Fibrinogen Gamma375 Arg→Trp Mutation (Fibrinogen Aguadilla) Causes Hereditary Hypofibrinogenemia, Hepatic Endoplasmic Reticulum Storage Disease and Cirrhosis

Protein Aggregation in the ER: Calm behind the Storm

As one of the largest organelles in eukaryotic cells, the endoplasmic reticulum (ER) plays a vital role in the synthesis, folding, and assembly of secretory and membrane proteins. To maintain its homeostasis, the ER is equipped with an elaborate network of protein folding chaperones and multiple quality control pathways whose cooperative actions safeguard the fidelity of protein biogenesis. However, due to genetic abnormalities, the error-prone nature of protein folding and assembly, and/or defects or limited capacities of the protein quality control systems, nascent proteins may become misfolded and fail to exit the ER. If not cleared efficiently, the progressive accumulation of misfolded proteins within the ER may result in the formation of toxic protein aggregates, leading to the so-called “ER storage diseases”. In this review, we first summarize our current understanding of the protein folding and quality control networks in the ER, including chaperones, unfolded protein response (UPR), ER-associated protein degradation (ERAD), and ER-selective autophagy (ER-phagy). We then survey recent research progress on a few ER storage diseases, with a focus on the role of ER quality control in the disease etiology, followed by a discussion on outstanding questions and emerging concepts in the field.

Whole Blood Thromboelastometry by ROTEM and Thrombin Generation by Genesia According to the Genotype and Clinical Phenotype in Congenital Fibrinogen Disorders

The outcome of congenital fibrinogen defects (CFD) is often unpredictable. Standard coagulation assays fail to predict the clinical phenotype. We aimed to assess the pheno- and genotypic associations of thrombin generation (TG) and ROTEM in CFD. We measured fibrinogen (Fg) activity and antigen, prothrombin fragments F1+2, and TG by ST Genesia^® with both Bleed- and ThromboScreen in 22 patients. ROTEM was available for 11 patients. All patients were genotyped for fibrinogen mutations. Ten patients were diagnosed with hypofibrinogenemia, nine with dysfibrinogenemia, and three with hypodysfibrinogenemia. Among the 17 mutations, eight were affecting the Fg γ chain, four the Fg Bβ chain, and five the Fg Aα chain. No statistical difference according to the clinical phenotypes was observed among FGG and FGA mutations. Median F1+2 and TG levels were normal among the different groups. Fg levels correlated negatively with F1+2 and peak height, and positively with lag time and time to peak. The pheno- and genotypes of the patients did not associate with TG. FIBTEM by ROTEM detected hypofibrinogenemia. Our study suggests an inverse link between low fibrinogen activity levels and enhanced TG, which could modify the structure–function relationship of fibrin to support hemostasis.

Heterogeneity of congenital afibrinogenemia, from epidemiology to clinical consequences and management

Fibrinogen is a complex protein playing a major role in coagulation. Congenital afibrinogenemia, characterized by the complete absence of fibrinogen, is associated with major hemostatic defects. Even though the clinical course is unpredictable and can be completely different among patients, severe bleeding is the prominent symptom. Patients are also at increased risk of thrombosis and sometimes suffer from spontaneous spleen rupture, bone cysts and defective wound healing. Due to the relative rarity of afibrinogenemia, there are no evidence-based strategies for helping physicians in care of these patients. Fibrinogen supplementation is the keystone to prevent or treat bleeding events. In addition, fibrinogen, a pleiotropic protein with numerous physiological roles in immunity, angiogenesis and tissue repair, is involved in many diseases. Indeed, depletion of fibrinogen in animal models of infections, tumors and neurological diseases has an effect on the clinical course. The consequences for patients with afibrinogenemia still need to be investigated.

Hepatic fibrinogen storage disease and hypofibrinogenemia caused by fibrinogen Aguadilla mutation: a case report

Hepatic fibrinogen storage disease is a rare autosomal dominant genetic disorder characterized by hypofibrinogenemia, as well as the retention of variant fibrinogen within the hepatocellular endoplasmic reticulum. Here, we describe an asymptomatic 4-year-old boy with abnormal liver function test results and unexpected hypofibrinogenemia. Liver biopsy showed circular eosinophil inclusion bodies in the hepato-cytoplasm. Immunostaining results of eosinophil inclusion bodies were positive for fibrinogen. Following pretreatment with diastase, the inclusion bodies failed to stain with the periodic acid–Schiff technique; moreover, immunostaining results were positive for fibrinogen, but negative for alpha-1-antitrypsin. Genetic analysis identified a heterozygous missense mutation c.1201C > T (p. Arg401Trp) within the fibrinogen γ-chain (FGG) gene and an additional single nucleotide polymorphism c.-58 A > G within the 5′-untranslated region of the fibrinogen Aα-chain (FGA) gene. Thus, the patient was diagnosed with hepatic fibrinogen storage disease. Our results indicate that, for patients who exhibit chronic liver disease with unexpected hypofibrinogenemia, hepatic fibrinogen storage disease should be considered in the differential diagnosis. Moreover, our findings emphasize the importance of molecular diagnosis in patients with cryptogenic liver disease.

Hereditary Hypofibrinogenemia with Hepatic Storage

Fibrinogen is a 340-kDa plasma glycoprotein constituted by two sets of symmetrical trimers, each formed by the Aα, Bβ, and γ chains (respectively coded by the FGA, FGB, and FGG genes). Quantitative fibrinogen deficiencies (hypofibrinogenemia, afibrinogenemia) are rare congenital disorders characterized by low or unmeasurable plasma fibrinogen antigen levels. Their genetic basis is represented by mutations within the fibrinogen genes. To date, only eight mutations, all affecting a small region of the fibrinogen γ chain, have been reported to cause hereditary hypofibrinogenemia with hepatic storage (HHHS), a disorder characterized by protein aggregation in the endoplasmic reticulum, hypofibrinogenemia, and liver disease of variable severity. Here, we will briefly review the clinic characteristics of HHHS patients and the histological feature of their hepatic inclusions, and we will focus on the molecular genetic basis of this peculiar type of coagulopathy.

Structural Characteristics in the γ Chain Variants Associated with Fibrinogen Storage Disease Suggest the Underlying Pathogenic Mechanism

Particular fibrinogen γ chain mutations occurring in the γ-module induce changes that hamper γ-γ dimerization and provoke intracellular aggregation of the mutant fibrinogen, defective export and plasma deficiency. The hepatic storage predisposes to the development of liver disease. This condition has been termed hereditary hypofibrinogenemia with hepatic storage (HHHS). So far, seven of such mutations in the fibrinogen γ chain have been detected. We are reporting on an additional mutation occurring in a 3.5-year-old Turkish child undergoing a needle liver biopsy because of the concomitance of transaminase elevation of unknown origin and low plasma fibrinogen level. The liver biopsy showed an intra-hepatocytic storage of fibrinogen. The molecular analysis of the three fibrinogen genes revealed a mutation (Fibrinogen Trabzon Thr371Ile) at exon 9 of the γ chain in the child and his father, while the mother and the brother were normal. Fibrinogen Trabzon represents a new fibrinogen γ chain mutation fulfilling the criteria for HHHS. Its occurrence in a Turkish child confirms that HHHS can present in early childhood and provides relevant epidemiological information on the worldwide distribution of the fibrinogen γ chain mutations causing this disease. By analyzing fibrinogen crystal structures and calculating the folding free energy change (ΔΔG) to infer how the variants can affect the conformation and function, we propose a mechanism for the intracellular aggregation of Fibrinogen Trabzon and other γ-module mutations causing HHHS.

Rethinking fibrinogen storage disease of the liver: ground glass and globular inclusions do not represent a congenital metabolic disorder but acquired collective retention of proteins

Three types of intracytoplasmic inclusions immunoreactive to fibrinogen are collectively diagnosed as hepatic fibrinogen storage disease. This study aimed to better characterize ground glass (type II) and globular (type III) fibrinogen inclusions by the pathological examination of 3 cases and a literature review. Three adults (age: 32-64 years; male/female = 2:1) were unexpectedly found to have fibrinogen-positive ground glass changes (type II inclusions) by liver needle biopsy, against a background of acute hepatitis E, resolving acute cholangitis, or severe lobular hepatitis of unknown etiology. One patient also had fibrinogen-positive intracytoplasmic globules (type III inclusions) in the first biopsy, but they were not present in a second biopsy. None had coagulation abnormalities or hypofibrinogenemia. On immunostaining, both inclusions were strongly positive for not only fibrinogen but also C-reactive protein and C4d. Ultrastructurally, ground glass changes corresponded to membrane-bound cytoplasmic inclusions containing amorphous, granular material. The pathological features of type II fibrinogen inclusions were identical to those of pale bodies in hepatocellular carcinoma. The literature review suggested that type I fibrinogen inclusions characterized by a polygonal appearance are strongly associated with mutations in fibrinogen genes, coagulopathy, and family history, whereas type II/III inclusions are immunoreactive to multiple proteins and typically develop in cases of other unrelated liver diseases. In conclusion, type II and III fibrinogen inclusions do not represent a true hereditary storage disease but instead the collective retention of multiple proteins. Given the lack of clinical significance, a less specific name (e.g., pale body) may be more appropriate for those inclusions.

Clinical Consequences and Molecular Bases of Low Fibrinogen Levels

The study of inherited fibrinogen disorders, characterized by extensive allelic heterogeneity, allows the association of defined mutations with specific defects providing significant insight into the location of functionally important sites in fibrinogen and fibrin. Since the identification of the first causative mutation for congenital afibrinogenemia, studies have elucidated the underlying molecular pathophysiology of numerous causative mutations leading to fibrinogen deficiency, developed cell-based and animal models to study human fibrinogen disorders, and further explored the clinical consequences of absent, low, or dysfunctional fibrinogen. Since qualitative disorders are addressed by another review in this special issue, this review will focus on quantitative disorders and will discuss their diagnosis, clinical features, molecular bases, and introduce new models to study the phenotypic consequences of fibrinogen deficiency.

Fibrinogen Gamma Chain Mutations Provoke Fibrinogen and Apolipoprotein B Plasma Deficiency and Liver Storage

p.R375W (Fibrinogen Aguadilla) is one out of seven identified mutations (Brescia, Aguadilla, Angers, Al du Pont, Pisa, Beograd, and Ankara) causing hepatic storage of the mutant fibrinogen γ. The Aguadilla mutation has been reported in children from the Caribbean, Europe, Japan, Saudi Arabia, Turkey, and China. All reported children presented with a variable degree of histologically proven chronic liver disease and low plasma fibrinogen levels. In addition, one Japanese and one Turkish child had concomitant hypo-APOB-lipoproteinemia of unknown origin. We report here on an additional child from Turkey with hypofibrinogenemia due to the Aguadilla mutation, massive hepatic storage of the mutant protein, and severe hypo-APOB-lipoproteinemia. The liver biopsy of the patient was studied by light microscopy, electron microscopy (EM), and immunohistochemistry. The investigation included the DNA sequencing of the three fibrinogen and APOB-lipoprotein regulatory genes and the analysis of the encoded protein structures. Six additional Fibrinogen Storage Disease (FSD) patients with either the Aguadilla, Ankara, or Brescia mutations were investigated with the same methodology. A molecular analysis revealed the fibrinogen gamma p.R375W mutation (Aguadilla) but no changes in the APOB and MTTP genes. APOB and MTTP genes showed no abnormalities in the other study cases. Light microscopy and EM studies of liver tissue samples from the child led to the demonstration of the simultaneous accumulation of both fibrinogen and APOB in the same inclusions. Interestingly enough, APOB-containing lipid droplets were entrapped within the fibrinogen inclusions in the hepatocytic Endoplasmic Reticulum (ER). Similar histological, immunohistochemical, EM, and molecular genetics findings were found in the other six FSD cases associated with the Aguadilla, as well as with the Ankara and Brescia mutations. The simultaneous retention of fibrinogen and APOB-lipoproteins in FSD can be detected in routinely stained histological sections. The analysis of protein structures unraveled the pathomorphogenesis of this unexpected phenomenon. Fibrinogen gamma chain mutations provoke conformational changes in the region of the globular domain involved in the "end-to-end" interaction, thus impairing the D-dimer formation. Each monomeric fibrinogen gamma chain is left with an abnormal exposure of hydrophobic patches that become available for interactions with APOB and lipids, causing their intracellular retention and impairment of export as a secondary unavoidable phenomenon.

The fibrous form of intracellular inclusion bodies in recombinant variant fibrinogen-producing cells is specific to the hepatic fibrinogen storage disease-inducible variant fibrinogen

Fibrinogen storage disease (FSD) is a rare disorder that is characterized by the accumulation of fibrinogen in hepatocytes and induces liver injury. Six mutations in the γC domain (γG284R, γT314P, γD316N, the deletion of γG346-Q350, γG366S, and γR375W) have been identified for FSD. Our group previously established γ375W fibrinogen-producing Chinese hamster ovary (CHO) cells and observed aberrant large granular and fibrous forms of intracellular inclusion bodies. The aim of this study was to investigate whether fibrous intracellular inclusion bodies are specific to FSD-inducible variant fibrinogen. Thirteen expression vectors encoding the variant γ-chain were stably or transiently transfected into CHO cells expressing normal fibrinogen Aα- and Bβ-chains or HuH-7 cells, which were then immunofluorescently stained. Six CHO and HuH-7 cell lines that transiently produced FSD-inducible variant fibrinogen presented the fibrous (3.2-22.7 and 2.1-24.5%, respectively) and large granular (5.4-25.5 and 7.7-23.9%) forms of intracellular inclusion bodies. Seven CHO and HuH-7 cell lines that transiently produced FSD-non-inducible variant fibrinogen only exhibit the large granular form. These results demonstrate that transiently transfected variant fibrinogen-producing CHO cells and inclusion bodies of the fibrous form may be useful in non-invasive screening for FSD risk factors for FSD before its onset.

Fibrinogen storage disease and cirrhosis associated with hypobetalipoproteinemia owing to fibrinogen Aguadilla in a Turkish child

BACKGROUND AND AIMS

Fibrinogen gene mutations can rarely result in hepatic fibrinogen storage disease (HFSD). Herein, we report on the first Turkish family carrying the mutation p.Arg375Trp (fibrinogen Aguadilla) in the γ-chain of the fibrinogen (FGG) gene.

METHODS

Clinical, laboratory and histopathological findings of the patient were documented. Molecular study of fibrinogen gene was performed in the patient and her family members.

RESULTS

The proband was 5 years old girl presenting with advanced liver fibrosis of unknown origin. The child had very low plasma levels of fibrinogen and hypobetalipoproteinemia. Immunomorphologic and electron microscopic studies showed selective and exclusive accumulation of fibrinogen within the endoplasmic reticulum in liver biopsy of the patient. Patient, mother, two sisters and one brother carried p.Arg375Trp mutation (fibrinogen Aguadilla) in FGG gene. The patient was treated with ursodeoxycholic acid and carbamazepine. After 3 months, carbamazepine was suspended upon family decision and unresponsiveness of carbamazepine.

CONCLUSIONS

HFSD is characterized by hypofibrinogenemia and accumulation of abnormal fibrinogen within hepatocytes. In addition, hypofibrinogenemia is associated with hypobetalipoproteinemia in Aguadilla mutation.

Hypofibrinogenemia and liver disease: a new case of Aguadilla fibrinogen and review of the literature

INTRODUCTION

Fibrinogen storage disease (FSD) is characterized by hypofibrinogenemia and hepatic inclusions due to impaired release of mutant fibrinogen which accumulates and aggregates in the hepatocellular endoplasmic reticulum. Liver disease is variable.

AIM

We studied a new Swiss family with fibrinogen Aguadilla. In order to understand the molecular peculiarity of FSD mutations, fibrinogen Aguadilla and the three other causative mutations, all located in the γD domain, were modelled.

METHOD

The proband is a Swiss girl aged 4 investigated because of fatigue and elevated liver enzymes. Protein structure models were prepared using the Swiss-PdbViewer and POV-Ray software.

RESULTS

The proband was found to be heterozygous for fibrinogen Aguadilla: FGG Arg375Trp. Familial screening revealed that her mother and maternal grandmother were also affected and, in addition, respectively heterozygous and homozygous for the hereditary haemochromatosis mutation HFE C282Y. Models of backbone and side-chain interactions for fibrinogen Aguadilla in a 10-angstrom region revealed the loss of five H-bonds and the gain of one H-bond between structurally important amino acids. The structure predicted for fibrinogen Angers showed a novel helical structure in place of hole 'a' on the outer edge of γD likely to have a negative impact on fibrinogen assembly and secretion.

CONCLUSION

The mechanism by which FSD mutations generate hepatic intracellular inclusions is still not clearly established although the promotion of aberrant intermolecular strand insertions is emerging as a likely cause. Reporting new cases is essential in the light of novel opportunities of treatment offered by increasing knowledge of the degradation pathway and autophagy.

Hepatic fibrinogen storage disease due to the fibrinogen γ375 Arg → Trp mutation "fibrinogen Aguadilla" is present in Arabs

The mutation γ375Arg → Trp (fibrinogen Aguadilla) is one of four mutations (Brescia, Aguadilla, Angers, and AI duPont) capable of causing hepatic storage of fibrinogen. It has been observed in four children from the Caribbean, Europe, and Japan, suffering from cryptogenic liver disease. We report the first case of hepatic fibrinogen storage disease in Arabs due to a mutation in the fibrinogen γ-chain gene in a 3-year-old Syrian girl presenting with elevated liver enzymes. The finding of an impressive accumulation of fibrinogen in liver cells raised the suspicion of endoplasmic reticulum storage disease. Sequencing of the fibrinogen genes revealed a γ375Arg → Trp mutation (fibrinogen Aguadilla) in the child and in her father. In conclusion, when confronted with chronic hepatitis of unknown origin, one should check the plasma fibrinogen level and look carefully for the presence of hepatocellular intracytoplasmic globular inclusions to exclude hepatic fibrinogen storage disease.

γ375W fibrinogen-synthesizing CHO cells indicate the accumulation of variant fibrinogen within endoplasmic reticulum

BACKGROUND

Hepatic endoplasmic reticulum (ER) storage disease (HERSD) associated with hypofibrinogenemia has been reported in patients with four types of heterozygous γ-chain variant fibrinogen in the C terminal region. Of interest, substitution of γR375W induced hypofibrinogenemia and HERSD, whereas γR375G induced dysfibrinogenemia.

OBJECTIVES

To analyze the synthesis of variant fibrinogen and morphological characteristics, we established variant fibrinogen-producing cells and compared them with wild-type fibrinogen-synthesizing cells.

METHODS

The fibrinogen γ-chain expression vectors coding γ375W and γ375G were altered by oligonucleotide-directed mutagenesis and transfected into Chinese hamster ovary (CHO) cells. Synthesis of fibrinogen (media and cell lysates) was measured by ELISA for each cloned cell line and morphological characteristics were observed by immunofluorescence and transmission electron microscopy.

RESULTS

The medium/cell lysate fibrinogen ratio of γ375W-CHO cells was markedly lower than that of the normal cells and γ375G-CHO cells. Immunostaining with anti-fibrinogen antibody showed only γ375W-CHO cells, but revealed two types of cells containing cytoplasmic inclusion bodies, scattered large-granular bodies and fibrous forms. Observation by confocal microscopy indicated that both inclusion bodies were colocalized with fibrinogen and ER-membrane protein; furthermore, transmission electron microscopic observation demonstrated dilatation of the ER by large-granular inclusion bodies and fibrous forms filled with regularly structured fibular materials within the dilated ER.

CONCLUSION

These results demonstrated that assembled and non-secreted γ375W fibrinogen was accumulated in the dilated ER and aggregated variant fibrinogen was seen as regularly structured fibular materials, which was similar to the fingerprint-like pattern observed at inclusion bodies in patients' hepatocytes affected with HERSD.

Novel fibrinogen mutation γ314Thr→Pro (fibrinogen AI duPont) associated with hepatic fibrinogen storage disease and hypofibrinogenaemia

Mutation in fibrinogen genes may lead to quantitative or qualitative disorders that result in bleeding, thrombosis or hepatic fibrinogen storage disease. Only three mutations in the fibrinogen γ gene have been identified that cause hepatic endoplasmic reticulum storage of mutant fibrinogen. To investigate the possibility of hepatic fibrinogen storage disease in a 4-year-old male with persistently elevated serum aminotransferases and preserved synthetic function except for a prolonged INR. After informed consent, liver and blood samples were obtained. Liver sections were examined by light microscopy, anti-fibrinogen immunolabelling and electron microscopy. Purified fibrinogen was analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and reverse phase high performance liquid chromatography; DNA sequencing was performed using a BigDye Terminator (v. 3.1) cycle sequencing kit. Four-year-old male with persistently elevated transaminases with an INR 1.5 but otherwise normal synthetic function. Fibrinogen activity and thrombin clotting time were abnormal at 0.47 g/L and 46 s respectively. Hepatic histological examination revealed portal inflammatory infiltrates with bridging fibrosis. Clumped eosinophilic material was observed in hepatocytes that was immunoreactive to fibrinogen antisera. Ultrastructural examination showed cytoplasmic inclusions arrayed in fingerprint-like patterns. DNA sequence analysis revealed heterozygosity for a novel γ314Thr →Pro mutation (fibrinogen AI duPont) in the fibrinogen γ gene. Protein analyses showed normal patterns of Aα, Bβ and γ chains suggesting that the variant γ allele was not expressed in plasma fibrinogen. We describe only the fourth mutation to be identified, γ314Thr→Pro (fibrinogen AI duPont), giving rise to hypofibrinogenaemia and hepatic fibrinogen storage disease.

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.

High prevalence of dysfibrinogenemia among patients with chronic thromboembolic pulmonary hypertension

The mechanism by which chronic thromboembolic pulmonary hypertension (CTEPH) develops after acute pulmonary thromboembolism is unknown. We previously reported that fibrin from CTEPH patients is relatively resistant to fibrinolysis in vitro. In the present study, we performed proteomic, genomic, and functional studies on fibrin(ogen) to investigate whether abnormal fibrin(ogen) might contribute to the pathogenesis of CTEPH. Reduced and denatured fibrinogen from 33 CTEPH patients was subjected to liquid chromatography-mass spectrometry analysis. Fibrinogen from 21 healthy controls was used to distinguish atypical from commonly occurring mass peaks. Atypical peaks were further investigated by targeted genomic DNA sequencing. Five fibrinogen variants with corresponding heterozygous gene mutations (dysfibrinogenemias) were observed in 5 of 33 CTEPH patients: Bbeta P235L/gamma R375W, Bbeta P235L/gamma Y114H, Bbeta P235L, Aalpha L69H, and Aalpha R554H (fibrinogens(San Diego I-V)). Bbeta P235L was found in 3 unrelated CTEPH patients. Functional analysis disclosed abnormalities in fibrin polymer structure and/or lysis with all CTEPH-associated mutations. These results suggest that, in some patients, differences in the molecular structure of fibrin may be implicated in the development of CTEPH after acute thromboembolism.

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.

Fibrinogen angers with a new deletion (gamma GVYYQ 346-350) causes hypofibrinogenemia with hepatic storage

INTRODUCTION

This study reports a family with chronically abnormal blood liver function tests (LFT) and congenital hypofibrinogenemia. The proposita had cirrhosis initially related to alcohol abuse and chronic viral hepatitis C (HCV), but abnormal LFT persisted even when alcohol intake was stopped and despite HCV treatment was efficient based on serum RNA negative testing.

RESULTS

Needle biopsy specimens of the proposita and her brother showed eosinophilic intra-cytoplasmic inclusions that reacted strongly with fibrinogen antisera on direct immunofluorescence. Electron microscopic examination showed that the rough endoplasmic reticulum was filled with inclusions that consisted of densely packed, curved tubular structures arranged in a fingerprint-like pattern. Coagulation studies revealed low functional and antigenic fibrinogen concentrations suggestive of hypofibrinogenemia. Amplification and DNA sequencing showed a heterozygous deletion of the a7690 to g7704 nucleotides of the gamma chain gene in the 3'end of exon 8 (g 7690_7704del14; Genbank access M10014); this deletion encompassed the splicing site at position 7703 and predicts in a new putative consensus splicing sequence (AATGgtatgtt). RNA was extracted from a liver specimen from the proposita's brother. The cDNA obtained by reverse transcription polymerase chain reaction confirmed the usage of a newly generated donor site at position 7688 of the genomic sequence resulting in an in-frame heterozygous 5 amino acid deletion (GVYYQ 346-350; p.G372_Q376del) and that this mutation is responsible for a new splicing site at position 7688 of the genomic sequence.

CONCLUSION

we suggest that the molecular defect in fibrinogen Angers results in an impaired assembly and causes defective secretion and hepatic storage of fibrinogen.

Changes in fibrinogen and fibrin induced by a peptide analog of fibrinogen gamma365-380

BACKGROUND

The effects of synthetic peptides with sequences derived from the gamma-chain of fibrinogen on the functional properties of fibrinogen and fibrin were investigated.

METHODS

Methods included thrombelastography, clot turbidity measurement, clot elasticity measurement, platelet aggregation, and scanning transmission electron microscopy (STEM).

RESULTS

Peptide gamma369-380 (NH(2)-WATWKTRWYSMK-COOH) showed the greatest impact on fibrin structure, compared with the 76 other overlapping dodecapeptides. Addition of this peptide, or peptide gamma365-380 (NH(2)-NGIIWATKTREWYSMK-COOH) to a mixture of fibrinogen and thrombin resulted a shorter clotting time, higher clot turbidity, lower clot elastic modulus, a higher degree of D-trimer and D-tetramer formation, and impaired plasmin proteolysis of the clot. In STEM, fibrin formed in the presence of peptide gamma369-380 consisted of a more extensive array of linear fibrils typically consisting of 20 or more molecules. Fibrils were better organized than those from non-peptide containing mixtures.

CONCLUSIONS

Replacement of the tryptophan residue gamma376 massively reduced the effect of the peptide on fibrin structure. Binding of the peptide to fibrinogen induces conformational changes, which result in accelerated clotting and increased lateral association of fibrin protofibrils. The results imply a relevant functional role of sites interacting with peptide gamma369-380 region in the fibrinogen molecule.

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.

Hepatobiliary pathology

PURPOSE OF REVIEW

Recent papers on disorders of the liver and biliary tract which clarify their pathogenesis and attendant morphologic changes are highlighted.

RECENT FINDINGS

The concept of 'bystander hepatitis' was cited in studies showing hepatic infiltration of CD8-positive T cells in the setting of extrahepatic infections such as influenza virus and severe acute respiratory syndrome. Diabetic liver lesions include glycogenic hepatopathy (in which poor diabetic control leads to swollen, glycogen-filled hepatocytes without fat, steatohepatitis or fibrosis) and diabetic hepatosclerosis in which there is diffuse perisinusoidal fibrosis (type IV collagen) without zonal predilection. Ground-glass hepatocellular inclusions (positive with periodic acid-Schiff stain for glycogen) were reported in three separate series of patients who were hepatitis B virus-negative, often transplant recipients, immunosuppressed and on multiple medications. A Banff consensus paper expertly compared and contrasted the histologic features which characterize the various causes of late liver allograft dysfunction.

SUMMARY

Informative papers emerged this past year concerning collateral damage to the liver in extrahepatic infections, diabetic lesions and causes of liver dysfunction after transplantation, among other topics.

Pathology teach and tell: fibrinogen storage disease in a child with hypofibrinogenemia and decreased ceruloplasmin

The authors present a clinical case of a patient with mild liver disease and coagulopathy. The diagnosis was reached through careful histologic examination of liver biopsy. Electron microscopy played an important role in confirming the diagnosis.