1/144. Fibrinogen St. Gallen I (gamma 292 Gly--> Val): evidence for structural alterations causing defective polymerization and fibrinogenolysis. Fibrinogen St. Gallen I was detected in an asymptomatic Swiss woman. Routine coagulation tests revealed a prolonged thrombin and reptilase time. Functionally measured fibrinogen levels were considerably lower than those determined immunologically. polymerization of fibrin monomers derived from purified fibrinogen was delayed in the presence of either calcium or EDTA. Normal fibrinopeptide a and B release by thrombin was established. An abnormal degradation of fibrinogen St. Gallen I by plasmin was observed. Fragment D1 of normal fibrinogen was fully protected against further proteolysis in the presence of 10 mM calcium, whereas fibrinogen St. Gallen I was partially further degraded to fragments D2 and D3. In the presence of 10 mM EDTA, the conversion of variant fragment D1 to D2 was accelerated whereas the degradation of fragment D2 to D3 was delayed in comparison to degradation of fragments D1 and D2 of normal fibrinogen. Three high-affinity calcium binding sites were found in both normal and variant fibrinogen. mutation screening with SSCP analysis suggested a mutation in exon VIII of the gamma-chain gene. Cycle sequencing of this gene portion revealed a single base substitution from G to T of the base 7527, leading to replacement of gamma 292 glycine by valine. The same mutation has already been described for the fibrinogen variant baltimore I. Molecular modeling was performed of a part of the gamma-chain containing the mutation site, based on recently published X-ray crystal structures of human fibrinogen fragment D and of a 30 kD C-terminal part of the gamma-chain. Significant structural alterations due to the substitution of glycine by valine at gamma 292 were observed, e.g. spreading of the protein backbone, probably leading to a modified accessibility of the plasmic cleavage sites in the gamma-chain at 356 Lys and 302 Lys. A shift of gamma 297 Asp that is involved in interactions of fragment D with the Gly-Pro-Arg-Pro-peptide was noted by molecular modeling. The latter observation is compatible with delayed polymerization of fibrin monomers. ( info) |
2/144. Bilateral vitreous hemorrhages in an infant with low fibrinogen levels. The finding of retinal or vitreous hemorrhage in a child under age 3 years may cause significant controversy with regard to the etiology, because it raises the suspicion of nonaccidental injury. blood dyscrasias have been documented to cause retinal and vitreous hemorrhages in adults and children, but they have rarely been reported to be the cause of retinal hemorrhages in neonates. We report on a patient with a low plasma fibrinogen level who had bilateral retinal hemorrhage that proceeded to vitreous hemorrhage. This subtle abnormality of the blood clotting cascade caused significant retinal and vitreous hemorrhage in a child without risk factors for abuse. ( info) |
3/144. Recurrent spontaneous intracerebral hemorrhage in a congenitally afibrinogenemic patient: diagnostic pitfalls and therapeutic options. BACKGROUND: Coagulation disorders can cause intracerebral bleeding that may be difficult to detect since subsequent aberrant clot formation may mask early detection. This is an important pitfall because, when diagnosed early, bleeding in these patients is treatable. CASE DESCRIPTION: A patient with congenital afibrinogenemia presented with recurrent hemiparesis. Spontaneous intracerebral hemorrhage was diagnosed, despite an initial negative CT scan. diagnosis, therapy, and complications of therapy are discussed. CONCLUSIONS: Intracerebral hemorrhage must be strongly suspected in any patient with a coagulation disorder presenting with matching clinical symptoms. Therapy must be installed immediately, before additional investigations, and should be continued even when initial neuroimaging is negative. ( info) |
4/144. Hypofibrinogenemia associated with a heterozygous missense mutation gamma153Cys to arg (Matsumoto IV): in vitro expression demonstrates defective secretion of the variant fibrinogen. We genetically analyzed a case of hypofibrinogenemia that showed no bleeding or thrombotic tendency. Direct sequencing of a polymerase chain reaction-amplified gamma-chain gene segment showed a novel nucleotide substitution. This heterozygous mutation encodes both Cys (TGT) and Arg (CGT) at residue 153. To examine the basis for the fibrinogen deficiency, we prepared expression vectors containing mutant gamma-chain DNAs encoding gamma153R and gamma153A for in vitro expression in Chinese hamster ovary (CHO) cells. enzyme-linked immunosorbent assay and immunoblot analysis of the culture media and cell lysates showed that cho cells transfected with gamma153R or gamma153A synthesized the variant gamma-chain, but did not secrete variant fibrinogen into the culture medium. Metabolic pulse-chase experiments showed that fibrinogen assembly was impaired when either variant gamma-chain was expressed. In cells expressing normal fibrinogen, assem- bly intermediates and intact fibrinogen were seen in cell lysates prepared after short (3 minutes) or long (1 hour) incubation with (35)S-methionine. Neither intermediates nor intact fibrinogen was seen with the variant gamma-chains. These data suggest that gamma-chains have an important early role in fibrinogen assembly. Thus, our results support the model for fibrinogen assembly proposed by Huang et al (J Biol Chem 268:8919, 1993), in which the first step in assembly is the formation of alphagamma or betagamma dimers, or both. This model implies that gammaCys153 has a critical role in the formation of these early assembly intermediates. We concluded that the gamma153Cys-->Arg substitution does not allow fibrinogen assembly and secretion, and this is manifest in vivo as a fibrinogen deficiency. We designated this variant as fibrinogen Matsumoto IV. ( info) |
5/144. Missense mutations in the human beta fibrinogen gene cause congenital afibrinogenemia by impairing fibrinogen secretion. Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by bleeding that varies from mild to severe and by complete absence or extremely low levels of plasma and platelet fibrinogen. Although several mutations in the fibrinogen genes associated with dysfibrinogenemia and hypofibrinogenemia have been described, the genetic defects of congenital afibrinogenemia are largely unknown, except for a recently reported 11-kb deletion of the fibrinogen Aalpha-chain gene. Nevertheless, mutation mechanisms other than the deletion of a fibrinogen gene are likely to exist because patients with afibrinogenemia showing no gross alteration within the fibrinogen cluster have been reported. We tested this hypothesis by studying the affected members of two families, one Italian and one Iranian, who had no evidence of large deletions in the fibrinogen genes. Sequencing of the fibrinogen genes in the 2 probands detected 2 different homozygous missense mutations in exons 7 and 8 of the Bbeta-chain gene, leading to amino acid substitutions Leu353Arg and Gly400Asp, respectively. Transient transfection experiments with plasmids expressing wild-type and mutant fibrinogens demonstrated that the presence of either mutation was sufficient to abolish fibrinogen secretion. These findings demonstrated that missense mutations in the Bbeta fibrinogen gene could cause congenital afibrinogenemia by impairing fibrinogen secretion. (blood. 2000;95:1336-1341) ( info) |
6/144. Hypofibrinogenemia in an individual with 2 coding (gamma82 A-->G and Bbeta235 P-->L) and 2 noncoding mutations. We investigated the molecular basis of hypofibrinogenemia in a man with a normal thrombin clotting time. Protein analysis indicated equal plasma expression of 2 different Bbeta alleles, and dna sequencing confirmed heterozygosity for a new Bbeta235 P-->L mutation. Protein analysis also revealed a novel gamma(D) chain, present at a ratio of 1:2 relative to the gamma(A) chain. mass spectrometry indicated a 14 d decrease in the gamma(D)-chain mass, and dna sequencing showed this was caused by a novel gamma82 A-->G substitution. dna sequencing established heterozygosity for 2 further mutations: T-->C in intron 4 of the Aalpha gene and A-->C in the 3' noncoding region of the Bbeta gene. Studies on the man's daughter, together with plasma expression levels, discounted both the Aalpha and Bbeta mutations as the cause of the low fibrinogen, suggesting that the gamma82 mutation caused the hypofibrinogenemia. This was supported by analysis of 31 normal controls in whom the Bbeta mutations were found at polymorphic levels, with an allelic frequency of 5% for the Bbeta235 mutation and 42% for the Bbeta 3' untranslated mutation. The gamma82 mutation was, however, unique to the propositus. Residue gamma82 is located in the triple helix that separates the E and D domains, and aberrant packing of the helices may explain the decreased fibrinogen concentration. (blood. 2000;95:1709-1713) ( info) |
7/144. Prenatal and peripartum management of congenital afibrinogenaemia. We experienced three cases and four successful deliveries with congenital afibrinogenaemia and propose the following guidelines for the prenatal and peripartum management: (i) genital bleeding usually begins at 5 weeks' gestation and spontaneous abortion always occurs at 6-8 weeks' gestation without fibrinogen infusion; (ii) the fibrinogen level must be at least 0.60 g/l and, if possible, higher than 1.0 g/l during the pregnancy; (iii) the necessary amounts of fibrinogen increase as the pregnancy progresses and the preterm labour occurs; (iv) the fibrinogen level under the continuous infusion of fibrinogen during labour must be at least 1.5 g/l and, if possible, higher than 2.0 g/l to prevent placental abruption; (v) the puerperium is usually uneventful with a reduced dose of fibrinogen infusion. ( info) |
8/144. Fibrinogen brescia: hepatic endoplasmic reticulum storage and hypofibrinogenemia because of a gamma284 Gly-->Arg mutation. The proposita suffered from liver cirrhosis and biopsy showed type 1 membrane-bound fiberglass inclusions. The hepatic inclusion bodies were weakly periodic acid-Schiff diastase-positive, and on immunoperoxidase staining reacted specifically with anti-fibrinogen antisera. Coagulation investigations revealed low functional and antigenic fibrinogen together with a prolonged thrombin time of 37 seconds (normal, 17 to 22 seconds) suggestive of a hypodysfibrinogenemia. dna sequencing of all three fibrinogen genes showed a single heterozygous mutation of GGG (Gly)-->CGG (Arg) at codon 284 of the gamma-chain gene. However, examination of purified fibrinogen chains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, reverse-phase high-performance liquid chromatography, ion-exchange high-performance liquid chromatography, and isoelectric focusing, failed to show any evidence of the mutant gamma(Br) chain in plasma fibrinogen. This finding was substantiated by electrospray ionization mass spectrometry, which showed only a normal gamma (and Bbeta) chain mass, but a large increase in the portion of their disialo isoforms. We speculate that misfolding of the variant protein causes hepatic retention and the subsequent hypofibrinogenemia, and that the functional defect (dysfibrinogenemia) results from hypersialylation of otherwise normal Bbeta and gamma chains consequent to the liver cirrhosis. These conclusions were supported by studies on six other family members with hypofibrinogenemia, and essentially normal clotting times, who were heterozygous for the gamma284 Gly-->Arg mutation. ( info) |
9/144. Homozygous truncation of the fibrinogen A alpha chain within the coiled coil causes congenital afibrinogenemia. The molecular basis of a novel congenital afibrinogenemia has been determined. The proposita, the only affected member in a consanguineous Norwegian family, suffers from a moderate to severe bleeding disorder due to the total absence of any detectable fibrinogen. Dot blots of solubilized platelets revealed a small amount of gamma chain but no A alpha or B beta chains, whereas no chains were detected in plasma dot blots. dna sequencing of the A alpha chain gene revealed a homozygous C-->T transversion 557 nucleotides from the transcription initiation site. This nucleotide change predicts the nonsense mutation A alpha 149 Arg (CGA)-->stop (TGA). Early truncation of the A alpha chain appears to result in defective assembly or secretion of fibrinogen, probably due to the removal of the C-terminal disulfide ring residues that are critically required for the formation of a stable 3-chained half molecule. (blood. 2000;96:773-775) ( info) |
10/144. A case of congenital afibrinogenemia: fibrinogen Hakata, a novel nonsense mutation of the fibrinogen gamma-chain gene. Congenital afibrinogenemia due to a novel homozygous nonsense mutation of the fibrinogen gamma-chain gene, fibrinogen Hakata, was found in an 18-year-old Japanese girl who had received supplemental fibrinogen therapy since she was 4 months old. The plasma fibrinogen concentrations of the proband were measured as less than 10 mg/dl by a functional method and less than 17 mg/dl by an immunological method. Fibrinogen concentrations of her family were in the range of 94-164 mg/dl. The proband and her family had no other clinical symptoms. Genomic dna of the proband and her family was isolated from leukocytes, and all exons of fibrinogen subunits and their intron/exon boundaries were analyzed. A genetic mutation, a guanine-to-thymine (G-to-T) transversion at the nucleotide position of 5860, was identified on exon 7 of the gamma-chain gene. This mutation changed the codon for the 231st residue of the gamma-chain from GAG (Glu) to TAG (stop). No other mutation was observed. Aalpha, Bbeta and gamma chains were observed in plasma of the heterozygous family members. However, only a trace amount of Aalpha chain and no gamma chain was detected in the plasma of the proband. ( info) |