Eltrombopag for the treatment of the inherited thrombocytopenia deriving from MYH9 mutations

Inherited Macrothrombocytopenia: Correlating Morphology, Epidemiology, Molecular Pathology and Clinical Features

Inherited macrothrombocytopenia is increasingly being recognized as a relatively common condition. This descriptive review aims at focusing on the different areas of advancement that have taken place with this condition with particular reference to India. A pubmed search of articles between January 1990 and October 2017 with the key words-macrothrombocytopenia, asymptomatic macrothrombocytopenia, macrothrombocytopenia India, syndromic macrothrombocytopenia, molecular pathology, megakaryopoiesis and platelet formation were searched. The shortlisted articles were then read. Review articles provided additional references and the articles thus obtained were also read. Special interest and research conducted by the authors provided further sources of information. A total of 487 articles were found of which 68 articles were related to our subject of review. Review articles were read and additional articles from the reference quoted. Forty-four percent of nonsyndromic Inherited macrothrombocytopenia showed mutations of MYH9, GP1BB, GP1Ba, GPIX, ABCG5 and 8, ACTN, FLI, TUBB and RUNX1 frequently in heterozygous state. All types of inheritance pattern namely autosomal dominant, recessive and sex linked patterns have been described. Syndromic causes of this phenomenon are well known and have been described. Many asymptomatic patients do have mild or moderate bleeding history. Clinical algorithms to differentiate chronic ITP associated macrothrombocytopenia from inherited variety have been explored. Inherited macrothrombocytopenia is an emerging area of interest in platelet biology with its implication in diagnosis, prognosis, genetic counseling, management and in transfusion medicine.

Congenital Disorders of Platelet Function and Number

Mucocutaneous bleeding symptoms and/or persistent thrombocytopenia occur in individuals with congenital disorders of platelet function and number. Apart from bleeding, these disorders are often associated with additional hematologic and clinical manifestations, including auditory, immunologic, and oncologic disease. Autosomal recessive, dominant, and X-linked inheritance patterns have been demonstrated. Precise delineation of the molecular cause of the platelet disorder can aid the pediatrician in the detection and prevention of specific disorder-associated manifestations and guide appropriate treatment and anticipatory care for the patient and family.

Clinic, pathogenic mechanisms and drug testing of two inherited thrombocytopenias, ANKRD26-related Thrombocytopenia and MYH9-related diseases

Inherited thrombocytopenias (ITs) are a heterogeneous group of disorders characterized by low platelet count resulting in impaired hemostasis. Patients can have spontaneous hemorrhages and/or excessive bleedings provoked by hemostatic challenges as trauma or surgery. To date, ITs encompass 32 different rare monogenic disorders caused by mutations of 30 genes. This review will focus on the major discoveries that have been made in the last years on the diagnosis, treatment and molecular mechanisms of ANKRD26-Related Thrombocytopenia and MYH9-Related Diseases. Furthermore, we will discuss the use a Thrombopoietin mimetic as a novel approach to treat the thrombocytopenia in these patients. We will propose the use of a new 3D bone marrow model to study the mechanisms of action of these drugs and to test their efficacy and safety in patients. The overall purpose of this review is to point out that important progresses have been made in understanding the pathogenesis of ANKRD26-Related Thrombocytopenia and MYH9-Related Diseases and new therapeutic approaches have been proposed and tested. Future advancement in this research will rely in the development of more physiological models to study the regulation of human platelet biogenesis, disease mechanisms and specific pharmacologic targets.

Hereditary thrombocytopenias: a growing list of disorders

The introduction of high throughput sequencing (HTS) techniques greatly improved the knowledge of inherited thrombocytopenias (ITs) over the last few years. A total of 33 different forms caused by molecular defects affecting at least 32 genes have been identified; along with the discovery of new disease-causing genes, pathogenetic mechanisms of thrombocytopenia have been better elucidated. Although the clinical picture of ITs is heterogeneous, bleeding has been long considered the major clinical problem for patients with IT. Conversely, the current scenario indicates that patients with some of the most common ITs are at risk of developing additional disorders more dangerous than thrombocytopenia itself during life. In particular, MYH9 mutations result in congenital macrothrombocytopenia and predispose to kidney failure, hearing loss, and cataracts, MPL and MECOM mutations cause congenital thrombocytopenia evolving into bone marrow failure, whereas thrombocytopenias caused by RUNX1, ANKRD26, and ETV6 mutations are characterized by predisposition to hematological malignancies. Making a definite diagnosis of these forms is crucial to provide patients with the most appropriate treatment, follow-up, and counseling. In this review, the ITs known to date are discussed, with specific attention focused on clinical presentations and diagnostic criteria for ITs predisposing to additional illnesses. The currently available therapeutic options for the different forms of IT are illustrated.

Eltrombopag use in a patient with Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an inherited X-linked disorder characterized by microthrombocytopenia, immunodeficiency, and eczema. Hematopoietic stem cell transplantation (HSCT) is the treatment of choice. Eltrombopag, a thrombopoietin receptor agonist, may be useful to prevent bleeding while awaiting HSCT. We present a case of a male with WAS, profound thrombocytopenia, and bleeding diathesis successfully managed with eltrombopag before HSCT. Eltrombopag was given for 32 weeks obtaining a stable platelet count without any platelet transfusion. The patient did not experience any bleeding symptom. Eltrombopag may be a suitable therapeutic option for patients with WAS and severe thrombocytopenia as "bridge" to definitive cure.

In vitro generation of platelets: Where do we stand?

Millions of platelets, specialized cells that participate in haemostatic and inflammatory functions, are transfused each year worldwide, but their supply is limited. Platelets are produced by megakaryocytes by extending proplatelets, directly into the bloodstream. Bone marrow structure and extracellular matrix composition together with soluble factors (e.g. Thrombopoietin) are key regulators of megakaryopoiesis by supporting cell differentiation and platelet release. Despite this knowledge, the scarcity of clinical cures for life threatening platelet diseases is in a large part due to limited insight into the mechanisms that control the developmental process of megakaryocytes and the mechanisms that govern the production of platelets within the bone marrow. To overcome these limitations, functional human tissue models have been developed and studied to extrapolate ex vivo outcomes for new insight on bone marrow functions in vivo. There are many challenges that these models must overcome, from faithfully mimicking the physiological composition and functions of bone marrow, to the collection of the platelets generated and validation of their viability and function for human use. The overall goal is to identify innovative instruments to study mechanisms of platelet release, diseases related to platelet production and new therapeutic targets starting from human progenitor cells.

Bleeding is not the main clinical issue in many patients with inherited thrombocytopaenias

Bleeding diathesis has been considered for a long time the main clinical issue impacting the lives of patients affected by inherited thrombocytopaenias. However, the number of known inherited thrombocytopaenias greatly increased in recent years, and careful evaluation of hundreds of patients affected by these 'new' disorders revealed that most of them are at risk of developing additional life-threatening disorders during childhood or adult life. These additional disorders are usually more serious and dangerous than low platelet count. For instance, it is known that mutations in RUNX1, ANKRD26 and ETV6 cause congenital thrombocytopaenia, but we now know that they also predispose to haematological malignancies. Similarly, MYH9 mutations result in congenital thrombocytopaenia and increase the risk of developing kidney failure, cataracts and hearing loss at a later stage, while MPL mutations cause a congenital thrombocytopaenia that almost always evolves into deadly bone marrow failure. Thus, identification of patients with these disorders is essential for evaluation of their prognosis, enabling effective genetic counselling, personalizing follow-up and giving appropriate treatments in case of development of additional diseases. Careful clinical evaluation and peripheral blood film examination are extremely useful tools in guiding the diagnostic process and identifying the candidate genes to be sequenced.

Bleeding risk of surgery and its prevention in patients with inherited platelet disorders

Excessive bleeding at surgery is a feared complication in patients with inherited platelet disorders. However, very few studies have evaluated the frequency of surgical bleeding in these hemorrhagic disorders. We performed a worldwide, multicentric, retrospective study to assess the bleeding complications of surgery, the preventive and therapeutic approaches adopted, and their efficacy in patients with inherited platelet disorders: the Surgery in Platelet disorders And Therapeutic Approach (SPATA) study. We rated the outcome of 829 surgical procedures carried out in 423 patients with well-defined forms of inherited platelet disorders: 238 inherited platelet function disorders and 185 inherited platelet number disorders. Frequency of surgical bleeding was high in patients with inherited platelet disorders (19.7%), with a significantly higher bleeding incidence in inherited platelet function disorders (24.8%) than in inherited platelet number disorders (13.4%). The frequency of bleeding varied according to the type of inherited platelet disorder, with biallelic Bernard Soulier syndrome having the highest occurrence (44.4%). Frequency of bleeding was predicted by a pre-operative World Health Organization bleeding score of 2 or higher. Some types of surgery were associated with a higher bleeding incidence, like cardiovascular and urological surgery. The use of pre-operative pro-hemostatic treatments was associated with a lower bleeding frequency in patients with inherited platelet function disorders but not in inherited platelet number disorders. Desmopressin, alone or with antifibrinolytic agents, was the preventive treatment associated with the lowest bleedings. Platelet transfusions were used more frequently in patients at higher bleeding risk. Surgical bleeding risk in inherited platelet disorders is substantial, especially in inherited platelet function disorders, and bleeding history, type of disorder, type of surgery and female sex are associated with higher bleeding frequency. Prophylactic pre-operative pro-hemostatic treatments appear to be required and are associated with a lower bleeding incidence.

Bone marrow morphology and disease progression in congenital thrombocytopenia: a detailed clinicopathologic and genetic study of eight cases

Patients with congenital thrombocytopenia have an increased risk of developing myeloid neoplasms. In these cases, the morphologic distinction between disease at baseline and at progression is challenging. This report analyzes clinicopathologic features of congenital thrombocytopenia with long-term follow-up at one referral center. Records from the last 20 years were searched for cases of congenital thrombocytopenia with bone marrow biopsies and peripheral blood smears. The clinical, morphologic, immunophenotypic, and molecular features were analyzed. Six adult and two pediatric patients were identified (six male, two female). Age range at first biopsy was 1-47 (median, 31) years. Underlying diseases included thrombocytopenia-absent radius syndrome, congenital thrombocytopenia with radial-ulnar synostosis, MYH9-related disorder, shortened telomere syndrome, congenital thrombocytopenia with ANKRD26 mutation, and familial platelet disorder with predisposition to acute myeloid leukemia. Four patients had myelodysplastic/myeloproliferative neoplasm-like marrow changes such as hypercellularity, increased myeloid to erythroid ratio, numerous micromegakaryocytes (highlighted by CD42b), and marrow fibrosis. Two patients had marrow hypoplasia and two had unremarkable marrow morphology. Three patients-all in the myelodysplastic/myeloproliferative neoplasm-like group-developed disease progression characterized by erythroid and myeloid dysplasia, elevated bone marrow blasts, and new cytogenetic abnormalities. Unlike non-familial myeloid neoplasms, congenital thrombocytopenia patients in the myelodysplastic/myeloproliferative neoplasm-like group had a long and indolent clinical course (average age at disease progression, 47 years). In summary, three distinct morphologic types of congenital thrombocytopenia were identified: a hyperplastic myelodysplastic/myeloproliferative neoplasm-like group, a hypoplastic bone marrow failure-like group, and a group with relatively normal marrow morphology. Emergence of cytogenetic abnormalities and dysplasia in non-megakaryocyte lineages correlated with disease progression.

Thrombopoetin receptor agonist therapy in thrombocytopenia: ITP and beyond

Eltrombopag is well established in treatment of severe immune thrombocytopenia (ITP) and is increasingly commonplace in second-line management. A role is also suggested for both bridging therapy for surgery, as well as treating thrombocytopenia due to non-immune aetiologies. We present the largest single-centre experience with eltrombopag, with our cohort of 62 patients. Patients with severe ITP (n = 34) had 91·2% response, which was sustained over a median of 18·5 months. In 41·4% of ITP cases (n = 14), complete response (CR- platelet count >100 × 10⁹ /l) was achieved and in 2 cases, therapy was stopped and CR maintained. In our bridging group (n = 15) with a higher baseline platelet count, 93·3% achieved a CR. In the non-ITP group (n = 13), a response was achieved in 76·9%. In all groups, side effects were transient, with the drug discontinued in 2 patients due to minor complications (rash, nausea, diarrhoea). We conclude that eltrombopag is both effective and well tolerated as therapy in severe ITP. It is also advantageous in ITP patients who do not normally require therapy, but need a temporary platelet count boost pre-procedure. Furthermore, there are potentially far wider implications for the use of eltrombopag in counteracting thrombocytopenia beyond ITP, which merit further investigation.

Beyond immune thrombocytopenia: the evolving role of thrombopoietin receptor agonists

Since its discovery, the thrombopoietin (TPO) pathway has been an important pharmaceutical target for the treatment of thrombocytopenia. The first generation of TPO mimetics included peptide agents sharing homology with endogenous TPO, but these introduced a risk of antibody formation to endogenous TPO and were not successful. However, second-generation TPO mimetics or TPO receptor agonists (RAs) are currently being used to treat thrombocytopenia associated with a number of conditions, such as immune thrombocytopenia (ITP), severe aplastic anaemia (SAA), and hepatitis C virus-associated chronic liver disease. Accumulating efficacy and safety data suggest that the role of TPO-RAs in the treatment of thrombocytopenia may evolve in the near future with broader use of these agents in ITP and SAA, as well as approval in other indications, potentially including myelodysplastic syndromes, chemotherapy-associated thrombocytopenia, and post-transplant thrombocytopenia. This review provides an overview of clinical data on the efficacy and safety of TPO-RAs, emphasising recent findings that may expand their clinical utility.

Eltrombopag, a thrombopoietin mimetic, crosses the blood-brain barrier and impairs iron-dependent hippocampal neuron dendrite development

Essentials Potential neurodevelopmental side effects of thrombopoietin mimetics need to be considered. The effects of eltrombopag (ELT) on neuronal iron status and dendrite development were assessed. ELT crosses the blood-brain barrier and causes iron deficiency in developing neurons. ELT blunts dendrite maturation, indicating a need for more safety studies before neonatal use.

SUMMARY

Background Thrombocytopenia is common in sick neonates. Thrombopoietin mimetics (e.g. eltrombopag [ELT]) might provide an alternative therapy for selected neonates with severe and prolonged thrombocytopenia, and for infants and young children with different varieties of thrombocytopenia. However, ELT chelates intracellular iron, which may adversely affect developing organs with high metabolic requirements. Iron deficiency (ID) is particularly deleterious during brain development, impairing neuronal myelination, dopamine signaling and dendritic maturation and ultimately impairing long-term neurological function (e.g. hippocampal-dependent learning and memory). Objective To determine whether ELT crosses the blood-brain barrier (BBB), causes neuronal ID and impairs hippocampal neuron dendrite maturation. Methods ELT transport across the BBB was assessed using primary bovine brain microvascular endothelial cells. Embryonic mouse primary hippocampal neuron cultures were treated with ELT or deferoxamine (DFO, an iron chelator) from 7 days in vitro (DIV) through 14 DIV and assessed for gene expression and neuronal dendrite complexity. Results ELT crossed the BBB in a time-dependent manner. 2 and 6 μm ELT increased Tfr1 and Slc11a2 (iron-responsive genes involved in neuronal iron uptake) mRNA levels, indicating neuronal ID. 6 μm ELT, but not 2 μm ELT, decreased BdnfVI, Camk2a and Vamp1 mRNA levels, suggesting impaired neuronal development and synaptic function. Dendrite branch number and length were reduced in 6 μm ELT-treated neurons, resulting in blunted dendritic arbor complexity that was similar to DFO-treated neurons. Conclusions Eltrombopag treatment during development may impair neuronal structure as a result of neuronal ID. Preclinical in vivo studies are warranted to assess ELT safety during periods of rapid brain development.

Inherited Thrombocytopenia with a Different Type of Gene Mutation: A Brief Literature Review and Two Case Studies

Hereditary thrombocytopenias are rare bleeding disorders, which cause a deficiency of platelets in early infancy. This group of disorders is sometimes associated with abnormal phenotypes, like absence of radius. Diagnosis of this type of thrombocytopenia is usually difficult; other causes of thrombocytopenia, such as immune disorders and infections, must be ruled out. The symptoms of hereditary thrombocytopenia also vary from seldom and mild to severe bleeding and occasionally may first occur in late childhood. In this group of patients, we must differentiate heritable disorders from the acquired types of thrombocytopenia, like immune thrombocytopenic purpura. It is also important to watch for pitfalls to avoid unnecessary and potentially hazardous treatment. Herein, we briefly review the recent literature on hereditary thrombocytopenia and then present the cases of two referred patients. The first case had suffered from persistent thrombocytopenia since early infancy and was diagnosed with congenital amegakaryocytic thrombocytopenia, while the other patient presented with Wiskott - Aldrich syndrome.

Genomics of platelet disorders

Genetic diagnosis in families with inherited platelet disorders (IPD) is not performed widely because of the genetic heterogeneity of this group of disorders and because in most cases, it is not possible to select single candidate genes for analysis using clinical and laboratory phenotypes. Next-generation sequencing (NGS) technology has revolutionized the scale and cost-effectiveness of genetic testing, and has emerged as a valuable tool for IPD. This review examines the potential utility of NGS as a diagnostic tool to streamline detection of causal variants in known IPD genes and as a vehicle for new gene discovery.

Alternative agents to prophylactic platelet transfusion for preventing bleeding in people with thrombocytopenia due to chronic bone marrow failure: a meta-analysis and systematic review

BACKGROUND

People with thrombocytopenia due to bone marrow failure are vulnerable to bleeding. Platelet transfusions have limited efficacy in this setting and alternative agents that could replace, or reduce platelet transfusion, and are effective at reducing bleeding are needed.

OBJECTIVES

To compare the relative efficacy of different interventions for patients with thrombocytopenia due to chronic bone marrow failure and to derive a hierarchy of potential alternative treatments to platelet transfusions.

SEARCH METHODS

We searched for randomised controlled trials (RCTs) in the Cochrane Central Register of Controlled Trials (the Cochrane Library 2016, Issue 3), MEDLINE (from 1946), Embase (from 1974), CINAHL (from 1937), the Transfusion Evidence Library (from 1980) and ongoing trial databases to 27 April 2016.

SELECTION CRITERIA

We included randomised controlled trials in people with thrombocytopenia due to chronic bone marrow failure who were allocated to either an alternative to platelet transfusion (artificial platelet substitutes, platelet-poor plasma, fibrinogen concentrate, recombinant activated factor VII (rFVIIa), desmopressin (DDAVP), recombinant factor XIII (rFXIII), recombinant interleukin (rIL)6 or rIL11, or thrombopoietin (TPO) mimetics) or a comparator (placebo, standard of care or platelet transfusion). We excluded people undergoing intensive chemotherapy or stem cell transfusion.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened search results, extracted data and assessed trial quality. We estimated summary risk ratios (RR) for dichotomous outcomes. We planned to use summary mean differences (MD) for continuous outcomes. All summary measures are presented with 95% confidence intervals (CI).We could not perform a network meta-analysis because the included studies had important differences in the baseline severity of disease for the participants and in the number of participants undergoing chemotherapy. This raised important concerns about the plausibility of the transitivity assumption in the final dataset and we could not evaluate transitivity statistically because of the small number of trials per comparison. Therefore, we could only perform direct pairwise meta-analyses of included interventions.We employed a random-effects model for all analyses. We assessed statistical heterogeneity using the I2 statistic and its 95% CI. The risk of bias of each study included was assessed using the Cochrane 'Risk of bias' tool. The quality of the evidence was assessed using GRADE methods.

MAIN RESULTS

We identified seven completed trials (472 participants), and four ongoing trials (recruiting 837 participants) which are due to be completed by December 2020. Of the seven completed trials, five trials (456 participants) compared a TPO mimetic versus placebo (four romiplostim trials, and one eltrombopag trial), one trial (eight participants) compared DDAVP with placebo and one trial (eight participants) compared tranexamic acid with placebo. In the DDAVP trial, the only outcome reported was the bleeding time. In the tranexamic acid trial there were methodological flaws and bleeding definitions were subject to significant bias. Consequently, these trials could not be incorporated into the quantitative synthesis. No randomised trial of artificial platelet substitutes, platelet-poor plasma, fibrinogen concentrate, rFVIIa, rFXIII, rIL6 or rIL11 was identified.We assessed all five trials of TPO mimetics included in this review to be at high risk of bias because the trials were funded by the manufacturers of the TPO mimetics and the authors had financial stakes in the sponsoring companies.The GRADE quality of the evidence was very low to moderate across the different outcomes.There was insufficient evidence to detect a difference in the number of participants with at least one bleeding episode between TPO mimetics and placebo (RR 0.86, 95% CI 0.56 to 1.31, four trials, 206 participants, low-quality evidence).There was insufficient evidence to detect a difference in the risk of a life-threatening bleed between those treated with a TPO mimetic and placebo (RR 0.31, 95% CI 0.04 to 2.26, one trial, 39 participants, low-quality evidence).There was insufficient evidence to detect a difference in the risk of all-cause mortality between those treated with a TPO mimetic and placebo (RR 0.74, 95%CI 0.52 to 1.05, five trials, 456 participants, very low-quality evidence).There was a significant reduction in the number of participants receiving any platelet transfusion between those treated with TPO mimetics and placebo (RR 0.76, 95% CI 0.61 to 0.95, four trials, 206 participants, moderate-quality evidence).There was no evidence for a difference in the incidence of transfusion reactions between those treated with TPO mimetics and placebo (pOR 0.06, 95% CI 0.00 to 3.44, one trial, 98 participants, very low-quality evidence).There was no evidence for a difference in thromboembolic events between TPO mimetics and placebo (RR 1.41, 95%CI 0.39 to 5.01, five trials, 456 participants, very-low quality evidence).There was no evidence for a difference in drug reactions between TPO mimetics and placebo (RR 1.12, 95% CI 0.83 to 1.51, five trials, 455 participants, low-quality evidence).No trial reported the number of days of bleeding per participant, platelet transfusion episodes, mean red cell transfusions per participant, red cell transfusion episodes, transfusion-transmitted infections, formation of antiplatelet antibodies or platelet refractoriness.In order to demonstrate a reduction in bleeding events from 26 in 100 to 16 in 100 participants, a study would need to recruit 514 participants (80% power, 5% significance).

AUTHORS' CONCLUSIONS

There is insufficient evidence at present for thrombopoietin (TPO) mimetics for the prevention of bleeding for people with thrombocytopenia due to chronic bone marrow failure. There is no randomised controlled trial evidence for artificial platelet substitutes, platelet-poor plasma, fibrinogen concentrate, rFVIIa, rFXIII or rIL6 or rIL11, antifibrinolytics or DDAVP in this setting.

Revealing eltrombopag's promotion of human megakaryopoiesis through AKT/ERK-dependent pathway activation

Eltrombopag is a small, non-peptide thrombopoietin mimetic that has been approved for increasing platelet count not only in immune thrombocytopenia and Hepatitis C virus-related thrombocytopenia, but also in aplastic anemia. Moreover, this drug is under investigation for increasing platelet counts in myelodysplastic syndromes. Despite current clinical practice, the mechanisms governing eltrombopag's impact on human hematopoiesis are largely unknown, in part due to the impossibility of using traditional in vivo models. To investigate eltrombopag's impact on megakaryocyte functions, we employed our established in vitro model for studying hematopoietic stem cell differentiation combined with our latest 3-dimensional silk-based bone marrow tissue model. Results demonstrated that eltrombopag favors human megakaryocyte differentiation and platelet production in a dose-dependent manner. These effects are accompanied by increased phosphorylation of AKT and ERK1/2 signaling molecules, which have been proven to be crucial in regulating physiologic thrombopoiesis. These data further clarify the different mechanisms of action of eltrombopag when compared to romiplostim, which, as we have shown, induces the proliferation of immature megakaryocytes rather than platelet production, due to the unbalanced activation of AKT and ERK1/2 signaling molecules. In conclusion, our research clarifies the underlying mechanisms that govern the action of eltrombopag on megakaryocyte functions and its relevance in clinical practice.

Preoperative use of platelets in a 6-year-old with acute appendicitis and a myosin heavy chain 9-related disorder: a case report and review of literature

BACKGROUND

Mutations of nonmuscle myosin heavy chain 9 (MYH9) gene are an autosomal dominant cause of inherited thrombocytopenia in children. MYH9 spectrum disorders include May-Hegglin anomaly and Sebastian, Fechtner, and Epstein syndromes. Patients with these disorders often present with macroplatelets and thrombocytopenia and have a mild bleeding tendency; extrahematologic manifestations (nephropathy, deafness, and cataracts) correlate with specific mutations. No definitive guidelines exist for preoperative prophylactic platelet (PLT) transfusion in these patients.

STUDY DESIGN AND METHODS

This was a case study and literature review.

RESULTS

A 6-year-old male presented with appendicitis. Review of records revealed that he and his siblings had thrombocytopenia; polymerase chain reaction amplification with DNA sequence analysis showed a variation in the MYH9 gene previously reported as a known cause of MYH9-related disorders. Involvement of other organ systems was not found on initial work-up. The patient's PLT count on admission was 20 × 10(9) /L. The degree of thrombocytopenia prompted transfusion of apheresis PLTs and he had good response (73 × 10(9) /L). After infusion he developed hives, rash, itching, and nausea, which resolved after administration of epinephrine and hydrocortisone. Transfusion reaction work-up was negative and symptoms were interpreted as an allergic reaction. The appendectomy was uneventful.

CONCLUSION

This patient's PLT count was within guidelines to warrant transfusion; however, some patients with MYH9 mutations have counts above the transfusion threshold. To the authors' knowledge, there are no set guidelines for preoperative prophylaxis in a patient with an MYH9 deficiency. The management of the bleeding diathesis in these patients, especially in the setting of invasive procedures, is uncertain.

Sporadic Epstein syndrome with macrothrombocytopenia, sensorineural hearing loss and renal failure

We report here a sporadic case of Epstein syndrome, one of the MYH9 disorders. A Japanese boy was first noted to have thrombocytopenia at 3 years of age. Blood smear showed giant platelets but no Döhle-like bodies in the neutrophils. He had no family history of thrombocytopenia, hearing loss, and/or renal failure. Thrombocytopenia took a chronic course and platelet count fluctuated in the range 18 000-46 000/μL, not responding to i.v. immunoglobulin or prednisolone treatment. The patient had episodes of gross nasal bleeding at 7 and 18 years of age. Mild hearing loss was suspected at 6, and proteinuria was first noted at 14 years of age. At the development of renal failure at 24 years of age, he was identified to have de novo R702H MYH9 mutation. This case illustrates the importance of suspecting MYH9 disorder even in cases of chronic macrothrombocytopenia without family history.

Diagnosis and treatment of inherited thrombocytopenias

Knowledge in the field of inherited thrombocytopenias (ITs) has greatly improved over the last 15 years. Several new genes responsible for thrombocytopenia have been identified leading to the definition of novel nosographic entities and to a much better characterization of the phenotypes of these diseases. To date, ITs encompass 22 disorders caused by mutations in 24 genes and characterized by different degrees of complexity and great variability in prognosis. Making a definite diagnosis is important for setting an appropriate follow-up, choosing the best treatments and providing proper counseling. Despite the abovementioned progress, diagnosis of ITs remains difficult and these disorders are still underdiagnosed. The purpose of this review is to provide an updated guide to the diagnosis of ITs based on simple procedures. Moreover, the currently available therapeutic options for these conditions are recapitulated and discussed.

β-1 tubulin R307H SNP alters microtubule dynamics and affects severity of a hereditary thrombocytopenia

BACKGROUND

Single nucleotide polymorphisms (SNPs) in platelet-associated genes partly explain inherent variability in platelet counts. Patients with monoallelic Bernard Soulier syndrome due to the Bolzano mutation (GPIBA A156V) have variable platelet counts despite a common mutation for unknown reasons.

OBJECTIVES

We investigated the effect of the most common SNP (R307H) in the hematopoietic-specific tubulin isotype β-1 in these Bernard Soulier patients and potential microtubule-based mechanisms of worsened thrombocytopenia.

PATIENTS/METHODS

Ninety-four monoallelic Bolzano mutation patients were evaluated for the R307H β-1 SNP and had platelet counts measured by three methods; the Q43P SNP was also evaluated. To investigate possible mechanisms underlying this association, we used molecular modeling of β-1 tubulin with and without the R307H SNP. We transfected SNP or non-SNP β-1 tubulin into MCF-7 and CMK cell lines and measured microtubule regrowth after nocodazole-induced depolymerization.

RESULTS

We found that patients with at least one R307H SNP allele had significantly worse thrombocytopenia; manual platelet counting revealed a median platelet count of 124 in non-SNP patients and 76 in SNP patients (both ×10(9)  L(-1) ; P < 0.01). The Q43P SNP had no significant association with platelet count. Molecular modeling suggested a structural relationship between the R307H SNP and microtubule stability via alterations in the M-loop of β tubulin; in vitro microtubule recovery assays revealed that cells transfected with R307H SNP β-1 had significantly impaired microtubule recovery.

CONCLUSIONS

Our data show that the R307H SNP is significantly associated with the degree of thrombocytopenia in congenital and acquired platelet disorders, and may affect platelets by altering microtubule behavior.

Thrombopoietin receptor agonists: a critical review

Thrombopoietic agents have created a paradigm shift in the management of chronic or poorly responsive immune thrombocytopenia (ITP). There are ample randomized, placebo-controlled trial data, as well as long-term data gathered for more than 5 years; short-term efficacy and safety are well documented and long-term efficacy and safety data are emerging. The purpose of this review will be to focus critically on what we know or do not know at this point about these agents. We review the evolution, efficacy and clinical use, side effects, special populations, and off-target effects of the thrombopoietic agents.

Treatment of pediatric primary immune thrombocytopenia with thrombopoietin receptor agonists

Chronic immune thrombocytopenia (ITP) occurs in approximately one fifth of children with primary ITP and is characterized by a significant lack of clinical data. A minority of these children exhibit bleeding and need treatment. Often standard therapy used for patients with newly diagnosed ITP is administered to stop bleeding and to increase the platelet count. These drugs are associated with adverse effects, which is particularly evident when used during long time. In adult patients with chronic ITP, thrombopoietin receptor agonists (TPO-RAs) demonstrated efficacy in approximately 80% of patients. These drugs have been studied intensely for registration purposes; however, for children and adolescents they are not yet approved and studies are ongoing. First experiences with these drugs show similar effects and safety as in adults, though based on very small numbers of children. These drugs have the potential to be used during long time, in order to increase platelets, to stop or prevent bleeding and to augment quality of life, making long-term safety an important issue.

Eltrombopag with gemcitabine-based chemotherapy in patients with advanced solid tumors: a randomized phase I study

Preventing chemotherapy-induced thrombocytopenia could avoid chemotherapy dose reductions and delays. The safety and maximum tolerated dose of eltrombopag, an oral thrombopoietin receptor agonist, with gemcitabine-based therapy was evaluated. Patients with advanced solid tumors and platelets ≤300 × 10⁹/L receiving gemcitabine plus cisplatin or carboplatin (Group A) or gemcitabine monotherapy (Group B) were randomized 3:1 to receive eltrombopag or placebo at a starting dose of 100 mg daily administered on days −5 to −1 and days 2–6 starting from cycle 2 of treatment. Nineteen patients (Group A, n = 9; Group B, n = 10) received eltrombopag 100 mg and seven (Group A, n = 3; Group B, n = 4) received matching placebo. Nine eltrombopag patients in Group A and eight in Group B had 38 and 54 occurrences of platelet counts ≥400 × 10⁹/L, respectively. Mean platelet nadirs across cycles 2–6 were 115 × 10⁹/L and 143 × 10⁹/L for eltrombopag-treated patients versus 53 × 10⁹/L and 103 × 10⁹/L for placebo-treated patients in Groups A and B, respectively. No dose-limiting toxicities were reported for eltrombopag; however, due to several occurrences of thrombocytosis, a decision was made not to dose-escalate eltrombopag to >100 mg daily. In Groups A and B, 14% of eltrombopag versus 50% of placebo patients required chemotherapy dose reductions and/or delays for any reason across cycles 3–6. Eltrombopag 100 mg once daily administered 5 days before and after day 1 of chemotherapy was well tolerated with an acceptable safety profile, and will be further tested in a phase II trial. Fewer patients receiving eltrombopag required chemotherapy dose delays and/or reductions compared with those receiving placebo.

Platelet diameters in inherited thrombocytopenias: analysis of 376 patients with all known disorders

Abnormalities of platelet size are one of the distinguishing features of inherited thrombocytopenias (ITs), and evaluation of blood films is recommended as an essential step for differential diagnosis of these disorders. Nevertheless, what we presently know about this subject is derived mainly from anecdotal evidence. To improve knowledge in this field, we evaluated platelet size on blood films obtained from 376 patients with all 19 forms of IT identified so far and found that these conditions differ not only in mean platelet diameter, but also in platelet diameter distribution width and the percentage of platelets with increased or reduced diameters. On the basis of these findings, we propose a new classification of ITs according to platelet size. It distinguishes forms with giant platelets, with large platelets, with normal or slightly increased platelet size, and with normal or slightly decreased platelet size. We also measured platelet diameters in 87 patients with immune thrombocytopenia and identified cutoff values for mean platelet diameter and the percentage of platelets with increased or reduced size that have good diagnostic accuracy in differentiating ITs with giant platelets and with normal or slightly decreased platelet size from immune thrombocytopenia and all other forms of IT.

Management of thrombocytopenia

Thrombocytopenia is one of the most common hematologic disorders, characterized by an abnormally low number of platelets from multiple causes. The normal count of thrombocytes (platelets) is between 150,000 and 450,000 per microliter. The clinical expression of thrombocytopenia has broad variation from asymptomatic to life-threatening bleeding. Various syndromes and diseases are associated with thrombocytopenia. Thrombocytopenia is sometimes a first sign of hematologic malignancies, infectious diseases, thrombotic microangiopathies, and autoimmune disorders, and is also a common side effect of many medications. There are more than 200 diseases that include low number of platelets among their symptoms. A brief discussion of the most common etiologies and management of them is provided in this review.

Milestones in understanding platelet production: a historical overview

The discovery of thrombopoietin (TPO, also termed THPO) in 1994 was a major achievement in understanding the regulation of platelet production. In prior decades, physiological studies had demonstrated that platelets were produced from bone marrow megakaryocytes and that the megakaryocytes responded to thrombocytopenia by increasing their number, size and DNA ploidy. In 1958, it was proposed that a 'thrombopoietin' must exist that regulated this interaction between the circulating platelet mass and the bone marrow megakaryocytes. After over three decades of effort, TPO was finally purified by five independent laboratories. TPO stimulated megakaryocyte colony-forming cell growth and increased the number, size and ploidy of megakaryocytes. When the genes for TPO or TPO receptor were eliminated in mice, megakaryocytes grew and platelets were made, but at 15% of their normal number. A first generation of recombinant human (rh) TPO molecules [rhTPO and pegylated recombinant human megakaryocyte growth and development factor (PEG-rhMGDF)] rapidly entered clinical trials in 1995 and increased platelet counts in humans undergoing non-myeloablative chemotherapy but not in those undergoing stem cell transplantation. Antibodies developed against PEG-rhMGDF and development of these recombinant thrombopoietins ended. A second generation of TPO receptor agonists (romiplostim and eltrombopag) was then developed. Neither of these TPO receptor agonists demonstrated any significant untoward effects and both are now licensed in many countries for the treatment of immune thrombocytopenia. This review describes the significant experiments that have surrounded the discovery of TPO and its clinical development.

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.

Exome sequencing reveals a thrombopoietin ligand mutation in a Micronesian family with autosomal recessive aplastic anemia

We recently identified 2 siblings afflicted with idiopathic, autosomal recessive aplastic anemia. Whole-exome sequencing identified a novel homozygous missense mutation in thrombopoietin (THPO, c.112C>T) in both affected siblings. This mutation encodes an arginine to cysteine substitution at residue 38 or residue 17 excluding the 21-amino acid signal peptide of THPO receptor binding domain (RBD). THPO has 4 conserved cysteines in its RBD that form 2 disulfide bonds. Our in silico modeling predicts that introduction of a fifth cysteine may disrupt normal disulfide bonding to cause poor receptor binding. In functional assays, the mutant-THPO-containing media shows two- to threefold reduced ability to sustain UT7-TPO cells, which require THPO for proliferation. Both parents and a sibling with heterozygous R17C change have reduced platelet counts, whereas a sibling with wild-type sequence has normal platelet count. Thus, the R17C partial loss-of-function allele results in aplastic anemia in the homozygous state and mild thrombocytopenia in the heterozygous state in our family. Together with the recent identification of THPO receptor (MPL) mutations and the effects of THPO agonists in aplastic anemia, our results have clinical implications in the diagnosis and treatment of patients with aplastic anemia and highlight a role for the THPO-MPL pathway in hematopoiesis in vivo.

First successful use of eltrombopag before surgery in a child with MYH9-related thrombocytopenia

MYH9-related disease (MYH9-RD) is one of the most frequent autosomal-dominant forms of inherited macrothrombocytopenias and is caused by mutations in MYH9 (nonmuscle myosin IIA), the gene coding for the heavy chain of the nonmuscle myosin IIA. Affected individuals can present with isolated thrombocytopenia, and whereas only some will have bleeding events requiring intervention, nearly all will require the use of prophylactic platelet transfusions before surgery. Here we report the first prophylactic use of eltrombopag before surgery in a child with MYH9-RD. Our patient was a 13-year-old girl with an MYH9 S96L missense mutation who required a tympanoplasty due to chronic otitis media. Pretreatment microscopic platelet count was 10 × 10(9)/L. The child was treated with eltrombopag starting 4 weeks before her planned surgery. On the day of surgery her platelet count was 70 × 10(9)/L. She required no platelet transfusions and no abnormal bleeding was reported either during surgery or postoperatively. Given these results, the first reported in a child, we suggest that the use of this thrombopoietic agent should be further evaluated as a useful presurgical prophylactic option in this hereditary thrombocytopenia, thus avoiding the use of platelet transfusions and their associated risks, which include alloimmunization and the transmission of infectious agents.

The biology of thrombopoietin and thrombopoietin receptor agonists

Thrombopoietin (TPO) is the major physiological regulator of platelet production. TPO binds the TPO receptor, activates JAK and STAT pathways, thus stimulating megakaryocyte growth and platelet production. There is no "sensor" of the platelet count; rather TPO is produced in the liver at a constant rate and cleared by TPO receptors on platelets. TPO levels are inversely proportional to the rate of platelet production. Early recombinant TPO molecules were potent stimulators of platelet production and increased platelets in patients with immune thrombocytopenia, chemotherapy-induced thrombocytopenia, myelodysplastic syndromes and platelet apheresis donors. Neutralizing antibodies formed against one recombinant protein and ended their development. A second generation of TPO receptor agonists, romiplostim and eltrombopag, has been developed. Romiplostim is an IgG heavy chain into which four TPO agonist peptides have been inserted. Eltrombopag is an oral small molecule. These activate the TPO receptor by different mechanisms to increase megakaryocyte growth and platelet production. After administration of either to healthy volunteers, there is a delay of 5 days before the platelet count rises and subsequently reaches a peak after 12-14 days. Both have been highly effective in treating ITP and hepatitis C thrombocytopenia. Studies in a wide variety of other thrombocytopenic conditions are underway.

Inherited thrombocytopenias frequently diagnosed in adults

The diagnosis of inherited thrombocytopenias is difficult, for many reasons. First, as they are all rare diseases, they are little known by clinicians, who therefore tend to suspect the most common forms. Second, making a definite diagnosis often requires complex laboratory techniques that are available in only a few centers. Finally, half of the patients have forms that have not yet been described. As a consequence, many patients with inherited thrombocytopenias are misdiagnosed with immune thrombocytopenia, and are at risk of receiving futile treatments. Misdiagnosis is particularly frequent in patients whose low platelet count is discovered in adult life, because, in these cases, even the inherited origin of thrombocytopenia may be missed. Making the correct diagnosis promptly is important, as we recently learned that some forms of inherited thrombocytopenia predispose to other illnesses, such as leukemia or kidney failure, and affected subjects therefore require close surveillance and, if necessary, prompt treatments. Moreover, medical treatment can increase platelet counts in specific disorders, and affected subjects can therefore receive drugs instead of platelet transfusions when selective surgery is required. In this review, we will discuss how to suspect, diagnose and manage inherited thrombocytopenias, with particular attention to the forms that frequently present in adults. Moreover, we describe four recently identified disorders that belong to this group of disorders that are often diagnosed in adults: MYH9-related disease, monoallelic Bernard-Soulier syndrome, ANKRD26-related thrombocytopenia, and familial platelet disorder with predisposition to acute leukemia.

Pathogenesis and management of inherited thrombocytopenias: rationale for the use of thrombopoietin-receptor agonists

Knowledge in the field of inherited thrombocytopenias (ITs) has considerably improved over the recent years. In the last 5 years, nine new genes whose mutations are responsible for thrombocytopenia have been identified, and this also led to the recognition of several novel nosographic entities, such as thrombocytopenias deriving from mutations in CYCS, TUBB1, FLNA, ITGA2B/ITGB3, ANKRD26 and ACTN1. The identification of novel molecular alterations causing thrombocytopenia together with improvement of methodologies to study megakaryopoiesis led to considerable advances in understanding pathophysiology of ITs, thus providing the background for proposing new treatments. Thrombopoietin-receptor agonists (TPO-RAs) represent an appealing therapeutic hypothesis for ITs and have been tested in a limited number of patients. In this review, we provide an updated description of pathogenetic mechanisms of thrombocytopenia in the different forms of ITs and recapitulate the current management of these disorders. Moreover, we report the available clinical and preclinical data about the role of TPO-RAs in ITs and discuss the rationale for the use of these molecules in view of pathogenesis of the different forms of thrombocytopenia of genetic origin.

Advances in megakaryocytopoiesis and thrombopoiesis: from bench to bedside

Megakaryocytopoiesis involves the commitment of haematopoietic stem cells, proliferation and terminal differentiation of megakaryocytic progenitors (MK-p) and maturation of megakaryocytes (MKs) to produce functional platelets. This complex process occurs in specialized niches in the bone marrow where MKs align adjacent to vascular endothelial cells, form proplatelet projections and release platelets into the circulation. Thrombopoietin (THPO, TPO) is the primary growth factor for the MK lineage and necessary at all stages of development. THPO is constitutively produced in the liver, and binds to MPL (c-Mpl) receptor on platelets and MKs. This activates a cascade of signalling molecules, which induce transcription factors to drive MK development and thrombopoiesis. Decreased turnover rate and platelet number result in increased levels of free THPO, which induces a concentration-dependent compensatory response of marrow-MKs to enhance platelet production. Newly developed thrombopoietic agents operating via MPL receptor facilitate platelet production in thrombocytopenic states, primarily immune thrombocytopenia. Other drugs are available for attenuating malignant thrombocytosis. Herein, we review the regulation of megakaryocytopoiesis and platelet production in normal and disease states, and the innovative drugs and therapeutic modalities to stimulate or decrease thrombopoiesis.

Function of eltrombopag-induced platelets compared to platelets from control patients with immune thrombocytopenia

Data on the in vivo function of platelets induced by the thrombopoietin receptor agonist eltrombopag are scarce. To assess a possible influence of eltrombopag we compared platelet function of eltrombopag-treated immune thrombocytopenia (ITP) patients (group 1; n=10) after treatment response to that from control ITP patients (group 2; n=12). We further analysed platelet function at baseline and after one, three, and four weeks of eltrombopag treatment and estimated daily changes of platelet function during the eltrombopag-induced platelet rise. The formation of platelet-monocyte aggregates (PMA), P-selectin expression [MFI], and platelet adhesion under high shear conditions (surface coverage, SC) in vivo and after in vitro addition of agonists (ADP, TRAP-6, Collagen) were similar between both groups after response to eltrombopag treatment. Only TRAP-6 induced a lower SC in the eltrombopag group (p=0.03). All platelet function parameters except for Collagen-induced P-selectin expression changed significantly during treatment with eltrombopag. PMA, naïve and after addition of ADP or TRAP-6 increased with increasing platelet counts. P-selectin expression decreased, when measured without and upon addition of ADP, increased in the presence of TRAP-6, and remained unchanged after addition of Collagen. SC increased during the eltrombopag-induced platelet rise. All significant changes of platelet function correlated to changes in platelet counts. Two patients developed venous thromboses during eltrombopag treatment, but no association with any distinct single platelet function parameter or combinations thereof was identifiable. Thus, eltrombopag-induced platelets function similar to those from control ITP patients without discernible increased hyper-reactivity.