Thrombosis-associated hypofibrinogenemia: novel abnormal fibrinogen variant FGG c.8G>A with oxidative posttranslational modifications.

Here, we present the first case of fibrinogen variant FGG c.8G>A. We investigated the behaviour of this mutated fibrinogen in blood coagulation using fibrin polymerization, fibrinolysis, fibrinopeptides release measurement, mass spectrometry (MS), and scanning electron microscopy (SEM). The case was identified by routine coagulation testing of a 34-year-old man diagnosed with thrombosis. Initial genetic analysis revealed a heterozygous mutation in exon 1 of the FGG gene encoding gamma chain signal peptide. Fibrin polymerization by thrombin and reptilase showed the normal formation of the fibrin clot. However, maximal absorbance within polymerization was lower and fibrinolysis had a longer degradation phase than healthy control. SEM revealed a significant difference in clot structure of the patient, and interestingly, MS detected several posttranslational oxidations of fibrinogen. The data suggest that the mutation FGG c.8G>A with the combination of the effect of posttranslational modifications causes a novel case of hypofibrinogenemia associated with thrombosis.

Recombinant γY278H Fibrinogen Showed Normal Secretion from CHO Cells, but a Corresponding Heterozygous Patient Showed Hypofibrinogenemia.

We identified a novel heterozygous hypofibrinogenemia, γY278H (Hiroshima). To demonstrate the cause of reduced plasma fibrinogen levels (functional level: 1.12 g/L and antigenic level: 1.16 g/L), we established γY278H fibrinogen-producing Chinese hamster ovary (CHO) cells. An enzyme-linked immunosorbent assay demonstrated that synthesis of γY278H fibrinogen inside CHO cells and secretion into the culture media were not reduced. Then, we established an additional five variant fibrinogen-producing CHO cell lines (γL276P, γT277P, γT277R, γA279D, and γY280C) and conducted further investigations. We have already established 33 γ-module variant fibrinogen-producing CHO cell lines, including 6 cell lines in this study, but only the γY278H and γT277R cell lines showed disagreement, namely, recombinant fibrinogen production was not reduced but the patients' plasma fibrinogen level was reduced. Finally, we performed fibrinogen degradation assays and demonstrated that the γY278H and γT277R fibrinogens were easily cleaved by plasmin whereas their polymerization in the presence of Ca2+ and "D:D" interaction was normal. In conclusion, our investigation suggested that patient γY278H showed hypofibrinogenemia because γY278H fibrinogen was secreted normally from the patient's hepatocytes but then underwent accelerated degradation by plasmin in the circulation.

Cryofibrinogen-associated glomerulonephritis accompanied by advanced gastric cancer.

We had a 72-year-old man with advanced gastric cancer, poorly differentiated adenocarcinoma, receiving chemotherapy with S-1 (tegafur, gimeracil, and oteracil potassium) plus oxaliplatin. Ascites developed despite remission of gastric cancer and metastasis. Given no malignant cells in ascites, leg edema, renal impairment, hypoalbuminemia, and massive proteinuria, we diagnosed as nephrotic syndrome with microscopic hematuria. Renal biopsy showed membranoproliferative glomerulonephritis with no deposition of immunoglobulins and complements. Of note, electronic microscopy found organized deposits with microtubular structures in the glomerular capillary lumens and subendothelial spaces. The liquid chromatography-tandem mass spectrometry method detected fibrinogen alpha chain, beta chain, gamma chain, and fibronectin, and we eventually diagnosed cryofibrinogen-associated glomerulonephritis. Cryofibrinogen was not detected in plasma. He was expired at 5 months following renal biopsy due to the progression of refractory nephrotic syndrome. In addition to the detailed assessment of specifically organized deposits, the analysis using liquid chromatography-tandem mass spectrometry method is useful to diagnose cryofibrinogen-associated glomerulonephritis. We should consider cryofibrinogen-associated glomerulonephritis as a differential diagnosis when the patients with malignancy showed abnormal urinalysis and renal impairment, though it is a rare disease.

Heterozygous variant fibrinogen γA289V (Kanazawa III) was confirmed as hypodysfibrinogenemia by plasma and recombinant fibrinogens.

INTRODUCTION: Congenital fibrinogen disorders are classified as afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia. However, difficulties are associated with discriminating between dysfibrinogenemia, hypofibrinogenemia, and hypodysfibrinogenemia using routine analyses. We previously reported a heterozygous variant fibrinogen (γA289V; Kanazawa III) as hypodysfibrinogenemia; however, the same variant had previously been described as hypofibrinogenemia. To clarify the production of γA289V fibrinogen, we expressed recombinant γA289V (r-γA289V) fibrinogen and compared it with wild-type (WT) and adjacent recombinant variant fibrinogens. METHODS: Target mutations were introduced into a fibrinogen γ-chain expression vector by site-directed mutagenesis, and the vector was then transfected into Chinese hamster ovary cells to produce recombinant fibrinogen. Fibrinogen was purified from the plasma of the proposita, and culture media and fibrinogen functions were analyzed using fibrin polymerization, plasmin protection, and FXIIIa-catalyzed fibrinogen cross-linking. RESULTS: The fibrinogen concentration ratio of the culture media to cell lysates was markedly lower for r-γA289V fibrinogen than for WT. Because the secretion of recombinant γF290L (r-γF290L) fibrinogen was similar to WT, we compared r-γF290L fibrinogen functions with WT. The fibrin polymerization of Kanazawa III plasma (K-III) fibrinogen was significantly weaker than normal plasma fibrinogen. Moreover, K-III fibrinogen showed a markedly reduced "D:D" interaction. However, all functions of r-γF290L fibrinogen were similar to WT. An in silico analysis confirmed the above results. CONCLUSION: The present results demonstrated that γA289 is crucial for the γ-module structure, and the γA289V substitution markedly reduced fibrinogen secretion. Moreover, K-III fibrinogen showed markedly reduced fibrin polymerization and "D:D" interactions. γA289V fibrinogen was confirmed as hypodysfibrinogenemia.

Characteristic electron-microscopic features of cryofibrinogen-associated glomerulonephritis: a case report.

BACKGROUND: Cryofibrinogenemia is a rare disorder that mainly affects the skin and occasionally the kidney. However, there are few published reports of cryofibrinogenemia-associated renal pathology. We therefore report a patient with cryofibrinogen-associated glomerulonephritis. Samples from this patient were examined by electron microscopy, laser microdissection, and liquid chromatography-tandem mass spectrometry (LC-MS/MS). CASE PRESENTATION: A 78-year-old Japanese man presented with declining renal function, proteinuria, and gross hematuria. Kidney biopsy showed a membranoproliferative pattern with crescent formation and dominant C3c deposition in which subendothelial deposits with uniquely organized electron-microscopic features were observed. Additional ultrastructural analysis of cryoprecipitates extracted from plasma revealed similar structures of the glomerular subendothelial deposits. LC-MS/MS identified an increase in fibrinogen α, ß, and γ chains, fibronectin, filamin-A, and C3. The glomerular lesions were diagnosed as cryofibrinogen-associated glomerulonephritis on the basis of these findings. CONCLUSIONS: Although there are few reports of cryofibrinogen-associated glomerulonephritis, we believe that accurate diagnosis can be achieved by performing LC-MS/MS and ultrastructural analysis.

Congenital fibrinogen disorders with repeated thrombosis.

Congenital dysfibrinogenemia is characterized with undetectable or low fibrinogen level by Clauss assay complicated by bleeding and/or thrombosis. These may lead to a diagnostic problem to some clinicians unfamiliar with this disease. We reported a case of congenital dysfibrinogenemia manifested as hemorrhage, repeated thrombosis, low fibrinogen levels through Clauss assay and but normal levels of fibrinogen through PT-derived tests. In conclusion, to patients with thrombosis complicated by decreased fibrinogen level, clinicians and laboratory physicians should be alert to the possibility of congenital dysfibrinogenemia.

Fibrin γ/γ' influences the secretion of fibrinolytic components and clot structure.

BACKGROUND: In healthy subjects fibrinogen γ/γ' circulates at 8-15% of the total plasma fibrinogen concentration. Elevated levels of this variant have been associated with arterial thrombosis, and its diminution with venous thrombosis. The aims of the present work were to analyze the structure of the fibrin network formed on the top of human dermal microvascular endothelial cells (HMEC-1) at different fibrinogen γ/γ' concentrations, as well as its influence on the secretion of fibrinolytic components. The kinetics of fibrin polymerization on top of HMEC-1 cells with 3, 10, and 30% fibrinogen γ/γ' was followed at 350 nm. The secretion of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI 1) by HMEC-1 were measured in the supernatant and cell lysates, after incubation with 1 nM thrombin, fibrin with 3, and 30% fibrinogen γ/γ', using commercial kits. The influence of fibrinogen γ/γ' on fibrin structure on the surface of the HMEC-1 was followed with laser scanning confocal microscopy (LSCM). RESULTS: The kinetics of fibrin formation on HMEC-1 with 3 and 10% fibrinogen γ/γ' were similar. However, with 30% fibrinogen γ/γ' both the slope and final turbity were approximately 50% less. The LSCM images showed the dramatic effects of increasing fibrinogen γ/γ' from 3 to 30%. The uPA and PAI 1 concentrations in culture supernatants HMEC-1 cells treated with thrombin or 30% γ/γ' fibrin were two-fold increased as compared to basal culture supernatants and 3% γ/γ' fibrin-treated HMEC-1. In all stimulatory conditions the intracellular concentration of uPA was higher than in supernatants. In contrast, the intracellular PAI 1 concentration was decreased as compared to that measured in the supernatant, including the basal condition. CONCLUSION: A concentration of 30% fibrin γ/γ' alter drastically fibrin structure on the cell surface and affects the secretion of uPA and PAI 1 through its capacity to bind thrombin.

Fibrinogen Columbus II: A novel c.1075G>T mutation in the FGG gene causing hypodysfibrinogenemia and thrombosis in an adolescent male.

Hypodysfibrinogenemia, the least frequently reported congenital fibrinogen disorder is characterized by low circulating levels of a dysfunctional protein, and is associated with phenotypic features of both hypo- and dysfibrinogenemia. Herein, we report an adolescent male with unprovoked venous thromboembolism and hypodysfibrinogenemia. Patient had recurrent, progressive thrombosis despite therapeutic anticoagulation with both low molecular weight heparin and warfarin. He had clinical and radiological improvement after transition to a direct thrombin inhibitor. Sequencing of the FGG gene identified a novel heterozygous mutation, c.1075G>T. Structural visualization of the identified variant was pursued and suggested that the mutation likely destabilizes the Ca2+ -binding site of fibrinogen resulting in pathogenicity.

Establishing the Transient Mass Balance of Thrombosis: From Tissue Factor to Thrombin to Fibrin Under Venous Flow.

OBJECTIVE: We investigated the coregulation of thrombin and fibrin as blood flows over a procoagulant surface. APPROACH AND RESULTS: Using microfluidic perfusion of factor XIIa-inhibited human whole blood (200 s-1 wall shear rate) over a 250-µm long patch of collagen/TF (tissue factor; ≈1 molecule per µm2) and immunoassays of the effluent for F1.2 (prothrombin fragment 1.2), TAT (thrombin-antithrombin complex), and D-dimer (post-end point plasmin digest), we sought to establish the transient mass balance for clotting under venous flow. F1.2 (but almost no free thrombin detected via TAT assay) continually eluted from clots when fibrin was allowed to form. Low-dose fluorescein-Phe-Pro-Arg-chloromethylketone stained fibrin-bound thrombin-a staining ablated by anti-γ'-fibrinogen or the fibrin inhibitor glypro-arg-pro but highly resistant to 7-minute buffer rinse, demonstrating tight binding of thrombin to γ'-fibrin. With fibrin polymerizing for 500 seconds, 92 000 thrombin molecules and 203 000 clot-associated fibrin monomer equivalents were generated per TF molecule (or per µm2). Fibrin reached 15 mg/mL in the pore space (porosity ≈0.5) of a 15-µm-thick thrombus core by 500 seconds and 30 mg/mL by 800 seconds. For a known rate of ≈60 FPA (fibrinopeptide-A) per thrombin per second, each thrombin molecule generated only 3 fibrin monomer equivalents during 500 seconds, indicating an intraclot thrombin half-life of ≈70 ms, much shorter than its diffusional escape time (≈10 seconds). By 800 seconds, gly-pro-arg-pro allowed 4-fold more F1.2 generation, consistent with gly-pro-arg-pro ablating fibrin's antithrombin-I activity and facilitating thrombin-mediated FXIa activation. CONCLUSIONS: Under flow, fibrinogen continually penetrates the clot, and γ'-fibrin regulates thrombin.

Sensing adhesion forces between erythrocytes and γ' fibrinogen, modulating fibrin clot architecture and function.

Plasma fibrinogen includes an alternatively spliced γ-chain variant (γ'), which mainly exists as a heterodimer (γAγ') and has been associated with thrombosis. We tested γAγ' fibrinogen-red blood cells (RBCs) interaction using atomic force microscopy-based force spectroscopy, magnetic tweezers, fibrin clot permeability, scanning electron microscopy and laser scanning confocal microscopy. Data reveal higher work necessary for RBC-RBC detachment in the presence of γAγ' rather than γAγA fibrinogen. γAγ' fibrinogen-RBCs interaction is followed by changes in fibrin network structure, which forms an heterogeneous clot structure with areas of denser and highly branched fibrin fibers. The presence of RBCs also increased the stiffness of γAγ' fibrin clots, which are less permeable and more resistant to lysis than γAγA clots. The modifications on clots promoted by RBCs-γAγ' fibrinogen interaction could alter the risk of thrombotic disorders.

Identification of Two Novel Fibrinogen Bß Chain Mutations in Two Slovak Families with Quantitative Fibrinogen Disorders.

Congenital fibrinogen disorders are caused by mutations in one of the three fibrinogen genes that affect the synthesis, assembly, intracellular processing, stability or secretion of fibrinogen. Functional studies of mutant Bß-chains revealed the importance of individual residues as well as three-dimensional structures for fibrinogen assembly and secretion. This study describes two novel homozygous fibrinogen Bß chain mutations in two Slovak families with afibrinogenemia and hypofibrinogenemia. Peripheral blood samples were collected from all subjects with the aim of identifying the causative mutation. Coagulation-related tests and rotational thromboelastometry were performed. All exons and exon-intron boundaries of the fibrinogen genes (FGA, FGB and FGG) were amplified by PCR followed by direct sequencing. Sequence analysis of the three fibrinogen genes allowed us to identify two novel homozygous mutations in the FGB gene. A novel Bß chain truncation (BßGln180Stop) was detected in a 28-year-old afibrinogenemic man with bleeding episodes including repeated haemorrhaging into muscles, joints, and soft tissues, and mucocutaneous bleeding and a novel Bß missense mutation (BßTyr368His) was found in a 62-year-old hypofibrinogenemic man with recurrent deep and superficial venous thromboses of the lower extremities. The novel missense mutation was confirmed by molecular modelling. Both studying the molecular anomalies and the modelling of fibrinogenic mutants help us to understand the extremely complex machinery of fibrinogen biosynthesis and finally better assess its correlation with the patient's clinical course.

Fibrinogen Mahdia: A congenitally abnormal fibrinogen characterized by defective fibrin polymerization.

INTRODUCTION: Congenital dysfibrinogenemia is a rare qualitative fibrinogen deficiency. Molecular defects that result in dysfibrinogenemia are usually caused by mutations which affect fibrinopeptide release, fibrin polymerization, fibrin cross-linking or fibrinolysis. AIM: Here, we investigated the genetic basis of hypodysfibrinogenemia in two Tunisian siblings with major bleeding. METHODS: Coagulation-related tests were performed on the patients and their family members. Functional analysis was performed in plasma fibrinogen to characterize fibrin polymerization. The sequences of fibrinogen genes were amplified and analysed by sequencing. RESULTS: Coagulation studies revealed a reduced functional and a borderline low antigenic fibrinogen plasma levels with prolonged thrombin and activated partial thromboplastin times. The fibrinogen is also characterized by a markedly impaired polymerization and could incorporate into fibrin fibres to a smaller extent (22%). Mutational screening disclosed a heterozygous single nucleotide deletion (G) at c.1025, resulting in a frameshift mutation (AαGly323GlufsX79) that is predicted to delete a part of the αC-domain containing some of the FXIII cross-linking sites. Both the normal and the aberrant Aα-chain (approximately 43 kDa) were detected by electrophoretic analysis in the patients. CONCLUSION: The new dysfunctional fibrinogen, Mahdia variant, describes its impact on fibrin assembly after the loss of the αC domains which are involved in the lateral aggregation of protofibrils. The study confirms that the truncated Aα-chain could be incorporated into mature fibrinogen molecules.

The amplitude of coagulation curves from thrombin time tests allows dysfibrinogenemia caused by the common mutation FGG-Arg301 to be distinguished from hypofibrinogenemia.

INTRODUCTION: Thrombin time (TT) tests are useful for diagnosing coagulation disorders involving abnormal fibrinogen but do not allow us to distinguish between qualitative and quantitative defects. However, with the widening availability of optical coagulation automates, more information about the coagulation process is becoming increasingly accessible. METHODS: In this study, we compared the coagulation curves of TT tests carried out with plasma from healthy donors with those from patients with acquired low Clauss fibrinogen levels or with dysfibrinogenemia caused by a heterozygous point mutation in the fibrinogen γ-chain that results in a p.Arg301(275)Cys substitution. The functional fibrinogen levels of these three groups of samples were also measured with the Clauss method, and their fibrinogen protein levels were determined by ELISA. RESULTS: Our data indicate that the amplitude and maximal velocity of coagulation curves from plasma samples from FGG p.Arg301(275)Cys dysfibrinogenemic patients were comparable to those from plasma samples with fibrinogen in the normal range, whereas the amplitude of coagulation curves from patients with acquired low fibrinogen levels was lower. CONCLUSIONS: Examination of the amplitude of coagulation curves generated during TT tests may provide additional information to enable the differential diagnoses of diseases following a low fibrinogen measurement by the Clauss method.

Thrombosis-associated antifibrinogen IgG1 κ impairs fibrin polymerization and enhances platelet activation.

The present study extends our previous investigation of circulating antibody/fibrinogen/C1q complexes (FgIgC) associated with thrombosis in a heterophenotypic AαR16C proband, by focusing on the molecular and functional characteristics of the FgIgC, isolated by cryoprecipitation, FgIgC components were demonstrated by SDS-PAGE and by rotary shadowing electron microscopy. Affinity chromatography was used to isolate IgG and fibrinogen from FgIgC. Thrombin-induced clots were examined by scanning electron microscopy and turbidity measurements. IgG/fibrinogen binding was measured by ELISA. Fibrinogen Aα1-19 peptides, cleaved by thrombin from fragment N-DSK, were examined by mass spectrometry. Clot stiffness, platelet release of P-selectin, and fibrinogen self-assembly were assessed by thromboelastography, flow cytometry, and atomic force microscopy, respectively. The FgIgC effects included the following: increased P-selectin release from gel-sieved platelets, finer fiber networks and decreased stiffness of its clots, and marked inhibition of fibrinogen self-assembly. The abnormal proband fibrinogen structure displayed phosphorylated AαR16C-AαR16C homodimers and AαR16C-glutathione heterodimers. ELISA measurements disclosed pronounced binding by proband fibrinogen to proband IgG, which was blocked by the IgG's Fab fragment and by proband, but not by normal plasmic fragment E1. There was appreciable, but much weaker, binding to normal fibrinogen, to its fragments E1, and D1, and to homodimeric AαR16C fibrinogen. The antibody's primary target epitope included heterodimeric AαR16C-glutathione; a secondary epitope resided in the D region. Moreover, both the enhanced platelet activation (i.e. increased P-selectin release induced by FgIgC) and the highly phosphorylated FpA (i.e. resulting in its accelerated release by thrombin) may have contributed to the thrombotic diathesis.

Fibrinogen splice variation and cross-linking: Effects on fibrin structure/function and role of fibrinogen γ' as thrombomobulin II.

Fibrin is an important matrix protein that provides the backbone to the blood clot, promoting tissue repair and wound healing. Its precursor fibrinogen is one of the most heterogeneous proteins, with an estimated 1 million different forms due to alterations in glycosylation, oxidation, single nucleotide polymorphisms, splice variation and other variations. Furthermore, ligation by transglutaminase factor XIII (cross-linking) adds to the complexity of the fibrin network. The structure and function of the fibrin network is in part determined by this natural variation in the fibrinogen molecule, with major effects from splice variation and cross-linking. This mini-review will discuss the direct effects of fibrinogen αEC and fibrinogen γ' splice variation on clot structure and function and also discuss the additional role of fibrinogen γ' as thrombomodulin II. Furthermore, the effects of cross-linking on clot function will be described. Splice variation and cross-linking are major determinants of the structure and function of fibrin and may therefore impact on diseases affecting bleeding, thrombosis and tissue repair.

Candidate gene analysis of the fibrinogen phenotype reveals the importance of polygenic co-regulation.

Fibrinogen and its functional aspects have been linked to cardiovascular disease. There is vast discrepancy between the heritability of fibrinogen concentrations observed in twin studies and the heritability uncovered by genome wide association studies. We postulate that some of the missing heritability might be explained by the pleiotropic and polygenic co-regulation of fibrinogen through multiple targeted genes, apart from the fibrinogen genes themselves. To this end we investigated single nucleotide polymorphisms (SNPs) in genes coding for phenotypes associated with total and γ' fibrinogen concentrations and clot properties. Their individual and accumulative associations with the fibrinogen variables were explored together with possible co-regulatory processes as a result of the gain and loss of transcription factor binding sites (TFBS). Seventy-eight SNPs spanning the APOB, APOE, CBS, CRP, F13A1, FGA, FGB, FGG, LDL-R, MTHFR, MTR, PCSK-9 and SERPINE-1 genes were included in the final analysis. A novel PCSK-9 SNP (rs369066144) was identified in this population, which associated significantly (p=0.04) with clot lysis time (CLT). Apart from SNPs in the fibrinogen (FGA, FGB and FGG) and FXIII (F13A1) genes, the fibrinogen phenotypes were also associated with SNPs in genes playing a role in lipid homeostasis (LDL-R, PCSK-9) together with CBS and CRP polymorphisms (particularly, CRP-rs3093068). The genetic risk scores, presenting accumulative genetic risk, were significantly associated (p≤0.007) with total and γ' fibrinogen concentrations, lag time, slope and CLT, highlighting the importance of a polygenetic approach in determining complex phenotypes. SNPs significantly associated with the fibrinogen phenotypes, resulted in a total of 75 TFBS changes, of which 35 resulted in a loss and 40 in a gain of TFBS. In terms of co-regulation, V$IRF4.02, V$E2FF and V$HIFF were of particular importance. The investigation into TFBS provided valuable insight as to how sequence divergences in seemingly unrelated genes can result in transcriptional co-regulation of the fibrinogen phenotypes. The observed associations between the identified SNPs and the fibrinogen phenotypes therefore do not imply direct effects on cardiovascular disease outcomes, but may prove useful in explaining more of the genetic regulation of the investigated fibrinogen phenotypes.

Thrombin and fibrinogen γ' impact clot structure by marked effects on intrafibrillar structure and protofibril packing.

Previous studies have shown effects of thrombin and fibrinogen γ' on clot structure. However, structural information was obtained using electron microscopy, which requires sample dehydration. Our aim was to investigate the role of thrombin and fibrinogen γ' in modulating fibrin structure under fully hydrated conditions. Fibrin fibers were studied using turbidimetry, atomic force microscopy, electron microscopy, and magnetic tweezers in purified and plasma solutions. Increased thrombin induced a pronounced decrease in average protofibril content per fiber, with a relatively minor decrease in fiber size, leading to the formation of less compact fiber structures. Atomic force microscopy under fully hydrated conditions confirmed that fiber diameter was only marginally decreased. Decreased protofibril content of the fibers produced by high thrombin resulted in weakened clot architecture as analyzed by magnetic tweezers in purified systems and by thromboelastometry in plasma and whole blood. Fibers produced with fibrinogen γ' showed reduced protofibril packing over a range of thrombin concentrations. High-magnification electron microscopy demonstrated reduced protofibril packing in γ' fibers and unraveling of fibers into separate protofibrils. Decreased protofibril packing was confirmed in plasma for high thrombin concentrations and fibrinogen-deficient plasma reconstituted with γ' fibrinogen. These findings demonstrate that, in fully hydrated conditions, thrombin and fibrinogen γ' have dramatic effects on protofibril content and that protein density within fibers correlates with strength of the fibrin network. We conclude that regulation of protofibril content of fibers is an important mechanism by which thrombin and fibrinogen γ' modulate fibrin clot structure and strength.