1/27. Induction of immune tolerance and suppression of anaphylaxis in a child with haemophilia B by simple plasmapheresis and antigen exposure.anaphylaxis to factor IX (FIX) in patients with haemophilia B is a rare and life-threatening complication that has been reported to occur in association with the development of inhibitors to FIX. Management of these patients is difficult. This report presents an 18-month-old boy with a frame-shift mutation of the FIX gene and FIX coagulant level of <1% who developed anaphylactoid reactions to low and high purity plasma-derived FIX concentration infusions and an inhibitor measuring 1.0 BU mL(-1). The patient was managed with simple plasmapheresis, a short course of corticosteroids and high-dose antigen exposure, which successfully induced long-lasting immune tolerance to FIX concentrates.- - - - - - - - - - ranking = 1keywords = antigen (Clic here for more details about this article) |
2/27. DDAVP (desmopressin; 1-deamino-cys-8-D-arginine-vasopressin) treatment in children with haemophilia B.We tested the response to desmopressin (1-deamino-cys-8-D-arginine-vasopressin; DDAVP) in four patients with haemophilia B [factor IX (F IX) at diagnosis 1.4-5%]. The activated partial thromboplastin time (aPTT) was significantly shortened in all patients. Although there was an up to 1.4-fold increase in F IX levels in three patients, maximal F IX activity remained below 10%. Much more prominent were the increases in F VIII (three- to fourfold), in von willebrand factor antigen (VWF:Ag; 2.5-fold) and particularly in VWF collagen-binding activity (VWF:CBA; fivefold). These changes were reflected by the prophylactic efficacy of DDAVP for dental surgery. After pretesting, DDAVP could be a useful drug for reducing the need for plasma products for prevention of minor surgical bleeding in patients with mild to moderate haemophilia B.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
3/27. Combined factor VIII and IX deficiency in a family.A family with combined deficiency of factor VIII and factor IX is reported. family study showed that the father and his nephew had mild factor VIII deficiency with normal von willebrand factor antigen and factor IX levels while his two sons had a reduced level of factor IX and normal factor VIII levels. His wife was found to have marginally reduced factor IX levels, whereas his daughter had reduced or normal levels of both factors VIII and IX. dna analysis using the intra- and extragenic markers of factor VIII and IX genes showed that mother is a carrier of haemophilia B and the daughter is a carrier for both haemophilia A and B. Thus, the combined deficiency observed was due to a chance association of two distinct genetic defects.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
4/27. Functional analysis of the EGF-like domain mutations Pro55Ser and Pro55Leu, which cause mild hemophilia b.We studied the functional role of two mutations, Pro55Ser and Pro55Leu, located in the N-terminal epidermal growth factor-like domain (EGF1) of coagulation factor (F) IX. Both mutations cause mild hemophilia b with habitual FIX coagulant activities of 10-12% and FIX antigen levels of 50%. We found that activation by FVIIa/TF and FXIa was normal for FIXPro55Ser, but resulted in proteolysis of FIXPro55Leu at Arg318-Ser319 with a concomitant loss of amidolytic activity, suggesting intramolecular communication between EGF1 and the serine protease domain in FIX. This was further supported by experiments using an anti-EGF1 monoclonal antibody. Activation of FX by FIXaPro55Ser was impaired in both the presence and the absence of phospholipid or FVIIIa, indicating that Pro55 is not directly involved in binding to FVIIIa. We also studied the effect of the two Pro55 mutations on Ca2 affinity and found only small changes. Thus, the Pro55Ser mutation causes hemophilia primarily through to an impaired ability to activate FX whereas at least in vitro the Pro55Leu defect interferes with the activation of FIX.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
5/27. hemophilia b caused by five different nondeletion mutations in the protease domain of factor IX.Factor IX is a multidomain protein and is the proenzyme of a serine protease, factor ixa, essential for hemostasis. In this report, we describe the molecular basis of hemophilia b (deficiency of factor IX activity) in five patients who have neither deletions nor rearrangements of the factor IX gene. By enzymatic amplification and sequencing of all exons and promoter regions, the following causative mutation in the protease domain of factor IX was identified in each patient: IXSchmallenberg: nucleotide 31,215G T, Ser365Ile; IXVarel: nucleotide 31,214A G, Ser365Gly; IXMechtal: nucleotide 31,211G C, Asp364His; IXDreihacken: nucleotide 30,864G A, Arg248Gln; and IXMonschau: nucleotide 30,855A T, Glu245Val. In IXVarel, nucleotide 31,213T was also replaced by C, which results in a silent mutation (GAT GAC) at Asp-364. Thus, this patient has a double base-pair substitution of TA to CG at nucleotides 31,213 and 31,214 but only a single amino acid change of Ser-365 to Gly. This patient also developed an antibody to factor IX during replacement therapy, which suggests that deletion of the factor IX gene is not necessary for development of the antibody in hemophilia b patients. The levels of plasma factor IX antigen in the patients ranged from 40% to 100% except for IXDreihacken (Arg248Gln), in which case it was approximately 4% of normal. The Ser365Gly and Ser365Ile mutants are nonfunctional because of lack of the active site serine residue. Mutant Asp364His is inactive because it cannot form the hydrogen bond between the carboxylate group of Asp-364 and the alpha-amino group of Val-181 generated after activation. As observed in other homologous serine proteases, this hydrogen bond is essential for maintaining the correct active site conformation in normal factor ixa (IXaN). Purified Arg248Gln had approximately 41% and Glu245Val had approximately 17% of the activity of normal factor IX (IXN) in a partial thromboplastin time (aPTT) assay. In immunodot blot experiments, the isolated Glu245Val mutant did and the Arg248Gln mutant did not bind to an anti-IXN monoclonal antibody that has been shown previously to inhibit the interaction of factor viiia with factor IXaN. We have recently shown that a high-affinity calcium binding site exists in the protease domain of IXN; among the proposed Ca(2 )-binding ligands is the carboxyl group of Glu-245. Further, a part of the epitope for the above antibody was shown to be contained in the 231 to 265 residue segment of factor IX.(ABSTRACT TRUNCATED AT 400 WORDS)- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
6/27. Characterization of the original Christmas disease mutation (cysteine 206serine): from clinical recognition to molecular pathogenesis. Christmas disease was first reported as a distinct clinical entity in two manuscripts published in 1952. The eponym associated with this disorder, is the surname of the first patient examined in detail and reported by Biggs and colleagues in a paper describing the clinical and laboratory features of seven affected individuals. This patient has severe factor IX coagulant deficiency (less than 0.01 units/ml) and no detectable circulating factor IX antigen (less than 0.01 units/ml). Coding sequence and splice junctions of the factor IX gene from this patient have been amplified in vitro through the polymerase chain reaction (PCR). One nucleotide substitution was identified at nucleotide 30,070 where a guanine was replaced by a cytosine. This mutation alters the amino acid encoded at position 206 in the factor IX protein from cysteine to serine. The non conservative nature of this substitution, the absence of this change in more than 200 previously sequenced factor IX genes and the fact that the remainder of the coding region of this gene was normal, all provide strong circumstantial evidence in favour of this change being the causative mutation in this patient. The molecular characterization of this novel mutation in the index case of Christmas disease, contributes to the rapidly expanding body of knowledge pertaining to Christmas disease pathogenesis.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
7/27. Hereditary deficiency of all vitamin k-dependent procoagulants and anticoagulants.Hereditary combined deficiency of vitamin k-dependent factors is a rare entity. We report a 7-year-old girl of Arab origin with hereditary deficiency of the procoagulants factors II, VII, IX and X and the natural anticoagulants proteins C and S. The patient is the tenth offspring of a consanguinous marriage and presented at 6 weeks with spontaneous intracerebral haemorrhage. Symptoms improved following plasma infusion. A sibling died at 5 d from uncontrollable umbilical bleeding. blood coagulation work-up at 6 years showed: factor II:C (activity) 12 U/dl, factor II:Ag (antigen) 40 U/dl; factor VII:C 12 U/dl; factor IX:C 36 U/dl, factor IX:Ag 57 U/dl; factor x:C 17 U/dl, factor x:Ag 54 U/dl; protein c activity 43 U/dl; protein c:Ag 45 U/dl; protein s:Ag 34 U/dl; levels of factors V:C and VIII:C were normal. Assays of coagulation factors in the parents and five of the siblings were within the normal range. Following acute infection and dilantin therapy procoagulant activity levels were reduced further and were partially increased after vitamin k infusion. Crossed immunoelectrophoresis of prothrombin in the presence of calcium lactate revealed a population of des-carboxyprothrombin. serum vitamin k epoxide levels were undetectable. The data suggest that the defect in our patient stems from abnormal carboxylation of the vitamin k-dependent proteins and that the mode of inheritance is autosomal recessive.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
8/27. Factor IX New london: substitution of proline for glutamine at position 50 causes severe hemophilia b.We describe a novel point mutation in the fourth exon of human factor IX (encoding the first EGF-like domain) in which cytosine is substituted for adenosine at position 10,401, resulting in the substitution of proline for glutamine at position 50 in the polypeptide chain. sequence analysis of all eight exons, all exon-intron junctions, 160 base pairs (bp) of dna 5' to the proposed translation start site, and 60 bp 3' to the translation termination site shows no other difference from the normal factor IX gene, with the exception of a previously described benign polymorphism at position 148 in the protein (Ala Thr). The affected subject has severe hemophilia b with no detectable factor IX activity despite normal factor IX antigen levels. We purified the abnormal factor IX by immunoaffinity chromatography and demonstrated that its activation by factor Xla is markedly delayed compared with normal factor lX. Once activated, the abnormal factor lX binds antithrombin iii in a 1:1 molar ratio, and the activated protein demonstrates catalytic activity, suggesting an intact active site. The mutation creates a new Bst Yl restriction endonuclease cleavage site. Restriction with Bst Yl shows the mutation in maternal dna and offers the possibility of direct carrier status analysis and prenatal diagnosis in kindreds with this mutation. We designate this new mutation factor lXNew london. This is the only reported mutation in the first EGF-like domain that causes severe hemophilia b.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
9/27. Factor IX Chongqing: a new mutation in the calcium-binding domain of factor IX resulting in severe hemophilia b.A Chinese patient with sporadic, severe hemophilia b was found to have a low level of total factor IX antigen (3.5 U/dl), but less apparent antigen in an assay using a calcium-dependent antibody fraction (1.1 U/dl). This suggested a defect in the factor IX Gla domain coded mainly by exon 2 of the factor IX gene. Exon 2 was therefore amplified and sequenced. An A to T substitution was found at nucleotide 6455 of the patient's factor IX gene. This transversion changes the codon for Glu 27 in normal factor IX to a codon for Val. Since Glu 27 becomes an essential Gla residue, the defect should result in altered calcium-binding or calcium-dependent conformation of the patient's factor IX. The introduction of a hydrophobic side chain also appears to affect the hemophilic protein's stability. In leukocyte dna from the patient's mother, the nucleotide sequence of exon 2 was entirely normal. Thus, barring somatic mosaicism within her germ cells, the new mutation occurred in oogenesis of her ovary.- - - - - - - - - - ranking = 0.4keywords = antigen (Clic here for more details about this article) |
10/27. Two factor IX mutations in the family of an isolated haemophilia B patient: direct carrier diagnosis by amplification mismatch detection (AMD).Rapid identification of gene defects allows definite carrier and prenatal diagnosis in virtually every family with haemophilia B. We report a study of the family of an isolated patient. Analysis of all the essential regions of the patient's factor IX gene (promoter, exons, transcript processing signals) revealed two mutations: one C T transition at residue 17762 and another at residue 30890. The former created a translation stop at codon 116, and the latter caused substitution of His 257 by Tyr. The translation stop is an obvious detrimental mutation, while the His 257 Tyr substitution has uncertain functional consequences. From analysis of other family members, it was found that the first mutation had occurred at grandpaternal gametogenesis, in keeping with the negative family history, while the second was of more remote origin and did not reduce the maternal grandfather's factor IX coagulant and antigen level. This neutral mutation (His 257 Tyr) pinpoints a poorly conserved amino acid in factor IX and related serine proteases. Its coexistence with a detrimental mutation stresses the need to examine all essential regions of a gene before attempting to interpret the functional consequences of its sequence changes.- - - - - - - - - - ranking = 0.2keywords = antigen (Clic here for more details about this article) |
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