonstration of decreased activity of one of the clotting factors. Due to the rarity of each of the individual factor deficiencies, purified factor concentrates are not as readily available as they are for haemophilia A and B. Treatment of rare clotting factor deficiencies consists of the most purified blood product available that contains the missing factor. Depending on which factor is deficient, either purified concentrates, prothrombin complex concentrates, cryoprecipitate, or fresh frozen plasma can be used. In addition, recombinant factor VIIa is available for treating factor VII deficient patients.

A G-to-A mutation in IVS-3 of the human gamma fibrinogen gene causing afibrinogenemia due to abnormal RNA splicing

Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by a hemorrhagic diathesis of variable severity. Although more than 100 families with this disorder have been described, genetic defects have been characterized in few cases. An investigation of a young propositus, offspring of a consanguineous marriage, with undetectable levels of functional and quantitative fibrinogen, was conducted. Sequence analysis of the fibrinogen genes showed a homozygous G-to-A mutation at the fifth nucleotide (nt 2395) of the third intervening sequence (IVS) of the γ-chain gene. Her first-degree relatives, who had approximately half the normal fibrinogen values and showed concordance between functional and immunologic levels, were heterozygtes. The G-to-A change predicts the disappearance of a donor splice site. After transfection with a construct, containing either the wild-type or the mutated sequence, cells with the mutant construct showed an aberrant messenger RNA (mRNA), consistent with skipping of exon 3, but not the expected mRNA. Sequencing of the abnormal mRNA showed the complete absence of exon 3. Skipping of exon 3 predicts the deletion of amino acid sequence from residue 16 to residue 75 and shifting of reading frame at amino acid 76 with a premature stop codon within exon 4 at position 77. Thus, the truncated γ-chain gene product would not interact with other chains to form the mature fibrinogen molecule. The current findings show that mutations within highly conserved IVS regions of fibrinogen genes could affect the efficiency of normal splicing, giving rise to congenital afibrinogenemia.

A G-to-A mutation in IVS-3 of the human gamma fibrinogen gene causing afibrinogenemia due to abnormal RNA splicing

Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by a hemorrhagic diathesis of variable severity. Although more than 100 families with this disorder have been described, genetic defects have been characterized in few cases. An investigation of a young propositus, offspring of a consanguineous marriage, with undetectable levels of functional and quantitative fibrinogen, was conducted. Sequence analysis of the fibrinogen genes showed a homozygous G-to-A mutation at the fifth nucleotide (nt 2395) of the third intervening sequence (IVS) of the γ-chain gene. Her first-degree relatives, who had approximately half the normal fibrinogen values and showed concordance between functional and immunologic levels, were heterozygtes. The G-to-A change predicts the disappearance of a donor splice site. After transfection with a construct, containing either the wild-type or the mutated sequence, cells with the mutant construct showed an aberrant messenger RNA (mRNA), consistent with skipping of exon 3, but not the expected mRNA. Sequencing of the abnormal mRNA showed the complete absence of exon 3. Skipping of exon 3 predicts the deletion of amino acid sequence from residue 16 to residue 75 and shifting of reading frame at amino acid 76 with a premature stop codon within exon 4 at position 77. Thus, the truncated γ-chain gene product would not interact with other chains to form the mature fibrinogen molecule. The current findings show that mutations within highly conserved IVS regions of fibrinogen genes could affect the efficiency of normal splicing, giving rise to congenital afibrinogenemia.