Fibrinogen Milano IV, another case of congenital dysfibrinogenemia with an abnormal fibrinopeptide A release (A alpha 16 Arg----His).

An abnormal fibrinogen, denoted as 'fibrinogen Milano IV', has been found in a 36-year-old woman without any bleeding manifestations or thrombotic tendency. Routine coagulation studies revealed prolonged thrombin and reptilase clotting times, very low plasma fibrinogen concentration determined by the functional assay but a normal fibrinogen concentration measured by the immunologic assay. Turbidity curves, measured following addition of thrombin to purified fibrinogen Milano IV, both in presence of calcium or EDTA, were markedly delayed. Release of fibrinopeptide B by thrombin was normal, whereas only half the normal amount of fibrinopeptide A was cleaved. The fibrinopeptide A peak of fibrinogen was preceded by an abnormal fibrinopeptide A*. Both peaks were collected for amino acid analysis which showed an exchange of arginine by histidine in position 16 of the A alpha chain of the fibrinopeptide A*.     

Fibrinogen Marburg: a homozygous case of dysfibrinogenemia, lacking amino acids A alpha 461-610 (Lys 461 AAA-->stop TAA).

In the A alpha-chain gene coding for an abnormal fibrinogen (fibrinogen Marburg) we identified a single base substitution (A-->T) that changes the codon A alpha 461 AAA (Lys) to TAA (Stop). The propositus was found to be homozygous for the mutation, whereas the father and five siblings were heterozygous, and three other siblings contained only the normal sequence. The stop codon at position 461 results in the deletion of the carboxyl-terminal segment A alpha 461-610. Purified fibrinogen Marburg contained an A alpha-chain with a relative molecular weight of approximately 47,000. The FpA release by thrombin was not affected by this deletion, whereas the fibrin polymerization was strongly decreased. The binding of endothelial cells to immobilized fibrinogen Marburg was almost completely abolished compared with normal fibrinogen. Fibrinogen Marburg contained a substantial amount of albumin linked to the fibrinogen molecule by disulfide bonds, and these fibrinogen-albumin complexes were also present in plasma. The plasma fibrinogen concentration of the propositus was measured by three different methods: a functional method (< 0.25 mg/mL), an immunologic method using polyclonal antibodies (0.6 mg/mL), and an immunologic method based on two monoclonal antibodies specific for the amino-terminus and carboxyl-terminus of the A alpha-chain (< 0.05 mg/mL). Using the two immunologic methods, it appeared that only 10% to 15% of the plasma fibrinogen of the heterozygous siblings was abnormal.     

Fibrinogen Kaiserslautern (γ 380 Lys to Asn): a new glycosylated fibrinogen variant with delayed polymerization

An adult woman diagnosed with cerebral thrombosis following a caesarean section was found to have severely prolonged thrombin and reptilase times. Five other family members also had prolonged, but variable, thrombin and reptilase times. Analysis of purified fibrinogen on reducing SDS-PAGE revealed an additional band, in all family members, which migrated immediately below the normal Bβ band. Western blotting indicated that this band was a gamma chain and endoglycosidase-F digestion established that it contained an additional oligosaccharide side chain. Partial acid hydrolysis localized the new oligosaccharide to the C-terminus of the gamma chain. Amplification of this region by PCR and subsequent DNA sequencing demonstrated a single base substitution altering the normal 380 Lys (AAG) codon to Asn (AAT), producing a new Asn-Lys-Thr glycosylation site. The propositus and one other family member were homozygous for this mutation but the remaining four family members were heterozygous. The polymerization of purified fibrin monomers from the propositus was grossly abnormal; however, the polymerization curve was almost normalized by the removal of terminal sialic acid residues. This suggests that the polymerization defect was primarily caused by additional negatively charged sialic acid residues present on the new oligosaccharide. Further analysis of the D domain of purified fibrinogen established that calcium binding to the high affinity site remained unaffected by the bulky carbohydrate side chain or negatively charged sialic acid residues.     

Fibrinogen Kaiserslautern (γ 380 Lys to Asn): a new glycosylated fibrinogen variant with delayed polymerization

An adult woman diagnosed with cerebral thrombosis following a caesarean section was found to have severely prolonged thrombin and reptilase times. Five other family members also had prolonged, but variable, thrombin and reptilase times. Analysis of purified fibrinogen on reducing SDS-PAGE revealed an additional band, in all family members, which migrated immediately below the normal Bβ band. Western blotting indicated that this band was a gamma chain and endoglycosidase-F digestion established that it contained an additional oligosaccharide side chain. Partial acid hydrolysis localized the new oligosaccharide to the C-terminus of the gamma chain. Amplification of this region by PCR and subsequent DNA sequencing demonstrated a single base substitution altering the normal 380 Lys (AAG) codon to Asn (AAT), producing a new Asn-Lys-Thr glycosylation site. The propositus and one other family member were homozygous for this mutation but the remaining four family members were heterozygous. The polymerization of purified fibrin monomers from the propositus was grossly abnormal; however, the polymerization curve was almost normalized by the removal of terminal sialic acid residues. This suggests that the polymerization defect was primarily caused by additional negatively charged sialic acid residues present on the new oligosaccharide. Further analysis of the D domain of purified fibrinogen established that calcium binding to the high affinity site remained unaffected by the bulky carbohydrate side chain or negatively charged sialic acid residues.     

Fibrinogen Chapel Hill II: Defective in reactions with thrombin, factor XIIIa and plasmin

Fibrinogen Chapel Hill II is a hereditary, abnormal fibrinogen which is characterized by poor substrate reactivity toward thrombin, factor XIIIa and plasmin. The patient has a low plasma level of clottable protein with normal antigen concentration, high amounts of fibrinogen related material in serum, and prolonged thrombin and reptilase clotting times. Fibrinopeptide release was decreased with both thrombin and ancrod, indicating that release of fibrinopeptide A from the abnormal fibrinogen was impaired. Sequence analysis indicated that the A peptide was normal. Light scattering indicated that the fibrils formed by thrombin were unusually short and thick. When clotted under crosslinking conditions gamma dimers formed normally but alpha polymer formation was defective. Under conditions which yielded complete plasmin digestion of normal fibrinogen only half of the patient fibrinogen was degraded beyond the fragment X stage. The rate of fibrinopeptide release from patient fragment X and NH2-terminal disulphide knot (N-DSK) was similar to that from the fibrinogen, indicating that the defect was contained within the N-DSK. A simple amino acid substitution could result in a conformational defect in the N-DSK sufficient to perturb the reactions involving thrombin, factor XIIIa and plasmin and also polymerization.     

A novel mutation (deletion of Aalpha-Asn 80) in an abnormal fibrinogen: fibrinogen Caracas VI. Consequences of disruption of the coiled coil for the polymerization of fibrin: peculiar clot structure and diminished stiffness of the clot.

An abnormal fibrinogen was identified in a 10-year-old male with a mild bleeding tendency; several years later, the patient developed a thrombotic event. Fibrin polymerization of plasma from the propositus and his mother, as measured by turbidity, was impaired. Plasmin digestion of fibrinogen and thrombin bound to the clot were both normal. The structure of clots from both plasma and purified fibrinogen was characterized by permeability, scanning electron microscopy and rheological measurements. Permeability of patients' clots was abnormal, although some measurements were not reliable because the clots were not mechanically stable. Consistent with these results, the stiffness of patients' clots was decreased approximately two-fold. Electron microscopy revealed that the patients' clots were very heterogeneous in structure. DNA sequencing of the propositus and his mother revealed a new unique point mutation that gives rise to a fibrinogen molecule with a missing amino acid residue at Aalpha-Asn 80. This new mutation, which would disrupt the alpha-helical coiled-coil structure, emphasizes the importance of this part of the molecule for fibrin polymerization and clot structure. This abnormal fibrinogen has been named fibrinogen Caracas VI.     

Fibrinogen Oviedo I. A new Spanish dysfibrinogenaemia

An abnormal fibrinogen was discovered in the plasma of a clinically asymptomatic woman. Laboratory evaluation of five members of the affected family showed low fibrinogen values in kinetic assays whereas the fibrinogen levels, tested by immunological procedures were normal. The patient's plasma had an inhibitory effect on the thrombin time of normal plasma. The calcium ions totally corrected the thrombin and reptilase times. Either low or high ionic strength prolonged the thrombin time of the proposita's purified fibrinogen. Kinetic analysis of clotting by monitoring transmission at 350 nm showed abnormally slow clotting with thrombin and reptilase. Assays were preformed in whole plasma as well as in purified fibrinogen. A delay in the rate of polymerization was evident when purified patient monomers were compared with those of normals. Immunoelectrophoretic, chromatofocusing, and isoelectrofusing experiments detected neither structural nor immunological abnormalities of fibrinogen. The rate of release of fibrinopeptide A by thrombin, measured by a specific immunoenzymatic method was also normal. HPLC analysis showed normal liberation of fibrinopeptides after prolonged thrombin action. Cross-linking of fibrin by factor XIII and lysis of fibrinogen by plasmin were normal. In view of these results, the defect of this dysfibrinogenemia, designated as Fibrinogen Oviedo I, probably could be due to conformational modifications in the D section of the molecule.     

Fibrinogen "New York"--an abnormal fibrinogen associated with thromboembolism: functional evaluation.

A 54-yr-old woman presented with a 23-yr history of repeated life-threatening thromboembolism. The presence of a qualitatively abnormal fibrinogen was suggested by the demonstration of delayed and incomplete coagulation of plasma or partially purified fibrinogen by thrombin or Reptilase. Two brothers showed a similar in vitro defect but were clinically not affected. The plasma fibrinogen concentration was 0.50-1.64 mg/ml when estimated by heat turbidity, clottability, or immunologic techniques. The serum contained 80-820 mug/ml of unclottable fibrinogen-related materials even after 24 hr exposure to thrombin. The fibrinogen-related material in the serum showed faster anodal mobility an immunoelectrophoresis than that of normal plasma. Immunodiffusion studies with rabbit antihuman fibrinogen antiserum showed lines of identity between control plasma and the patient's plasma and serum. Studies of the kinetics of thrombin action on fibrinogen demonstrated impaired release of fibrinopeptide A and B and defective polymerization of preformed fibrin monomers. The maximum amount of fibrinopeptide A released by exhaustive treatment with thrombin was similar (per milligram protein) for both the patient's and control fibrinogen. This abnormal fibrinogen varient is tentatively designated fibrinogen "New York"; its possible identity with one of the previously described abnormal fibrinogens has not been excluded.     

Fibrinogen Milano. VI: A heterozygous dysfibrinogenemia (A alpha 16 Arg----His) with bleeding tendency

Congenital heterozygous dysfibrinogenemia was diagnosed in a young woman with bleeding tendency. 3 other asymptomatic members of her family (mother and the 2 sisters) had abnormal fibrinogen. The proposita's plasma exhibited prolonged thrombin and reptilase times. Plasma fibrinogen concentration determined by functional assay was 0.3 g/l, whereas immunologic assay revealed normal fibrinogen levels. Turbidity curves, representing the rate of thrombin-induced fibrin formation, were markedly delayed both in the presence and absence of Ca2+. Isoelectric focusing and SDS electrophoresis of reduced fibrinogen showed normal charge and size of the subunit chains. Release of fibrinopeptide B by thrombin was normal, whereas HPLC elution diagrams of fibrinopeptide A showed an abnormal peak A* with a slightly shorter retention time than the normal fibrinopeptide A. The amino acid analysis showed that the arginine in peak A* is replaced by histidine (A alpha 16 Arg----His).     

Dysfibrinogenaemia Characterized by Abnormal Fibrin Monomer Polymerization and Normal Fibrinopeptide A Release

S ummary . Routine testing on plasma from a patient due to undergo a coronary artery bypass graft operation revealed a prolonged thrombin clotting time associated with a normal plasma fibrinogen level when this was determined by a method not dependent upon the rate of fibrin formation. Fibrinogen purified from the patient's plasma by precipitation with β-alanine also gave a prolonged thrombin time and this confirmed the presence of a dysfibrinogenaemia. Increasing calcium chloride concentration, addition of protamine sulphate and decreasing ionic strength all produced a partial correction of the clotting defect. Addition of normal plasma to patient's plasma failed to correct the prolonged thrombin clotting time and a pH dependence of the defect was also observed. Kinetic studies of fibrinopeptide release, using a specific radioimmunoassay, demonstrated no delay in the release of patient fibrinopeptide A. The functional defect was localized as an abnormality in the polymerization of fibrin monomers by studying fibrin monomers prepared and isolated from plasma and from purified fibrinogen solution. An electrophoretic examination of the patient's fibrinogen using both agarose and polyacrylamide gels failed to demonstrate any alteration in mobility or any structural defect associated with the polypeptide chains Aα, Bβ and γ. All seven of the living siblings of the propositus and also his daughter showed no abnormality in any clotting assay. However, because the propositus did not suffer from liver disease it has been assumed that the abnormality is genetic in origin.     

A new congenital abnormal fibrinogen Ise characterized by the replacement of B beta glycine-15 by cysteine

A new case of heterozygous dysfibrinogenemia characterized by the replacement of NH2-terminal amino acid of fibrin beta-chain was found in a 50-year-old man. Despite a prolonged thrombin time, the propositus' fibrinogen had a normal reptilase time with the normal release of fibrinopeptide A. Release of fibrinopeptide B by thrombin was strongly affected, but a very high concentration of thrombin almost completely released fibrinopeptide B with a normal elution pattern on reversed-phase high performance liquid chromatography (HPLC). Lysylendopeptidase-cleavage of purified B beta-chains analyzed on HPLC showed the decrease of one peptide compared with the normal and the appearance of an abnormal peptide peak. These peptides were treated with thrombin and further separated on HPLC. Amino acid sequence analysis of the abnormal peptide demonstrated that B beta glycine-15, NH2-terminus of the fibrin beta-chain, was replaced by cysteine. These findings will be of particular importance because they strongly support the hypothesis that the NH2-terminal portion of the fibrin beta-chain is involved in the polymerization reaction by thrombin. The propositus' daughter and two sisters had the same abnormal fibrinogen. This unique inherited abnormal fibrinogen was designated as fibrinogen Ise. During these studies, we found that a very high concentration of thrombin cleaves not only the A alpha Arg19-Val20 bond but also the COOH-terminal region of alpha-chains, which results in the generation of further degraded alpha-chains with apparent molecular weights of 44,000 or less.     

Fibrinogen Kyoto II, a new congenitally abnormal molecule, characterized by the replacement of A alpha proline-18 by leucine

A new case of heterozygous dysfibrinogenemia characterized by an amino acid replacement in the NH2-terminal region of the fibrin alpha-chain was found in a 27-year-old woman with a bleeding problem. Her one-stage prothrombin time and activated partial thromboplastin time were slightly prolonged, and the purified fibrinogen from this patient had a markedly prolonged thrombin or reptilase time. Release of fibrinopeptides A and B was normal, but the polymerization of fibrin monomers was impaired. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified fibrinogen under the reduced condition showed no abnormalities in the apparent molecular weights of its three chains. Reverse-phase high performance liquid chromatography (HPLC) of the lysylendopeptidase-cleaved purified A alpha-chains showed a decrease in one peptide compared with the normal amount and the appearance of an abnormal peptide peak. These peptides were treated with thrombin and further separated on HPLC. Amino acid sequence analysis of the abnormal peptide indicated that A alpha proline-18, the second residue from the NH2-terminus of the fibrin alpha-chain, was replaced by leucine. The synthetic peptide Gly-Pro-Arg-Pro inhibited both thrombin- and reptilase-induced fibrin aggregation, but Gly-Leu-Arg-Pro showed little or no inhibition under the same conditions. The discovery of this abnormal fibrinogen supports the findings that A alpha proline-18 is important as part of the polymerization site in the NH2-terminus of the fibrin alpha-chain. The propositus' mother had the same abnormal fibrinogen. This unique inherited abnormal fibrinogen was designated as fibrinogen Kyoto II.     

The rate of fibrinopeptide B release modulates the rate of clot formation: a study with an acquired inhibitor to fibrinopeptide B release

An asymptomatic 50-year-old male with a gamma globulin paraprotein was found to have prolonged prothrombin time, activated partial thromboplastin time, and thrombin time but a normal reptilase time. The prolonged clotting times were not the result of a factor deficiency because they were not corrected by the addition of normal plasma. Instead, this patient had an antibody that delayed thrombin-mediated fibrinopeptide B release thereby producing an apparent dysfibrinogenaemia. His isolated IgG prolonged the thrombin clotting time of both normal plasma and fibrinogen. Precincubation of his IgG with fibrinopeptide B, but not with fibrinopeptide A or thrombin, decreased its ability to prolong the thrombin clotting time. The patient's purified IgG but not control IgG delayed thrombin-mediated fibrinopeptide B release from fibrinogen without affecting the release of fibrinopeptide A. These studies define a novel, clinically silent dysfibrinogenaemia due to an antibody that delays thrombin-mediated fibrinopeptide B release from fibrinogen thereby markedly prolonging the clotting times.     

Episodes of increased fibronectin level observed in a patient suffering from recurrent thrombosis related to congenital hypodysfibrinogenaemia (fibrinogen Malmoe)

A study has been conducted in a Swedish patient with severe thrombotic disease and repeated miscarriages related to a hypodysfibrinogenaemia with defective thrombin binding to the abnormal fibrin. The hypodysfibrinogenaemia was found in several members of the family. The patient also had an increased concentration of fibronectin in her plasma at two different occasions. This would appear to be unrelated to the abnormal fibrinogen since a normal concentration of fibronectin has been found in her relatives presenting the same fibrinogen anomaly, and in the patient at two other times. In conclusion, the thrombotic disorder in this patient presenting a congenital hypodysfibrinogenaemia may be explained by the defective thrombin binding to fibrin.     

Fibrinogen Mitaka II: a hereditary dysfibrinogen with defective thrombin binding caused by an A alpha Glu-11 to Gly substitution

A new type of A alpha Glu-11 to Gly substitution has been identified in a congenitally abnormal fibrinogen, fibrinogen Mitaka II, derived from a 14-year-old female suffering from easy bruising since childhood. Plasma of the patient and fibrinogen purified therefrom were found to clot slowly by thrombin but in a normal fashion by ancrod, a thrombin- like snake venom enzyme. The ancrod-clotted fibrin gels were normally solid and turbid, whereas the thrombin-clotted gels were initially fragile and transparent but became gradually normalized during further incubation. On reverse-phase high-performance liquid chromatography, there was an additional peptide group eluted distinctly later than the corresponding normal fibrinopeptide A in the clot-liquor of the patient's samples. Sequence analysis of these aberrant peptides and isolated A alpha chains of the patient's fibrinogen showed that Glu at position 11 of the abnormal A alpha chain had been replaced by Gly. Studies using 125I-labeled thrombin showed that the binding with thrombin was evidently reduced for her fibrinogen and the aberrant fibrinopeptide A as compared with that for the normal controls, indicating that A alpha Glu-11 may be critical for the fibrinogen- thrombin interaction. Indeed, A alpha Glu-11 of fibrinogen has recently been proposed to stabilize the local conformation, including the beta- turn, and to form a salt bridge between its side-chain carboxyl group and the guanidino group of Arg-173 of thrombin based on crystallographic analyses using analogs of fibrinopeptide A complexed with thrombin (Stubb et al, Eur J Biochem 206:187, 1992 and Martin et al, J Biol Chem 267:7911, 1992).     

Acquired dysfibrinogenemia secondary to mithramycin toxicity

A 58-year-old black woman with IgD multiple myeloma developed a hemorrhagic diathesis within 48 hours after receiving mithramycin (20 micrograms/kg/day) for therapy of hypercalcemia. Her coagulation studies were characterized by prolonged prothrombin, partial thromboplastin, thrombin, and reptilase clotting times. Her plasma and partially purified fibrinogen were inhibitory to the clotting of normal plasma and fibrinogen. The patient's isolated fibrinogen showed a normal rate of fibrinopeptide release, but her fibrin monomer aggregation was markedly abnormal. These studies document the development of a dysfibrinogenemia secondary to mithramycin toxicity.     

Fibrinogen Geneva, a new case of A alpha 16 Arg----Cys dysfibrinogenaemia

A new congenital variant of fibrinogen, from which only half the normal amount of fibrinopeptide A can be released by thrombin, was found in three members of a family having no major bleeding or thrombotic tendency. Following carboxamidomethylation of the reduced fibrinogen chains, an abnormal peptide was cleaved by thrombin from the amino terminus of the A alpha-chain (A* alpha 1-19) and isolated by reversed phase high-performance liquid chromatography. Amino acid analysis indicated the presence of carboxymethyl cysteine in this A alpha-chain fragment which in normal fibrinogen is devoid of cysteine. We conclude that fibrinogen Geneva is another fibrinogen variant with the substitution A alpha 16 Arg----Cys.     

Fibrinogen Baltimore II: congenital hypodysfibrinogenemia with delayed release of fibrinopeptide B and decreased rate of fibrinogen synthesis.

A congenital hypodysfibrinogenemia, fibrinogen Baltimore II, was found in a young asymptomatic Caucasian female. Prothrombin, partial thromboplastin, and euglobulin lysis times were normal, as were platelet function and coagulation factor assays. Subnormal plasma fibrinogen levels were found using chronometric, rate-independent, and immunologic assay methods. Kinetic analysis of fibrinopeptide release revealed a delay in the thrombin-catalyzed release of fibrinopeptide B from the abnormal protein. Proteolysis of fibrinopeptide A by thrombin or Arvin, fibrin monomer polymerization, and fibrin polymer ligation occurred at normal rates. Catabolism of radiolabeled autologous and homologous fibrinogen was also normal, but the fibrinogen synthetic rate was less than half the normal value. Comparison of the coagulation characteristics of fibrinogen Baltimore II with those of other abnormal fibrinogens indicates that it represents a unique example of hypodysfibrinogenemia.     

Inhibitor of the thrombin time in systemic amyloidosis: a common coagulation abnormality

Patients with primary systemic amyloidosis (AL) often experience bleeding, and we report a newly recognized coagulation abnormality in AL. Of 103 patients with primary systemic AL studied over 2 years, 41 had prolongation of the thrombin time (range, 25 to 46 seconds; normal, less than 22 seconds) and reptilase time (range, 17 to 39 seconds; normal, 14 to 16 seconds). The fibrinogen from the plasma of 36 patients was precipitated by beta-alanine and diluted to a concentration of approximately 200 mg/dL. The thrombin times of the precipitated fibrinogens were normal in 34 patients, implying that an inhibitor was responsible for the abnormal tests. The addition of patient fibrinogen-free plasma to normal plasma prolonged the thrombin times, and this result confirmed the presence of an inhibitor. The inhibitor is more likely to be present in patients with nephrotic syndrome (20 of our patients) and congestive heart failure (six). A circulating monoclonal protein (24 patients), the presence of amyloid liver involvement (eight), and the presence of amyloid neuropathy (nine) were not predisposing factors. Only one patient had deficiency of factor X. We conclude that inhibition of fibrinogen conversion to a fibrin clot rather than dysfibrinogenemia is the cause of the prolonged thrombin time in primary systemic AL.