Structure and Function of Fibrinogen: Insights from Dysfibrinogens

Application of supervised machine learning algorithms to predict the risk of hidden blood loss during the perioperative period in thoracolumbar burst fracture patients complicated with neurological compromise

Background

Machine learning (ML) is a type of artificial intelligence (AI) and has been utilized in clinical research and practice to construct high-performing prediction models. Hidden blood loss (HBL) is prevalent during the perioperative period of spinal treatment and might result in a poor prognosis. The aim of this study was to develop a ML-based model for identifying perioperative HBL-related risk factors in patients with thoracolumbar burst fracture (TBF).

Methods

In this study, single-central TBF patients were chosen. The medical information on patients, including clinical characteristics, laboratory indicators, and surgery-related parameters, was extracted. After comparing various ML model algorithms, we selected the best model with high performance. The model was validated using the internal validation set before performing recursive feature elimination (RFE) to determine the importance of HBL-related risk factors. The area under the receiver operating characteristic (AUC) curve, accuracy (ACC), sensitivity, and specificity were reported as critical model measures for evaluating predictive performance.

Results

In this study, 62 (38.5%) of the 161 TBF patients were positive for HBL. There was a significant statistical difference in age, body mass index (BMI), diabetes, hypertension, Beta (percentage of vertebral restoration), duration of operation, and other pre-operative laboratory indicators between the HBL-positive and HBL-negative groups. Nine ML-based models were built and validated, with the Random Forest model having the greatest AUC in both the training set (0.905) and internal validation set (0.864). Furthermore, following RFE, age, duration of operation, Beta, pre-operative fibrinogen (Fib), and activated partial thromboplastin time (APTT) were identified as the five main important risk factors in patients with TBF during the perioperative period.

Conclusion

In this study, we built and validated ML algorithms for an individualized prediction of HBL-related risk factors in the perioperative period of TBF. The importance of HBL-related risk factors could be determined, which contributes to clinicians' decision-making and improves perioperative management.

Analysis of risk factors for perioperative hidden blood loss in unilateral biportal endoscopic spine surgery: a retrospective multicenter study

Background

Hidden blood loss (HBL) represents an important complication of unilateral biportal endoscopic (UBE) spine surgery. This study aimed to evaluate HBL and its possible risk factors among patients undergoing UBE surgery for lumbar degenerative diseases.

Methods

This multicentric retrospective study was conducted in 3 different medical centers between July 2020 and April 2021. Data of patients who underwent UBE surgery were extracted by electronic medical record system. The patient’s demographic characteristics and blood loss-related parameters were recorded. We calculated the amount of HBL and explored the association between patient’s characteristics and HBL using Pearson or Spearman correlation analysis. Multivariate linear regression analysis was conducted to identify independent risk factors of HBL.

Results

A total of 136 patients (55 females and 81 males, age range 43 to 74 years) were included in this study. A substantial amount of HBL (469.5 ± 195.3 ml, 57.6% of TBL, total blood loss) occurred following UBE surgery. Multiple linear regression analysis indicated that the risk factors of HBL were as follows: age (P = 0.000), number of fusion levels (P = 0.015), American Society of Anesthesiologists (ASA) classification (P = 0.046), surgery time (P = 0.017), patient’s blood volume (PBV, P = 0.026), total blood loss (TBL, P = 0.001), postoperative (i.e., day 2 or 3) hematocrit (Hct, P = 0.034), Hct loss (P = 0.005), and fibrinogen (P = 0.028).

Conclusions

A certain amount of HBL occurs in UBE surgery and cannot be ignored in daily clinical practice. The age, number of fusion levels, ASA classification, surgery time, PBV, TBL, postoperative Hct, Hct loss, and fibrinogen are independent risk factors for HBL.

Nano-Bio Interaction between Blood Plasma Proteins and Water-Soluble Silicon Quantum Dots with Enabled Cellular Uptake and Minimal Cytotoxicity

A better understanding of the compatibility of water-soluble semiconductor quantum dots (QDs) upon contact with the bloodstream is important for biological applications, including biomarkers working in the first therapeutic spectral window for deep tissue imaging. Herein, we investigated the conformational changes of blood plasma proteins during the interaction with near-infrared light-emitting nanoparticles, consisting of Pluronic F127 shells and cores comprised of assembled silicon QDs terminated with decane monolayers. Albumin and transferrin have high quenching constants and form a hard protein corona on the nanoparticle. In contrast, fibrinogen has low quenching constants and forms a soft protein corona. A circular dichroism (CD) spectrometric study investigates changes in the protein’s secondary and tertiary structures with incremental changes in the nanoparticle concentrations. As expected, the addition of nanoparticles causes the denaturation of the plasma proteins. However, it is noteworthy that the conformational recovery phenomena are observed for fibrinogen and transferrin, suggesting that the nanoparticle does not influence the ordered structure of proteins in the bloodstream. In addition, we observed enabled cellular uptake (NIH3T3 Fibroblasts) and minimal cytotoxicity using different cell lines (HeLa, A549, and NIH3T3). This study offers a basis to design QDs without altering the biomacromolecule’s original conformation with enabled cellular uptake with minimal cytotoxicity.

Current management of patients with severe von Willebrand disease type 3: a 2012 update

Von Willebrand disease type 3 (VWD3) is the most severe form of this bleeding disorder due to the almost complete deficiency of von Willebrand factor (VWF). VWD3 is inherited as an autosomal recessive trait. While heterozygous carriers exhibit mild or no bleeding symptoms, most patients with VWD3, which is characterized by undetectable levels of VWF antigen (VWF:Ag) and reduced concentrations (<20 IU/dl) of factor VIII (FVIII), show severe bleeding symptoms. Although the incidence of VWD3 is rare, the condition is of considerable interest because of its severe clinical presentation, the need for replacement therapy and the risk of alloantibodies following infusion of plasma-derived VWF concentrates. This review, based on clinical experience, provides an update on the clinical, laboratory and molecular markers of VWD3 that can be useful for determining the optimal therapeutic approach in these patients.

Expression studies of missense mutations p.D141Y, p.C275S located in the propeptide of von Willebrand factor in patients with type 3 von Willebrand disease

Missense mutations are not considered a common cause of type 3 von Willebrand's disease (VWD), the most severe defect of von Willebrand factor (VWF) characterized by undetectable levels of this protein in plasma and platelets. Nevertheless, several missense mutations have been identified in these patients. In this study, we report the cases of two Italian patients with type 3 VWD, both compound heterozygotes for different missense mutations and null alleles, p.D141Y/c.2016_2019del and p.C275S/p.W222X. We performed in vitro expression studies of the candidate missense mutations, both located in the D1 domain of VWF propeptide, to confirm their link with the disease and to understand the mechanisms of type 3 VWD responsible in these patients. Mutant and wild-type (WT) expression vectors were used for transient transfection and co-transfection studies in COS-7 cells. Single construct transfections of both missense mutations showed a strongly reduced but detectable secretion of recombinant (r)VWFs (approximately 15% of WT), with essentially only dimers being visualized on multimeric analysis. As expected, expression of a single construct of either mutation with the WT, showed mildly reduced secretion (approximately 40% of WT) and a full set of multimers. These expression studies indicate that the two amino acids D141 and C275 are key residues in the tertiary structure of the VWF propeptide. Their replacement with a tyrosine and a serine, respectively, might compromise propeptide folding, affecting both its intracellular survival and its capacity to mediate multimerization. Co-expression of hybrid rVWFs confirmed the recessive inheritance pattern of these missense mutations.

The fibrinogen Aalpha R16C mutation results in fibrinolytic resistance

The fibrinogen Aalpha R16C mutation is a common cause of dysfibrinogenaemia and has been previously associated with both bleeding and thrombosis. However, the mechanism underlying the thrombotic phenotype has not yet been elucidated. This report characterises the defect in fibrinolysis seen as a result of the Aalpha R16C mutation. A young patient with dysfibrinogenaemia (fibrinogen Hershey III) was found to be heterozygous for the Aalpha R16C mutation. Functional assays were performed on the purified fibrinogen to characterise clot formation and lysis with plasmin and trypsin. Consistent with previous results, clot formation was diminished. Unexpectedly, fibrinolysis was also delayed. Plasminogen activation was normal, ruling out decreased plasmin generation as the mechanism behind the fibrinolytic resistance. Western blot analysis showed no difference in the amount of bound alpha2-antiplasmin or albumin. When clot lysis was assayed with trypsin substituted for plasminogen, a significant delay was also observed, indicating that defective binding to plasminogen could not explain the fibrinolytic resistance. These results suggest that the defective fibrinolysis is due to increased proteolytic resistance, most likely reflecting changes in clot structure.

Insights into von Willebrand factor proteolysis: clinical implications

The proteolysis of von Willebrand factor (VWF) by the recently discovered metalloprotease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin repeats), is a normal processing step in VWF biochemistry. Emerging data indicate that this step may be influenced by a variety of factors, some of which favour increased proteolysis and some of which compromise proteolysis. The former may predispose to bleeding, whilst the latter appears to be the underlying mechanism for thrombotic thrombocytopenic purpura (TTP). The new insights support the concept of "risk" in bleeding, particularly in the case of type 1 von Willebrand disease (VWD), in much the same way that risk is considered in venous thrombosis. This review presents relevant current knowledge of VWF proteolysis by ADAMTS13, and a novel model of how this may be implicated in type 1 VWD is proposed, based on events at the vessel wall at a time of haemostatic challenge.

Fibrinogen Mannheim II: a novel gamma307 His-->Tyr substitution in the gammaD domain causes hypofibrinogenemia

BACKGROUND

In recent years it has become clear that the molecular investigation of hypofibrinogenemia provides unique insight into regions of the fibrinogen molecule that are important in molecular assembly, secretion and stability.

OBJECTIVES

To investigate a case of hypofibrinogenemia at the molecular level.

PATIENTS AND METHODS

The study was conducted on a 37-year-old woman from Mannheim, Germany, who had an antigenic plasma fibrinogen concentration of 0.86 g L(-1). Mutation screening was performed by DNA sequencing and the effect of the identified mutation was investigated at the protein level.

RESULTS

Analysis of exon 8 of the fibrinogen gamma gene identified a heterozygous CAT-->TAT transition at codon 307. This novel His-->Tyr substitution was not detected when plasma fibrinogen was analyzed by electrospray ionization mass spectrometry. The mutation predicts a mass increase of 26 Da in the gamma chain, but purified gamma chains had a normal mass, indicating non-expression of the gamma(Tyr307) chain in plasma fibrinogen.

CONCLUSIONS

This work reports a novel gamma307 His-->Tyr mutation (fibrinogen Mannheim II) that causes hypofibrinogenemia. Crystal structures show that His307 is located immediately adjacent to three residues that have been implicated in fibrin polymerization at the D:D interface. However, the histidine residue appears critical in maintaining structure of the fibrinogen gammaD domain, rather than in determining function.

–455G/A β-fibrinogen gene polymorphism, factor V Leiden, prothrombin G20210A mutation and MTHFR C677T, and placental vascular complications

Hyperfibrinogenaemia is associated with systemic arterial and venous thromboembolism and therefore may contribute to placental vascular disease associated with obstetric complications. The fibrinogen-raising -455G/A beta-fibrinogen gene polymorphism may enhance the physiological increase in fibrinogen levels during pregnancy and thereby predispose to obstetric complications. This retrospective case-control study looked at the association between the beta-fibrinogen gene polymorphism -455G/A, the hereditary thrombophilic markers factor V Leiden, prothrombin G20210A mutation (PGM) and C677T methylene tetrahydrofolate reductase (MTHFR), and obstetric complications associated with placental vascular disease. The study group (n = 247) comprised 147 women (90 Caucasian) who met the clinical criteria and a control group of 100 parous women (90 Caucasian) with no history of obstetric or medical complications. No significant differences were observed in the -455A allelic frequencies of the patient and normal control groups, with (allelic frequencies, 0.156 and 0.178, respectively; P = 0.5716, chi2 test, odds ratio = 1.17, 95% confidence interval = 0.65-2.13) or without (allelic frequencies, 0.129 and 0.170, respectively; P = 0.2077, chi2 test, odds ratio = 1.38, 95% confidence interval = 0.81-2.35) the exclusion of non-Caucasian women. There was an increased prevalence of factor V Leiden among Caucasian patients compared with normal controls (allelic frequencies, 0.056 and 0.017, respectively; P = 0.048, chi2 test, odds ratio = 0.29, 95% confidence interval = 0.05-1.15) but there were no differences in the prevalences of PGM or MTHFR. These data suggest that factor V Leiden is associated with an increased risk of obstetric complications, but that the -455A allele of beta-fibrinogen, PGM and MTHFR do not appear to be implicated.

Substitution of the gamma-chain Asn308 disturbs the D:D interface affecting fibrin polymerization, fibrinopeptide B release, and FXIIIa-catalyzed cross-linking

Crystallographic structures indicate that gamma-chain residue Asn308 participates in D:D interactions and indeed substitutions of gammaAsn308 with lysine or isoleucine have been identified in dysfibrinogens with impaired polymerization. To probe the role of Asn308 in polymerization, we synthesized 3 variant fibrinogens: gammaAsn308 changed to lysine (gammaN308K), isoleucine (gammaN308I), and alanine (gammaN308A). We measured thrombin-catalyzed polymerization by turbidity, fibrinopeptide release by high-performance liquid chromatography, and factor XIIIa-catalyzed cross-linking by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the absence of added calcium, polymerization was clearly impaired with all 3 variants. In contrast, at 0.1 mM calcium, only polymerization of gammaN308K remained markedly abnormal. The release of thrombin-catalyzed fibrinopeptide B (FpB) was delayed in the absence of calcium, whereas at 1 mM calcium FpB release was delayed only with gammaN308K. Factor XIIIa-catalyzed gamma-gamma dimer formation was delayed with fibrinogen (in absence of thrombin), whereas with fibrin (in presence of thrombin) gamma-gamma dimer formation of only gammaN308K was delayed. These data corroborate the recognized link between FpB release and polymerization. They show fibrin cross-link formation likely depends on the structure of protofibrils. Together, our results show substitution of Asn308 with a hydrophobic residue altered neither polymer formation nor polymer structure at physiologic calcium concentrations, whereas substitution with lysine altered both.

Two novel fibrinogen variants found in patients with pulmonary embolism and their families

BACKGROUND

The occurrence of dysfibrinogen is quite rare in comparison with other hemostatic defects, specially in cases of venous thrombosis.

OBJECTIVES

Fibrinogen is known to have multiple functions, which are not evaluated by simple coagulation testing. We have used gel electrophoresis to search for new mutations.

PATIENTS AND METHODS

Specimens of purified fibrinogen from 217 consecutive patients with familial or recurrent or early thrombosis and from 490 control subjects were evaluated by electrophoresis. Plasma fibrinogen levels and coagulation-dependent tests (electromechanical and optical coagulometric determinations, immunological measurement, thrombin and Reptilase(R) times) were normal.

RESULTS

Two novel familial variants were detected. For a 42-year-old patient, an in-frame 117 base pair insertion in the Aalpha-chain gene caused a 5-kDa mobility shift of the Aalpha chain. This corresponds to a 39 amino acid duplication in the connector domain (fibrinogen Champagne au Mont d'Or). This pattern was also found in the patient's mother and child. A second 31-year-old patient presented an extra band under non-reducing conditions, 30 kDa larger than HMW fibrinogen and reacting with antifibrinogen antibodies (fibrinogen Lozanne). A heterozygous 5909A-->G mutation was found on the Bbeta-chain gene leading to heterozygous Bbeta Tyr236--> stop codon. The predicted truncated Bbeta chain could participate in chain assembly. Two family members were also affected, one of whom had suffered early venous thrombosis.

CONCLUSIONS

Electrophoretic testing of apparently normal fibrinogens can reveal new variants which may be clinically relevant.

Fibrinogen Magdeburg I: a novel variant of human fibrinogen with an amino acid exchange in the fibrinopeptide A (Aalpha 9, Leu-->Pro)

INTRODUCTION

The exchange of Aalpha 16, Arg for Cys or His is the most common molecular defect in dysfibrinogenemia directly affecting the thrombin cleavage site involved in fibrinopeptide A (FPA) release. Other amino acid exchanges within the fibrinopeptide A have been only rarely reported.

MATERIALS AND METHODS

In clinically asymptomatic dysfibrinogenemic patients with low functional plasma fibrinogen (Fg) levels and prolonged thrombin time but normal or slightly prolonged batroxobin (reptilase) time, mutation analysis was carried out by direct sequencing of the coding regions of the three fibrinogen genes. Isolated fibrinogen was functionally characterized for thrombin- or batroxobin-induced fibrinopeptide release and fibrin formation. Fibrinogen and fibrinopeptides were structurally studied by electrophoretic techniques or high-performance liquid chromatography.

RESULTS AND CONCLUSIONS

Molecular analysis revealed heterozygosity for a novel missense mutation T1182C in the FGA gene causing the amino acid exchange Aalpha 9, Leu-->Pro. Fibrin generation induced by thrombin was moderately impaired, whereas batroxobin-induced fibrin formation was almost normal. Release of the abnormal fibrinopeptide A by thrombin was delayed but fibrin monomer aggregation was almost normal. Cleavage of Aalpha chains by batroxobin was only slightly delayed. Fibrinopeptides A of the patient fibrinogen did not show any gross abnormality in chromatographic behaviour. This new molecular variant designated fibrinogen Magdeburg I supports the view that amino acid residue Leu-9 in the Aalpha chain as part of a small hydrophobic cluster is involved in the interaction with an apolar binding site of thrombin, thus adding to our understanding of the thrombin-fibrinogen interaction crucial in coagulation.

Human plasma fibrinogen measurement derived from activated partial thromboplastin time clot formation

Prothrombin time-derived measurement of fibrinogen (PTd) has already been described. Activated partial thromboplastin time-derived measurement of fibrinogen (aPTTd) has not yet been clearly defined. Using an MDA II coagulometer (Organon Teknika, Durham, North Carolina, USA), we have therefore compared fibrinogen levels determined with Clauss, PTd, and aPTTd assays and an enzyme immunoassay (EIA) in 172 samples. Of these, 47 were from pre-operative controls, 18 from patients with liver disease, 28 from patients with hyperfibrinogenaemia, 33 from patients treated with vitamin K antagonists, 22 from patients treated with unfractionated heparin and 24 from haemophilic patients. Within the normal range, interassay and intra-assay variations were comparable. For control samples, PTd, aPTTd and Clauss assays were well correlated, without any systematic error. EIA was also correlated but values were slightly higher (mean of difference = 0.24). Pathological samples showed an overestimation of fibrinogen when using PTd measurements in patients treated with vitamin K antagonists, as well as when using aPTTd measurements in patients presenting with factor VIII and factor IX deficiencies. These results indicate that, despite expected financial savings, aPTTd fibrinogen measurements should not be used without restriction. PTd and aPTTd fibrinogen determinations are provided without any additional cost. Their comparison with Clauss fibrinogen results may constitute a validation tool or have additional diagnostic utility (e.g. identifying polymerization abnormalities in case of dissimilar results).

Molecular genetics of type 2 von Willebrand disease

Type 2 von Willebrand disease (VWD) is characterized by a wide heterogeneity of functional and structural defects. These abnormalities' cause either defective von Willebrand factor (VWF)-dependent platelet function in subtypes 2A, 2B, and 2M or defective VWF-factor VIII (FVIII) binding in subtype 2N. The diagnoses of types 2A, 2B, and 2M VWD may be guided by the observation of disproportionately low levels of ristocetin cofactor activity or collagen-binding capacity relative to VWF antigen. The abnormal platelet-dependent function is often associated with the absence of high molecular weight (HMW) multimers (type 2A, type 2B), but the HMW multimers may also be present (type 2M, some type 2B), and supranormal multimers may exist ("Vicenza" variant). The observation of a low FVIII-to-VWF:Ag ratio is a hallmark of type 2N VWD. in which the FVIII levels depend on the severity of the FVIII-binding defect. Today, the identification of mutations in particular domains of the pre-pro-VWF is helpful in classifying these variants and providing further insight into the structure-function relationship and the biosynthesis of VWF. Thus, mutations in the D2 domain, involved in the multimerization process, are found in patients with type 2A, formerly named IIC VWD. Mutations located in the D' domain or in the N terminus of the D3 domain define type 2N VWD. Mutations in the D3 domain characterize Vicenza and IIE patients. Mutations in the A1 domain may modify the binding of VWF multimers to platelets, either increasing (type 2B) or decreasing (type 2M, 2A/2M) the affinity of VWF for platelets. In type 2A VWD, molecular abnormalities identified in the A2 domain, which contains a specific proteolytic site, are associated with alterations in folding, impairing VWF secretion or increasing its susceptibility to proteolysis. Finally, a mutation localized in the carboxy-terminus CK domain, which is crucial for the dimerization of the VWF subunit, has been identified in a rare subtype 2A, formerly named IID.

End-linked homodimers in fibrinogen Osaka VI with a Bβ-chain extension lead to fragile clot structure

The authors have identified a 12-residue carboxyl-terminal extension of Lys-Ser-Pro-Met-Arg-Arg-Phe-Leu-Leu-Phe-Cys-Met in a dysfibrinogen derived from a woman heterozygotic for this abnormality and associated with severe bleeding. This extension is due to a T-to-A mutation that creates AAG encoding Lys at the stop (TAG) codon, thus translating 36 base pairs in the noncoding region of the Bβ gene. The extra Cys residues appear to be involved in 1 or 2 disulfide bonds between 2 adjacent abnormal fibrinogen molecules, forming a fibrinogen homodimer as indicated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Indeed, about half of the fibrinogen molecules exist as end-linked dimers oriented in parallel or with an angle, as observed by transmission electron microscopy. These end-linked dimers may well alter the conformations of D and DD regions on fibrin assembly, leading to increased fiber branching at their sites in the growing protofibrils. By scanning electron microscopy, the Osaka VI fibrin network appears to have a lacelike structure composed of highly branched, thinner fibers than the normal fibrin architecture. Such fibrin networks may be easily damaged to form large pores when fluids are allowed to pass through the gels. The fragility of Osaka VI fibrin clots, further confirmed by permeation and compaction studies, may account for the massive bleeding observed in this patient.

End-linked homodimers in fibrinogen Osaka VI with a Bβ-chain extension lead to fragile clot structure

The authors have identified a 12-residue carboxyl-terminal extension of Lys-Ser-Pro-Met-Arg-Arg-Phe-Leu-Leu-Phe-Cys-Met in a dysfibrinogen derived from a woman heterozygotic for this abnormality and associated with severe bleeding. This extension is due to a T-to-A mutation that creates AAG encoding Lys at the stop (TAG) codon, thus translating 36 base pairs in the noncoding region of the Bβ gene. The extra Cys residues appear to be involved in 1 or 2 disulfide bonds between 2 adjacent abnormal fibrinogen molecules, forming a fibrinogen homodimer as indicated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Indeed, about half of the fibrinogen molecules exist as end-linked dimers oriented in parallel or with an angle, as observed by transmission electron microscopy. These end-linked dimers may well alter the conformations of D and DD regions on fibrin assembly, leading to increased fiber branching at their sites in the growing protofibrils. By scanning electron microscopy, the Osaka VI fibrin network appears to have a lacelike structure composed of highly branched, thinner fibers than the normal fibrin architecture. Such fibrin networks may be easily damaged to form large pores when fluids are allowed to pass through the gels. The fragility of Osaka VI fibrin clots, further confirmed by permeation and compaction studies, may account for the massive bleeding observed in this patient.

Difference in electrophoretic mobility and plasmic digestion profile between four recombinant fibrinogens, gamma 308K, gamma 308I, gamma 308A, and wild type (gamma 308N)

We have produced recombinant gamma-chain variant fibrinogens, gamma308K, gamma308I, and gamma308A simultaneously with wild-type fibrinogen, gamma-308N, by genetic protein engineering using Chinese hamster ovary cells. Although all three variant fibrinogens are a result of a single amino acid substitution, the aberrant gamma-chains of gamma308K and gamma308I fibrinogens migrated faster than gamma308N. Furthermore, plasmic digestion profiles were examined in the presence of 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or 1 mM CaCl2. In the presence of EGTA, the three variant fibrinogens were digested into D1 and D2 fragments slightly faster than wild type. In addition, the D2 fragment derived from gamma308K was further digested into D3 by plasmin much faster than that from gamma308N. These data suggest that cleavage of gamma356Lys-gamma357Ala bond by plasmin in gamma308K, gamma308I, and gamma308A is slightly accelerated and the gamma302Lys-gamma303Phe bond is cleaved by plasmin rapidly in only the gamma308K variant. Furthermore, the substitution of Lys for gamma308Asn results in the generation of a new plasmin cleavage site between gamma308Lys and gamma309Gly in the presence of EGTA. In conclusion, a substitution at residue gamma308Asn may cause a conformational change in the gammachain of fragment D affecting polymerization and plasmin cleavage.

Identification of a dysfibrinogen, the substitution of gamma308Asn(AAT) to Lys(AAG), using coagulation tests, immunoblot analysis, and allele-specific polymerase chain reaction

During the past 3 years, we encountered 12 new cases suspected of being dysfibrinogenemias, via plasma coagulation screening tests, which included determination of fibrinogen concentration both by thrombin time and immunologic methods. We performed sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions and immunoblot analysis for these plasma fibrinogens. We identified two cases that were characterized by two distinct gamma-chain bands, similar to previous observations with Matsumoto-II (the substitution of gamma308Asn to Lys). Therefore, in order to identify the gamma308Lys variant easily and rapidly, we established an allele-specific polymerase chain reaction (AS-PCR). AS-PCR results indicated that the two cases were indeed heterozygous for the gamma308Lys variant; ten other cases were negative for this mutation. In conclusion, the ratio of fibrinogen concentrations determined by functional and antigenic methods in combination with the immunoblot analysis made these cases attractive for identifying the gamma308Lys mutation. The AS-PCR method proved to be a useful procedure to identify the gamma308K mutation.