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A R Giles

Publications and source records attributed to A R Giles.

At least 55 records · Page 3Linked to original sources
PubMed1988

Carrier detection strategy in haemophilia A: the benefits of combined DNA marker analysis and coagulation testing in sporadic haemophilic families.

A province wide study of carrier detection methods in haemophilia A is reported. The principal objective of this project was to compare the relative merits of coagulation testing and DNA marker analysis in carrier diagnosis for a large unselected haemophilic population. Factor VIII:C (F.VIII:C) and von Willebrand factor antigen (vWf:Ag) were measured on plasma samples sent to a central laboratory. Coagulation results were analysed by a logistic regression model of discrimination. Of 91 potential carriers tested, 15% had indeterminate coagulation test carrier probabilities. Two restriction fragment length polymorphisms were analysed in 123 women (42 obligate carriers and 81 potential carriers). The BcII polymorphism within the F.VIII gene and the locus DXS 52, approximately 5 cM (centimorgan) from F.VIII were used as DNA markers. Of the 81 potential carriers tested with RFLP analysis, a carrier diagnosis was achieved in 52%. Studies with the F.VIII intragenic BgII polymorphism in 23 of these families gave no additional information. Thirty-nine potential carriers remained undiagnosed after DNA marker analysis. Twenty-seven of these women were from families with a sporadic case of haemophilia. In this group of 27 women, 14 were found to have high probability carrier estimates derived from their coagulation tests. Combined coagulation and RFLP data was available in 42 potential carriers. Disagreement between DNA and coagulation carrier diagnoses was found in four instances. In each case, the coagulation data resulted in a carrier probability of indeterminate value. This study emphasizes some of the limitations associated with DNA marker linkage analysis as it pertains to haemophilia A carrier detection. Where a previous family history exists and appropriate females are informative for the DNA markers, this type of analysis is very productive. However, large numbers of potential carriers from 'sporadic' haemophilia families were a factor in this project. With this in mind, an optimal service for haemophilia A carrier diagnosis must continue to offer reliable coagulation test probabilities in addition to DNA marker studies.

Blood Coagulation Tests↗
PubMed1988

A detailed morphological evaluation of the evolution of the haemostatic plug in normal, factor VII and factor VIII deficient dogs.

A standardized injury of the nail cuticle of normal, factor VII and factor VIII deficient dogs was used to study the evolution of the morphological changes occurring within the forming and formed haemostatic plug at the site of vascular injury. The morphological changes occurring were documented by light and transmission electron microscopy (TEM). Randomized measurements were made of the distances between adjacent platelets as a function of platelet interdigitation or compaction and the degree of dilatation of the open canalicular system (OCS) was used as an indicator of the degree of platelet activation. Fibrin deposition was noted both in terms of its location and the point in time at which it first appeared. TEM demonstrated major differences between the factor VIII deficient and the normal and factor VII deficient groups. In the normal animals the intermembrane distance showed noticeable changes with the platelets becoming tightly interdigitated at the time bleeding stopped. During the same period the OCS became dilated. These changes, which were not seen in the factor VIII deficient animals, continued until many platelets lost their intracellular content and became balloon cells or ghosts and fibrinous transformation became prominent. Although those events did occur in the factor VII deficient state, each was delayed and resulted in significant differences between the factor VII and normal animals suggesting that the extrinsic pathway may play an important role in initiating the changes noted. The results suggested that the generation of thrombin and/or factor Xa is essential to promote the initial stabilization of the platelet plug as well as initiating its subsequent consolidation by fibrinous transformation.

Animals↗
PubMed1988

Factor VIII-bypassing activity of bovine tissue factor using the canine hemophilic model.

The bleeding disorder of hemophilia A currently treated by replacement therapy of the missing coagulation factor, factor VIII, is frequently complicated by the development of neutralizing antibodies. The therapeutic potential of attenuated forms of the lipid-associated glycoprotein tissue factor, a known initiator of coagulation, was investigated as a factor VIII-by-passing activity. The protein moiety of tissue factor (Apo-TF) was partially purified and exhibited minimal procoagulant activity before relipidation in vitro. In pilot studies, Apo-TF injection into rabbits previously anticoagulated with an antibody to factor VIII was found to have a procoagulant effect. The efficacy of the material was further demonstrated when injection of Apo-TF in hemophilic dogs resulted in a normalization of the cuticle bleeding time. Little or no change in the blood parameters associated with disseminated intravascular coagulation was observed at lower doses, although mild to moderate effects were seen at higher doses. These data suggest a novel role for Apo-TF preparations as a potential therapeutic agent for hemophiliacs with antibodies to factor VIII once the potential thrombogenicity of such materials is evaluated.

Animals↗
PubMed1988

In vivo characterization of recombinant factor VIII in a canine model of hemophilia A (factor VIII deficiency).

Infusion studies of recombinant factor VIII were performed in hemophilic (factor VIII-deficient) animals. Functional activity was determined using a standardized model of bleeding and kinetic characteristics charted by performing assays of factor VIII functional and antigenic activities over time. To obtain an adequate comparison with plasma-derived factor VIII, a crossover study in two animals was performed in which each animal received either recombinant factor VIII or a highly purified plasma-derived factor VIII on day 1 and the alternative three days later (day 4). Both factor VIII preparations were functionally effective with complete correction of the cuticle bleeding time occurring one hour after infusion. The observed recovery was full and close to predicted for both preparations. The survival curves obtained for both functional and antigenic activities for both preparations were virtually identical and within the anticipated range determined from previous experiments using infusions of conventional factor VIII preparations. The plasma half-disappearance time (T 1/2) for recombinant factor VIII and plasma-derived factor VIII was 9.2 and 7.9 hours, respectively. Plasma samples obtained following infusion were subjected to chromatography on Sepharose 4B. The elution profile of factor VIII antigen activity was compared with that obtained with the infusates. A clear shift in profile was observed with the plasma samples, suggesting complexing of the infused factor VIII material with circulating canine von Willebrand factor (vWF). The elution profile of vWF antigen was superimposable, thus providing further evidence in support of this assumption. The study provided evidence that recombinant factor VIII possesses full functional activity in vivo, binds to circulating vWF, and exhibits normal recovery and survival characteristics.

Animals↗
PubMed1987

Use of platelet concentrate in eastern Ontario.

To better understand the reasons for the increasing use of platelet concentrate in Canada, we undertook a 4-month study of platelet concentrate transfusion in six eastern Ontario hospitals in 1985. A total of 4801 units of platelet concentrate were transfused on 687 occasions to 303 patients; the average number of transfusions per patient was 2.3, the average number of units per transfusion 7.0 and the average number of units per patient 15.8. The cardiovascular service used the largest proportion of units (28%), aortocoronary bypass grafting being the most common procedure. The mean pretransfusion platelet count for the medical and oncology services was about 30.0 X 10(9)/L, compared with 155.5 X 10(9)/L for the cardiovascular service. An increment in platelet count 1 hour after transfusion was noted with 238 (75%) of the transfusions for which the data were available; the average increment was 3.4 X 10(9)/L per unit of platelet concentrate transfused. When the data for patients who did not respond were excluded, the average increment was 6.9 X 10(9)/L. Single-donor platelet concentrate was requested for only half of the transfusions to which no response was detected. The current medical literature supports the appropriate use of platelet concentrate in patients with thrombocytopenia due to chemotherapy, but prophylactic platelet transfusion for patients undergoing cardiovascular bypass procedures is being questioned. We advise continued surveillance of the use of these products and re-evaluation of the aims of platelet transfusion therapy.

Blood Transfusion↗
PubMed1987

Carrier detection in the hemophilias.

The subject of carrier detection in the hemophilias has received new impetus in the past several years. Treatment complications arising from clotting factor concentrates have become more evident and earlier prenatal diagnosis and new genetic markers for the clotting factor genes have focused interest on this area. Until now, carrier diagnosis has relied upon standard pedigree analysis and clotting factor assays. The results obtained using these methods are probabilistic, and the coagulation tests are unavoidably influenced by the effects of random X chromosome inactivation and the inherent variability of the methods involved. With the cloning and characterization of both factor IX and factor VIII genes, has come the capability of using gene analysis to diagnose the carrier state. This usually involves the detection of restriction fragment length polymorphisms (RFLPs) and their use as linked markers for the defective clotting factor gene. In hemophilia A, the combined use of three intragenic RFLPs and two closely linked, highly polymorphic extragenic markers will make carrier information available to approximately 90% of kindred. In hemophilia B, phenotypic analysis has been complicated by the more heterogeneous expression of the gene defect. To date, five intragenic and one closely linked RFLP have been reported, as well as two protein polymorphisms detectable by monoclonal antibody immunoassays. With the combined use of these genetic markers it is likely that accurate carrier assignment will be available to more than 80% of hemophilia B families.

Female↗
PubMed1987

Recombination between the factor VIII gene and the DXS52 locus gives the most probable genetic order as centromere-fra(X)-DXS15-DXS52-F8C-telomere.

The linkage relationship between the factor VIII gene (F8C) and the DXS52 locus was examined in 8 families. Two recombinations were identified in 35 informative meioses (Zmax = 5.67; theta = 0.05), one in a family with hemophilia A, the other in a family with the fra(X) syndrome. Based on the latter recombination, the most probable order of loci was determined to be centromere-fra(X)-DXS15-DXS52-F8C-telomere. When these data are added to those reported previously the most probable genetic distance between F8C and DXS52 is 3 cM (Z = 14.62). Identification of these and other recombinations suggests that the use of DXS52 as a genetic marker for carrier detection and prenatal diagnosis of hemophilia A has an error rate between 3-5%.

Chromosome Fragility↗
PubMed1987

Type IIB von Willebrand's disease presenting as thrombocytopenia during pregnancy.

Type IIb von Willebrand's disease has been found to be associated with the development of thrombocytopenia following the infusion of DDAVP (desmopressin). It has also been associated with sporadic thrombocytopenia and evidence of spontaneous platelet aggregation. A family with documented Type IIb von Willebrand's disease is described, where two of the affected females presented with moderate to severe thrombocytopenia developing during pregnancy with reversal to normal or minimally reduced platelet counts in the early post gestational period. In each case, the levels of factor VIII:C, von Willebrand factor antigen and von Willebrand factor ristocetin co-factor activity rose during pregnancy but there were notable discrepancies between the levels of each in any one individual. It is suggested that pregnancy resulted in increased synthesis of the variant form of von Willebrand factor resulting in progressively increasing platelet/variant form von Willebrand factor interaction and subsequent thrombocytopenia. Whether this reflects consumption or sequestration remains uncertain. Although spontaneous platelet aggregation was observed in some family members, the majority did not exhibit this phenomenon. Circulating platelet aggregates could not be detected. Both pregnancies were relatively uneventful and there is no history of unusual bleeding associated with pregnancy in the family. These observations suggest that Type IIb von Willebrand's disease should be considered in the differential diagnosis of thrombocytopenia developing during pregnancy, particularly in those individuals where evidence supporting the diagnosis of immune mediated thrombocytopenia is not forthcoming. Where the diagnosis of Type IIb von Willebrand's disease is established, active intervention other than confinement in a hospital with experience in haemostatic disorders is probably not required as the development of thrombocytopenia does not appear to exert an additive effect on the underlying defect relating to the variant form of von Willebrand's disease.

Female↗
PubMed1987

Carrier detection of haemophilia A using DNA markers in families with an isolated affected male.

The carrier status of women in five families with an isolated haemophilia male was assessed by pedigree analysis, coagulation factor assays and DNA markers. In three families, ten women could be given very low risks of being carriers based on DNA analysis. In two of the families the DNA markers identified the mutation as originating in either the maternal or maternal grandfather's germ cell. Combined DNA and coagulation data suggested that the affected male in a third family was a de novo mutation. DNA analysis of the affected male in another family identified a large deletion of the F8 gene which was present in his mother and three sisters, suggesting that the grandmother was a carrier. A combination of coagulation factor data and DNA marker assessment can determine the carrier status of the majority of females in families with isolated affected haemophilia A males.

DNA↗
PubMed1987

Erythroblast multinuclearity in bone marrow and spleen. Congenital dyserythropoietic anemia-like abnormalities without functional evidence of dyserythropoiesis.

A dyserythropoietic syndrome with coincidental immune thrombocytopenia seen during pregnancy is discussed. The morphological and serological results in this case most resemble type II congenital dyserythropoietic anemia. However, functional evidence of dyserythropoiesis was absent and the patient was not anemic. Splenectomy was performed for the resistant thrombocytopenia and microscopic examination of the spleen showed evidence of extramedullary dyserythropoiesis. The significance of these findings is discussed with regard to the spectrum of recognized dyserythropoietic disorders and the unusual discrepancy between the abnormal morphology and the absence of functional dyserythropoiesis.

Adult↗
PubMed1986

Prolonged thrombocytopenia in post-transfusion purpura (PTP) associated with changes in the crossed immunoelectrophoretic pattern of von Willebrand factor (vWF), circulating immune complexes and endothelial cell cytotoxicity.

A 39-year-old multigravida presented with a platelet count of 2 X 10(9)/112 d after a blood transfusion. The clinical presentation was typical of post-transfusional purpura (PTP). She was successfully managed with intensive plasma exchange with plasma replacement. Replacement with albumin saline was unsuccessful. Elevated levels of immune complexes were detected on presentation but were reduced to normal levels by plasma exchange but were elevated again during relapse. Raised levels of circulating platelet aggregates and platelet-aggregating activity were found during relapse but were absent during remission. Crossed immunoelectrophoresis of vWF showed a left shift suggesting the presence of abnormally high molecular weight multimeric forms. In contrast, multimeric assay of the same samples were within normal limits suggesting that the shift noted on crossed immunoelectrophoresis may have resulted from complexing of vWF with some other components. Immunological studies demonstrated the presence of endothelial cell cytotoxicity and lymphocytotoxicity in the patient's serum. It is concluded that the thrombocytopenia observed in PTP may not occur as a direct result of the immunological event initiating the disorder but rather indirectly via the release of vWF consequent upon endothelial cell damage which, either alone or in combination with another factor, possible immune complexes, induces intravascular platelet aggregation and sequestration. There were significant similarities between the case reported and recent observations in thrombotic thrombocytopenic purpura suggesting that these syndromes may have aetiological factors in common.

Adult↗
PubMed1985

In vivo studies of the role of factor VII in hemostasis.

The effect of both congenital and acquired factor VII deficiency on the cuticle bleeding time (CBT) was evaluated in dogs. The CBT has been previously documented to be a sensitive indicator of factor VIII:C deficiency in hemophilic dogs. Serial CBT determinations were made on normal dogs treated with high-dose warfarin. At 48 hours post-treatment, the CBT was normal, although the factor VII level was less than 1%, whereas the levels of factors II, IX, and X were 44%, 25%, and 17%, respectively. At 120 hours the CBT became abnormal when all vitamin K-dependent clotting factors had dropped to less than 18%. Administration of a plasma concentrate of factors II, IX, and X corrected the CBT, despite the factor VII level remaining at less than 1%. Similar studies in a congenitally factor VII-deficient dog (factor VII less than 2%) confirmed that this deficiency state was not associated with an abnormality of the CBT. Administration of heparin to both normal and factor VII-deficient animals was associated with prolongation of the CBT, but the heparin dose required in the normal animals was substantially higher than in the factor VII-deficient animals. These data do not suggest that factor VII/VIIa has an exclusive role in generating factor Xa, either directly or indirectly, by way of factor IXa generation, in vivo. However, the increase in heparin sensitivity of the factor VII-deficient animals does suggest that factor VII/VIIa may, in some circumstances, present a significant alternative pathway of factor X activation, although the activation pathway involved cannot be determined from the studies performed.

Animals↗
PubMed1984

A platelet release defect induced by aspirin or penicillin G does not increase gastrointestinal blood loss in thrombocytopenic rabbits.

Gastrointestinal blood loss was compared in groups of normal and thrombocytopenic animals treated with medications known to induce qualitative platelet dysfunction. Thrombocytopenia was induced in rabbits by the intraperitoneal injection of busulphan dissolved in polyethylene glycol (PEG) at a dose of 60 mg/kg. Control animals received PEG alone; each group subsequently received daily intravenous injections of penicillin G, aspirin, sodium salicylate or isotonic saline. Mean daily gastrointestinal blood loss was determined by monitoring the appearance of 51Cr radioactivity in the faeces following the administration of 51Cr-labelled erythrocytes prior to the administration of the test and control therapies. The administration of penicillin G was not associated with increased gastrointestinal blood loss in the thrombocytopenic animals as compared with the saline treated thrombocytopenic controls. Platelet aggregation studies confirmed the presence of a mild but significant defect in platelet aggregation. Aspirin produced a more pronounced defect in platelet aggregation but did not induce increased bleeding in the normal animals as compared with the controls, nor did it exacerbate the bleeding in thrombocytopenic animals. Sodium salicylate did not produce an aggregation defect and did not significantly modify gastrointestinal blood loss. It was concluded that drug-induced qualitative platelet dysfunction does not necessarily increase bleeding through intact vessels despite previous evidence of a significant effect on platelet plug formation as monitored by the bleeding time.

Animals↗