Congenital disorders associated with platelet dysfunctions

Treatment of Inherited Platelet Disorders: Current Status and Future Options

Inherited platelet disorders (IPDs) comprise a heterogeneous group of entities that manifest with variable bleeding tendencies. For successful treatment, the underlying platelet disorder, bleeding severity and location, age, and sex must be considered in the broader clinical context. Previous information from the AWMF S2K guideline #086-004 (www.awmf.org) is evaluated for validity and supplemented by information of new available and future treatment options and clinical scenarios that need specific measures. Special attention is given to the treatment of menorrhagia and risk management during pregnancy in women with IPDs. Established treatment options of IPDs include local hemostatic treatment, tranexamic acid, desmopressin, platelet concentrates, and recombinant activated factor VII. Hematopoietic stem cell therapy is a curative approach for selected patients. We also provide an outlook on promising new therapies. These include autologous hematopoietic stem cell gene therapy, artificial platelets and nanoparticles, and various other procoagulant treatments that are currently tested in clinical trials in the context of hemophilia.

Bernard Soulier syndrome: A case report from Pakistan

Bernard Soulier Syndrome should be suspected in patients with bleeding disorder symptoms and significant family history, where consanguineous marriages are common. Diagnosis can be confirmed using a ristocetin test and a peripheral blood smear.

Platelets drive fibronectin fibrillogenesis using integrin αIIbβ3

Platelets interact with multiple adhesion proteins during thrombogenesis, yet little is known about their ability to assemble fibronectin matrix. In vitro three-dimensional superresolution microscopy complemented by biophysical and biochemical methods revealed fundamental insights into how platelet contractility drives fibronectin fibrillogenesis. Platelets adhering to thrombus proteins (fibronectin and fibrin) versus basement membrane components (laminin and collagen IV) pull fibronectin fibrils along their apical membrane versus underneath their basal membrane, respectively. In contrast to other cell types, platelets assemble fibronectin nanofibrils using αIIbβ3 rather than α5β1 integrins. Apical fibrillogenesis correlated with a stronger activation of integrin-linked kinase, higher platelet traction forces, and a larger tension in fibrillar-like adhesions compared to basal fibrillogenesis. Our findings have potential implications for how mechanical thrombus integrity might be maintained during remodeling and vascular repair.

Gray Platelet Syndrome Presenting With Pancytopenia, Splenomegaly, and Bone Marrow Fibrosis

OBJECTIVES

Gray platelet syndrome (GPS) is a rare platelet storage pool disorder associated with a marked decrease or absence of platelet α-granules and their contents. It is characterized clinically by mild to moderate bleeding; moderate macrothrombocytopenia with large, agranular platelets; splenomegaly; and bone marrow fibrosis. Electron microscopy confirms markedly reduced or absent α-granules in platelets and megakaryocytes. The classic description of GPS is caused by homozygous mutations in NBEAL2 (neurobeachinlike 2).

METHODS

A 28-year-old Hispanic man with a history of easy bruising and occasional episodes of epistaxis sought treatment for pancytopenia and splenomegaly. Peripheral blood smear and bone marrow analysis, electron microscopy, and next-generation sequencing were performed.

RESULTS

Large and agranular platelets were present in the peripheral blood. There was bone marrow fibrosis. Electron microscopy of the platelets showed absence of α-granules. Next-generation sequencing revealed a germline apparently homozygous nonsense variant in the NBEAL2 gene: c.5674C>T, p.Gln1892X (p.Q1829X).

CONCLUSIONS

The differential diagnosis of GPS includes a myeloid neoplasm such as myelodysplastic syndrome with bone marrow fibrosis. The availability of diagnostic genetic panels for hereditable platelet disorders can assist in the recognition of GPS and other platelet disorders. We also describe a previously unreported pathogenic germline homozygous nonsense variant in the NBEAL2 gene: c.5674C>T, p.Gln1892X (p.Q1829X) in a patient with GPS.

Platelet transfusion for patients with platelet dysfunction: effectiveness, mechanisms, and unanswered questions

PURPOSE OF REVIEW

In this review, we discuss current clinical guidelines and potential underlying mechanisms regarding platelet transfusion therapy in patients at risk of bleeding, comparing management of patients with thrombocytopenia versus those with qualitative platelet disorders.

RECENT FINDINGS

Platelet transfusion therapy is highly effective in managing bleeding in patients with hypoproliferative thrombocytopenia. Clinical trials have demonstrated that platelet transfusion can be used at a lower trigger threshold and reduced platelet doses, and may be used therapeutically rather than prophylactically in some situations, although additional data are needed. In patients with inherited platelet disorders such as Glanzmann's Thrombasthenia or those with RASGRP2 mutations, platelet transfusion may be ineffective because of competition between transfused and endogenous platelets at the site of vascular injury. Successful management of these patients may require transfusion of additional platelet units, or mechanism-driven combination therapy with other pro-hemostatic agents. In patients on antiplatelet therapy, timing of transfusion and inhibitor mechanism-of-action are key in determining therapeutic success.

SUMMARY

Expanding our understanding of the mechanisms by which transfused platelets exert their pro-hemostatic function in various bleeding disorders will improve the appropriate use of platelet transfusion.

Functional Assessment of Platelet Dense Granule ATP Release

OBJECTIVES

This study was undertaken to explore the feasibility of assessing platelet dense granule release in response to platelet stimuli, using less than 1 mL of whole blood (WB).

METHODS

Optimization of the luciferin-luciferase (LL) assay for ATP release, together with additional modifications, was applied to 1:10 diluted WB.

RESULTS

LL assay optimization using nonstirred 1:10 diluted WB resulted in dense granule ATP release in response to thrombin receptor-activating peptide (TRAP) of similar magnitude to that observed using stirred platelet-rich plasma. Stirring of the 1:10 diluted WB restored collagen-induced dense granule secretion. Addition of lyophilized, formalin-fixed platelets, together with stirring, restored dense granule secretion responsiveness to ADP. TRAP, ADP, and collagen all stimulated ATP release in 1:10 diluted WB under the optimized conditions of this study at levels close to those observed using platelet-rich plasma. Blood sample reconstitution experiments offer hope that this assay may prove robust down to WB platelet counts as low as 50 × 103/μL.

CONCLUSIONS

Platelet dense granule release in response to a number of classic stimuli, including ADP, was accomplished from less than 1 mL WB with minimal specimen processing, using widely available reagents and instrumentation.

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

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/FcRassociate 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.

Identification of a pathogenic TUBB1 variant in a Chinese family with congenital macrothrombocytopenia through whole genome sequencing

Congenital macrothrombocytopenia is a genetically heterogeneous group of rare disorders. We herein report a large Chinese family presented with phenotypic variability involving thrombocytopenia and/or giant platelets. Whole genome sequencing (WGS) of the proband and one of his affected brothers identified a potentially pathogenic c.952 C > T heterozygous variant in the TUBB1 gene. This p.R318W β1-tubulin variant was also identified in three additional siblings and five members of the next generation. These findings were consistent with an autosomal dominant inheritance with incomplete penetrance. Moreover, impaired platelet agglutination in response to ristocetin was detected in the patient's brother. Half of the family members harboring the p.R318W mutation displayed significantly decreased external release of p-selectin by stimulated platelets. The p.R318W β1-tubulin mutation was identified for the first time in a Chinese family with congenital macrothrombocytopenia using WGS as an unbiased sequencing approach. Affected individuals within the family demonstrated impaired platelet aggregation and/or release functions.

Harmonizing light transmission aggregometry in the Netherlands by implementation of the SSC-ISTH guideline

Light transmission aggregometry (LTA) is considered the gold standard method for evaluation of platelet function. However, there are a lot of variation in protocols (pre-analytical procedures and agonist concentrations) and results. The aim of our study was to establish a national LTA protocol, to investigate the effect of standardization and to define national reference values for LTA. The SSC guideline was used as base for a national procedure. Almost all recommendations of the SSC were followed e.g. no adjustment of PRP, citrate concentration of 109 mM, 21 needle gauge, fasting, resting time for whole blood and PRP, centrifugation time, speed and agonists concentrations. LTA of healthy volunteers was measured in a total of 16 hospitals with 5 hospitals before and after standardization. Results of more than 120 healthy volunteers (maximum aggregation %) were collected, with participating laboratories using 4 different analyzers with different reagents. Use of low agonist concentrations showed high variation before and after standardization, with the exception of collagen. For most high agonist concentrations (ADP, collagen, ristocetin, epinephrine and arachidonic acid) variability in healthy subjects decreased after standardization. We can conclude that a standardized Dutch protocol for LTA, based on the SSC guideline, does not result in smaller variability in healthy volunteers for all agonist concentrations.

Development of a Nonradioactive Platelet Serotonin Uptake and Release Assay by Micro-Liquid Chromatography Tandem Mass Spectrometry Using Minimal Blood Volume

OBJECTIVES

Analysis of platelet functional responses to stimuli is presently quite limited with respect to measurement of dense granule secretion. We sought to develop a nonradioactive assay of stimulated serotonin release using liquid chromatography tandem mass spectrometry (LC-MS/MS).

METHODS

Citrated whole blood (200 μL) was incubated with deuterated serotonin (d45-HT). Following uptake by platelets, blood was diluted 10-fold and aliquots were incubated with platelet stimuli. Following stimulation, blood was further diluted, centrifuged, and supernatant was assayed for released d45-HT by micro-LC-MS/MS.

RESULTS

This study demonstrated a broad linear range of 50 to 2,000 pg/mL d45-HT, with a total precision of less than 15.0% coefficient of variation at all quality control levels and a limit of quantitation of 50 pg/mL.

CONCLUSIONS

Quantification of d45-HT by micro-LC-MS/MS assay offers a highly sensitive, nonradioactive methodology for quantitating platelet serotonin uptake and dense granule secretion, requiring only small volumes of patient blood.

Essential thrombocytosis with recurrent spontaneous abortion in the mid trimester: A case report

RATIONALE

Essential thrombocytosis (ET) is a myeloproliferative neoplasm characterized by clonal proliferation of the megakaryocytic lineage within the bone marrow and phenotypically by an elevated platelet count in peripheral blood. Common vascular complications include thrombosis, microvascular disturbances, and hemorrhage. ET with recurrent spontaneous abortion as the primary symptom is rare.

PATIENT CONCERNS

A 30-year-old pregnant woman (gestational age: 8 weeks) with a history of recurrent spontaneous abortion in the mid trimester was admitted to our hospital for further management.

DIAGNOSIS

The diagnosis of ET was made based on the platelet count, bone marrow biopsy, and molecular biology testing.

INTERVENTIONS

The patient was treated with interferon, heparin, and aspirin.

OUTCOMES

The infant was delivered by cesarean section without complication at 28 weeks gestation due to placental abruption. The child remained healthy with no developmental abnormalities during follow-up for 2 years.

LESSONS

Recurrent spontaneous abortion in the mid trimester might be associated with ET. Thus, a detailed investigation including blood routine examination to identify an abnormal platelet count is warranted for pregnant patients with such a history in order to facilitate timely treatment.

Variation in Platelet Delta Granules Over Time in Young Women Undergoing Evaluation for Heavy Menstrual Bleeding

Delta-granule platelet storage pool deficiency (δ-PSPD) is a qualitative platelet function defect associated with variable bleeding phenotypes. Platelet electron microscopy (EM) is commonly utilized to evaluate for δ-PSPD, but intrapatient variability in platelet δ-granule numbers by EM is currently unknown. Fifteen young women aged 11 to 17 years presenting to a young women's hematology clinic for the evaluation of heavy menstrual bleeding underwent platelet EM testing at their initial hematology clinic visit and at 1 and 3 months later. Platelet aggregation of platelet-rich plasma by light transmission was also performed on all patients at their initial visit. Eight patients had average δ-granules per platelet consistently ≥2. Three patients were found to have average δ-granules per platelet <2 on initial testing, 2 of which reverted to ≥2 on subsequent testing. When initial average δ-granules per platelet was ≥2, initial repeat testing remained so in 83% (95% confidence interval [CI], 52%-98%) of cases and subsequent repeat testing remained so in 75% (95% CI, 43%-95%) of the cases. Platelet aggregation testing was abnormal in 53% of patients, and there was no apparent correlation between platelet EM findings and platelet aggregation testing. In this small group of young women presenting for the evaluation of bleeding symptoms, we found that almost half of the patients had substantial variability in platelet EM results. Given other identified limitations in platelet EM testing, and the intrapatient variability identified in this study, providers should use caution in utilizing EM in isolation to diagnose δ-PSPD.

Bernard Soulier Syndrome: 10 years' experience at a tertiary care hospital

OBJECTIVE

To determine clinical manifestations and laboratory findings in patients with BSS diagnosed through platelet aggregometry followed in a tertiary care hospital in Lahore, Pakistan.

METHODS

The retrospective study comprised patients who presented in Hematology and Transfusion Medicine Department of The Children Hospital & Institute of Child Health, Lahore with the relevant diagnosis from 2006 to 2013. The result of all the patients were collected on a predesigned proforma. Medical data was scrutinized to collect age, gender, clinical findings along with results of complete blood count, bleeding time and platelet aggregation studies for the diagnosis of Bernard Soulier Syndrome.

RESULTS

Among 49 patients, 26 patients were females and 23 males. The mean age of the patients was 5±2.5 years. 81% had a family history of consanguinity. The most common presenting symptom included epistaxis seen in 73.4% patients. Complete blood count demonstrated decreased platelets in 85.7% of patients ranging from 20 X 109/L to 130 X 109/L. Anemia was seen in 67.3% and 93.8% had prolonged bleeding time. Peripheral blood smears demonstrated giant platelets in all patients. The majority of patients 65.3% had mild bleeding episodes. Platelet aggregation studies showed normal aggregation with ADP, Collagen and Epinephrine in 100% of our patients whereas all showed no response of aggregation with Ristocetin.

CONCLUSION

Our data is consistent with other reports regarding clinical presentation of BSS, but we report large number of BSS patients from our area, emphasizing significance to provide diagnostic services in Pakistan to find out exact magnitude of disease.

Life-threating outcomes after dental implantation in patient with idiopathic thrombocytopenic purpura: a case report and review of literature

BACKGROUND

Patients with chronic ITP (idiopathic thrombocytopenia) frequently do not require comprehensive medication for daily life. Usually, it had been regarded that postoperative bleeding after a simple or surgical extraction is easily controlled by simple local measures even in patients with ITP. This lack of regular medication usage can sometimes lead practitioners or patients to underestimate the potential life-threatening risk of ITP. There had been no report on postoperative hemorrhage in a patient with ITP related to dental implant surgery.

CASE PRESENTATION

This report presented a life-threatening postoperative hemorrhage after dental implant surgery in an adult with chronic ITP and subsequent emergency management after severe bleeding and airway compromise.

CONCLUSION

The presented case emphasizes the thorough hematological evaluation of the patients even for patients who do not take any specific medications for asymptomatic, chronic ITP.

My patient is thrombocytopenic! Is (s)he? Why? And what shall I do?

Solving the riddle of a thrombocytopenic patient is a difficult and fascinating task. The spectrum of possible aetiologies is wide, ranging from an in vitro artefact to severe treatment-resistant thrombocytopenic bleeding conditions, or even life-threatening prothrombotic states. Moreover, thrombocytopenia by itself does not protect from thrombosis and sometimes a patient with a low platelet count requires concomitant antithrombotic treatment as well. In order to identify and treat the cause and the effects of the thrombocytopenia, you have to put together several pieces of information, solving a unique jig-jaw puzzle.

The present work is not a textbook article about thrombocytopenia, rather a collection of differential diagnostic thoughts, treatment concepts, and some basic knowledge, that you can retrieve when facing your next thrombocytopenic patient. Enjoy reading it, but most importantly enjoy taking care of patients with a low platelet count. I bet the present work will assist you in this challenging and rewarding clinical task.

Angeborene Thrombozytenfunktionsstörungen

Angeborene Thrombozytopathien können zu Blutungssymptomen unterschiedlichen Schweregrades führen, da die Thrombozyten nicht mehr ihre Funktion nach einer Gefäß-verletzung erfüllen können. In manchen Fällen sind Thrombozytopathien schwierig zu diagnostizieren und können Probleme in der Therapie und im Management verursachen. Dieser Review beschreibt den klinischen und molekulargenetischen Phänotyp der verschiedenen angeborenen Thrombozytopathien. Die angeborenen Thrombozytopathien werden entsprechend des Thrombozytendefekts eingeteilt: Rezeptordefekte (Adhäsion oder Aggregation), Sekretionsdefekte und Zytoskelettdefekte.

Die am besten charakterisierten thrombozytären Rezeptordefekte sind die Glanzmann Thrombasthenie (Defekt des Integrins [uni03B1]IIb[uni03B2]3) und das Bernard-Soulier Syndrom (Defekt des GPIb/IX/V Rezeptors). Umfassende Fall-berichte über die Blutungsdiathese sowie die Untersuchung der Thrombozytenaggregation bzw. -agglutination und Rezeptorexpression von Patienten, die an der Glanzmann Thrombasthenie (GT) oder am Bernard-Soulier Syndrom (BSS) leiden, sollen diesen Review ergänzen. Darüber hinaus wird das HermanskyPudlak Syndrom (HPS) als eine bedeutende Störung der [uni03B4]-Granula Sekretion zusammen mit einer Fallbeschreibung eines Patienten, der an HPS Typ 1 leidet, beschrieben.

Storage pool diseases illuminate platelet dense granule biogenesis

Platelet dense granules (DGs) are membrane bound compartments that store polyphosphate and small molecules such as ADP, ATP, Ca²⁺, and serotonin. The release of DG contents plays a central role in platelet aggregation to form a hemostatic plug. Accordingly, congenital deficiencies in the biogenesis of platelet DGs underlie human genetic disorders that cause storage pool disease and manifest with prolonged bleeding. DGs belong to a family of lysosome-related organelles, which also includes melanosomes, the compartments where the melanin pigments are synthesized. These organelles share several characteristics including an acidic lumen and, at least in part, the molecular machinery involved in their biogenesis. As a result, many genes affect both DG and melanosome biogenesis and the corresponding patients present not only with bleeding but also with oculocutaneous albinism. The identification and characterization of such genes has been instrumental in dissecting the pathways responsible for organelle biogenesis. Because the study of melanosome biogenesis has advanced more rapidly, this knowledge has been extrapolated to explain how DGs are produced. However, some progress has recently been made in studying platelet DG biogenesis directly in megakaryocytes and megakaryocytoid cells. DGs originate from an endosomal intermediate compartment, the multivesicular body. Maturation and differentiation into a DG begins when newly synthesized DG-specific proteins are delivered from early/recycling endosomal compartments. The machinery that orchestrates this vesicular trafficking is composed of a combination of both ubiquitous and cell type-specific proteins. Here, we review the current knowledge on DG biogenesis. In particular, we focus on the individual human and murine genes encoding the molecular machinery involved in this process and how their deficiencies result in disease.

Erythrocyte and platelet proteomics in hematological disorders

Erythrocytes undergo ineffective erythropoesis, hemolysis, and premature eryptosis in sickle cell disease and thalassemia. Abnormal hemoglobin variants associated with hemoglobinopathy lead to vesiculation, membrane instability, and loss of membrane asymmetry with exposal of phosphatidylserine. This potentiates thrombin generation resulting in activation of the coagulation cascade responsible for subclinical phenotypes. Platelet activation also results in the release of microparticles, which express and transfer functional receptors from platelet membrane, playing key roles in vascular reactivity and activation of intracellular signaling pathways. Over the last decade, proteomics had proven to be an important field of research in studies of blood and blood diseases. Blood cells and its fluidic components have been proven to be easy systems for studying differential expressions of proteins in hematological diseases encompassing hemoglobinopathies, different types of anemias, myeloproliferative disorders, and coagulopathies. Proteomic studies of erythrocytes and platelets reported from several groups have highlighted various factors that intersect the signaling networks in these anucleate systems. In this review, we have elaborated on the current scenario of anucleate blood cell proteomes in normal and diseased individuals and the cross-talk between the two major constituent cell types of circulating blood.

A Novel Homozygous c.800C>G Substitution in GP1BA Exon 2 in a Kuwaiti Family with Bernard-Soulier Syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is a congenital bleeding disorder characterised by thrombocytopenia, giant platelets and decreased platelet adhesion resulting from genetic alterations of the glycoprotein (GP) Ib/IX/V complex.

OBJECTIVES

Three sisters with a lifelong bleeding history and a provisional diagnosis of BSS were referred for further characterisation of their bleeding diathesis. The siblings' symptoms varied in severity from skin and gum bleeding to menorrhagia associated with iron-deficiency anaemia requiring regular transfusion of red cells and platelets. The parents were consanguineous but did not demonstrate any bleeding disorder.

METHODS

The family were investigated using standard haematological techniques, platelet aggregometry, platelet membrane GP analysis and DNA sequencing of the genes encoding the GPIb/IX complex.

RESULTS

All 3 sisters had thrombocytopenia and giant platelets. Platelet aggregation and flow cytometry studies confirmed the lack of aggregation with ristocetin and a markedly reduced GPIb/IX surface expression. Molecular analysis demonstrated a novel homozygous c.800C>G substitution in GP1BA exon 2 leading to a serine 267 Ter stop codon in all 3 siblings.

CONCLUSIONS

A novel, nonsense mutation was identified as the cause of the bleeding disorder in this family. This is the first reported BSS mutation identified in a family from Kuwait.

Use of next-generation sequencing and candidate gene analysis to identify underlying defects in patients with inherited platelet function disorders

BACKGROUND

Inherited platelet function disorders (PFDs) are heterogeneous, and identification of the underlying genetic defects is difficult when based solely on phenotypic and clinical features of the patient.

OBJECTIVE

To analyze 329 genes regulating platelet function, number, and size in order to identify candidate gene defects in patients with PFDs.

PATIENTS/METHODS

Targeted analysis of candidate PFD genes was undertaken after next-generation sequencing of exomic DNA from 18 unrelated index cases with PFDs who were recruited into the UK Genotyping and Phenotyping of Platelets (GAPP) study and diagnosed with platelet abnormalities affecting either Gi signaling (n = 12) or secretion (n = 6). The potential pathogenicity of candidate gene defects was assessed using computational predictive algorithms.

RESULTS

Analysis of the 329 candidate PFD genes identified 63 candidate defects, affecting 40 genes, among index cases with Gi signaling abnormalities, while 53 defects, within 49 genes, were identified among patients with secretion abnormalities. Homozygous gene defects were more commonly associated with secretion abnormalities. Functional annotation analysis identified distinct gene clusters in the two patient subgroups. Thirteen genes with significant annotation enrichment for 'intracellular signaling' harbored 16 of the candidate gene defects identified in nine index cases with Gi signaling abnormalities. Four gene clusters, representing 14 genes, with significantly associated gene ontology annotations were identified among the cases with secretion abnormalities, the most significant association being with 'establishment of protein localization.'

CONCLUSION

Our findings demonstrate the genetic complexity of PFDs and highlight plausible candidate genes for targeted analysis in patients with platelet secretion and Gi signaling abnormalities.

Functional comparison of induced pluripotent stem cell- and blood-derived GPIIbIIIa deficient platelets

Human induced pluripotent stem cells (hiPSCs) represent a versatile tool to model genetic diseases and are a potential source for cell transfusion therapies. However, it remains elusive to which extent patient-specific hiPSC-derived cells functionally resemble their native counterparts. Here, we generated a hiPSC model of the primary platelet disease Glanzmann thrombasthenia (GT), characterized by dysfunction of the integrin receptor GPIIbIIIa, and compared side-by-side healthy and diseased hiPSC-derived platelets with peripheral blood platelets. Both GT-hiPSC-derived platelets and their peripheral blood equivalents showed absence of membrane expression of GPIIbIIIa, a reduction of PAC-1 binding, surface spreading and adherence to fibrinogen. We demonstrated that GT-hiPSC-derived platelets recapitulate molecular and functional aspects of the disease and show comparable behavior to their native counterparts encouraging the further use of hiPSC-based disease models as well as the transition towards a clinical application.

Sp1/Sp3 transcription factors regulate hallmarks of megakaryocyte maturation and platelet formation and function

Sp1 and Sp3 belong to the specificity proteins (Sp)/Krüppel-like transcription factor family. They are closely related, ubiquitously expressed, and recognize G-rich DNA motifs. They are thought to regulate generic processes such as cell-cycle and growth control, metabolic pathways, and apoptosis. Ablation of Sp1 or Sp3 in mice is lethal, and combined haploinsufficiency results in hematopoietic defects during the fetal stages. Here, we show that in adult mice, conditional pan-hematopoietic (Mx1-Cre) ablation of either Sp1 or Sp3 has minimal impact on hematopoiesis, whereas the simultaneous loss of Sp1 and Sp3 results in severe macrothrombocytopenia. This occurs in a cell-autonomous manner as shown by megakaryocyte-specific (Pf4-Cre) double-knockout mice. We employed flow cytometry, cell culture, and electron microscopy and show that although megakaryocyte numbers are normal in bone marrow and spleen, they display a less compact demarcation membrane system and a striking inability to form proplatelets. Through megakaryocyte transcriptomics and platelet proteomics, we identified several cytoskeleton-related proteins and downstream effector kinases, including Mylk, that were downregulated upon Sp1/Sp3 depletion, providing an explanation for the observed defects in megakaryopoiesis. Supporting this notion, selective Mylk inhibition by ML7 affected proplatelet formation and stabilization and resulted in defective ITAM receptor-mediated platelet aggregation.

Towards the targeted management of Chediak-Higashi syndrome

Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive congenital immunodeficiency caused by mutations in CHS1, a gene encoding a putative lysosomal trafficking protein. In the majority of patients, this disorder is typically characterized by infantile-onset hemophagocytic lymphohistiocytosis (HLH), which is lethal unless allogeneic transplantation is performed. A small number of individuals have the attenuated form of the disease and do not benefit from transplant. Improved outcomes of transplantation have been reported when performed before the development of HLH, thus it is important to quickly differentiate patients that present with the childhood form of disease and to prematurely enroll them into a transplantation protocol. In addition, this would also preclude those that exhibit clinical phenotypes of adolescent and adult CHS from this treatment. Patients with an absence of cytotoxic T lymphocyte (CTL) function have a high risk for developing HLH, and could therefore benefit the most from early hematopoietic stem cell transplantation (HSCT). However, although normal CTL cytotoxicity or bi-allelic missense mutations do not exclude the occurrence of HLH in childhood, a more conservative approach is justified. This article summarizes recent advances in the clinical characterization of CHS patients, provides updates on promising new testing methods, and focuses on specific therapeutic approaches.

Inherited, congenital and acquired disorders by hemostasis (vascular, platelet & plasmatic phases) with repercussions in the therapeutic oral sphere

The hemostasis alterations, either congenital or hereditary origin, and acquired, are circumstances that hinder oral care to patients who suffer them and also generates in the professional who has to attend, high stress. Bleeding control once established and dental treatment planning, both in the aspect of preparation, as the realization of the odonto-stomatological therapeutic, has suffered updates that do need to remember certain aspects of the care of these patients. But we must not forget that the hematologist or internist who controls the patient's medical condition, is a cornerstone for the planning and implementation of treatment plans. We must also remember that, in certain circumstances, treatment should be performed in a hospital setting. In this review, we aim to provide the odonto-stomatologist guidance on how to address the problem and provide simple and updated guidelines to apply in the treatment of these people.

Chediak-higashi syndrome presented as accelerated phase: case report and review of the literature

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disease, characterized by partial oculocutaneous albinism, recurrent pyogenic infections (skin, mucosa and respiratory system), and neurologic deficit. The hallmark of this syndrome is the presence of abnormal intracytoplasmic giant granules in all granule containing cells including leukocytes in blood and bone marrow. A majority (85 %) of patients with CHS develop an accelerated phase consisting of a lymphoproliferative syndrome with hemophagocytosis and infiltration of most tissues. This phase is characterized by fever, jaundice, hepatosplenomegaly, lymphadenopathy, pancytopenia and neurological abnormalities. In this paper, we report a case of CHS presented as accelerated phase in a 9-month-old girl child.

Systems biology of megakaryocytes

The molecular pathways that regulate megakaryocyte production have historically been identified through multiple candidate gene approaches. Several transcription factors critical for generating megakaryocytes were identified by promoter analysis of megakaryocyte-specific genes, and their biological roles then verified by gene knockout studies; for example, GATA-1, NF-E2, and RUNX1 were identified in this way. In contrast, other transcription factors important for megakaryopoiesis were discovered through a systems approach; for example, c-Myb was found to be critical for the erythroid versus megakaryocyte lineage decision by genome-wide loss-of-function studies. The regulation of the levels of these transcription factors is, for the most part, cell intrinsic, although that assumption has recently been challenged. Epigenetics also impacts megakaryocyte gene expression, mediated by histone acetylation and methylation. Several cytokines have been identified to regulate megakaryocyte survival, proliferation, and differentiation, most prominent of which is thrombopoietin. Upon binding to its receptor, the product of the c-Mpl proto-oncogene, thrombopoietin induces a conformational change that activates a number of secondary messengers that promote cell survival, proliferation, and differentiation, and down-modulate receptor signaling. Among the best studied are the signal transducers and activators of transcription (STAT) proteins; phosphoinositol-3-kinase; mitogen-activated protein kinases; the phosphatases PTEN, SHP1, SHP2, and SHIP1; and the suppressors of cytokine signaling (SOCS) proteins. Additional signals activated by these secondary mediators include mammalian target of rapamycin; β(beta)-catenin; the G proteins Rac1, Rho, and CDC42; several transcription factors, including hypoxia-inducible factor 1α(alpha), the homeobox-containing proteins HOXB4 and HOXA9, and a number of signaling mediators that are reduced, including glycogen synthase kinase 3α(alpha) and the FOXO3 family of forkhead proteins. More recently, systematic interrogation of several aspects of megakaryocyte formation have been conducted, employing genomics, proteomics, and chromatin immunoprecipitation (ChIP) analyses, among others, and have yielded many previously unappreciated signaling mechanisms that regulate megakaryocyte lineage determination, proliferation, and differentiation. This chapter focuses on these pathways in normal and neoplastic megakaryopoiesis, and suggests areas that are ripe for further study.

Congenital thrombocytopenia: clinical manifestations, laboratory abnormalities, and molecular defects of a heterogeneous group of conditions

Once considered exceptionally rare, congenital thrombocytopenias are increasingly recognized as a heterogeneous group of disorders characterized by a reduction in platelet number and a bleeding tendency that may range from very mild to life threatening. Although some of these disorders affect only megakaryocytes and platelets, others involve different cell types and may result in characteristic phenotypic abnormalities. This review elaborates the clinical presentation and laboratory manifestations of common congenital thrombocytopenias in addition to exploring our understanding of the molecular basis of these disorders and therapeutic interventions available.

Bleeding diathesis and hemophilias

Patients with hemophilia and other congenital bleeding disorders are at risk for development of central nervous system (CNS) hemorrhage and can present with acute or chronic neurologic symptoms. These disorders are generally caused by qualitative or quantitative deficiency of components of hemostasis such as coagulation proteins, von Willebrand factor, or platelets. Rapid diagnosis and specific medical management such as coagulation factor replacement therapy are mandatory to minimize the morbidity and mortality of CNS bleeding. Therefore, the objective of this chapter is to introduce neurologists to the physiology of hemostasis and to provide an overview of the clinical presentation, and management of inherited bleeding disorders that can potentially present with CNS bleeding. Since hemophilia is the most common bleeding disorder encountered in clinical practice, more emphasis is placed on management of hemophilia. Additionally, neurologic manifestations related to the bleeding diathesis in patients with hemophilia are elaborated.

Human platelet antigens - 2013

To date, 33 human platelet alloantigens (HPAs) have been identified on six functionally important platelet glycoprotein (GP) complexes and have been implicated in alloimmune platelet disorders including foetal and neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura (PTP) and multitransfusion platelet refractoriness (MPR). The greatest number of recognized HPA (20 of 33) resides on the GPIIb/IIIa complex, which serves as the receptor for ligands important in mediating haemostasis and inflammation. These include HPA-1a, the most commonly implicated HPA in FNAIT and PTP in Caucasian populations. Other platelet GP complexes, GPIb/V/IX, GPIa/IIa and CD109, express the remaining 13 HPAs. Of the recognized HPAs, 12 occur as six serologically and genetically defined biallelic 'systems' where the -a form designates the higher frequency allele and the -b form, the lower. Twenty-one other HPAs are low-frequency or rare antigens for which postulated higher frequency -a alleles have not yet been identified as antibody specificities. In addition to the HPA markers, platelets also express ABO and human leucocyte antigen (HLA) antigens; antibodies directed at the former are occasionally important in FNAIT, and to the latter, in MPR.

Platelet dysfunction in thrombosis patients treated with vitamin K antagonists and recurrent bleeding

BACKGROUND

Recurrent bleeding can complicate the treatment of thrombosis patients with vitamin K antagonists (VKA), even at a well-regulated level of anticoagulation. In this proof-of-principle study, we investigated whether alterations in platelet function or von Willebrand factor (vWf) contribute to a bleeding phenotype in these patients.

METHODS

In this case-control study 33 well-regulated patients without bleeding events (controls) and 33 patients with recurrent bleeding (cases) were retrospectively included. Thrombin generation and vWf were determined in plasma. Platelet function was assessed by light transmission aggregometry and flow cytometry using a validated panel of agonists.

RESULTS

Thrombin generation was similarly reduced in controls and cases, in comparison to normal plasma. Plasma vWf level was above the normal range in 85% of controls and 67% of the cases. vWf activity was similarly increased in all patients in comparison to healthy volunteers. Platelet aggregation was in the normal range for almost all patients irrespective of the type of agonist. However, in response to a low collagen dose, platelets from 21% of controls and 27% of cases showed diminished responses. Agonist-induced secretion of alpha- and dense-granules or integrin αIIbβ3 activation were affected in platelets from neither controls nor cases.

CONCLUSION

Recurrent bleeding in well-controlled patients on VKA therapy is not explained by anti-hemostatic changes in platelet or vWf function.

Platelet morphology analysis

Platelets are very small blood cells (1.5-3 μm), which play a major role in primary haemostasis and in coagulation mechanisms. Platelet characterization requires their counting (see Chapter 15 ) associated with accurate morphology analysis. We describe the major steps in order to correctly obtain stained blood films, which can be analyzed by optical microscope. Platelet morphology abnormalities are found in acquired malignant hematological diseases such myeloproliferative or myelodysplastic syndromes and acute megakaryoblastic leukemia. A careful analysis of the platelet size and morphology, by detecting either normal platelets with or without excessive anisocytosis, microplatelets, or large/giant platelets, will contribute to inherited thrombocytopenia diagnosis and gather substantial data when looking for an acquired platelet disorders.

Evaluation of participants with suspected heritable platelet function disorders including recommendation and validation of a streamlined agonist panel

Light transmission aggregometry (LTA) is used worldwide for the investigation of heritable platelet function disorders (PFDs), but interpretation of results is complicated by the feedback effects of ADP and thromboxane A(2) (TxA(2)) and by the overlap with the response of healthy volunteers. Over 5 years, we have performed lumi-aggregometry on 9 platelet agonists in 111 unrelated research participants with suspected PFDs and in 70 healthy volunteers. Abnormal LTA or ATP secretion test results were identified in 58% of participants. In 84% of these, the patterns of response were consistent with defects in Gi receptor signaling, the TxA(2) pathway, and dense granule secretion. Participants with defects in signaling to Gq-coupled receptor agonists and to collagen were also identified. Targeted genotyping identified 3 participants with function-disrupting mutations in the P2Y(12) ADP and TxA(2) receptors. The results of the present study illustrate that detailed phenotypic analysis using LTA and ATP secretion is a powerful tool for the diagnosis of PFDs. Our data also enable subdivision at the level of platelet-signaling pathways and in some cases to individual receptors. We further demonstrate that most PFDs can be reliably diagnosed using a streamlined panel of key platelet agonists and specified concentrations suitable for testing in most clinical diagnostic laboratories.

Platelet biogenesis and functions require correct protein O-glycosylation

Platelets express a variety of membrane and secreted glycoproteins, but the importance of glycosylation to platelet functions is poorly understood. To explore the importance of O-glycosylation, we generated mice with a targeted deletion of Cosmc in murine endothelial/hematopoietic cells (EHC) (EHC Cosmc(-/y)). X-linked Cosmc encodes an essential chaperone that regulates protein O-glycosylation. This targeted mutation resulted in lethal perinatal hemorrhage in the majority of mice, and the surviving mice displayed severely prolonged tail-bleeding times and macrothrombocytopenia. EHC Cosmc(-/y) platelets exhibited a marked decrease in GPIb-IX-V function and agonist-mediated integrin αIIbβ3 activation, associated with loss of interactions with von Willebrand factor and fibrinogen, respectively. Significantly, three O-glycosylated glycoproteins, GPIbα, αIIb, and GPVI normally on platelet surfaces that play essential roles in platelet functions, were partially proteolyzed in EHC Cosmc(-/y) platelets. These results demonstrate that extended O-glycans are required for normal biogenesis of the platelets as well as the expression and functions of their essential glycoproteins, and that variations in O-glycosylation may contribute to altered hemostasis.

Novel and recurrent mutations of ITGA2B and ITGB3 genes in Korean patients with Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder caused by defective glycoprotein, αIIb and β3, encoded by ITGA2B and ITGB3 genes, respectively. We herein describe four unrelated Korean patients with genetically confirmed GT. Two patients were homozygous for c.1913+5G>T (IVS11+5G>T) mutation of ITGB3 with a signature of founder effect. The other two patients were compound heterozygous for two mutations of ITGA2B: c.[2333A>C];[2975delA] (p.[Q778P];[E992Gfs*30]) and c.[1750C>T];[2333A>C] (p.[R584X];[Q778P]). The c.2975delA mutation was a novel frameshift mutation of ITGA2B. Although from a limited number of patients, these results suggests c.1913+5G>T of ITGB3 is a recurrent mutation in Korean patients with GT.

Inherited platelet disorders and oral health

Platelets play a key role in thrombosis and hemostasis. Accumulation of platelets at the site of vascular injury is the first step in the formation of hemostatic plugs, which play a pivotal role in preventing blood loss after injury. Platelet adhesion at sites of injury results in spreading, secretion, recruitment of additional platelets, and formation of platelet aggregates. Inherited platelet disorders are rare causes of bleeding syndromes, ranging from mild bruising to severe hemorrhage. The defects can reflect deficiency or dysfunction of platelet surface glycoproteins, granule contents, cytoskeletal proteins, platelet pro-coagulant function, and signaling pathways. For instance, Bernard-Soulier syndrome and Glanzmann thrombasthenia are attributed to deficiencies of glycoprotein Ib/IX/V and GPIIb/IIIa, respectively, and are rare but severe platelet disorders. Inherited defects that impair platelet secretion and/or signal transduction are among the most common forms of mild platelet disorders and include gray platelet syndrome, Hermansky-Pudlak syndrome, and Chediak-Higashi syndrome. When necessary, desmopressin, antifibrinolytic agents, and transfusion of platelets remain the most common treatment of inherited platelet disorders. Alternative therapies such as recombinant activated factor VII are also available for a limited number of situations. In this review, we will discuss the management of patients with inherited platelet disorders in various clinical situations related to dental cares, including surgical intervention.

Successful Management of Acute Catastrophic Juvenile Vaginal Bleeding in Glanzmann's Thromboasthenia by Uterine Tamponade: A Case Report and Review of The Literature

Glanzmann's thromboasthenia (GT) is a rare platelet disorder, due to membrane defects involving glycoprotein GP IIb/IIIa complex. Symptoms appear in infancy with episodes of bruising, gingival bleeding, epistaxis, or at the time of menarche acute episode of uterine bleeding. Hormonal therapy and antifibrinolytic agents are first-line treatment. Platelet transfusion is given to control hemorrhage when medical treatment fails. However, repeated transfusions may result in development of platelet refractioness, due to development of antibodies against membrane glycoprotein. Activated recombinant FVII is licensed for use in acute control of bleeding in GT. Here we report a case of acute juvenile uterine bleeding at menarche, which responded successfully to uterine tamponade. To our knowledge, this is the first case report on use of balloon tamponade for control of acute catastrophic juvenile bleeding at menarche.

Correction of murine Bernard-Soulier syndrome by lentivirus-mediated gene therapy

Bernard-Soulier syndrome (BSS) is an inherited bleeding disorder caused by a defect in the platelet glycoprotein (GP) Ib-IX-V complex. The main treatment for BSS is platelet transfusion but it is often limited to severe bleeding episodes or surgical interventions due to the risk of alloimmunization. We have previously reported successful expression of human GPIbα (hGPIbα) in human megakaryocytes using a lentiviral vector (LV) encoding human GP1BA under control of the platelet-specific integrin αIIb promoter (2bIbα). In this study, we examined the efficacy of this strategy for the gene therapy of BSS using GPIbα(null) as a murine model of BSS. GPIbα(null) hematopoietic stem cells (HSC) transduced with 2bIbα LV were transplanted into lethally irradiated GPIbα(null) littermates. Therapeutic levels of hGPIbα expression were achieved that corrected the tail bleeding time and improved the macrothrombocytopenia. Sequential bone marrow (BM) transplants showed sustained expression of hGPIbα with similar phenotypic correction. Antibody response to hGPIbα was documented in 1 of 17 total recipient mice but was tolerated without any further treatment. These results demonstrate that lentivirus-mediated gene transfer can provide sustained phenotypic correction of murine BSS, indicating that this approach may be a promising strategy for gene therapy of BSS patients.

Platelet receptors

Well-understood functions for "traditional" platelet receptors are described, but "newer" receptors are equally discussed. Receptors are described biochemically (structure, ligand(s), protein partners, and function) and whenever possible, their clinical importance (mutations, polymorphisms, syndrome) are highlighted.

Mechanobiology of platelets: techniques to study the role of fluid flow and platelet retraction forces at the micro- and nano-scale

Coagulation involves a complex set of events that are important in maintaining hemostasis. Biochemical interactions are classically known to regulate the hemostatic process, but recent evidence has revealed that mechanical interactions between platelets and their surroundings can also play a substantial role. Investigations into platelet mechanobiology have been challenging however, due to the small dimensions of platelets and their glycoprotein receptors. Platelet researchers have recently turned to microfabricated devices to control these physical, nanometer-scale interactions with a higher degree of precision. These approaches have enabled exciting, new insights into the molecular and biomechanical factors that affect platelets in clot formation. In this review, we highlight the new tools used to understand platelet mechanobiology and the roles of adhesion, shear flow, and retraction forces in clot formation.

Thrombocytopenia resulting from mutations in filamin A can be expressed as an isolated syndrome

Filaminopathies A caused by mutations in the X-linked FLNA gene are responsible for a wide spectrum of rare diseases including 2 main phenotypes, the X-linked dominant form of periventricular nodular heterotopia (FLNA-PVNH) and the otopalatodigital syndrome spectrum of disorders. In platelets, filamin A (FLNa) tethers the principal receptors ensuring the platelet-vessel wall interaction, glycoprotein Ibα and integrin αIIbβ3, to the underlying cytoskeleton. Hemorrhage, coagulopathy, and thrombocytopenia are mentioned in several reports on patients with FLNA-PVNH. Abnormal platelet morphology in 2 patients with FLNA-PVNH prompted us to examine a third patient with similar platelet morphology previously diagnosed with immunologic thrombocytopenic purpura. Her enlarged platelets showed signs of FLNa degradation in Western blotting, and a heterozygous missense mutation in FLNA was detected. An irregular distribution of FLNa within the total platelet population was shown by confocal microscopy for all 3 patients. In vitro megakaryocyte cultures showed an abnormal differentiation, including an irregular distribution of FLNa with a frayed aspect, the presence of enlarged α-granules, and an abnormal fragmentation of the cytoplasm. Mutations in FLNA may represent an unrecognized cause of macrothrombocytopenia with an altered platelet production and a modified platelet-vessel wall interaction.