A new type of congenital dysfibrinogenaemia with defective fibrin lysis--Dusard syndrome: possible relation to thrombosis

One Hundred Years of Congenital Fibrinogen Disorders

Congenital fibrinogen disorders encompass a broad range of fibrinogen defects characterized by a wide molecular and clinical spectrum. From the first clinical description of afibrinogenemia in 1920, many major achievements have contributed to a better understanding of these complex disorders. The finding of causative mutations in all three fibrinogen genes has contributed to reveal the molecular mechanisms involved in biosynthesis of the fibrinogen molecule and to clarify the basic processes of fibrin polymerization and fibrinolysis. The compilation of abundant cases with detailed genetic, biological, and clinical features has enabled the classification of congenital fibrinogen disorders into several types and subtypes. Thus, the recent classification of congenital fibrinogen disorder is based not only on the clottable and antigenic fibrinogen levels but also on the patient's clinical phenotype and genotype. Fibrinogen supplementation is the cornerstone of bleeding management in fibrinogen disorders. Since the discovery of blood fractionation, the method of production of fibrinogen concentrate has been progressively modified to significantly improve purity and safety. Nevertheless, the availability of such products is still limited to a few countries and the optimal threshold of fibrinogen to target is still not established. In this review, we describe the major advances that have characterized 100 years of congenital fibrinogen disorders, focusing on afibrinogenemia and dysfibrinogenemia.

Acute ischemic stroke in adolescents

OBJECTIVE

Adolescence represents a transition period between childhood and adulthood, and only limited information exists about stroke characteristics in this population. Our aim was to describe the clinical and neuroradiologic features, etiologies, initial management, and outcome of ischemic stroke in adolescents.

METHODS

This retrospective cohort study evaluated all consecutive patients 10 to 18 years with a first-ever ischemic stroke hospitalized between 2007 and 2017 in 10 French academic centers representing a population of ≈10 million. Extracted data from the national database served as validation.

RESULTS

A total of 60 patients were included (53% male, median age 15.2 years). Diagnosis at first medical contact was misevaluated in 36%, more frequently in posterior than anterior circulation strokes (55% vs 20% respectively, odds ratio 4.8, 95% confidence interval 1.41-16.40, p = 0.01). Recanalization treatment rate was high (n = 19, 32%): IV thrombolysis (17%), endovascular therapy (11.7%), or both IV and intra-arterial thrombolysis (3.3%); safety was good (only 1 asymptomatic hemorrhagic transformation). Despite thorough etiologic workup, 50% of strokes remained cryptogenic. The most common determined etiologies were cardioembolism (15%), vasculitis and autoimmune disorders (12%, occurring exclusively in female patients), and arterial dissections (10%, exclusively in male patients). Recurrent ischemic cerebrovascular events occurred in 12% (median follow-up 19 months). Recurrence rate was 50% in patients with identified vasculopathy but 0% after cryptogenic stroke. Functional outcome was favorable (Rankin Scale score 0-2 at day 90) in 80% of cases.

CONCLUSIONS

Ischemic strokes in adolescents harbor both pediatric and adult features, emphasizing the need for multidisciplinary collaboration in their management. Recanalization treatments appear feasible and safe.

Fibrinogen αC domain: Its importance in physiopathology

ABSTRACT

Fibrinogen, involved in coagulation, is a soluble protein composed of two sets of disulfide-bridged Aα, Bβ, and γ-chains. In this review, we present the clinical implications of the αC domain of the molecule in Alzheimer's disease, hereditary renal amyloidosis and a number of thrombotic and hemorrhagic disorders. In Alzheimer's disease, amyloid beta peptide (Aβ) is increased and binds to the αC domain of normal fibrinogen, triggering increased fibrin(ogen) deposition in patients' brain parenchyma. In hereditary renal amyloidosis, fibrinogen is abnormal, with mutations located in the fibrinogen αC domain. The mutant αC domain derived from fibrinogen degradation folds incorrectly so that, in time, aggregates form, leading to amyloid deposits in the kidneys. In these patients, no thrombotic tendency has been observed. Abnormal fibrinogens with either a point mutation in the αC domain or a frameshift mutation resulting in absence of a part of the αC domain are often associated with either thrombotic events or bleeding. Mutation of an amino acid into cysteine (as in fibrinogens Dusart and Caracas V) or a frameshift mutation yielding an unpaired cysteine in the αC domain is often responsible for thrombotic events. Covalent binding of albumin to the unpaired cysteine via a disulphide bridge leads to decreased accessibility to the fibrinolytic enzymes, hence formation of poorly degradable fibrin clots, which explains the high incidence of thrombosis. In contrast, anomalies due to a frameshift mutation in the αC connector of the molecule, provoking deletion of a great part of the αC domain, are associated with bleeding.

Highly Elevated Quantitative D-Dimer Assay Values Increase the Likelihood of Venous Thromboembolism

Objectives  In patients with suspected venous thromboembolism (VTE), the D-dimer assay is commonly utilized as part of the workup. The assay is primarily used to determine whether to proceed with radiographic imaging. We compared D-dimer levels in patients suspected of having VTE. We hypothesized that higher D-dimer values predict a higher likelihood of subsequent VTE diagnosis.

Methods  We conducted a secondary analysis of a multinational, prospective observational study of low- to intermediate-risk adult patients presenting to the emergency department with suspicion of VTE. Demographic and clinical data were collected in a structured manner. Advanced imaging including ultrasound, computed tomography (CT) pulmonary angiography, and ventilation/perfusion scanning was obtained at the discretion of the treating physicians. Imaging was evaluated by board-certified radiologists in real time. D-dimer values' bins were evaluated using a logistic regression model.

Results  We evaluated 1,752 patients for suspected deep vein thrombosis (DVT), with 191 (10.4%) DVT positive. We evaluated 1,834 patients for suspected pulmonary embolism (PE), with 108 (5.9%) PE positive. Higher D-dimer values in both groups were associated with higher likelihood of subsequent VTE diagnosis, with D-dimer values > 3,999 ng/mL in both groups having the highest incidence of VTE. More than 50% of those patients were VTE positive.

Conclusions  Increasing D-dimer values predict increased likelihood of being found VTE positive in this patient population. Among those in the highest D-dimer category, > 3,999 ng/mL, over half of patients were VTE positive. Further research could determine additional nuance in D-dimer as a tool to work up suspected VTE.

A novel mutation in exon 2 of FGB caused by c.221G>T † substitution, predicting the replacement of the native Arginine at position 74 with a Leucine (p.Arg74Leu † ) in a proband from a Kurdish family with dysfibrinogenaemia and familial venous and arterial thrombosis

Dysfibrinogenaemias may present in either congenital or acquired form and are disorders of fibrinogen structure which may or may not be associated with abnormal function. More than 100 point mutations with single amino acid substitutions have been identified in over 400 families. These lead to defective DNA in the translated fibrinogen molecule. Such cases have improved our understanding of the fibrinogen–fibrin structure. Six members of a consanguineous family including a female proband, a female sibling, three male siblings and a daughter, with ages between 29 years and 53 years presented with early onset venous and premature arterial thromboembolic disease were investigated for a pro-thrombotic tendency associated with dysfibrinogenaemia. The family was investigated using standard coagulation assays and DNA sequencing of the genes encoding the FGA, FGB and FGG. All cases have dysfibrinogenaemia with a fibrinogen level 1.4 to 1.5 (1.9–4.3 g/L). Thrombophilia testing (including AT, PS & PC, F5 G1691A (FV Leiden)/F2 (prothombin G20210A) genotypes, homocysteine, antiphosphlipid antibody, paroxysmal nocturnal haemoglobinuria by flow cytometry and Janus Kinase-2 (exon 14)) were normal. PCR amplification and sequencing of exon 2 of FBG revealed a heterozygous mutation for a c.221G> T^†substitution, predicting the replacement of the native Arginine at position 74 with a Leucine (p.Arg74Leu^†). In silico analysis of p.Arg74Leu strongly support pathogenicity. A novel mutation was identified in exon 2 of FGB caused by c.221G> T^† substitution, predicting the replacement of Arginine at position 74 with a Leucine (p.Arg74Leu^†) in a proband from a Kurdish family with dysfibrinogenaemia and familial venous and arterial thrombosis.

Fibrin clot structure in patients with congenital dysfibrinogenaemia

The clinical phenotype of patients with congenital dysfibrinogenaemia is highly heterogeneous, from absence of symptoms to mild bleeding, or thrombosis. A few mutations are associated with a specific phenotype, but generally the clinical course is not predictable. We investigated whether fibrin clot properties are correlated with the patient's phenotype and/or genotype. Ex vivo plasma fibrin clot characteristics, including turbidity, fibrinolysis, clot permeability and fibrin fibre density assessed by laser scanner confocal microscopy were investigated in 24 genotyped patients with congenital dysfibrinogenaemia compared to normal pool plasma. Compared to normal pool plasma, the patients were characterised by slower fibrin polymerisation (lag time, 345.10 ± 22.98 vs. 166.00s), thinner fibrin fibres (maximum absorbance, 0.15 ± 0.01 vs. 0.31), prolonged clot lysis time (23.72 ± 0.97 vs. 20.32 min) and larger clot pore size (21.5×10(-9) ± 4.48×10(-9) vs. 7.96×10(-9)cm(2)). Laser scanning confocal microscopy images confirmed disorganised fibrin networks in all patients. Patients with tendency to bleed showed an increased permeability compared to asymptomatic patients (p=0.01) and to patients with a thrombotic history (p=0.02) while patients with thrombotic history had a tendency to have a prolonged clot lysis time. Fibrin clot properties were similar among hotspot mutations. Further studies including a larger number of patients are needed to evaluate whether analysis of permeability and clot lysis time may help to distinguish the clinical phenotype in these patients and to assess differences according to the genotype.

Dysfibrinogenemia: from molecular anomalies to clinical manifestations and management

Congenital dysfibrinogenemia is a qualitative congenital fibrinogen disorder characterized by normal antigen levels of a dysfunctional fibrinogen. The diagnosis is usually based on discrepancies between fibrinogen activity and antigen levels, but could require more specialized techniques for the assessment of fibrinogen function, owing to some limitations in routine assays. Molecular abnormalities, which are frequently heterozygous missense mutations localized in exon 2 of FGA and exon 8 of FGG, lead to defects in one or more phases of fibrinogen to fibrin conversion, fibrin network formation, and other important functions of fibrinogen. The clinical phenotype is highly heterogeneous, from no manifestations to bleeding and/or thrombotic events. Asymptomatic propositi and relatives with the predisposing genotype are at risk of developing adverse outcomes during the natural course of the disease. Correlations between genotype and phenotype have not yet been clearly established, with the exception of some abnormal fibrinogens that severely increase the risk of thrombosis. Functional analysis of polymerization and fibrinolysis, structural studies of the fibrin network and the viscoelastic properties of fibrin clot could help to predict the phenotype of congenital dysfibrinogenemia, but have not yet been evaluated in detail. The management is essentially based on personal and family history; however, even individuals who are still asymptomatic and without a family history should be carefully assessed and monitored. Particular situations, such as pregnancy, delivery, and surgery, require a multidisciplinary approach.

Natural history of patients with congenital dysfibrinogenemia

We conducted a multicenter study of 101 patients with congenital dysfibrinogenemia (CD) to characterize the incidence of hemorrhagic and thrombotic events as well as complications of pregnancy and surgery. At the time of diagnosis, 10.9% and 13.9% had experienced major bleeding and thrombotic events, respectively. During a mean follow-up of 8.8 years after CD diagnosis, the incidence of major bleeding and thrombotic events was 2.5 and 18.7 per 1000 patient-years, respectively, with estimated cumulative incidences at age 50 years of 19.2% and 30.1%. We identified 111 pregnancies with an overall incidence of spontaneous abortions and postpartum hemorrhage of 19.8% and 21.4%, respectively. The risk of postpartum hemorrhage was associated with a previously identified bleeding phenotype (odds ratio, 5.8; 95% CI, 1.2 to 28.0). Among 137 surgical procedures analyzed, 9 (6.5%) were complicated by abnormal bleeding. Propositi vs relatives, sex, mutation hotspots, fibrinogen levels, and activity:antigen ratios were not associated with the risk of thrombotic or bleeding outcomes. In conclusion, the results of our study, the largest in genotyped CD and the first including long-term history, indicate that propositi with CD and their relatives carry not only a high risk of major bleeding, including postpartum hemorrhage, but also of thrombotic event.

New combinational assay using soluble fibrin and d-dimer determinations: a promising strategy for identifying patients with suspected venous thromboembolism

Aim

To establish a new and reliable assay for quantification of the soluble fibrin (SF) in combination with that of D-dimer for early diagnosis of venous thromboembolism.

Methods and Samples

The SF assay is based on D-dimer generated after incubation of plasma with tissue-type plasminogen activator (t-PA). SF and standard D-dimer assays, run in blind, were used to test 119 untreated outpatients with clinically suspected deep-vein thrombosis (DVT, 49 patients) or pulmonary embolism (PE, 70 patients) consulting at the emergency unit of the hospital. Thromboses were confirmed by current imaging methods such as ultrasonography, scintigraphy, computed tomographic pulmonary angiography (CTPA) and ventilation/perfusion scan.

Results

SF assay was validated in 270 healthy volunteers [51.8% males; mean age years ± SD: 41±13; age range 19 to 65]. Among these normal plasmas, SF levels were ≤200 ng/mL in 97.8% of them, and 200–250 ng/mL in the remainder [26–46 years old; 50% males]. ROC curves were used to determine the SF cut-off value for plasma SF positivity, which was found to be 300 ng/mL. In patients with suspected venous thromboembolism, SF sensitivities for DVT and PE (92% and 94%, respectively) were comparable to those of D-dimer (96% and 94%), whereas SF specificities (86% and 95%) were higher than those of D-dimer (50% and 54%). Positive-predictive values for SF (89% and 94%) were again higher than those of D-dimer (70% and 65%) in DVT and PE. The amount of circulating SF normalized rapidly after anticoagulant therapy.

Conclusion

Results from this small group of patients suggest that the evaluation of plasma SF, in combination with that of D-dimer, represents a potentially useful tool for the early diagnosis of venous thromboembolism, provided that the patients have not been treated previously by anticoagulants.

Whole blood clots are more resistant to lysis than plasma clots--greater efficacy of rivaroxaban

INTRODUCTION

Defective thrombolysis, a thrombotic risk factor, can be attributed to the formation of a compact clot poorly accessible to fibrinolytic enzymes. Venous thrombi, rich in red blood cells (RBCs), and arterial thrombi containing various amounts of RBCS, plasma and whole blood (WB) clot permeability and degradability were compared. The effect of rivaroxaban, a potent direct factor Xa inhibitor, was also evaluated.

MATERIALS AND METHODS

Fibrin permeability was determined by flow measurement through the clot. Clot degradability was evaluated by the amount of D-dimer generated by clot perfusion with plasminogen and tissue plasminogen activator. Fibrin clot structure was assessed by confocal microscopy.

RESULTS

WB clot permeability (KS) and degradability were 6.7- and 38-fold lower, respectively, compared with plasma clots. This is attributed to 1) occlusion of fibrin pores by RBCs and 2) a consistent increase in thrombin generation due to platelets and RBCs inducing formation of a tighter clot. Rivaroxaban added to plasma or WB before clotting, in reducing thrombin generation, led to the formation of a looser clot that is more degradable by fibrinolytic enzymes. Permeability and degradability of whole blood clots formed in the presence of rivaroxaban were very similar to those of plasma clots.

CONCLUSION

The resistance to fibrinolysis of WB clots was reduced considerably when clots were formed with rivaroxaban. These results may have implications for the development of antithrombotic agents.

In vitro fibrin clot formation and fibrinolysis using heterozygous plasma fibrinogen from γAsn319, Asp320 deletion dysfibrinogen, Otsu I

INTRODUCTION

We have reported a heterozygous dysfibrinogenemia, fibrinogen Otsu I, caused by the deletion of gammaAsn319 and gammaAsp320, which was originally identified in the dysfibrinogen Vlissingen/Frankfurt IV (V/FIV) associated with thrombosis. Unlike the V/FIV family, the Otsu propositus showed no thrombotic tendencies. To analyze the relationship between thrombosis and the heterozygous plasma variant fibrinogen, we used purified plasma fibrinogen from the Otsu patient and compared it with a normal control.

MATERIALS AND METHODS

Thrombin-induced fibrin clot formation and clot structure were observed by fibrin polymerization and scanning electron microscopy, respectively. For in vitro observation of fibrinolysis, plasmin generation and clot lysis assays were performed by the addition of tissue type plasminogen activation (tPA) and plasminogen.

RESULTS AND CONCLUSIONS

Polymerization of Otsu was markedly impaired, while fibrin fibers were much thicker and the density of the bundles of fibrin fibers was less and porous compared with normal. Lysis of the Otsu clot was not significantly different from normal when a tPA and plasminogen mixture was overlaid onto the clots. For Otsu, the penetration of the tPA/plasminogen mixture into the clot was much faster than normal and the protection against plasmin cleavage was impaired; however, tPA-induced plasmin activation of the Otsu fibrin was slower than that of normal fibrin, resulting in a clot lysis of Otsu similar to normal.

The alphaC domains of fibrinogen affect the structure of the fibrin clot, its physical properties, and its susceptibility to fibrinolysis

The functions of the alphaC domains of fibrinogen in clotting and fibrinolysis, which have long been enigmatic, were determined using recombinant fibrinogen truncated at Aalpha chain residue 251. Scanning electron microscopy and confocal microscopy revealed that the fibers of alpha251 clots were thinner and denser, with more branch points than fibers of control clots. Consistent with these results, the permeability of alpha251 clots was nearly half that of control clots. Together, these results suggest that in normal clot formation, the alphaC domains enhance lateral aggregation to produce thicker fibers. The viscoelastic properties of alpha251 fibrin clots differed markedly from control clots; alpha251 clots were much less stiff and showed more plastic deformation, indicating that interactions between the alphaC domains in normal clots play a major role in determining the clot's mechanical properties. Comparing factor XIIIa cross-linked alpha251 and control clots showed that gamma chain cross-linking had a significant effect on clot stiffness. Plasmin-catalyzed lysis of alpha251 clots, monitored with both macroscopic and microscopic methods, was faster than lysis of control clots. In conclusion, these studies provide the first definitive evidence that the alphaC domains play an important role in determining the structure and biophysical properties of clots and their susceptibility to fibrinolysis.

Fibrinogen and fibrin structure and functions

Fibrinogen molecules are comprised of two sets of disulfide-bridged Aalpha-, Bbeta-, and gamma-chains. Each molecule contains two outer D domains connected to a central E domain by a coiled-coil segment. Fibrin is formed after thrombin cleavage of fibrinopeptide A (FPA) from fibrinogen Aalpha-chains, thus initiating fibrin polymerization. Double-stranded fibrils form through end-to-middle domain (D:E) associations, and concomitant lateral fibril associations and branching create a clot network. Fibrin assembly facilitates intermolecular antiparallel C-terminal alignment of gamma-chain pairs, which are then covalently 'cross-linked' by factor XIII ('plasma protransglutaminase') or XIIIa to form 'gamma-dimers'. In addition to its primary role of providing scaffolding for the intravascular thrombus and also accounting for important clot viscoelastic properties, fibrin(ogen) participates in other biologic functions involving unique binding sites, some of which become exposed as a consequence of fibrin formation. This review provides details about fibrinogen and fibrin structure, and correlates this information with biological functions that include: (i) suppression of plasma factor XIII-mediated cross-linking activity in blood by binding the factor XIII A2B2 complex. (ii) Non-substrate thrombin binding to fibrin, termed antithrombin I (AT-I), which down-regulates thrombin generation in clotting blood. (iii) Tissue-type plasminogen activator (tPA)-stimulated plasminogen activation by fibrin that results from formation of a ternary tPA-plasminogen-fibrin complex. Binding of inhibitors such as alpha2-antiplasmin, plasminogen activator inhibitor-2, lipoprotein(a), or histidine-rich glycoprotein, impairs plasminogen activation. (iv) Enhanced interactions with the extracellular matrix by binding of fibronectin to fibrin(ogen). (v) Molecular and cellular interactions of fibrin beta15-42. This sequence binds to heparin and mediates platelet and endothelial cell spreading, fibroblast proliferation, and capillary tube formation. Interactions between beta15-42 and vascular endothelial (VE)-cadherin, an endothelial cell receptor, also promote capillary tube formation and angiogenesis. These activities are enhanced by binding of growth factors like fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF), and cytokines like interleukin (IL)-1. (vi) Fibrinogen binding to the platelet alpha(IIb)beta3 receptor, which is important for incorporating platelets into a developing thrombus. (vii) Leukocyte binding to fibrin(ogen) via integrin alpha(M)beta2 (Mac-1), which is a high affinity receptor on stimulated monocytes and neutrophils.

Novel Aalpha chain truncation (fibrinogen Perth) resulting in low expression and impaired fibrinogen polymerization

A young woman with a history of menorrhagia and easy bruising presented with a functional fibrinogen concentration of 1.8 mg mL(-1), a gravimetric concentration of 3.3 mg mL(-1) and a prolonged thrombin clotting time of 32 s. Both reverse phase analysis and reducing SDS-PAGE revealed a normal profile of Aalpha, Bbeta, and gamma chains. However, non-reducing gels revealed a broadened 340-kDa band, while the 305-kDa band was normal, suggesting a C-terminal truncation of the Aalpha chain. DNA sequencing of all exons and intron boundaries revealed a single heterozygous cytosine deletion at nucleotide 4841 of the Aalpha gene predicting a frameshift and the incorporation of 23 new residues (LMKLPSSTLPQLEKHSQVSSHLC) before termination after residue 517. In agreement with a predicted mass decrease of 9953 Da, the measured mass of the Aalpha(Perth) chain was 56 242 Da, while that of the normal Aalpha(A) chain was 66 189 Da. Tryptic mapping of isolated Aalpha chains revealed a new [M + 2H] ion at 607 m z(-1), corresponding to the predicted penultimate peptide LPSSTLPQLEK. The variant chain was poorly incorporated into plasma fibrinogen at a ratio of Aalpha(Perth)/Aalpha(A) of 0.15 : 1, suggesting the Aalpha(Perth) chain might be out-competed by normal chains during molecular assembly in the hepatocyte. Despite the low expression, polymerization curves showed a decreased V(max) and final turbidity, suggesting the fibrinogen Perth clots are composed of thinner fibers. However, the fibrinolytic rate was very similar to that of the control.

The structure and function of the alpha C domains of fibrinogen

The alpha C domains have been localized on fibrinogen and fibrin. Several model systems have been developed to study their functions. Analysis of the amino acid sequence of the alpha C domains suggested that each is made up of a globular and an extended portion. Microcalorimetry confirmed this result and showed that the two alpha C domains interact intramolecularly. Electron microscopy of fibrinogen with a monoclonal antibody to the alpha C domains demonstrated that these regions normally interact with the central portion of the molecule. In the conversion from fibrinogen to fibrin there is a large scale conformational change, such that the alpha C domains dissociate from the central region and are available for intermolecular interaction. Experiments with highly purified and well characterized fragment X monomer, missing either one or both of the alpha C domains, indicate that intermolecular interactions between alpha C domains are important for the enhancement of lateral aggregation during fibrin polymerization. Isolated alpha C fragments polymerized at neutral pH and interacted with the alpha C domains of fibrin monomer to influence clot formation. Several dysfibrinogenemias in which there are amino acid substitutions in, or truncations of, the alpha C domains revealed that these changes can have dramatic effects on polymerization and clot structure. The polymerization of A alpha 251 recombinant fibrinogen, that contains A alpha chains truncated at residue 251, was altered, as were the mechanical properties and the rate of fibrinolysis of the clots. Altogether, these results help to define the role of the alpha C domains in determining the structure and properties of clots.

Hereditary disorders of fibrinogen

Fibrinogen, a 340-kDa plasma protein, is composed of two identical molecular halves each consisting of three non-identical A alpha-, B beta- and gamma-chain subunits held together by multiple disulfide bonds. Fibrinogen is shown to have a trinodular structure; that is, one central nodule, the E domain, and two identical outer nodules, the D-domains, linked by two coiled-coil regions. After activation with thrombin, a pair of binding sites comprising Gly-Pro-Arg is exposed in the central nodule and combines with its complementary binding site a in the outer nodule of another molecules. By using crystallographic analysis, the alpha-amino group of alpha Gly-1 is shown to be juxtaposed between gamma Asp-364 and gamma Asp-330, and guanidino group of alpha Arg-3 between the carboxyl group of gamma Asp-364 and gamma Gln-329 in the a site. Half molecule-staggered, double-stranded protofibrils are thus formed. Upon abutment of two adjacent D domains on the same strand, D-D self association takes place involving Arg-275, Tyr-280, and Ser-300 of the gamma-chain on the surface of the abutting two D domains. Thereafter, carboxyl-terminal regions of the alpha-chains are untethered and interact with those of other protofibrils leading to the formation of thick fibrin bundles and networks. Although many enigmas still remain concerning the exact mechanisms of these molecular interactions, fibrin assembly proceeds in a highly ordered fashion. In this review, these molecular interactions of fibrinogen and fibrin are discussed on the basis of the data provided by hereditary dysfibrinogens on introducing representative molecules at each step of fibrin clot formation.

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.

Identification and characterization of novel tPA- and plasminogen-binding sites within fibrin(ogen) alpha C-domains

Molecular defects in the alphaC-domains of some abnormal fibrinogens have been associated with impaired fibrin-mediated activation of plasminogen (Pg) by its activator tPA, suggesting the involvement of these domains in fibrinolysis. To test this suggestion, we expressed in E. coli the alphaC-fragment (residues Aalpha221-610) corresponding to the entire alphaC-domain as well as its NH(2)- and COOH-terminal halves (residues Aalpha221-391 and Aalpha392-610) and tested their effects on activation of Pg and their interaction with Pg and tPA. When the activation was monitored by cleavage of a chromogenic substrate with newly formed plasmin, the reaction was much more efficient in the presence of the alphaC-fragment. This stimulation was abolished upon digestion of the alphaC-fragment with plasmin. In surface plasmon resonance experiments, both tPA and Pg bound to the immobilized alphaC-fragment with K(d)s of 33 and 32 nM, respectively. Similar results were obtained by ELISA. This binding occurred via independent sites since saturating amounts of Pg did not prevent binding of tPA and vice versa. Both sites were localized in the COOH-terminal half of the alphaC-domain since the Aalpha392-610 fragment bound both tPA and Pg and was an effective stimulator whereas Aalpha221-391 was inactive. These results indicate that the fibrinogen alphaC-domains contain novel high-affinity tPA- and Pg-binding sites that play an important role in the regulation of fibrinolysis.

Anticoagulant proteins in childhood venous and arterial thrombosis: a review

Thrombotic disease is less frequent in children than in adults, but may result in severe morbidity and mortality. The coagulation system is balanced to provide rapid activation to stop bleeding and appropriate inhibition to prevent unwanted clot extension. It is regulated by fibrinolysis and by three major anticoagulant pathways: the protein C, antithrombin, and tissue factor pathway inhibitor systems. Acquired or inherited abnormalities of coagulation proteins or hemostatic regulatory mechanisms, particularly when combined with dehydration or the presence of indwelling catheters, may pose a high risk for thrombosis. Thrombosis in a child warrants investigation of potential underlying prothrombotic conditions. These include acquired antiphospholipid antibodies or the lupus anticoagulant as well as abnormalities of the inherited anticoagulant factors including protein C, protein S, antithrombin, and Factor V Leiden. Other abnormalities may result in heightened levels of otherwise normal coagulation proteins such as hyperprothrombinemia due to the prothrombin 20210 mutation. A large survey of children with thrombosis indicated that Factor V Leiden, protein C deficiency, and increased lipoprotein(a) were found most commonly. The most severe predisposition occurs with homozygous protein S or protein C deficiency with resultant purpura fulminans in the newborn. The risk of thrombosis in children with heterozygous deficiencies of anticoagulant proteins is not well defined, although it is clear that combined heterozygotes or a combination of an inherited and an acquired defect heightens the risk for thrombosis. Treatment of thrombosis primarily involves a rapidly acting anticoagulant such as heparin or low-molecular-weight heparin to prevent extension, and long-term anticoagulation with warfarin may be instituted to prevent recurrence. Fibrinolytic therapy is infrequently used because of the risk of serious bleeding complications and is reserved for selected cases of arterial thrombosis to initiate rapid reperfusion of ischemic tissue or used in those patients with a large venous thrombosis and pulmonary emboli causing hemodynamic compromise.

Familial thrombophilia associated with fibrinogen Paris V: Dusart syndrome

We report on a family with a history of venous thromboembolism associated with fibrinogen Paris V (fibrinogen A-Arg554→Cys). Ten members experienced thrombotic events, including 4 with fatal pulmonary emboli. Pulmonary embolism was the presenting feature in 4. Those with the mutation and a history of thrombosis had somewhat higher fibrinogen concentrations than those with the mutation and no thrombosis (294 ± 70 mg/dL vs 217 ± 37 mg/dL, respectively). The Paris V mutation consistently caused a prolongation of the reptilase time, and fibrin clots containing the abnormal fibrinogen were more translucent than normal clots. Given the early onset of symptoms and the initial presentation with pulmonary embolism in some family members, it was justifiable to offer prophylactic anticoagulation with warfarin to carriers of the mutation. Fibrinogen Paris V has now been reported in 4 apparently unrelated families, indicating that it is a relatively common cause of dysfibrinogenemia-associated thrombosis.

Familial thrombophilia associated with fibrinogen Paris V: Dusart syndrome

We report on a family with a history of venous thromboembolism associated with fibrinogen Paris V (fibrinogen A-Arg554→Cys). Ten members experienced thrombotic events, including 4 with fatal pulmonary emboli. Pulmonary embolism was the presenting feature in 4. Those with the mutation and a history of thrombosis had somewhat higher fibrinogen concentrations than those with the mutation and no thrombosis (294 ± 70 mg/dL vs 217 ± 37 mg/dL, respectively). The Paris V mutation consistently caused a prolongation of the reptilase time, and fibrin clots containing the abnormal fibrinogen were more translucent than normal clots. Given the early onset of symptoms and the initial presentation with pulmonary embolism in some family members, it was justifiable to offer prophylactic anticoagulation with warfarin to carriers of the mutation. Fibrinogen Paris V has now been reported in 4 apparently unrelated families, indicating that it is a relatively common cause of dysfibrinogenemia-associated thrombosis.

More porous fibrin gel structure obtained by interaction with Lys-plasminogen than with Glu-plasminogen

The effect of Glu1- and Lys78-plasminogen on the assembly and structure of fibrin gels was studied in purified fibrinogen-thrombin system and in plasminogen-free plasma, using turbidity, liquid permeation and three-dimensional (3D) confocal laser microscopy methods. In the purified fibrinogen system using the turbidity method, the final optical density of the fibrin gels increased with increasing concentrations of Lys-plasminogen. The fiber mass/length ratio mu increased with increasing concentrations of both Glu1- and Lys78-plasminogen, the effect of Lys78-plasminogen being much stronger. The permeability coefficient (Ks) analyzed with the permeation method revealed that fibrin gels formed in the presence of Lys78-plasminogen were more permeable (porous) than the control gels. The effect on the gel structure was inhibited by the fibrinolytic inhibitor epsilon-aminocaproic acid. The same results were obtained in plasma milieu for both mu and Ks as in the purified system, i.e. the gels became more porous with increasing concentrations of Lys78-plasminogen. 3D microscopy pictures of the gels verified the findings.

Factor XIIIa Cross-Linking of the Marburg Fibrin: Formation of αm·γn-Heteromultimers and the α-Chain–Linked Albumin·γ Complex, and Disturbed Protofibril Assembly Resulting in Acquisition of Plasmin Resistance Relevant to Thrombophila

The truncated Aα-chain of fibrinogen Marburg is partly linked with albumin by a disulfide bond. Based on the recovery of the first six amino acid residues assigned to the subunit polypeptides of fibrinogen (the Aα-and γ-chains) and albumin, 0.33 mol of albumin was estimated to be linked to 1 mol of the Marburg fibrinogen. When the Marburg fibrinogen was clotted with thrombin-factor XIIIa-Ca2+, various αmγnheteromultimers were produced, and part of the albumin was cross-linked to the γ-chain. Acid-solubilized Marburg fibrin monomer failed to form large aggregates that could be detected by monitoring turbidity at A350, but it was able to enhance tissue-type plasminogen-activator–catalyzed plasmin generation, though not as avidly as the normal control, indicating that the double-stranded protofibrils had, to some extent, been constructed. This idea seems to be supported by normal factor XIIIa–catalyzed cross-linking of the fibrin γ-chains. However, the cross-linked Marburg fibrin, being apparently fragile and translucent, was highly resistant against plasmin, and its subunit components were considerably retained for 48 hours as noted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Although the exact mechanisms are still unclear, the albumin-incorporated factor XIIIa–cross-linked Marburg fibrin seems to have undergone a critical structural alteration(s) to acquire resistance against plasmin. This aquisition of plasmin resistance may be contributed to the postoperative pelvic vein thrombosis and recurrent pulmonary embolisms in the patient after caesarian section for her first delivery at the age of 20 years.

Factor XIIIa Cross-Linking of the Marburg Fibrin: Formation of αm·γn-Heteromultimers and the α-Chain–Linked Albumin·γ Complex, and Disturbed Protofibril Assembly Resulting in Acquisition of Plasmin Resistance Relevant to Thrombophila

The truncated Aα-chain of fibrinogen Marburg is partly linked with albumin by a disulfide bond. Based on the recovery of the first six amino acid residues assigned to the subunit polypeptides of fibrinogen (the Aα-and γ-chains) and albumin, 0.33 mol of albumin was estimated to be linked to 1 mol of the Marburg fibrinogen. When the Marburg fibrinogen was clotted with thrombin-factor XIIIa-Ca2+, various αmγnheteromultimers were produced, and part of the albumin was cross-linked to the γ-chain. Acid-solubilized Marburg fibrin monomer failed to form large aggregates that could be detected by monitoring turbidity at A350, but it was able to enhance tissue-type plasminogen-activator–catalyzed plasmin generation, though not as avidly as the normal control, indicating that the double-stranded protofibrils had, to some extent, been constructed. This idea seems to be supported by normal factor XIIIa–catalyzed cross-linking of the fibrin γ-chains. However, the cross-linked Marburg fibrin, being apparently fragile and translucent, was highly resistant against plasmin, and its subunit components were considerably retained for 48 hours as noted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Although the exact mechanisms are still unclear, the albumin-incorporated factor XIIIa–cross-linked Marburg fibrin seems to have undergone a critical structural alteration(s) to acquire resistance against plasmin. This aquisition of plasmin resistance may be contributed to the postoperative pelvic vein thrombosis and recurrent pulmonary embolisms in the patient after caesarian section for her first delivery at the age of 20 years.

Point-of-care fibrinolytic tests: the other side of blood coagulation

Point-of-care (POC) coagulation tests with paramagnetic iron oxide particles have provided alternatives to testing previously done only in the laboratory. With this technology, POC fibrinolytic tests have followed quietly the trail blazed by POC clotting tests and have found specific applications. These include rapid verification of in vivo thrombolytic drug action by in vitro testing with subsequent quantitative drug monitoring of the systemic lytic state, and also the determination of in vitro thrombolytic drug response before the drug is actually administered, to individualize therapy by selection of the most appropriate drug. Other applications include POC coagulation factor assays associated with fibrinolysis, and most recently the POC screening of patients with fibrinolytic defects. In this latter application, plasma from cardiac catheterization (n = 19) and venous thrombosis (n = 47) patient groups were tested. Controls consisted of two independent donor pools (n = 10, n = 21) as negatives and two plasma samples with known genetic defects in the fibrinogen molecule (Aα554 Arg → Cys) as positives.

The relationship between the fibrinogen D domain self-association/cross-linking site (gammaXL) and the fibrinogen Dusart abnormality (Aalpha R554C-albumin): clues to thrombophilia in the "Dusart syndrome"

Cross-linking of fibrinogen at its COOH-terminal gamma chain cross-linking site occurs in the presence of factor XIIIa due to self-association at a constitutive D domain site ("gammaXL"). We investigated the contribution of COOH-terminal regions of fibrinogen Aalpha chains to the gammaXL site by comparing the gamma chain cross-linking rate of intact fibrinogen (fraction I-2) with that of plasma fraction I-9, plasmic fraction I-9D, and plasmic fragment D1, which lack COOH-terminal Aalpha chain regions comprising approximately 100, approximately 390, and 413 residues, respectively. The cross-linking rates were I-2 > I-9 > 1-9D = D1, and indicated that the terminal 100 or more Aalpha chain residues enhance gammaXL site association. Fibrinogen Dusart, whose structural abnormality is in the COOH-terminal "alphaC" region of its Aalpha chain (Aalpha R554C-albumin), is associated with thrombophilia ("Dusart Syndrome"), and is characterized functionally by defective fibrin polymerization and clot structure, and reduced plasminogen binding and tPA-induced fibrinolysis. In the presence of XIIIa, the Dusart fibrinogen gamma chain cross-linking rate was about twice that of normal, but was normalized in proteolytic fibrinogen derivatives lacking the Aalpha chain abnormality, as was reduced plasminogen binding. Electron microscopy showed that albumin-bound Dusart fibrinogen "alphaC" regions were located in the vicinity of D domains, rather than at their expected tethered location near the fibrinogen E domain. In addition, there was considerable fibrinogen aggregation that was attributable to increased intermolecular COOH-terminal Aalpha chain associations promoted by untethered Dusart fibrinogen aC domains. We conclude that enhanced Dusart fibrinogen self-assembly is mediated through its abnormal alphaC domains, leads to increased gammaXL self-association and gamma chain cross-linking potential, and contributes to the thrombophilia that characterizes the "Dusart Syndrome."

Factor XIIIa-catalyzed cross-linking of recombinant alpha C fragments of human fibrinogen

Direct measurements of the structure and function of the COOH-terminal portion of the A alpha chain (residues 220-610) of human fibrinogen have been hampered by the difficulty of isolating intact fragments derived from this protease-sensitive region. Here, we overcame this problem by expressing two fragments, alpha C45K (A alpha 221-610) and a truncated version of it, alpha C30K (A alpha 368-610), in Escherichia coli. Both proteins were purified to homogeneous state, and their integrity was confirmed at protein level by sequencing. Upon treatment with factor XIIIa, the alpha C45K fragment but not the alpha C30K fragment formed polymers similar to those derived from fibrin clots. Sequence analysis of cross-linked alpha C45K polymers revealed involvement in the cross-linking reaction of at least three Gln residues (221, 237, 328) in the NH2-terminal region of the fragment and four Lys residues (539, 556, 580, 601) located in the COOH-terminal part of the molecule. In addition, a fraction of alpha C45K fragment was found in an intramolecular cross-linked form, suggesting a high level of flexibility of its polypeptide chain and consistent with the location of its donor and acceptor residues in clusters near the ends of the molecule. The alpha C30K fragment, lacking the NH2-terminal Gln residues, was not able to form polymers or internally cross-linked monomers. Thus, the C-terminal part of the A alpha chain comprises an autonomous, functionally active, and flexible region that plays a key role in alpha polymer formation and stabilization of fibrin clots by factor XIIIa.

The ultrastructure of fibrinogen Caracas II molecules, fibers, and clots

Fibrinogen Caracas II is an abnormal fibrinogen involving the mutation of A alpha serine 434 to N-glycosylated asparagine. Some effects of this mutation on the ultrastructure of fibrinogen Caracas II molecules, fibers, and clots were investigated by electron microscopy. Electron microscopy of rotary shadowed individual molecules indicated that most of the alphaC domains of fibrinogen Caracas II do not interact with each other or with the central domain, in contrast to control fibrinogen. Negatively contrasted Caracas II fibers were thinner and less ordered than control fibers, and many free fiber ends were observed. Scanning electron microscopy of whole clots revealed the presence of large pores bounded by local fiber networks made up of thin fibers. Permeation experiments also indicated that the average pore diameter was larger than that of control clots. The viscoelastic properties of the Caracas II clot, as measured by a torsion pendulum, were similar to those of control clots. Both the normal stiffness and increased permeability of the Caracas II clots are consistent with the observation that subjects with this dysfibrinogenemia are asymptomatic.

Fibrinogen Dusart: electron microscopy of molecules, fibers and clots, and viscoelastic properties of clots

Ultrastructural perturbations resulting from defects in polymerization of fibrinogen Dusart, a congenital dysfibrinogenemia with the amino acid substitution A alpha 554 arginine to cysteine, were investigated by a variety of electron microscope studies. Polymerization of this mutant fibrinogen on addition of thrombin is impaired, producing clots with decreased porosity and increased resistance to fibrinolysis, resulting in thrombotic complications in the family members with this dysfibrinogenemia. Electron microscopy of rotary-shadowed individual molecules revealed that, in contrast to control fibrinogen, most of the alpha C domains of fibrinogen or fibrin Dusart appeared to be free-swimming appendages that do not exhibit intra- or intermolecular interactions either with each other or with the central domains. The location of albumin on the alpha C domains was demonstrated by electron microscopy using anti-albumin antibodies. Electron microscopy of negatively contrasted fibrin Dusart fibers indicated that they were less ordered than control fibers and had additional mass visible. Electron microscopy of freeze-dried, unidirectionally shadowed fibers showed that they were twisted with a shorter pitch. Scanning electron microscopy revealed that intact clots were made up of thin fibers with many branch points and very small pore sizes. The viscoelastic properties of Dusart fibrin clots measured with a torsion pendulum indicated a marked increase in stiffness consistent with the structural observations.

Dysfibrinogenemia: a case with thrombosis (fibrinogen Richfield) and an overview of the clinical and laboratory spectrum

Fibrinogen Richfield exemplifies a dysfibrinogen associated with a life-long thrombotic tendency. The evaluation of this novel case indicates that, like similar thrombotic dysfibrinogenemias, the abnormal protein polymerizes abnormally and demonstrates impaired clot dissolution. A survey of other cases of dysfibrinogenemia indicates that the relatively common abnormalities of Fibrinopeptide A release are generally asymptomatic or associated with bleeding, polymerization abnormalities are likely to be asymptomatic or associated with thrombosis (or occasionally bleeding), and complex abnormalities or additional, independent hemostatic defects are rather common. Thrombin and Reptilase clotting times are not helpful in distinguishing between the subsets, but clinical history, fibrinopeptide release, and polymerization studies may be useful. Abnormalities of fibrinogen function tend to correlate with changes in molecular domains related to binding and hydrolysis.

Pathophysiology of fibrinolysis

The observed association between abnormal fibrinolysis and a tendency toward bleeding or thrombosis demonstrates the (patho)physiological importance of the fibrinolytic system. Deficient fibrinolysis represents an important haemostatic abnormality associated with thrombosis. A decreased fibrinolytic activity may be due to a defective synthesis and/or release of tissue-type plasminogen activator (t-PA) from the vessel wall, to a deficiency or functional defect in the plasminogen or fibrinogen molecule or more frequently to increased levels of t-PA inhibitor. Alternatively, excessive fibrinolysis due to increased levels of t-PA, to alpha 2-antiplasmin deficiency or to plasminogen activator inhibitor-1 (PAI-1) deficiency, may result in bleeding tendency.

Fibrinogenemia Tampere--a dysfibrinogenemia with defective gelation and thromboembolic disease

Fibrinogen Tampere was found in a woman with severe thromboembolic disease. The thrombin induced clotting time of her plasma and purified fibrinogen was slightly prolonged. The activation of fibrinogen Tampere appeared to be normal but subsequent gelation was defective. We studied fibrin gels formed at different ionic strengths and at different fibrinogen and calcium concentrations by liquid permeation, turbidity, and 3D laser microscopy. Crosslinking was studied by SDS-gel electrophoresis. The gels formed from fibrinogen Tampere were at ionic strength above 0.2 much tighter and had lower fiber mass-length ratios than normal gels as judged by permeability and turbidity data. At ionic strength 0.15 and at different calcium concentrations analysis by permeability showed the same results for fibrinogen Tampere as for normal gels. Analysis by turbidity at ionic strength 0.15 suggested swelling of the fibers at low calcium concentrations. 3D microscopy revealed perturbed clot architecture under all conditions. In fibrin gels from fibrinogen Tampere, the gamma-chain crosslinking was normal but the crosslinking of alpha-chains was delayed at ionic strength 0.2 and also at lower ionic strengths on lowering the calcium concentration. The abnormal gelation may be due to a mutation in the fibrinogen molecule. Tendency to form tight fibrin gels and/or insufficient crosslinked fibrin matrix may be pathogenetic in this thrombotic disease.

Fibrinogen Guarenas I: partial characterization of a new dysfibrinogenemia with an altered rate of fibrinopeptide release and an impaired polymerization

A congenitally abnormal fibrinogen was isolated from the blood of a young woman with a severe bleeding diathesis. Coagulation tests showed a prolonged Thrombin and Reptilase time partially corrected by Ca2+. Polymerization of thrombin induced preformed fibrin monomers was severely impaired. Thrombin caused the release of fibrinopeptides with normal retention times on HPLC. However, the rate of release was abnormally slow and the total amount of fibrinopeptide A (FpA) released reached only approximately 50% of the theoretical maximum. The rate and quantity of FpA release was normal when Reptilase was used. Transmission Electron Microscopy (TEM) of Thrombin induced clots showed an altered clot structure characterized by a reduced mean fiber diameter. The mother has a polymerization defect similar to the propositus, her fibrinopeptide release is unaffected however. The father has a minor fibrinopeptide release defect suggesting the presence of two populations of fibrinogen. This study supports the idea that the fibrinogen isolated from the propositus has two defects inherited as separate genetic traits. This fibrinogen has been named Fibrinogen Guarenas I.

Molecular basis for fibrinogen Dusart (A alpha 554 Arg-->Cys) and its association with abnormal fibrin polymerization and thrombophilia

The molecular defect in the abnormal fibrinogen Dusart (Paris V) that is associated with thrombophilia was determined by sequence analysis of genomic DNA that had been amplified using the polymerase chain reaction. The propositus was heterozygous for a single base change (C-->T) in the A alpha-chain gene, resulting in the amino acid substitution A alpha 554 Arg-->Cys. Restriction analysis of the amplified DNA derived from the family members showed that his father and his two sons were also heterozygous. Electron microscopic studies on fibrin formed from purified fibrinogen Dusart demonstrated fibers that were much thinner than in normal fibrin. In contrast to the previously observed defective binding of plasminogen, the binding of thrombospondin to immobilized fibrinogen Dusart was similar to that of normal fibrinogen. Immunoblot analysis of plasma fibrinogen demonstrated that a substantial part of the fibrinogen Dusart molecules were disulfide-linked to albumin. The plasma of the affected family members also contained fibrinogen-albumin complexes. Furthermore, small amounts of high molecular weight complexes containing fibrinogen were detected in all the heterozygous individuals. These data indicate that the molecular abnormality in fibrinogen Dusart (A alpha 554 Arg-->Cys) results in defective lateral association of the fibrin fibers and disulfide-linked complex formation with albumin, and is associated with a family history of recurrent thrombosis in the affected individuals.

Fibrinogen date: congenital hypodysfibrinogenemia associated with decreased binding of tissue-plasminogen activator

A new case of congenital hypodysfibrinogenemia associated with a thrombotic tendency (thrombosis of the peroneal artery, the pulmonary artery and the deep veins of the lower extremities), is reported. Clotting time using Reptilase was significantly prolonged. The low levels of plasma fibrinogen were demonstrated using both thrombin time (Clauss) method (45.0 mg/ml) and radial immunodiffusion technique (106.1 mg/ml). The fibrinogen is also characterized by a defective polymerization of fibrin monomers. Furthermore, the important functional property of this fibrinogen is that the patient's fibrin adsorbs approximately 31-38% of added tissue-plasminogen activator (t-PA) at the time of fibrin formation, whereas control fibrin can adsorb about 79% of added t-PA. This result could provide an explanation for the thrombotic tendency in this patient. This variant fibrinogen appears to have unique characteristics and has been designated as "Fibrinogen Date," according to the city where the proband has lived.

Superficial thrombophlebitis. I. Primary hypercoagulable states

This review concentrates on those disorders in which superficial thrombophlebitis can be a significant or presenting clinical sign. Primary hypercoagulable states are those conditions associated with an increased risk of thrombosis caused by a specific measurable defect in the proteins of coagulation and/or fibrinolytic systems. These disorders are frequently inherited and include deficiencies of antithrombin III, heparin cofactor 2, protein C, protein S, abnormal fibrinolytic activity, dysfibrinogenemia, and Hageman trait. Patients with a lupus anticoagulant and anticardiolipin antibody syndrome with thrombotic episodes are also considered to have a primary hypercoagulable state. The physiology, pathophysiology, clinical characteristics, and treatment of primary hypercoagulable states are reviewed.

Screening for inherited thrombotic disorders

In order to determine a scheme for the screening of inherited thrombotic disorders, abnormalities considered as predisposing to thrombosis have been reviewed. Owing to the low prevalence of biological alterations, a selection of patients is required: documented venous thromboses, possibly at unusual sites (mesenteric vein, portal, cerebral veins), occurring before the age of 40 in patients with a positive family history of thromboses are relatively frequently associated with coagulation abnormalities. In addition, patients with skin necrosis at the initiation of oral anticoagulants, or with repeated superficial vein thrombosis or unexplained arterial occlusions at a young age might be included for screening. Tests have also to be selected. Some abnormalities, such as congenital deficiencies in antithrombin III, protein C and protein S, are recognized risk factors and have to be searched. Some others cannot be at present considered as definite risk factors (e.g., dysfibrinogenemias or deficiencies in factor XII), but their detection is easy by routine tests: prothrombin time, fibrinogen assay. Other abnormalities are recognized risk factors (or not) and need specific uncommon tests (e.g., study of fibrinolysis). Each time a biological abnormality is found, it is important to verify it is isolated since combined deficiencies have been observed and we should be able to answer the question whether the abnormality is the cause or the consequence of thrombosis, or a coincidence. Finally, in our experience, even in well selected patients, a coagulation disorder is detected in less than 30% of patients, so that new tests are needed to improve our knowledge in this field.

Hemostasis associated with abnormalities of fibrinolysis

Hemostatic plugs consist of platelet aggregates and fibrin mesh containing blood cells and plasma components. Hemostatic efficiency depends on the rate of formation of hemostatic plugs as well as the structural integrity and stability of the formed hemostatic plugs. Fibrin elements are major constituents contributing to the structural integrity and stability, but they are subject to fibrinolytic activity occurring spontaneously after fibrin formation. Fibrinolysis is usually suppressed by endogenous inhibitors. Increase of a profibrinolytic component or deficiency of an inhibitor would result in an accelerated fibrinolysis, causing a premature lysis of hemostatic plugs before restoration of injured vessels, leading to a hemorrhagic tendency. Such a state can be seen typically in patients with congenital deficiency of alpha 2-plasmin inhibitor or a hereditary increase of plasminogen activator, and it is also seen in acquired situations such as amyloidosis, liver cirrhosis, disseminated intravascular coagulation (particularly in patients with acute promyelocytic leukemia) and thrombolytic therapy. The hemorrhagic tendency can be well controlled by an administration of an antifibrinolytic agent: epsilon-aminocaproic acid or tranexamic acid. In contrast to an accelerated fibrinolysis causing a hemorrhagic tendency, retarded fibrinolysis may predispose an individual to a thrombotic tendency. Retarded fibrinolysis may be due to either an increase in plasminogen activator inhibitors or decrease of plasminogen activators. Quantitative or qualitative deficiency of plasminogen may also lead to a thrombotic tendency.