Genetic Variants in the FGB and FGG Genes Mapping in the Beta and Gamma Nodules of the Fibrinogen Molecule in Congenital Quantitative Fibrinogen Disorders Associated with a Thrombotic Phenotype.

Fibrinogen is a hexameric plasmatic glycoprotein composed of pairs of three chains (Aα, Bß, and γ), which play an essential role in hemostasis. Conversion of fibrinogen to insoluble polymer fibrin gives structural stability, strength, and adhesive surfaces for growing blood clots. Equally important, the exposure of its non-substrate thrombin-binding sites after fibrin clot formation promotes antithrombotic properties. Fibrinogen and fibrin have a major role in multiple biological processes in addition to hemostasis and thrombosis, i.e., fibrinolysis (during which the fibrin clot is broken down), matrix physiology (by interacting with factor XIII, plasminogen, vitronectin, and fibronectin), wound healing, inflammation, infection, cell interaction, angiogenesis, tumour growth, and metastasis. Congenital fibrinogen deficiencies are rare bleeding disorders, characterized by extensive genetic heterogeneity in all the three genes: FGA, FGB, and FGG (enconding the Aα, Bß, and γ chain, respectively). Depending on the type and site of mutations, congenital defects of fibrinogen can result in variable clinical manifestations, which range from asymptomatic conditions to the life-threatening bleeds or even thromboembolic events. In this manuscript, we will briefly review the main pathogenic mechanisms and risk factors leading to thrombosis, and we will specifically focus on molecular mechanisms associated with mutations in the C-terminal end of the beta and gamma chains, which are often responsible for cases of congenital afibrinogenemia and hypofibrinogenemia associated with thrombotic manifestations.

Mild factor XIII deficiency and concurrent hypofibrinogenemia: effect of pregnancy.

Factor XIII (FXIII) deficiency is a rare bleeding disorder. Patients with mild congenital FXIII deficiency tend to be asymptomatic, but may demonstrate significant bleeding symptoms with surgery, trauma, and pregnancy. Postpartum hemorrhage has been described in mild FXIII deficiency. We present a case of mild FXIII deficiency and concurrent hypofibrinogenemia manifested by recurrent postpartum hemorrhage, menorrhagia, and miscarriage. Mutational analysis identified a previously unreported heterozygous mutation of the FXIIIA subunit (p.Trp315Arg). No mutation was noted in the fibrinogen gene. FXIII levels decreased approximately 50% from nonpregnant levels to their nadir during labor, whereas fibrinogen levels rose approximately 1.5-fold from decreased nonpregnant levels to their peak at the time of labor. This case illustrates the course of mild FXIII and fibrinogen deficiencies during pregnancy, labor, and postpartum, and raises possible management options for prevention of antepartum and postpartum hemorrhage in women with these deficiencies.

Role of fibrinogen in acute ischemic kidney injury.

Renal ischemia-reperfusion (I/R) is associated with activation of the coagulation system and accumulation of blood clotting factors in the kidney. The aim of the present study was to examine the functional impact of fibrinogen on renal inflammation, damage, and repair in the context of I/R injury. In this study, we found that I/R was associated with a significant increase in the renal deposition of circulating fibrinogen. In parallel, I/R stress induced the de novo expression of fibrinogen in tubular epithelial cells, as reflected by RT-PCR, immunofluorescence, and in situ hybridization. In vitro, fibrinogen expression was induced by oncostatin M and hyper-IL-6 in primary tubular epithelial cells, and fibrinogen-containing medium had an inhibitory effect on tubular epithelial cell adhesion and migration. Fibrinogen(+/-) mice showed similar survival as wild-type mice but better preservation in early postischemic renal function. In fibrinogen(-/-) mice, renal function and survival were significantly worse than in fibrinogen(+/-) mice. Renal transplant experiments revealed reduced expression of tubular damage markers and attenuated proinflammatory cytokine expression but increased inflammatory cell infiltrates and transforming growth factor-ß expression in fibrinogen(-/-) isografts. These data point to heterogeneous effects of fibrinogen in renal I/R injury. While a complete lack of fibrinogen may be detrimental, partial reduction of fibrinogen in heterozygous mice can improve renal function and overall outcome.

Surgical wound healing in bleeding disorders.

Animal experiments have shown that a number of bleeding disorders may affect wound healing (WH), including haemophilia B, deficiency of factor XIII and abnormalities of fibrinogen. Therefore, normal healing requires adequate haemostatic function for the appropriate time frame (up to 4 weeks in the clean and uncontaminated wound). Many factors may affect WH, including impaired haemostasis, diabetes, poor nutrition, insufficient oxygenation, infection, smoking, alcoholism, old age, stress and obesity. The gold standard for the correct care of surgical wounds in patients with bleeding disorders includes wound dressing and comprehensive standard care (haemostasis, nutritional support, treatment of co-morbidities, offloading, reperfusion therapy and compression). Although complications of surgical wounds healing in patients with bleeding disorders are uncommon, a low level of the deficient factor for an insufficient period of time could cause WH complications such as haematomas, infection, and skin necrosis and dehiscence. Clinical experience and animal experiments appear to indicate that, to get a satisfactory healing of surgical wounds and avoid potential complications of WH, a good level of haemostasis is necessary for 2-3 weeks after surgery. However, many treaters would regard this recommendation at odds with (i.e. more aggressive than) current standards. Unfortunately no additional clinical evidence for this recommendation can be provided.

Afibrinogenemia resulting from homozygous nonsense mutation in A alpha chain gene associated with multiple thrombotic episodes.

Congenital afibrinogenemia is a rare disorder characterized by the absence in circulating fibrinogen, a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta and gamma). Although predisposition to thrombosis is a well known feature of dysfibrinogenemia, the relatively frequent thrombotic manifestations seen in congenital afibrinogenemia are puzzling. We herein report a mutational analysis of a young afibrinogenemic man from Turkey with multiple thrombo-embolic events involving both arteries and veins. Purified DNAs of the propositus was used for amplification by polymerase chain reaction of all the exons of the A subunit gene with primers allowing the analysis of the intron-exon boundaries. Analysis of the genes coding for the three fibrinogen chains of the propositus found a homozygous G to A transition in the exon 5 of the A alpha chain gene (g.g4277a; access number gi458553). The TGG to TGA codon change predicts a homozygous W315X in the A alpha chain (p.W334X when referring to the translation initiation codon). Both parents and his brother were found to carry this heterozygous mutation. This is the first report of a patient homozygous for this rare mutation associated with afibrinogenemia. Our patient was free of known risk factors as well as diseases associated with thrombosis including atherosclerosis, vasculitis, Buerger's disease, and it seems therefore probable that afibrinogenemia itself might have contributed to both arterial and venous thrombosis.

Efficacy and tolerability of human fibrinogen concentrate administration to patients with acquired fibrinogen deficiency and active or in high-risk severe bleeding.

BACKGROUND AND OBJECTIVES: Fibrinogen deficiency is a cause for massive haemorrhage whose management in emergency situations is the subject of debate. Plasma-derived fibrinogen concentrates are indicated for reversing the haemorrhagic diathesis found in congenital and acquired deficiencies. MATERIALS AND METHODS: We report on the results of an observational study that evaluated the effects of fibrinogen concentrates in patients suffering from various forms of acquired severe hypofibrinogenaemia with life-threatening consumptive thrombo-haemorrhagic disorders (surgery, trauma and digestive haemorrhage), or underlying disease states that limit fibrinogen synthesis (hepatic dysfunction, haematological malignancies). RESULTS: Sixty-nine patients were identified and included, in whom most of the processes (62%) corresponded to consumptive hypofibrinogenaemia. After a median dose of 4 g, a mean absolute increase of 1.09 g/l in plasma fibrinogen was measured and coagulation parameters were significantly improved (P < 0.001). Mortality rates of 32.3% and 44.2% were reported after 24 h and 72 h, respectively. CONCLUSION: We conclude that the administration of fibrinogen concentrates in unresponsive, life-threatening haemorrhage with acquired hypofibrinogenaemia improves laboratory measures of coagulation, and may also be life saving. Although observational in nature, our data indicate a direct relationship between plasma fibrinogen levels and survival in acquired fibrinogen deficiency. Further studies are warranted to ascertain a clear relationship between fibrinogen levels and survival.

The past decade: fibrinogen.

This paper reviews the advances in understanding of fibrinogen structure and function, its genetic and environmental determinants, role in the process of hemostasis, platelet aggregation, plasma viscosity and erythrocyte aggregation, cellular and matrix interactions, inflammation, wound healing, tumor development, atherogenesis and involvement in pathogenesis of diseases, that have been made over the past decade. Future studies will seek to define precise mechanisms of complex gene-environment interactions that influence fibrinogen levels and its complex role in the pathogenesis of fibrinogen-associated diseases.

Maternal fibrinogen is necessary for embryonic development.

Fibrinogen (Fg) is a precursor of fibrin, which is one of the main components of blood clots generated during the hemostatic response. Beyond its important role in hemostasis, Fg is involving in several physiologic and pathophysiologic states, such as infection, wound healing, the progression of certain types of tumors, and the severity of atherosclerosis. In addition, Fg has a critical role in maintaining pregnancy. Ovulation, fertilization, and implantation of the fertilized egg to the uterine wall can occur in afibrinogenemic women. However, all pregnancies in these patients resulted in spontaneous miscarriage. Fg supplemental therapy allows the patients to sustain the pregnancy. Mice with a total fibrinogen deficiency (FG-/-) reproduce the human experience. Despite of successes with fibrinogen supplementation, "paradoxical thrombosis" sometimes occurs, wherein supplemental therapies cause catastrophic thrombosis, such as pulmonary and mesenteric venous thrombosis. In these therapies, syncytial knots, hyaline membrane, and multiple recent infarctions with abruptio placenta were also observed. These findings indicate that the dosage regimen of Fg in afibrinogenemia-related pregnancies needs to be optimized according to other coagulation markers, such as thrombin-antithrombin complex (TAT) concentration, which represents the extent of thrombin formation. In addition, baseline thrombin assays would be helpful to predict the potential for paradoxical thrombosis during the supplemental therapy offered during pregnancy.

Afibrinogenemia Congénita. Reporte de un Caso

La afibrinogenemia congénita, descrita en 1920, es un raro transtorno hemorrágico de carácter autosómico recesivo. Estos pacientes a pesar de tener una sangre totalmente incouguable, no suelen presentar graves hemorragias o hemertrosis espontaneas, pero los traumatismos o las intervenciones quirurgicas pueden ir seguidas de graves hmorragias. En el siguiente articulo se presenta el caso de una paciente de 2 meses de edad que se hospitalizo en el servicio de pediatria del Hospital de la Victoria en Santafé de Bogotá (Colombia) y que cumplio con los criterios clinicos y paraclinicos para dicha entidad

Fibrinogen-independent aggregation and deaggregation of human platelets: studies in two afibrinogenemic patients.

Platelets from two afibrinogenemic patients were used to determine whether fibrinogen is essential for platelet aggregation and to examine whether released fibrinogen contributes to the stabilization of platelet aggregates when platelets have been induced to aggregate and release their granule contents by stimulation with thrombin. The addition of adenosine diphosphate (ADP) to platelet-rich plasma (PRP) or to suspensions of washed platelets from the afibrinogenemic patients caused the formation of small aggregates, which was either not inhibited or only slightly inhibited by the F(ab')2 fragments of an antibody to fibrinogen but was inhibited by an antibody (10E5) to glycoprotein IIb/IIIa. Thus there is a component of ADP-induced platelet aggregation that is not dependent on fibrinogen or other plasma proteins but is dependent on glycoprotein IIb/IIIa. There was little difference in the extent of aggregation and the release of granule contents of normal and afibrinogenemic platelets in response to the release-inducing agents collagen, platelet-activating factor (PAF), sodium arachidonate, or thrombin. With normal or afibrinogenemic platelets, aggregation by thrombin (0.2 U/mL or higher) was not inhibited by the F(ab')2 fragments of an antibody to human fibrinogen. Deaggregation by combinations of inhibitors of platelets aggregated by 1 U/mL thrombin showed no difference between platelets from afibrinogenemic and control subjects, indicating that released fibrinogen does not make a major contribution to the stabilization of platelet aggregates formed by thrombin stimulation.

von Willebrand factor interaction with the glycoprotein IIb/IIa complex. Its role in platelet function as demonstrated in patients with congenital afibrinogenemia.

We have studied three afibrinogenemic patients, who had only trace amounts of plasma and platelet fibrinogen as measured by radioimmunoassay, and demonstrate here that the residual aggregation observed in their platelet-rich plasma is dependent upon von Willebrand factor (vWF) binding to the platelet membrane glycoprotein (GP)IIb/IIIa complex. The abnormality of aggregation was more pronounced when ADP, rather than thrombin, collagen, or the combination of ADP plus adrenaline was used to stimulate platelets. With all stimuli, nevertheless, the platelet response was completely inhibited by a monoclonal antibody (LJP5) that is known to block vWF, but not fibrinogen binding to GPIIb/IIIa. Addition of purified vWF to the afibrinogenemic plasma resulted in marked increase in the rate and extent of aggregation, particularly when platelets were stimulated with ADP. This response was also completely blocked by LJP5. Addition of fibrinogen, however, restored normal aggregation even in the presence of LJP5, a finding consistent with the knowledge that antibody LJP5 has no effect on platelet aggregation mediated by fibrinogen binding to GPIIb/IIIa. Two patients gave their informed consent to receiving infusion of 1-desamino-8-D-arginine vasopressin (DDAVP), a vasopressin analogue known to raise the vWF levels in plasma by two- to fourfold. The bleeding time, measured before and 45 min after infusion, shortened from greater than 24 min to 12 min and 50 s in one patient and from 16 min to 9 min and 30 s in the other. Concurrently, the rate and extent of ADP-induced platelet aggregation improved after DDAVP infusion. The pattern, however, reversed to baseline levels within 4 h. The concentration of plasma vWF increased after DDAVP infusion, but that of fibrinogen remained at trace levels. We conclude that vWF interaction with GPIIb/IIIa mediates platelet-platelet interaction and may play a role in primary hemostasis.