scholarly journals Thromboxane A2 Deficit Diagnosis in a Patient with Suspicion of Von Willebrand Disease

2021 ◽  
pp. 1-4
Author(s):  
Francisco Jaramillo ◽  
Esteban Echeverri-Fernandez ◽  
Maria Juliana Varela ◽  
Francisco Jaramillo
Keyword(s):  
Platelet Aggregation ◽  
Coagulation Factor ◽  
Thromboxane A2 ◽  
Von Willebrand Disease ◽  
Severe Bleeding ◽  
Augmentation Mammoplasty ◽  
Normal Platelet ◽  
Platelet Disorder ◽  
Platelet Signaling ◽  
High Level

Thromboxane A2 receptor deficiency is a qualitative platelet disorder that partially impedes adequate platelet signaling and aggregation. Generally, these patients have mild hemorrhagic manifestations in basal conditions, but may show severe bleeding when faced with a hemostatic challenge. We present the case of a 30-year-old female patient that arrives at the Hematology service with an undiagnosed bleeding disorder. She presented hemorrhagic complications during an augmentation mammoplasty and during an exodontia procedure, yet, during a C-section she presented none. At the first consultation she had normal coagulation factor levels by coagulometry, and normal platelet aggregation test for ADP, ristocetin, collagen and epinephrine. A platelet aggregation test for arachidonic acid confirmed thromboxane A2 deficit disorder. Thromboxane A2 deficit disorder is a rare qualitative platelet disorder that requires an extensive knowledge of coagulation and platelet function and tests, and a high level of clinical suspicion. These tests are especially difficult to interpret during pregnancy due to normal modifications to bodily function during this process.

Essential Athrombia

1975 ◽  
Vol 33 (02) ◽  
pp. 278-285 ◽  
Author(s):  
Şeref Inceman ◽  
Yücel Tangün
Keyword(s):  
Platelet Aggregation ◽  
Bleeding Time ◽  
Bleeding Tendency ◽  
Clot Retraction ◽  
Platelet Factor ◽  
Prolonged Bleeding Time ◽  
Normal Platelet ◽  
Aggregation Response ◽  
Platelet Disorder ◽  
Fibrinogen Content

SummaryA constitutional platelet function disorder in a twelve-year-old girl characterized by a lifelong bleeding tendency, prolonged bleeding time, normal platelet count, normal clot retraction, normal platelet factor 3 activity and impaired platelet aggregation was reported.Platelet aggregation, studied turbidimetrically, was absent in the presence of usual doses of ADP (1–4 μM), although a small wave of primary aggregation was obtained by very large ADP concentrations (25–50 μM). The platelets were also unresponsive to epinephrine, thrombin and diluted collagen suspensions. But an almost normal aggregation response occurred with strong collagen suspensions. The platelets responded to Ristocetin. Pelease of platelet ADP was found to be normal by collagen and thrombin, but impaired by kaolin. Platelet fibrinogen content was normal.The present case, investigated with recent methods, confirms the existence of a type of primary functional platelet disorder characterized solely by an aggregation defect, described in 1955 and 1962 under the name of “essential athrombia.”

Propofol-Induced Bleeding Dyscrasia: A Case Report.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3894-3894
Author(s):  
Rabih C. Fahed ◽  
Thomas K. Schulz2
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Bleeding Time ◽  
Postoperative Bleeding ◽  
Sigmoid Resection ◽  
Von Willebrand Disease ◽  
Prior History ◽  
Normal Platelet ◽  
Anesthetic Drugs ◽  
Relative Safety

Abstract Propofol is one of the most commonly used anesthetic drugs, with rapid induction, maintenance and recovery times. Its relative safety has resulted in it becoming a popular choice for general anesthesia. A 56 y o woman with no prior history of bleeding underwent laparoscopic cholecystectomy. Postoperatively she experienced bleeding to the degree that open laparotomy was required to achieve hemostasis.Two years later, she underwent open sigmoid resection under propofol anesthesia for refractory diverticulitis. Severe postoperative bleeding ensued, necessitating IV fluid resuscitation and transfusion of packed red blood cells.Template bleeding time was repeatedly greater than 20 minutes on the first postoperative day. Platelet count, coagulation studies, von Willebrand disease assays, fibrinogen level and fibrinolytic system assays were found to be normal. Platelet aggregation in response to arachidonic acid was decreased at 9% (reference 60 - 120 %). The patient received platelet transfusions; hemostasis was achieved and the template bleeding time returned to normal on the second postoperative day and remained normal on repeat testing several weeks later. A few reports have shown an increased bleeding with propofol, which is thought to be related to inhibition of thromboxane A2 synthesis and increased synthesis of leucocyte nitric oxide. Some studies show increased bleeding even without any change in the template bleeding time. In summary, we report a case of a propofol-induced life threatening bleeding dyscrasia associated with a prolonged template bleeding time and platelet aggregation studies consistent with decreased response to arachidonic acid. This rarely reported complication should always be in the differential diagnosis of postoperative bleeding given the widespread usage of propofol anesthesia in major surgeries.

Tissue-Specific Transgene Expression in Induced Pluripotent Stem (iPS) Cell-Derived Megakaryocytes: Correction of Glanzmann Thrombasthenia (GT)

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 387-387
Author(s):  
Spencer K. Sullivan ◽  
Jason A. Mills ◽  
Li Zhai ◽  
Prasuna Paluru ◽  
Karen Vo ◽  
...  
Keyword(s):  
Transgene Expression ◽  
Surface Expression ◽  
Ips Cells ◽  
Severe Bleeding ◽  
Mrna Levels ◽  
Ips Cell ◽  
Platelet Disorder ◽  
Single Allele ◽  
Aavs1 Locus ◽  
High Level

Abstract Abstract 387 Megakaryocyte-specific transgene expression in patient-derived iPS cells offers a new approach to study and potentially treat disorders that affect megakaryocytes and platelets. The feasibility of this method was demonstrated in GT, a disorder resulting from an absence of functional platelet integrin alphaIIb/beta3, leading to impaired platelet aggregation and clinically presenting with severe bleeding. While rare, GT can serve as a model of an inherited platelet disorder that would benefit from corrective cell therapy. For this study, iPS cells were generated from the peripheral blood of healthy controls and two patients with GT. Patient 1 is homozygous for a novel alphaIIb exon/intron 4 splice site mutation, leading to an alternatively spliced transcript and premature stop codon. Patient 2 is homozygous for a previously reported alphaIIb missense mutation in exon 8 (p.G273D), leading to impaired intracellular transport and surface expression of the heterodimer. Both patients express <5% alphaIIb/beta3 on the surface of their platelets, which was confirmed in IPS cell-derived megakaryocytes. To achieve megakaryocyte-specific expression, transgene constructs were created using the murine proximal GPIbalpha promoter driving either an eGFP reporter or wild type alphaIIb cDNA. These constructs were inserted into the AAVS1 safe harbor locus using zinc finger nuclease-mediated homologous recombination. When targeted to a single allele of the AAVS1 locus in human ES cells, the GPIbalpha promoter driving eGFP showed a high-level of expression in ES cell-derived megakaryocytes. Inserting the GPIbalpha promoter driving alphaIIb into a single allele of the AAVS1 locus in GT iPS cells restored ∼60% surface expression of integrin alphaIIb/beta3 when compared to control iPS cell-derived megakaryocytes. Transgenic alphaIIb mRNA levels were similar to endogenous alphaIIb mRNA levels in differentiated megakaryocytes. When stimulated with thrombin, corrected GT iPS cell-derived megakaryocytes demonstrated both PAC-1 antibody binding and fibrinogen binding. This study shows the GPIbalpha promoter construct targeted to the AAVS1 locus drives a high-level of expression in iPS cell-derived megakaryocytes, which offers a novel tool to study megakaryocyte and platelet biology in samples obtained from affected individuals. For GT, this study demonstrates a higher level of correction than seen with a lentiviral approach. To our knowledge, this is the first report of the generation and correction of iPS cell lines from patients with a disease affecting platelet function. Disclosures: No relevant conflicts of interest to declare.

Identification of p.W246L As a Novel Mutation in the GP1BA Gene Responsible for Platelet-Type von Willebrand Disease

2014 ◽  
Vol 40 (02) ◽  
pp. 151-160 ◽  
Author(s):  
Adriana Woods ◽  
Analia Sanchez-Luceros ◽  
Emilse Bermejo ◽  
Juvenal Paiva ◽  
Maria Alberto ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Novel Mutation ◽  
In Silico Analysis ◽  
Von Willebrand Disease ◽  
Severe Bleeding ◽  
Low Concentrations ◽  
Healthy Control ◽  
Spontaneous Platelet Aggregation ◽  
Von Willebrand ◽  
Willebrand Factor

Platelet-type von Willebrand disease (PT-VWD) and type 2B von Willebrand disease (2B-VWD) are rare bleeding disorders characterized by increased ristocetin-induced platelet aggregation (RIPA) at low concentrations of ristocetin. Diagnosis of either condition is not easy and the differential diagnosis between the two entities is especially challenging as evidenced by high levels of misdiagnosis of both conditions, but particularly PT-VWD. Five mutations in the GP1BA gene related to PT-VWD and less than 50 patients are currently reported worldwide. We herein describe a patient with severe bleeding symptoms, macrothrombocytopenia, mild spontaneous platelet aggregation, positive RIPA at 0.3 and 0.4 mg/mL, von Willebrand factor ristocetin cofactor (VWF:RCo) to antigen (VWF:Ag) < 0.2, normal VWF propeptide/VWF:Ag ratio, and RIPA mixing tests and cryoprecipitate challenge positive for PT-VWD. GP1BA gene was studied in the patient, in his mother, and in 100 healthy control subjects. We identified a heterozygous substitution G > T located at nucleotide 3805 in the g.DNA of the patient's GP1BA gene, resulting in a Trp to Leu amino acid change at residue 246 (p.W246L). This mutation was absent in his unaffected mother and also in the 100 controls, and was predicted as damaging by in silico analysis. The residue W246 is located within the VWF-binding region and exists in a strongly conserved position in the phylogenetic tree, which is expected to be unable to tolerate substitutions without changing its functional characteristics. These findings argue strongly in favor of the view that this substitution does not represent a polymorphism and is therefore responsible for the PT-VWD phenotype of the patient.

The roles of αIIbβ3-mediated outside-in signal transduction, thromboxane A2, and adenosine diphosphate in collagen-induced platelet aggregation

Blood ◽  
2003 ◽  
Vol 101 (7) ◽  
pp. 2646-2651 ◽  
Author(s):  
Moon J. Cho ◽  
Junling Liu ◽  
Tamara I. Pestina ◽  
Shirley A. Steward ◽  
Dennis W. Thomas ◽  
...  
Keyword(s):  
Thromboxane A2 ◽  
Adenosine Diphosphate ◽  
Dense Granule ◽  
Signaling Proteins ◽  
Platelet Signaling ◽  
Protein Kinase C Inhibitor ◽  
Dense Granule Secretion ◽  
Granule Secretion ◽  
High Level ◽  
Granule Release

Collagen-induced activation of platelets in suspension leads to αIIbβ3-mediated outside-in signaling, granule release, thromboxane A2 (TxA2) production, and aggregation. Although much is known about collagen-induced platelet signaling, the roles of TxA2 production, adenosine diphosphate (ADP) and dense-granule secretion, and αIIbβ3-mediated outside-in signaling in this process are unclear. Here, we demonstrate that TxA2 and ADP are required for collagen-induced platelet activation in response to a low, but not a high, level of collagen and that αIIbβ3-mediated outside-in signaling is required, at least in part, for this TxA2 production and ADP secretion. A high level of collagen can activate platelets deficient in PLCγ2, Gαq, or TxA2 receptors, as well as platelets treated with a protein kinase C inhibitor, Ro31-8220. Thus, activation of αIIbβ3 in response to a high level of collagen does not require these signaling proteins. Furthermore, a high level of collagen can cause weak TxA2 and ADP-independent aggregation, but maximal aggregation induced by a high level of collagen requires TxA2 or secretion.

scholarly journals Inherited platelet diseases with normal platelet count: phenotypes, genotypes and diagnostic strategy

Haematologica ◽  
2020 ◽  
Author(s):  
Paquita Nurden ◽  
Simon Stritt ◽  
Remi Favier ◽  
Alan T. Nurden
Keyword(s):  
Platelet Count ◽  
Platelet Function ◽  
Critical Role ◽  
Tyrosine Kinase Receptor ◽  
Severe Bleeding ◽  
Diagnostic Strategy ◽  
Normal Platelet Count ◽  
Normal Platelet ◽  
Platelet Disorder ◽  
Platelet Disorders

Inherited platelet disorders resulting from platelet function defects and a normal platelet count cause a moderate or severe bleeding diathesis. Since the description of Glanzmann thrombasthenia resulting from defects of ITGA2B and ITGB3, new inherited platelet disorders have been discovered, facilitated by the use of high throughput sequencing and genomic analyses. Defects of RASGRP2 and FERMT3 responsible for severe bleeding syndromes and integrin activation have illustrated the critical role of signaling molecules. Important are mutations of P2RY12 encoding the major ADP receptor causal for an inherited platelet disorder with inheritance characteristics that depend on the variant identified. Interestingly, variants of GP6 encoding the major subunit of the collagen receptor GPVI/FcRγ associate only with mild bleeding. The numbers of genes involved in dense granule defects including Hermansky-Pudlak and Chediak Higashi syndromes continue to progress and are updated. The ANO6 gene encoding a Ca2+-activated ion channel required for phospholipid scrambling is responsible for the rare Scott syndrome and decreased procoagulant activity. A novel EPHB2 defect in a familial bleeding syndrome demonstrates a role for this tyrosine kinase receptor independent of the classical model of its interaction with ephrins. Such advances highlight the large diversity of variants affecting platelet function but not their production, despite the difficulties in establishing a clear phenotype when few families are affected. They have provided insights into essential pathways of platelet function and have been at the origin of new and improved therapies for ischemic disease. Nevertheless, many patients remain without a diagnosis and requiring new strategies that are now discussed.

Whole Blood Impedance Aggregometry: A New Tool for Severe Inherited Platelet Disorder Diagnosis?

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 5266-5266 ◽  
Author(s):  
Celine Desconclois ◽  
Vincent Valarche ◽  
Tewfik Boutekedjiret ◽  
Martine Raphael ◽  
Marie Dreyfus ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Function ◽  
Whole Blood ◽  
Von Willebrand Disease ◽  
Fast Method ◽  
Normal Ranges ◽  
Platelet Function Disorders ◽  
Platelet Disorder ◽  
Platelet Disorders ◽  
Von Willebrand

Abstract Abstract 5266 Diagnosis and characterization of platelet function disorders may be challenging. It requires multiple laboratory data including the assessment of platelet functions. Platelet function analysis is most commonly performed using light transmission aggregometry (LTA). LTA is a time-consuming method requiring centrifugation steps and large blood volumes. It is difficult to perform in children and in cases of thrombocytopenia. In contrast, platelet aggregation in whole blood using impedancemetry (WBI) is a fast method, allows omission of centrifugation steps and performance of platelet function studies under more physiological conditions with small samples size. It is based on the change of resistance proportional to the amount of platelets sticking to two electrodes where an alternating current is applied. Multiplate® (for “multiple electrode aggregometry”, Dynabite Medical) is a new generation of WBI aggregometer using diluted blood and single-use test cells containing twin electrodes that reduce the variation of results. We have already showed the good Multiplate® performance concerning ristocetin-induced platelet aggregation in a population of 30 patients with characterized von Willebrand disease (Valarche et al, 2011). Our aim in this ongoing study was to assess the performance of WBI in patients with inherited platelet function disorders. We tested 8 patients including 2 unrelated patients with Glanzmann Thrombasthenia (GT), 2 unrelated patients with Bernard-Soulier Syndrome (BSS), 1 patient with Gray Platelet Syndrome (GPS) and 3 patients from the same family with a platelet type von Willebrand disease (PTVWD). GT, BSS, and PTVWD diagnosis were confirmed using genotyping. BSS and GPS patients had chronic thrombocytopenia. GT, BSS, GPS and 1/3 PTVWD had platelet function tests with LTA in parallel. WBI was performed on heparinized whole blood diluted at ½ in NaCl at 37°C and triggered using high (0.77 mg/mL, WBI RH) and low (0.5 mg/mL, WBI RL) final ristocetin concentrations, ADP (6.5 Âμ Mol, WBI ADP) and collagen (3.2 Âμg/mL, WBI Coll). Results were expressed in arbitrary unit (AU) corresponding to the area under the aggregation curve observed during 6 min. Normal ranges indicated in brackets were based on the mean +/− 2 SD of 30 healthy volunteers' results. Results highlighted in grey are those out of the normal ranges (Table 1).Table 1:Results of the 8 patients with inherited platelet disorders.PatientsPlatelet count (109/L)WBI RH (AU) [>500]WBI RL (AU) [<150]WBI ADP (AU) [>550]WBI Coll (AU) [>500]GT 116923441443GT 224955417ND7BSS 134371119129BSS 230254733582GPS7916217ND42PTVWD22099493ND338PTVWD231116560ND1092PTVWD2341174168ND852 All patients except those with PTVWD had decreased results with WBI. However, as expected, patients with GT had flat traces using WBI ADP and WBI Coll but normal or only decreased curves (234 – 554 AU) using WBI RH. On the opposite, BSS patients had flat traces using WBI RH but detectable curves using WBI ADP (191 – 335 AU) despite decreased platelet count. The thrombocytopenic GPS patient has a flat trace using WBI Coll and decreased WBI RH (162 AU). Members of the PTVWD family had normal results except a slightly increased result with WBI RH in 1/3 patients. Finally, LTA results performed in 6/8 patients were all in accordance with those of the WBI. In conclusion, in 8 patients with well characterized inherited platelet disorders, WBI was able to detect all abnormalities except PTVWD. In such cases, different ristocetin concentrations use might be critical to increase sensitivity. In our hands, WBI was able to discriminate disorders involving platelet glycoprotein (GP) IIb-IIIa from GP Ib-IX-V: GT patients exhibited flat traces using WBI ADP and WBI Coll, whereas patients with BSS exhibited flat traces with ristocetin. These preliminary results need to be confirmed on a larger population of patients with various characterized platelet function disorders. They suggest that WBI using the Multiplate® analyzer, which is a fast, easy and blood-preserving test, could be a valuable extra step before or in addition to the classic LTA for the diagnosis of severe inherited platelet disorders. Disclosures: No relevant conflicts of interest to declare.

Mutations of the Platelet Thromboxane A2 (TXA2) Receptor in Patients Characterized by the Absence of TXA2–induced Platelet Aggregation despite Normal TXA2 Binding Activity

1999 ◽  
Vol 82 (11) ◽  
pp. 1528-1531 ◽  
Author(s):  
Wataru Higuchi ◽  
Akira Hattori ◽  
Yoshifusa Aizawa ◽  
Ichiro Fuse
Keyword(s):  
Platelet Aggregation ◽  
Mutational Analysis ◽  
Thromboxane A2 ◽  
Binding Activity ◽  
Single Amino Acid ◽  
Mutant Type ◽  
Platelet Disorder ◽  
Group A ◽  
Txa2 Receptor ◽  
Group B

SummaryPreviously, we reported five cases of platelet dysfunction characterized by the absence of thromboxane A2 (TXA2) – induced platelet aggregation despite normal TXA2 binding activity. In this platelet disorder, patients were divided into two groups; i.e. those whose platelets lacked or did not lack phospholipase C (PLC) activation (Group A and Group B, respectively) (Thromb Haemost 1996; 76: 1080). Furthermore, in one of the patients, we showed that a single amino acid substitution (Arg60 to Leu) in the first cytoplasmic loop of the TXA2 receptor (TXR) was responsible for this platelet disorder. However, mutational analysis of the TXR in the remaining patients has not been performed. Based on this background, we investigated the mutations of the TXR in these patients, and found that all of the patients have the same abnormality of the TXR (Arg60 → Leu), although the Group A patients were homozygous and the Group B patients were heterozygous for this mutation.This mutation is the only abnormality which has been found in this platelet disorder, and in patients heterozygous for this mutation, the mutant type TXR suppresses wild-type receptor-mediated platelet aggregation by a mechanism independent of PLC activation.

Platelet Function Disorders in Bleeding Patients without Other Coagulopathies

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 4650-4650
Author(s):  
Francine R. Dembitzer ◽  
Ellinor I.B. Peerschke ◽  
Caroline Cromwell ◽  
Xiaofei Zhang ◽  
Louis M. Aledort
Keyword(s):  
Platelet Aggregation ◽  
Board Of Directors ◽  
Platelet Function ◽  
Coagulation Factor ◽  
Clinical History ◽  
Study Cohort ◽  
Advisory Committees ◽  
Normal Platelet ◽  
Platelet Function Disorders ◽  
Age Range

Abstract Introduction: We present a series of 105 patients referred for hematologic consultation to evaluate a clinical bleeding disorder. Little is known regarding the prevalence of non-genetic qualitative platelet disorders and which of these might respond to desmopressin. Methods: Patients were assessed over a two-year period, from December 2011 through December 2013. Patients, who were found to have neither von Willebrand's disease nor coagulation factor deficiencies, nor quantitative platelet defects, were tested for platelet function abnormalities by PFA-100 (Dade Behring, Marburg, Germany) and platelet aggregation and secretion studies using lumi aggregation (Chrono-Log Corp., Havertown, PA, USA). Selected patients with abnormal platelet function were given a trial of intravenous desmopressin to determine efficacy, and platelet function studies were repeated 2 hours later. Results: Of the 105 referred patients (26 males, age range 15-83 years; 79 females, age range 21-86 years), 67 with either normal (n=43) or abnormal (n=24) PFA-100 results were not evaluated further based on their clinical history and presentation. 18 patients with abnormal PFA-100 results, consisting of Collagen/ADP, Collagen/Epinephrine, or both, had platelet aggregation and secretion studies performed. 16 of these patients had abnormal platelet aggregation and secretion studies, while 2 patients had normal studies. In addition, 20 patients with normal PFA-100 results underwent platelet aggregation and secretion studies. Of these, 17 had abnormal platelet aggregation and secretion predominantly in response to two or more weak agonists, including ADP, epinephrine and/or arachidonic acid. Only 3 of these 20 patients had normal platelet aggregation and secretion. Of the 16 patients with both abnormal PFA-100 and abnormal platelet aggregation and secretion tests, 11 underwent subsequent pre- and post- desmopressin platelet function testing. 7 of the 11 patients showed improvement or complete normalization of at least one PFA-100 parameter, i.e., either Collagen/ADP, Collagen/Epinephrine, or both. However, results of platelet aggregation and secretion tests remained unchanged, irrespective of PFA-100 results. Conclusions: In the present study, platelet aggregation and secretion studies in patients with no other coagulopathies revealed platelet function defects in approximately 30% of the study cohort. Platelet function defects were in response to weak agonists, including ADP, epinephrine, and/or arachidonic acid.Our data support the recent SCC ISTH recommendations against the use of PFA-100 for platelet function screening.We recommend that the hematologist carefully assess the bleeding history, and, if significant, pursue platelet aggregation and secretion studies to identify potential platelet function defects. Disclosures Aledort: Baxter Healthcare: Membership on an entity's Board of Directors or advisory committees, Other: DSMB Participation; Kedrion BioPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Pathogenetic Analysis of Five Cases with a Platelet Disorder Characterized by the Absence of Thromboxane A2(TXA2)-Induced Platelet Aggregation in Spite of Normal TXA2 Binding Activity

1996 ◽  
Vol 76 (06) ◽  
pp. 1080-1085 ◽  
Author(s):  
Ichiro Fuse ◽  
Akira Hattori ◽  
Masao Mito ◽  
Wataru Higuchi ◽  
Kazuaki Yahata ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Phosphatidic Acid ◽  
Phospholipase C ◽  
Bleeding Time ◽  
Thromboxane A2 ◽  
Binding Activity ◽  
Normal Limits ◽  
Signaling Mechanisms ◽  
Platelet Disorder ◽  
Txa2 Receptor

SummaryFive patients with mild bleeding tendencies characterized by defective thromboxane A2 (TXA2)-induced platelet aggregation are reported. The platelets of all the patients had the ability to bind exogenous TXA2. Bleeding time was markedly prolonged in one patient. In three of the five patients, synthetic TXA2 mimetic (STA2)-induced platelet responses, including IP3 formation, Ca2+ mobilization, phosphatidic acid formation and GTPase activities were selectively defective, suggesting impaired coupling between the TXA2 receptor and phospholipase C activation. However, in the remaining two patients, these responses were all within normal limits. This suggests that the defective site of this type of platelet disorder is heterogenous and that signaling mechanisms other than the TXA2 receptor-phospholipase C pathway are also involved in TXA2-induced platelet aggregation.

Sign in / Sign up

Export Citation Format

Share Document