Eltrombopag for the treatment of inherited thrombocytopenias: a phase II clinical trial

Bioprinting Soft 3D Models of Hematopoiesis using Natural Silk Fibroin-Based Bioink Efficiently Supports Platelet Differentiation

Hematopoietic stem and progenitor cells (HSPCs) continuously generate platelets throughout one's life. Inherited Platelet Disorders affect ≈ 3 million individuals worldwide and are characterized by defects in platelet formation or function. A critical challenge in the identification of these diseases lies in the absence of models that facilitate the study of hematopoiesis ex vivo. Here, a silk fibroin-based bioink is developed and designed for 3D bioprinting. This bioink replicates a soft and biomimetic environment, enabling the controlled differentiation of HSPCs into platelets. The formulation consisting of silk fibroin, gelatin, and alginate is fine-tuned to obtain a viscoelastic, shear-thinning, thixotropic bioink with the remarkable ability to rapidly recover after bioprinting and provide structural integrity and mechanical stability over long-term culture. Optical transparency allowed for high-resolution imaging of platelet generation, while the incorporation of enzymatic sensors allowed quantitative analysis of glycolytic metabolism during differentiation that is represented through measurable color changes. Bioprinting patient samples revealed a decrease in metabolic activity and platelet production in Inherited Platelet Disorders. These discoveries are instrumental in establishing reference ranges for classification and automating the assessment of treatment responses. This model has far-reaching implications for application in the research of blood-related diseases, prioritizing drug development strategies, and tailoring personalized therapies.

Analysis of clinical characteristics and treatment efficacy in two pediatric cases of ANKRD26-related thrombocytopenia

ANKRD26-related thrombocytopenia (ANKRD26-RT or THC2, MIM 188 000), an autosomal dominant thrombocytopenia, is unresponsive to immunosuppressive therapy and susceptible to hematological malignancies. A large number of pediatric patients are diagnosed with immune thrombocytopenia (ITP) every year; however, thrombocytopenia of genetic origin is often missed. Extensive characterization of ANKRD26-RT will help prevent missed diagnosis and misdiagnosis. Furthermore, identification of ANKRD26-RT will help in the formulation of an accurate diagnosis and a treatment plan. In our study, we report cases of two Chinese pediatric patients with ANKRD26-RT and analyze their clinical characteristics, gene mutations, and treatment modalities. Both patients were 1-year-old and presented with mild bleeding (World Health Organization(WHO) score grade 1), different degrees of platelet reduction, normal mean platelet volume, and megakaryocyte maturation impairment not obvious. Genetic tests revealed that both patients had ANKRD26 gene mutations.Patient 1 had a mutation c.-140C>G of the 5' untranslated region (UTR), and patient 2 had a mutation of c.-127A>T of 5'UTR. Both patients were treated with eltrombopag, and the treatment was no response, with no adverse reactions.

Successful administration of eltrombopag in preparation for peritoneal dialysis catheter placement in a girl with MYH9-related disease

MYH9-related disease is an autosomal dominant disorder characterized by macrothrombocytopenia, nephropathy, inclusion bodies in leukocytes, sensorineural hearing loss, and cataract. Severe cases require kidney replacement therapy in the patient's second decade of life; thrombocytopenia constitutes a major risk factor for hemorrhagic complications during dialysis initiation or kidney transplantation. Prophylactic platelet transfusion prior to surgery is commonly administered to affected patients in these cases. However, transfusion in such patients has limitations other than the general risk of allergic reactions and blood-borne infections; it may also trigger alloimmunization, leading to platelet transfusion resistance or the development of anti-donor antibodies in potential kidney transplant recipients. Here, we describe prophylactic administration of eltrombopag, an oral thrombopoietin receptor agonist, prior to laparoscopic peritoneal dialysis catheter placement in a 15-year-old girl with MYH9-related disease. Her platelet count was approximately 30 × 103/μL at baseline; it increased to 61 × 103/μL on the day before surgery, thereby avoiding the need for platelet transfusions. There were no major bleeding or adverse events associated with eltrombopag administration. Thus, eltrombopag may be a safe and effective alternative to prophylactic platelet transfusions in patients with MYH9-related disease.

Hereditary platelet disorders associated with germ line variants in RUNX1, ETV6, and ANKRD26

Hereditary platelet disorders (HPDs) are a group of blood disorders with variable severity and clinical impact. Although phenotypically there is much overlap, known genetic causes are many, prompting the curation of multigene panels for clinical use, which are being deployed in increasingly large-scale populations to uncover missing heritability more efficiently. For some of these disorders, in particular RUNX1, ETV6, and ANKRD26, pathogenic germ line variants in these genes also come with a risk of developing hematological malignancy (HM). Although they may initially present as similarly mild-moderate thrombocytopenia, each of these 3 disorders have distinct penetrance of HM and a different range of somatic alterations associated with malignancy development. As our ability to diagnose HPDs has improved, we are now faced with the challenges of integrating these advances into routine clinical practice for patients and how to optimize management and surveillance of patients and carriers who have not developed malignancy. The volume of genetic information now being generated has created new challenges in how to accurately assess and report identified variants. The answers to all these questions involve international initiatives on rare diseases to better understand the biology of these disorders and design appropriate models and therapies for preclinical testing and clinical trials. Partnered with this are continued technological developments, including the rapid sharing of genetic variant information and automated integration with variant classification relevant data, such as high-throughput functional data. Collective progress in this area will drive timely diagnosis and, in time, leukemia preventive therapeutic interventions.

Application and investigation of thrombopoiesis-stimulating agents in the treatment of thrombocytopenia

Platelets, derived from a certain subpopulation of megakaryocytes, are closely related to hemostasis, coagulation, metastasis, inflammation, and cancer progression. Thrombopoiesis is a dynamic process regulated by various signaling pathways in which thrombopoietin (THPO)-MPL is dominant. Thrombopoiesis-stimulating agents could promote platelet production, showing therapeutic effects in different kinds of thrombocytopenia. Some thrombopoiesis-stimulating agents are currently used in clinical practices to treat thrombocytopenia. The others are not in clinical investigations to deal with thrombocytopenia but have potential in thrombopoiesis. Their potential values in thrombocytopenia treatment should be highly regarded. Novel drug screening models and drug repurposing research have found many new agents and yielded promising outcomes in preclinical or clinical studies. This review will briefly introduce thrombopoiesis-stimulating agents currently or potentially valuable in thrombocytopenia treatment and summarize the possible mechanisms and therapeutic effects, which may enrich the pharmacological armamentarium for the medical treatment of thrombocytopenia.

Successful Eltrombopag Therapy in a Child with MYH9-Related Inherited Thrombocytopenia

Inherited thrombocytopenias represents a heterogenous group of diseases characterized by a congenital reduction in the platelet count that could lead to a bleeding tendency. MYH9-related disorders are characterized by large platelets and congenital thrombocytopenia. Thrombopoietin-receptor agonists: eltrombopag and romiplostim are currently approved in many countries for the treatment of different forms of acquired thrombocytopenia, such as immune thrombocytopenia. We report, instead, the successful use of eltrombopag to treat inherited thrombocytopenia in a patient with an MHY9-related disease. This is the first report of a chronic use of eltrombopag to elevate platelets in MYH9-related disorders without side effects.

Generation of a thrombopoietin-deficient thrombocytopenia model in zebrafish

BACKGROUND

The production of platelets is tightly regulated by thrombopoietin (THPO). Mutations in the THPO gene cause thrombocytopenia. Although mice lacking Thpo present with thrombocytopenia, predicting phenotypes and pathogenicity of novel THPO mutations in mice is limited. Zebrafish can be a powerful tool for fast validation and study of candidate genes of human hematological diseases and have already been used as a model of human thrombocytopenia.

OBJECTIVES

We aim to investigate the role of Thpo in zebrafish thrombopoiesis and to establish a Thpo-deficient zebrafish model. The model could be applied for illustrating the clinically discovered human THPO variants of which the clinical significance is not known and to evaluate the effect of THPO receptor agonists (THPO-Ras), as well as a screening platform for new drugs.

METHODS

We generated a thpo loss-of-function zebrafish model using CRISPR/Cas9. After disruption of zebrafish thpo, thposzy6 zebrafish presented with a significant reduction of thpo expression and developed thrombocytopenia. Furthermore, we performed in vivo studies with zebrafish with the thposzy6 mutation and found two human clinical point mutations (c.091C > T and c.112C > T) that were responsible for the thrombocytopenia phenotype. In addition, effects of THPO-RAs used as therapeutics against thrombocytopenia were evaluated in the Tg(mpl:eGFP);thposzy6 line.

RESULTS AND CONCLUSIONS

Zebrafish with the mutation thposzy6 presented with a significant reduction of thpo expression and developed thrombocytopenia. Thpo loss-of-function zebrafish model can serve as a valuable preclinical model for thrombocytopenia caused by thpo-deficiency, as well as a tool to study human clinical THPO variants and evaluate the effect of THPO-RAs.

Treatment of inherited thrombocytopenias

The new techniques of genetic analysis have made it possible to identify many new forms of inherited thrombocytopenias (IT) and study large series of patients. In recent years, this has changed the view of IT, highlighting the fact that, in contrast to previous belief, most patients have a modest bleeding diathesis. On the other hand, it has become evident that some of the mutations responsible for platelet deficiency predispose the patient to serious, potentially life-threatening diseases. Today's vision of IT is, therefore, very different from that of the past and the therapeutic approach must take these changes into account while also making use of the new therapies that have become available in the meantime. This review, the first devoted entirely to IT therapy, discusses how to prevent bleeding in those patients who are exposed to this risk, how to treat it if it occurs, and how to manage the serious illnesses to which patients with IT may be predisposed.

Diagnosis and clinical management of Wiskott-Aldrich syndrome: current and emerging techniques

INTRODUCTION

Wiskott-Aldrich syndrome (WAS) serves as the prototype of how variants in a gene which encodes a protein central to actin cytoskeletal homeostasis can manifest clinically in a variety of ways including infection, atopy, autoimmunity, inflammation, bleeding, neutropenia, non-malignant lymphoproliferation, and malignancy. Despite the discovery of the WAS gene almost 30 years ago, our understanding of the pathophysiological mechanisms underlying WAS continues to unfold.

AREAS COVERED

This review will provide an overview of the approach to the diagnosis of WAS as well as the management of its associated complications. Advances in the use of allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy as well as the associated challenges unique to WAS will be discussed.

EXPERT OPINION

Basic research, combined with clinical research focusing on longitudinal analysis of WAS patients, will help clarify determinants that influence WAS pathogenesis as well as clinical complications and outcomes. Advances in curative approaches including the use of alternative donor HSCT for WAS continue to evolve. Gene therapy employing safer and more effective protocols ensuring full correction of WAS will provide life-saving benefit to WAS patients that are unable to undergo HSCT.

Clinical Features, Cancer Biology, Transplant Approach and Other Integrated Management Strategies for Wiskott-Aldrich Syndrome

Wiskott–Aldrich syndrome (WAS) is a rare X-linked recessive inborn error of immunity (IEI) first described in 1937. Classic WAS is characterized by the triad of thrombocytopenia with small platelets, recurrent infections due to combined immunodeficiency, and eczema. Hematopoietic stem cell transplantation (HSCT) was the only curative option available for five decades, with excellent outcomes reported for matched sibling donors (MSD) and matched unrelated donors (MUD). More recently, alternative donor transplants such as umbilical cord blood (UCB) and haploidentical transplant have emerged as viable options due to improvements in better graft selection, cell dosing, and effective allograft manipulation measures. Gene therapy is another potential curative option with promising results, yet currently is offered only as part of a clinical trial.

Severe Congenital Thrombocytopenia Characterized by Decreased Platelet Sialylation and Moderate Complement Activation Caused by Novel Compound Heterozygous Variants in GNE

Background

Hereditary thrombocytopenias constitute a genetically heterogeneous cause of increased bleeding. We report a case of a 17-year-old boy suffering from severe macrothrombocytopenia throughout his life. Whole genome sequencing revealed the presence of two compound heterozygous variants in GNE encoding the enzyme UDP-N-acetyl-glucosamine-2-epimerase/N-acetylmannosamine kinase, crucial for sialic acid biosynthesis. Sialic acid is required for normal platelet life span, and biallelic variants in GNE have previously been associated with isolated macrothrombocytopenia. Furthermore, sialic acid constitutes a key ligand for complement factor H (FH), an important inhibitor of the complement system, protecting host cells from indiscriminate attack.

Methods

Sialic acid expression and FH binding to platelets and leukocytes was evaluated by flow cytometry. The binding of FH to erythrocytes was assessed indirectly by measuring the rate of complement mediated hemolysis. Complement activation was determined by measuring levels of C3bBbP (alternative pathway), C4d (classical/lectin pathway) and soluble terminal complement complex assays.

Results

The proband exhibited markedly decreased expression of sialic acid on platelets and leukocytes. Consequently, the binding of FH was strongly reduced and moderate activation of the alternative and classical/lectin complement pathways was observed, together with an increased rate of erythrocyte lysis.

Conclusion

We report two previously undescribed variants in GNE causing severe congenital macrothrombocytopenia in a compound heterozygous state, as a consequence of decreased platelet sialylation. The decreased sialylation of platelets, leukocytes and erythrocytes affects the binding of FH, leading to moderate complement activation and increased hemolysis.

The Copenhagen founder variant GP1BA c.58T>G is the most frequent cause of inherited thrombocytopenia in Denmark

BACKGROUND

The classic Bernard-Soulier syndrome (BSS) is a rare inherited thrombocytopenia (IT) associated with severe thrombocytopenia, giant platelets, and bleeding tendency caused by homozygous or compound heterozygous variants in GP1BA, GP1BB, or GP9. Monoallelic BSS (mBSS) associated with mild asymptomatic macrothrombocytopenia caused by heterozygous variants in GP1BA or GP1BB may be a frequent cause of mild IT.

OBJECTIVE

We aimed to examine the frequency of mBSS in a consecutive cohort of patients with IT and to characterize the geno- and phenotype of mBSS probands and their family members. Additionally, we set out to examine if thrombopoietin (TPO) levels differ in mBSS patients.

PATIENTS/METHODS

We screened 106 patients suspected of IT using whole exome- or whole genome sequencing and performed co-segregation analyses of mBSS families. All probands and family members were phenotypically characterized. Founder mutation analysis was carried out by certifying that the probands were unrelated and the region around the variant was shared by all patients. TPO was measured by solid phase sandwich ELISA.

RESULTS

We diagnosed 14 patients (13%) with mBSS associated with heterozygous variants in GP1BA and GP1BB. Six unrelated probands carried a heterozygous variant in GP1BA (c.58T>G, p.Cys20Gly) and shared a 2.0 Mb region on chromosome 17, confirming that it is a founder variant. No discrepancy of TPO levels between mBSS patients and wild-type family members (P > .05) were identified.

CONCLUSION

We conclude that the most frequent form of IT in Denmark is mBSS caused by the Copenhagen founder variant.

Report of clinical presentations and two novel mutations in patients with Wiskott-Aldrich syndrome/X-linked Thrombocytopenia

Wiskott-Aldrich syndrome (WAS)/X-linked thrombocytopenia (XLT) is a rare X-linked disease characterized by thrombocytopenia, eczema, and recurrent infection. In addition, WAS/XLT increases incidence of autoimmune diseases and malignancies. We reported 7 male patients, 2 with WAS and 5 with XLT, from 6 different families. Two novel mutations, p.Gly387GlufsTer58 and p.Ala134Asp, were identified in patients with WAS. Both patients had severe clinical phenotypes compatible with classic WAS and developed lethal outcomes with intracranial hemorrhage. Other than that, one patient with XLT developed pineoblastoma.

Advances in understanding the pathogenesis of hereditary macrothrombocytopenia

Low platelet count, or thrombocytopenia, is a common haematological abnormality, with a wide differential diagnosis, which may represent a clinically significant underlying pathology. Macrothrombocytopenia, the presence of large platelets in combination with thrombocytopenia, can be acquired or hereditary and indicative of a complex disorder. In this review, we discuss the interpretation of platelet count and volume measured by automated haematology analysers and highlight some important technical considerations relevant to the analysis of blood samples with macrothrombocytopenia. We review how large cohorts, such as the UK Biobank and INTERVAL studies, have enabled an accurate description of the distribution and co-variation of platelet parameters in adult populations. We discuss how genome-wide association studies have identified hundreds of genetic associations with platelet count and mean platelet volume, which in aggregate can explain large fractions of phenotypic variance, consistent with a complex genetic architecture and polygenic inheritance. Finally, we describe the large genetic diagnostic and discovery programmes, which, simultaneously to genome-wide association studies, have expanded the repertoire of genes and variants associated with extreme platelet phenotypes. These have advanced our understanding of the pathogenesis of hereditary macrothrombocytopenia and support a future clinical diagnostic strategy that utilises genotype alongside clinical and laboratory phenotype data.

A Deep Dive into the Pathology of Gray Platelet Syndrome: New Insights on Immune Dysregulation

The gray platelet syndrome (GPS) is a rare platelet disorder, characterized by impaired alpha-granule biogenesis in megakaryocytes and platelets due to NBEAL2 mutations. Typical clinical features include macrothrombocytopenia, bleeding and elevated vitamin B12 levels, while bone marrow fibrosis and splenomegaly may develop during disease progression. Recently, the involvement of other blood lineages has been highlighted, revealing the role of NBEAL2 outside the megakaryocyte-platelet axis. Low leukocyte counts, decreased neutrophil granulation and impaired neutrophil extracellular trap formation represent prominent findings in GPS patients, reflecting deranged innate immunity and associated with an increased susceptibility to infection. In addition, low numbers and impaired degranulation of NK cells have been demonstrated in animal models. Autoimmune diseases involving different organs and a spectrum of autoantibodies are present in a substantial proportion of GPS patients, expanding the syndromic spectrum of this disorder and pointing to dysregulation of the adaptive immune response. Low-grade inflammation, as evidenced by elevation of liver-derived acute-phase reactants, is another previously unrecognized feature of GPS which may contribute to disease manifestations. This review will focus on the mechanisms underlying the pathogenesis of blood cell abnormalities in human GPS patients and NBEAL2-null animal models, providing insight into the effects of NBEAL2 in hemostasis, inflammation and immunity.

Thrombopoietin receptor agonists for marrow failure: A concise clinical review

Bone marrow failure is characterized by a disruption of hematopoietic stem cell (HSC) homeostasis and function, which causes decreased blood counts. Germline and somatic mutations within HSCs and immune dysregulation contribute to the pathogenesis of marrow failure. Allogeneic HSC transplant is a potentially curative therapy for marrow failure, although not all patients are candidates for this procedure. Immune suppressive therapy (IST) is an effective treatment for patients with aplastic anemia (AA) and select patients with myelodysplastic syndromes, but some patients fail to respond or relapse after IST. Over the past decade, the oral thrombopoietin receptor agonist eltrombopag has become a therapeutic option for AA in combination with frontline IST, and as a single agent for relapsed and refractory patients after IST. In this review, we highlight current knowledge of thrombopoietin receptor agonist mechanisms of action, and clinical indications and toxicities in patients with marrow failure, including the risk of clonal evolution.

Diagnosing Inherited Platelet Disorders: Modalities and Consequences

Inherited platelet disorders (IPDs) are a group of rare conditions featured by reduced circulating platelets and/or impaired platelet function causing variable bleeding tendency. Additional hematological or non hematological features, which can be congenital or acquired, distinctively mark the clinical picture of a subgroup of patients. Recognizing an IPD is challenging, and diagnostic delay or mistakes are frequent. Despite the increasing availability of next-generation sequencing, a careful phenotyping of suspected patients-concerning the general clinical features, platelet morphology, and function-is still demanded. The cornerstones of IPD diagnosis are clinical evaluation, laboratory characterization, and genetic testing. Achieving a diagnosis of IPD is desirable for several reasons, including the possibility of tailored therapeutic strategies and individual follow-up programs. However, detailed investigations can also open complex scenarios raising ethical issues in case of IPDs predisposing to hematological malignancies. This review offers an overview of IPD diagnostic workup, from the interview with the proband to the molecular confirmation of the suspected disorder. The main implications of an IPD diagnosis are also discussed.

A Novel Use of Romiplostim for SARS-CoV-2-induced Thrombocytopenia

The literature regarding coronavirus disease of 2019 (COVID-19) infection in pediatrics indicates that children have less severe clinical presentations and lower mortality rates. There remains limited data regarding hematologic sequelae in pediatric patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Romiplostim has shown a platelet response in pediatric patients with chronic immune thrombocytopenic purpura, and eltrombopag is proven to increase platelet counts in patients with inherited thrombocytopenia. We review SARS-CoV-2-associated thrombocytopenia and present a pediatric patient with acute on chronic thrombocytopenia in the setting of COVID-19 with subsequent platelet recovery using romiplostim.

Miniaturized 3D bone marrow tissue model to assess response to Thrombopoietin-receptor agonists in patients

Thrombocytopenic disorders have been treated with the Thrombopoietin-receptor agonist Eltrombopag. Patients with the same apparent form of thrombocytopenia may respond differently to the treatment. We describe a miniaturized bone marrow tissue model that provides a screening bioreactor for personalized, pre-treatment response prediction to Eltrombopag for individual patients. Using silk fibroin, a 3D bone marrow niche was developed that reproduces platelet biogenesis. Hematopoietic progenitors were isolated from a small amount of peripheral blood of patients with mutations in ANKRD26 and MYH9 genes, who had previously received Eltrombopag. The ex vivo response was strongly correlated with the in vivo platelet response. Induced Pluripotent Stem Cells (iPSCs) from one patient with mutated MYH9 differentiated into functional megakaryocytes that responded to Eltrombopag. Combining patient-derived cells and iPSCs with the 3D bone marrow model technology allows having a reproducible system for studying drug mechanisms and for individualized, pre-treatment selection of effective therapy in Inherited Thrombocytopenias.

Platelets are tiny cell fragments essential for blood to clot. They are created and released into the bloodstream by megakaryocytes, giant cells that live in the bone marrow. In certain genetic diseases, such as Inherited Thrombocytopenia, the bone marrow fails to produce enough platelets: this leaves patients extremely susceptible to bruising, bleeding, and poor clotting after an injury or surgery.

Certain patients with Inherited Thrombocytopenia respond well to treatments designed to boost platelet production, but others do not. Why these differences exist could be investigated by designing new test systems that recreate the form and function of bone marrow in the laboratory. However, it is challenging to build the complex and poorly understood bone marrow environment outside of the body.

Here, Di Buduo et al. have developed an artificial three-dimensional miniature organ bioreactor system that recreates the key features of bone marrow. In this system, megakaryocytes were grown from patient blood samples, and hooked up to a tissue scaffold made of silk. The cells were able to grow as if they were in their normal environment, and they could shed platelets into an artificial bloodstream. After treating megakaryocytes with drugs to stimulate platelet production, Di Buduo et al. found that the number of platelets recovered from the bioreactor could accurately predict which patients would respond to these drugs in the clinic.

This new test system enables researchers to predict how a patient will respond to treatment, and to tailor therapy options to each individual. This technology could also be used to test new drugs for Inherited Thrombocytopenias and other blood-related diseases; if scaled-up, it could also, one day, generate large quantities of lab-grown blood cells for transfusion.

A Review of Romiplostim Mechanism of Action and Clinical Applicability

Thrombocytopenia results from a variety of conditions, including radiation, chemotherapy, autoimmune disease, bone marrow disorders, pathologic conditions associated with surgical procedures, hematopoietic stem cell transplant (HSCT), and hematologic disorders associated with severe aplastic anemia. Immune thrombocytopenia (ITP) is caused by immune reactions that accelerate destruction and reduce production of platelets. Thrombopoietin (TPO) is a critical component of platelet production pathways, and TPO receptor agonists (TPO-RAs) are important for the management of ITP by increasing platelet production and reducing the need for other treatments. Romiplostim is a TPO-RA approved for use in patients with ITP in the United States, European Union, Australia, and several countries in Africa and Asia, as well as for use in patients with refractory aplastic anemia in Japan and Korea. Romiplostim binds to and activates the TPO receptor on megakaryocyte precursors, thus promoting cell proliferation and viability, resulting in increased platelet production. Through this mechanism, romiplostim reduces the need for other treatments and decreases bleeding events in patients with thrombocytopenia. In addition to its efficacy in ITP, studies have shown that romiplostim is effective in improving platelet counts in various settings, thereby highlighting the versatility of romiplostim. The efficacy of romiplostim in such disorders is currently under investigation. Here, we review the structure, mechanism, pharmacokinetics, and pharmacodynamics of romiplostim. We also summarize the clinical evidence supporting its use in ITP and other disorders that involve thrombocytopenia, including chemotherapy-induced thrombocytopenia, aplastic anemia, acute radiation syndrome, perisurgical thrombocytopenia, post-HSCT thrombocytopenia, and liver disease.

Inherited Platelet Disorders: An Updated Overview

Platelets play a major role in hemostasis as ppwell as in many other physiological and pathological processes. Accordingly, production of about 10¹¹ platelet per day as well as appropriate survival and functions are life essential events. Inherited platelet disorders (IPDs), affecting either platelet count or platelet functions, comprise a heterogenous group of about sixty rare diseases caused by molecular anomalies in many culprit genes. Their clinical relevance is highly variable according to the specific disease and even within the same type, ranging from almost negligible to life-threatening. Mucocutaneous bleeding diathesis (epistaxis, gum bleeding, purpura, menorrhagia), but also multisystemic disorders and/or malignancy comprise the clinical spectrum of IPDs. The early and accurate diagnosis of IPDs and a close patient medical follow-up is of great importance. A genotype-phenotype relationship in many IPDs makes a molecular diagnosis especially relevant to proper clinical management. Genetic diagnosis of IPDs has been greatly facilitated by the introduction of high throughput sequencing (HTS) techniques into mainstream investigation practice in these diseases. However, there are still unsolved ethical concerns on general genetic investigations. Patients should be informed and comprehend the potential implications of their genetic analysis. Unlike the progress in diagnosis, there have been no major advances in the clinical management of IPDs. Educational and preventive measures, few hemostatic drugs, platelet transfusions, thrombopoietin receptor agonists, and in life-threatening IPDs, allogeneic hematopoietic stem cell transplantation are therapeutic possibilities. Gene therapy may be a future option. Regular follow-up by a specialized hematology service with multidisciplinary support especially for syndromic IPDs is mandatory.

Role of Thrombopoietin Receptor Agonists in Inherited Thrombocytopenia

In the last decade, improvements in genetic testing have revolutionized the molecular diagnosis of inherited thrombocytopenias (ITs), increasing the spectrum of knowledge of these rare, complex and heterogeneous disorders. In contrast, the therapeutic management of ITs has not evolved in the same way. Platelet transfusions have been the gold standard treatment for a long time. Thrombopoietin receptor agonists (TPO-RA) were approved for immune thrombocytopenia (ITP) ten years ago and there is evidence for the use of TPO-RA not only in other forms of ITP, but also in ITs. We have reviewed in the literature the existing evidence on the role of TPO-RAs in ITs from 2010 to February 2021. A total of 24 articles have been included, 4 clinical trials, 3 case series and 17 case reports. A total of 126 patients with ITs have received TPO-RA. The main diagnoses were Wiskott–Aldrich syndrome, MYH9-related disorder and ANKRD26-related thrombocytopenia. Most patients were enrolled in clinical trials and were treated for short periods of time with TPO-RA as bridging therapies towards surgical interventions, or other specific approaches, such as hematopoietic stem cell transplantation. Here, we have carried out an updated and comprehensive review about the efficacy and safety of TPO-RA in ITs.

Anticoagulation in Patients with Platelet Disorders

Platelet disorders comprise heterogeneous diseases featured by reduced platelet counts and/or impaired platelet function causing variable bleeding symptoms. Despite their bleeding diathesis, patients with platelet disorders can develop transient or permanent prothrombotic conditions that necessitate prophylactic or therapeutic anticoagulation. Anticoagulation in patients with platelet disorders is a matter of concern because the bleeding risk could add to the hemorrhagic risk related to the platelet defect. This review provides an overview on the evidence on anticoagulation in patients with acquired and inherited thrombocytopenia and/or platelet dysfunction. We summarize tools to evaluate and balance bleeding- and thrombotic risks and describe a practical approach on how to manage these patients if they have an indication for prophylactic or therapeutic anticoagulation.

Learning the Ropes of Platelet Count Regulation: Inherited Thrombocytopenias

Inherited thrombocytopenias (IT) are a group of hereditary disorders characterized by a reduced platelet count sometimes associated with abnormal platelet function, which can lead to bleeding but also to syndromic manifestations and predispositions to other disorders. Currently at least 41 disorders caused by mutations in 42 different genes have been described. The pathogenic mechanisms of many forms of IT have been identified as well as the gene variants implicated in megakaryocyte maturation or platelet formation and clearance, while for several of them the pathogenic mechanism is still unknown. A range of therapeutic approaches are now available to improve survival and quality of life of patients with IT; it is thus important to recognize an IT and establish a precise diagnosis. ITs may be difficult to diagnose and an initial accurate clinical evaluation is mandatory. A combination of clinical and traditional laboratory approaches together with advanced sequencing techniques provide the highest rate of diagnostic success. Despite advancement in the diagnosis of IT, around 50% of patients still do not receive a diagnosis, therefore further research in the field of ITs is warranted to further improve patient care.

Eltrombopag use for refractory immune thrombocytopenia in pregnancy: A case report

BACKGROUND

Immune thrombocytopenic purpura (ITP) is a rare autoimmune disorder that involves platelet destruction in the spleen. Eltrombopag (Promacta®), a thrombopoietin agonist, has been used in non-pregnant patients to manage ITP, but few cases of its use in pregnancy have been reported.

CASE PRESENTATION

We present a case of a pregnant patient at 26 weeks of gestation with severe refractory ITP. After first-line therapies failed, the patient was treated with the drug eltrombopag. The patient had no response to initial therapy, and the fetus developed supraventricular tachycardia (SVT). This resolved with maternal digoxin but the patient elected to stop the eltrombopag. The patient refused further experimental and second-line treatments, and after a multidisciplinary meeting a decision was made to deliver by cesarean section at 30 weeks of gestation due to severe refractory ITP and allow other therapies to be tried postpartum. Preeclampsia and neonatal atrial flutter were encountered in the postpartum period but both mother and baby had good outcomes.

CONCLUSION

Refractory ITP in pregnancy is not well studied. Eltrombobag could have maternal and fetal side-effects but a multidisciplinary approach to management leads to favorable maternal and fetal outcomes.

Inherited thrombocytopenias: an updated guide for clinicians

The great advances in the knowledge of inherited thrombocytopenias (ITs) made since the turn of the century have significantly changed our view of these conditions. To date, ITs encompass 45 disorders with different degrees of complexity of the clinical picture and very wide variability in the prognosis. They include forms characterized by thrombocytopenia alone, forms that present with other congenital defects, and conditions that predispose to acquire additional diseases over the course of life. In this review, we recapitulate the clinical features of ITs with emphasis on the forms predisposing to additional diseases. We then discuss the key issues for a rational approach to the diagnosis of ITs in clinical practice. Finally, we aim to provide an updated and comprehensive guide to the treatment of ITs, including the management of hemostatic challenges, the treatment of severe forms, and the approach to the manifestations that add to thrombocytopenia.

Efficacy of romiplostim in treatment of thrombocytopenia in children with Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is a life-threatening primary immunodeficiency associated with bleeding of variable severity due to thrombocytopenia. Correction of the thrombocytopenia is of paramount importance for most WAS patients. We report a retrospective analysis of the safety and efficacy of romiplostim treatment in reducing thrombocytopenia and bleeding tendency in 67 children (median age 1·3 years) with genetically confirmed WAS, followed in eight months (range, 1-12 months). Complete or partial primary responses regarding platelet counts were observed in 22 (33%) and 18 (27%) subjects, respectively. Yet, even in the non-responder group, the risk of haemorrhagic events decreased significantly, to 21%, after the first month of treatment. The responses tended to be durable and stable over time, with no significant fluctuations in platelets counts. The results of this retrospective study of a large cohort of WAS patients demonstrates that romiplostim can be used to increase platelet counts and reduce the risks of life-threatening bleeding in WAS patients awaiting haematopoietic stem cell transplantation or forgoing the procedure for various reasons.

Clinical management, ethics and informed consent related to multi-gene panel-based high throughput sequencing testing for platelet disorders: Communication from the SSC of the ISTH

Molecular diagnostics of inherited platelet disorders (IPD) has been revolutionized by the implementation of high-throughput sequencing (HTS) approaches. A conclusive diagnosis using HTS tests can be obtained quickly and cost-effectively in many, but not all patients. The expanding use of HTS tests has raised concerns regarding complex variant interpretation and the ethical implications of detecting unsolicited findings such as variants in IPD genes RUNX1, ETV6, and ANKRD26, which are associated with increased leukemic risk. This guidance document has been developed and written by a multidisciplinary team of researchers and clinicians, with expertise in hematology, clinical and molecular genetics, and bioethics, alongside a RUNX1 patient advocacy representative. We recommend that for clinical diagnostics, HTS for IPD should use a multigene panel of curated diagnostic-grade genes. Critically, we advise that an HTS test for clinical diagnostics should only be ordered by a clinical expert that is: (a) fully aware of the complexity of genotype-phenotype correlations for IPD; (b) able to discuss these complexities with a patient and family members before the test is initiated; and (c) able to interpret and appropriately communicate the results of a HTS diagnostic report, including the implication of variants of uncertain clinical significance. Each patient should know what an HTS test could mean for his or her clinical management before initiating a test. We hereby propose an exemplified informed consent document that includes information on these ethical concerns and can be used by the community for implementation of HTS of IPD in a clinical diagnostic setting. This paper does not include recommendations for HTS of IPD in a research setting.

Eltrombopag for the Treatment of Severe Inherited Thrombocytopenia

Inherited thrombocytopenias correspond to a group of hereditary disorders characterized by a reduced platelet count, platelet dysfunction, and a family history of thrombocytopenia. It is commonly associated with mucocutaneous bleeding. Thrombocytopenia results from mutations in genes involved in megakaryocyte differentiation, platelet formation, and clearance. Here we report on a patient presenting with severe syndromic inherited thrombocytopenia manifesting as spontaneous mucocutaneous bleeds, requiring frequent platelet transfusions. Thrombocytopenia was explained by the presence of 4 mutations in 3 hematopoietic transcription factor genes: FLI1, RUNX1, and ETV6. The patient was successfully treated with high-dose eltrombopag at 150 mg/day, an orally available non-peptide thrombopoietin receptor agonist. Since the start of treatment 23 months ago, the manifestations of bleeding have resolved, and no platelet transfusions or corticosteroids have been required. The patient has no clinical or laboratory evidence of myeloid malignancy so far.

Inherited Platelet Disorders: Diagnosis and Management

Inherited platelet disorders are rare but they can have considerable clinical impacts, and studies of their causes have advanced understanding of platelet formation and function. Effective hemostasis requires adequate circulating numbers of functional platelets. Quantitative, qualitative and combined platelet disorders with a bleeding phenotype have been linked to defects in platelet cytoskeletal elements, cell surface receptors, signal transduction pathways, secretory granules and other aspects. Inherited platelet disorders have variable clinical presentations, and diagnosis and management is often challenging. Evaluation begins with detailed patient and family histories, including a bleeding score. The physical exam identifies potential syndromic features of inherited platelet disorders and rules out other causes. Laboratory investigations include a complete blood count, blood film, coagulation testing and Von Willebrand factor assessment. A suspected platelet function disorder is further assessed by platelet aggregation, flow cytometry, platelet dense granule release and/or content, and genetic testing. The management of platelet function disorders aims to minimize the risk of bleeding and achieve adequate hemostasis when needed. Although not universal, platelet transfusion remains a crucial component in the management of many inherited platelet disorders.

Updates in diagnosis of the inherited platelet disorders

PURPOSE OF REVIEW

To provide a comprehensive update on the current available methodologies and techniques for diagnosis of inherited platelet disorders (IPD).

RECENT FINDINGS

The contributions of many groups have resulted in the significant progress in the molecular diagnosis of IPD including the identification of many genes responsible for the various phenotypes. The widespread use and availability of next-generation sequencing has brought to the forefront ethical challenges associated with nontargeted sequencing as well as provided us with novel variants to functionally validate. These requirements have driven the development of novel tools for functional assessment of platelets, although none of the novel techniques beyond sequencing have yet taken clinical hold.

SUMMARY

Much work is ongoing on functional and molecular assessment of platelet disorders and the incorporation of combined assessments is likely to yield the highest diagnostic results.

Eltrombopag to allow chemotherapy in a patient with MYH9-related inherited thrombocytopenia and pancreatic cancer

Chemotherapy is the mainstay of treatment for advanced pancreatic cancer however, due to possible myelotoxicity, it is used with caution in patients with thrombocytopenia, especially when severe. TPO-receptor agonists have been employed for chemotherapy-induced thrombocytopenia, however treatment with TPO-receptor agonists to allow chemotherapy in patients with inherited thrombocytopenia has not been reported so far. We report the first successful use of eltrombopag to prevent chemotherapy-induced thrombocytopenia in a patient with MHY9-related disorder and pancreatic cancer. Treatment with eltrombopag allowed to attain a safe and stable platelet count for several months sufficient to permit chemotherapy and to allow the patient to undergo endoscopic placement of a biliary stent with no bleeding complications.

Diagnosis of Inherited Platelet Disorders on a Blood Smear

Inherited platelet disorders (IPDs) are rare diseases featured by low platelet count and defective platelet function. Patients have variable bleeding diathesis and sometimes additional features that can be congenital or acquired. Identification of an IPD is desirable to avoid misdiagnosis of immune thrombocytopenia and the use of improper treatments. Diagnostic tools include platelet function studies and genetic testing. The latter can be challenging as the correlation of its outcomes with phenotype is not easy. The immune-morphological evaluation of blood smears (by light- and immunofluorescence microscopy) represents a reliable method to phenotype subjects with suspected IPD. It is relatively cheap, not excessively time-consuming and applicable to shipped samples. In some forms, it can provide a diagnosis by itself, as for MYH9-RD, or in addition to other first-line tests as aggregometry or flow cytometry. In regard to genetic testing, it can guide specific sequencing. Since only minimal amounts of blood are needed for the preparation of blood smears, it can be used to characterize thrombocytopenia in pediatric patients and even newborns further. In principle, it is based on visualizing alterations in the distribution of proteins, which result from specific genetic mutations by using monoclonal antibodies. It can be applied to identify deficiencies in membrane proteins, disturbed distribution of cytoskeletal proteins, and alpha as well as delta granules. On the other hand, mutations associated with impaired signal transduction are difficult to identify by immunofluorescence of blood smears. This review summarizes technical aspects and the main diagnostic patterns achievable by this method.

Thrombopoietin receptor agonists in hereditary thrombocytopenias

Hereditary thrombocytopenias (HTPs) constitute a heterogeneous group of diseases characterized by a reduction in platelet count and a potential bleeding risk. As a result of advances in diagnostic methods, HTPs are increasingly being identified, and appear to be less rare than previously thought. Most HTPs do not have effective treatments, except for platelet transfusion when bleeding occurs and in preparation for procedures associated with a risk of bleeding. Preliminary clinical evidence suggests that thrombopoietin receptor agonists (TPO-RAs) with an established use in the treatment of certain acquired thrombocytopenias are well tolerated and provide clinical benefits in patients with some forms of HTP. These drugs may therefore be considered for the treatment of HTPs in clinical practice. However, caution and close monitoring are recommended, owing to the absence of long-term safety data and the potential risks posed by prolonged bone marrow stimulation in certain HTPs. In this review, we summarize the available clinical data on TPO-RAs in the treatment of HTPs, and discuss their use in patients with these disorders. We believe that TPO-RAs will play a major role in the treatment of HTPs, particularly myosin heavy chain 9-related disease, Wiskott-Aldrich syndrome, X-linked thrombocytopenia, and thrombocytopenia caused by THPO mutations.