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

Thromboembolism adverse event profiles of thrombopoietin receptor agonists: a real-world, pharmacovigilance study

BACKGROUND

Thrombopoietin receptor agonists (TPO-RAs) are currently approved for the treatment of thrombocytopenia in different conditions. The relationship between TPO-RAs and thromboembolic events (TEEs) remains controversial.

RESEARCH DESIGN AND METHODS

We extracted TPO-RAs adverse reaction reports after their marketing until now, using the FDA adverse event reporting system (FAERS). Positive signals were detected by reporting odds ratios (RORs). And the Weibull shape parameter test was utilized to analyze the time-to-onset profiles.

RESULT

Thromboembolic events accounted for 8.97% among TPO-RAs reports. Increased reporting of TEEs was related to TPO-RAs treatment compared with the entire FAERS database [ROR = 2.65 (2.56, 2.73)]. In addition, venous thrombotic events [ROR = 4.13 (3.92, 4.35)] were reported more frequently than arterial events ROR = 1.81 (1.7, 1.93)]. Age over 60 years [odds ratio (OR) = 1.10 (1.01, 1.20), p = 0.029] and weight over 80 kg [OR = 1.36 (1.17, 1.58), p < 0.001] of patients might have higher risk of TEEs during TPO-RAs therapy.

CONCLUSION

Evidence from the real world suggested that TPO-RAs were associated with higher incidence of TEEs, particularly venous thrombosis. The risk of TPO-RAs-associated TEEs mostly happened in the early stages of treatment and decreased over time.

Unraveling MYH9-related disease: A case study on misdiagnosis with idiopathic thrombocytopenic purpura, confirmed through genetic

This paper presents a detailed analysis of a case initially misdiagnosed as Idiopathic Thrombocytopenic Purpura (ITP), which was later correctly identified as MYH9-related disease (MYH9-RD), a rare genetic disorder characterized by thrombocytopenia, large platelets, and Döhle-like inclusion bodies in neutrophils. Using advanced slide reading technology, our team identified hallmark features of MYH9-RD in the patient's blood samples, leading to genetic testing that confirmed a spontaneous mutation in the MYH9 gene. This report highlights the diagnostic journey, emphasizing the crucial role of recognizing specific hematologic signs to accurately diagnose MYH9-RD. By comparing our findings with existing literature, we highlight the genetic underpinnings and clinical manifestations of MYH9-RD, emphasizing the necessity for heightened awareness and diagnostic precision in clinical practice to prevent similar cases of misdiagnosis. This case demonstrates the importance of integrating genetic testing into routine diagnostic protocols for unexplained thrombocytopenia, paving the way for improved patient care and treatment outcomes.

MYH9-related inherited thrombocytopenia: the genetic spectrum, underlying mechanisms, clinical phenotypes, diagnosis, and management approaches

Inherited thrombocytopenias have been considered exceedingly rare for a long time, but recent advances have facilitated diagnosis and greatly enabled the discovery of new causative genes. MYH9-related disease (MYH9-RD) represents one of the most frequent forms of inherited thrombocytopenia, usually presenting with nonspecific clinical manifestations, which renders it difficult to establish an accurate diagnosis. MYH9-RD is an autosomal dominant-inherited thrombocytopenia caused by deleterious variants in the MYH9 gene encoding the heavy chain of nonmuscle myosin IIA. Patients with MYH9-RD usually present with thrombocytopenia and platelet macrocytosis at birth or in infancy, and most of them may develop one or more extrahematologic manifestations of progressive nephritis, sensorial hearing loss, presenile cataracts, and elevated liver enzymatic levels during childhood and adult life. Here, we have reviewed recent advances in the study of MYH9-RD, which aims to provide an updated and comprehensive summary of the current knowledge and improve our understanding of the genetic spectrum, underlying mechanisms, clinical phenotypes, diagnosis, and management approaches of this rare disease. Importantly, our goal is to enable physicians to better understand this rare disease and highlight the critical role of genetic etiologic analysis in ensuring accurate diagnosis, clinical management, and genetic counseling while avoiding ineffective and potentially harmful therapies for MYH9-RD patients.

Update on the Use of Thrombopoietin-Receptor Agonists in Pediatrics

This review summarizes the rationale and current data on the use of thrombopoietin receptor agonists (TPO-RAs) for treating severe thrombocytopenia in infants, children, and adolescents. It focuses on substances that have been approved by the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) for pediatric patients. Romiplostim and eltrombopag are already established as second-line treatment for persistent or chronic immune thrombocytopenia (ITP). As in adults, TPO-RAs are currently also evaluated in severe aplastic anemia (SAA), chemotherapy-induced thrombocytopenia (CIT), myelodysplastic syndromes (MDS), and poor engraftment after hematopoietic stem cell transplantation in pediatric and adolescent patients. Moreover, studies on the implication of TPO-RA in treating rare inherited thrombocytopenias, such as Wiskott-Aldrich syndrome (WAS), congenital amegakaryocytic thrombocytopenia (CAMT), or MYH9-associated thrombocytopenia, deserve future attention. Current developments include testing of avatrombopag and lusutrombopag that are approved for the treatment of thrombocytopenia associated with chronic liver disease (CLD) in adult patients. In pediatric and adolescent medicine, we expect in the near future a broader use of TPO-RAs as first-line treatment in primary ITP, thereby considering immunomodulatory effects that increase the rate of sustained remission off-treatment, and a selective use in rare inherited thrombocytopenias based on current clinical trials.

Knowledge map of thrombopoietin receptor agonists: A bibliometric analysis

Thrombopoietin receptor agonists (TPO-RAs) have been widely used to treat thrombocytopenia, however, a scientometric profile of TPO-RAs research is lacking. Methods: This study uses VOSviewer, CiteSpace, and R software to provide an overview of current research, highlight study hotspots, and predict future research directions of TPO-RAs. Results: One thousand seven hundred and nineteen relevant studies from 1993 to 2022 with 43962 citations were identified from the Web of Science Core Collection. Over three decades, the USA has been leading TPO-RAs publications. Industries and academic institutions have been actively involved in TPO-RAs research, with funding provided by pharmaceutical companies and public funding bodies. The most productive and cited journals are British Journal of Hematology and Blood, respectively. When author keywords were categorised into three clusters, i.e., cluster 1 (immune thrombocytopenic purpura (ITP)), cluster 2 (avatrombopag, lusutrombopag, and thrombocytopenia), and cluster 3 (TPO-RAs for ITP and off-label drug use), ITP was found to be the current research hotspot, while oral TPO-RAs and licensed or unlicensed drug indications of thrombocytopenic diseases require further investigation. Conclusion: This study has generated the knowledge map of TPO-RAs, which provides a dynamic roadmap for future research in this field.

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.

Avatrombopag improves thrombocytopenia in MYH9-related disorder following eltrombopag treatment failure

MYH9-related disorder (MYH9-RD) is autosomal dominant thrombocytopenia caused by mutations in the MYH9 gene, which codes for the non-muscle myosin-IIA heavy chain. We present a case of a 24-year-old Chinese man with MYH9-RD who was initially misdiagnosed with immune thrombocytopenia. Whole-exome sequencing and Sanger sequencing revealed a novel missense mutation in the MYH9 gene at the position of c.4550 G > T (p.G1517V) in exon 32. The same phenotype was observed in the proband, his mother, and his brother, in addition to macrothrombocytopenia and Dohle-like bodies in neutrophil granulocytes without non-hematologic manifestations. Following failed treatment with eltrombopag, avatrombopag, which was not mentioned before in the MYH9-RD treatment, was administered to the patient, and thrombocytopenia improved. In this case report, we present a novel pathogenic mutation and show the potential of avatrombopag for temporarily increasing the platelet count in patients with MYH9-RD.

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.

A novel nonsense variant in TPM4 caused dominant macrothrombocytopenia, mild bleeding tendency and disrupted cytoskeleton remodeling

BACKGROUND

Rare inherited thrombocytopenias are caused by alterations in genes involved in megakaryopoiesis, thrombopoiesis and/or platelet release. Diagnosis is challenging due to poor specificity of platelet laboratory assays, large numbers of culprit genes, and difficult assessment of the pathogenicity of novel variants.

OBJECTIVES

To characterize the clinical and laboratory phenotype, and identifying the underlying molecular alteration, in a pedigree with thrombocytopenia of uncertain etiology.

PATIENTS/METHODS

Index case was enrolled in our Spanish multicentric project of inherited platelet disorders due to lifelong thrombocytopenia and bleeding. Bleeding score was recorded by ISTH-BAT. Laboratory phenotyping consisted of blood cells count, blood film, platelet aggregation and flow cytometric analysis. Genotyping was made by whole-exome sequencing (WES). Cytoskeleton proteins were analyzed in resting/spreading platelets by immunofluorescence and immunoblotting.

RESULTS

Five family members displayed lifelong mild thrombocytopenia with a high number of enlarged platelets in blood film, and mild bleeding tendency. Patient's platelets showed normal aggregation and granule secretion response to several agonists. WES revealed a novel nonsense variant (c.322C>T; p.Gln108*) in TPM4 (NM_003290.3), the gene encoding for tropomyosin-4 (TPM4). This variant led to impairment of platelet spreading capacity after stimulation with TRAP-6 and CRP, delocalization of TPM4 in activated platelets, and significantly reduced TPM4 levels in platelet lysates. Moreover, the index case displayed up-regulation of TPM2 and TPM3 mRNA levels.

CONCLUSIONS

This study identifies a novel TPM4 nonsense variant segregating with macrothrombocytopenia and impaired platelet cytoskeletal remodeling and spreading. These findings support the relevant role of TPM4 in thrombopoiesis and further expand our knowledge of TPM4-related thrombocytopenia.

Off-Label Use of Thrombopoietin Receptor Agonists: Case Series and Review of the Literature

Since their license in 2008, studies on thrombopoietin receptor agonists (TPO-RAs) are proceeding at a fast pace. Their favorable efficacy and safety profile makes them good candidates for the management of thrombocytopenia in different settings, even beyond their current indications. In the last 10 years, we faced patients with refractory thrombocytopenia that required treatment with off-label TPO-RA, despite the paucity of data in the literature and the possible risks, particularly that of thrombosis. We hereby report our 10-year real-life single-center experience of TPO-RA used off-label. Fourteen patients were divided into three groups according to the etiology of thrombocytopenia: myelodysplastic syndromes, post-transplantation, and lymphoproliferative diseases. Clinical features and results are reported within each group. Overall, TPO-RA proved effective in all these conditions achieving responses also in heavily pretreated patients. The overall response rate (ORR) was 100% in patients with thrombocytopenia after transplantation and in those with lymphoproliferative diseases and 75% in patients with myelodysplastic syndromes. The median duration of therapy was 285 days (range 93–1,513 days). Four patients (29%) discontinued treatment because of lack of response (n=2) or a sustained response (n=2). No grade 3–4 adverse events occurred, particularly no thrombosis. In our real-life experience, TPO-RAs were effective and safe and proved of value in the challenging management of patients with refractory thrombocytopenia associated with different conditions.

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.

Myosin Heavy Chain 9 (MYH9)-Related Congenital Macrothrombocytopenia

Myosin heavy chain 9 (MYH9)-related hereditary macrothrombocytopenia is caused by mutation of the MYH9 gene encoding the heavy chain A of non-muscle myosin of class II. We present a case that emphasizes the importance of awareness of rare disorders which could potentially avoid over-investigation, especially in benign conditions.

A 72-year-old Caucasian female presented for preoperative evaluation for cataract extraction. She was noted to have thrombocytopenia of 30 K/uL along with elevated creatinine. She denied any acute symptoms except for a prolonged history of easy bruising. Physical exam revealed bruising over the extremities. Upon further questioning, she was previously investigated for thrombocytopenia and had multiple diagnostic as well as therapeutic interventions including bone marrow biopsies, steroids, intravenous immunoglobulins with no improvement. Her family history is consistent with low platelet counts for at least three generations. Peripheral blood smear showed large platelets, normal red and white blood cells with Döhle bodies. Further genetic testing revealed an inherited MYH9 mutation which is autosomal dominant.

MYH9-related disorders are characterized by macrothrombocytopenia, often associated with glomerulonephritis, sensorineural deafness, cataracts, and cytoplasmic inclusion bodies within leukocytes. Management is mainly conservative and directed towards the prevention of iron deficiency anemia in young females. The use of desmopressin, in combination with tranexamic acid, is recommended in a perioperative setting. Our case emphasizes the importance of history-taking skills that could potentially minimize further diagnostic or therapeutic interventions in this benign genetic disorder.

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.

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.

Spontaneous and recurrent subdural haematoma in a patient with May-Hegglin anomaly

Both acute and chronic subdural haematomas typically occur following trauma. Non-traumatic causes are less common, but aetiologies include arteriovenous malformation, intracranial aneurysm rupture, tumour-associated haemorrhage and coagulopathies. May-Hegglin anomaly is an example of a coagulopathy, which is caused by a mutation in the gene encoding non-muscle myosin heavy chain 9 (MYH9) and therefore falls into a group of diseases referred to as MYH9-related diseases (MYH9-RD). The symptomology of MYH9-RD is often mild, and patients tend to experience epistaxis, gingival bleeding and bruising. Life-threatening haemorrhage rarely occurs. In this short report, we describe a patient with known May-Hegglin anomaly who presented with a potentially life-threatening, spontaneous subdural haematoma requiring surgery on two occasions. This is only the second such report in the literature, and the first of spontaneous and recurrent haemorrhage in association with May-Hegglin anomaly.

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.

The May-Hegglin anomaly: a rare cause of a common complaint

May-Hegglin anomaly is the presentation of a qualitative platelet disorder characterised by large platelets, thrombocytopenia and granulocyte inclusions as a result of mutations in the MYH9 gene. Though often overlooked given its rarity, it should be considered in patients who present with epistaxis, bruising, menorrhagia and easy bleeding as it can be mistaken for other diagnoses resulting in unnecessary treatments and tests. Our case study reports one presentation of this anomaly and can help broaden awareness of the presentation of this type of patient.

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.

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.

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.

Successful cochlear implantation in a patient with Epstein syndrome during long-term follow-up

Epstein syndrome is a rare disease characterized by macrothrombocytopenia, nephritis and progressive sensorineural hearing loss (SNHL). This syndrome is presently recognized as an autosomal dominant disease caused by mutations of non-muscle myosin heavy chain 9 (MYH9). Little information is available about the progress of SNHL, the efficacy of cochlear implants (CI) or the perioperative management of thrombocytopenia in patients with Epstein syndrome. We herein report a case of a patient with Epstein syndrome with the MYH9:c.2105G>A:p.R702H variant who underwent cochlear implantation after 27 years of follow-up for her progressive SNHL. The deterioration rates of hearing were 3.48 dB/year on the right ear and 2.46 dB/year on the left ear. The patient derived benefits from CI and had a speech recognition test result (for sentences) of 93% at 6-months postoperatively. Thrombocytopenia was successfully managed without any bleeding complications by using eltrombopag, an oral thrombopoietic agent, making transfusion of platelets unnecessary. The accurate diagnosis of Epstein syndrome was made only after long-term follow-up as the thrombocytopenia was initially diagnosed as idiopathic thrombocytopenic purpura. This case report highlights the perioperative management of thrombocytopenia, the progress of SNHL and the potential pitfalls of diagnosis.

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.

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.

Inherited thrombocytopenias: history, advances and perspectives

Over the last 100 years the role of platelets in hemostatic events and their production by megakaryocytes have gradually been defined. Progressively, thrombocytopenia was recognized as a cause of bleeding, first through an acquired immune disorder; then, since 1948, when Bernard-Soulier syndrome was first described, inherited thrombocytopenia became a fascinating example of Mendelian disease. The platelet count is often severely decreased and platelet size variable; associated platelet function defects frequently aggravate bleeding. Macrothrombocytopenia with variable proportions of enlarged platelets is common. The number of circulating platelets will depend on platelet production, consumption and lifespan. The bulk of macrothrombocytopenias arise from defects in megakaryopoiesis with causal variants in transcription factor genes giving rise to altered stem cell differentiation and changes in early megakaryocyte development and maturation. Genes encoding surface receptors, cytoskeletal and signaling proteins also feature prominently and Sanger sequencing associated with careful phenotyping has allowed their early classification. It quickly became apparent that many inherited thrombocytopenias are syndromic while others are linked to an increased risk of hematologic malignancies. In the last decade, the application of next-generation sequencing, including whole exome sequencing, and the use of gene platforms for rapid testing have greatly accelerated the discovery of causal genes and extended the list of variants in more common disorders. Genes linked to an increased platelet turnover and apoptosis have also been identified. The current challenges are now to use next-generation sequencing in first-step screening and to define bleeding risk and treatment better.

An integrated approach to inherited platelet disorders: results from a research collaborative, the Sydney Platelet Group

Inherited disorders of platelet function (IPFD) and/or number (IPND) are heterogeneous conditions that result in variable mucocutaneous bleeding symptoms as a result of deranged primary haemostasis caused by platelet dysfunction or thrombocytopenia. Diagnosis is important to guide post-operative bleeding prophylactic strategies, to avoid treatment with inappropriate medications, and inform prognosis. Achieving an accurate diagnosis has traditionally been hampered by the requirement of multiple, often complex, laboratory tests that are not always available at single centres. To improve the diagnosis of these disorders a research collaborative was established, the Sydney Platelet Group, that explored an integrated approach combining traditional and contemporary platelet phenotypic and genetic diagnostic platforms available at four Sydney tertiary hospitals. Herein we report the outcomes of the first 50 patients evaluated using this approach. The cohort included 22 individuals with suspected IPFD and 28 with thrombocytopenia. Bleeding scores were higher in individuals with IPFD (mean 5.75; SD 4.83) than those with IPNDs (mean 2.14; SD 2.45). In cases with suspected IPFD, diagnosis to the level of the defective pathway was achieved in 71% and four individuals were found not to have a definitive platelet function defect. Dense granule secretion disorders were the most common platelet pathway abnormality detected (n=5). Mean bleeding scores in these individuals were not significantly different to individuals with defects in other commonly detected platelet pathways (dense granules, signal transduction and 'undetermined'). A molecular diagnosis was achieved in 52% of individuals with IPNDs and 5% with IPFD. Likely pathogenic and pathogenic variants detected included variants associated with extra-haematological complications (DIAPH1, MYH9) and potential for malignancy (ANKRD26 and RUNX1). The level of platelet investigation undertaken by this initiative is currently not available elsewhere in Australia and initial results confirm the utility of this integrated phenotypic-genetic approach.

Next-generation sequencing for the diagnosis of MYH9-RD: Predicting pathogenic variants

The heterogeneous manifestations of MYH9‐related disorder (MYH9‐RD), characterized by macrothrombocytopenia, Döhle‐like inclusion bodies in leukocytes, bleeding of variable severity with, in some cases, ear, eye, kidney, and liver involvement, make the diagnosis for these patients still challenging in clinical practice. We collected phenotypic data and analyzed the genetic variants in more than 3,000 patients with a bleeding or platelet disorder. Patients were enrolled in the BRIDGE‐BPD and ThromboGenomics Projects and their samples processed by high throughput sequencing (HTS). We identified 50 patients with a rare variant in MYH9. All patients had macrothrombocytes and all except two had thrombocytopenia. Some degree of bleeding diathesis was reported in 41 of the 50 patients. Eleven patients presented hearing impairment, three renal failure and two elevated liver enzymes. Among the 28 rare variants identified in MYH9, 12 were novel. HTS was instrumental in diagnosing 23 patients (46%). Our results confirm the clinical heterogeneity of MYH9‐RD and show that, in the presence of an unclassified platelet disorder with macrothrombocytes, MYH9‐RD should always be considered. A HTS‐based strategy is a reliable method to reach a conclusive diagnosis of MYH9‐RD in clinical practice.

Eltrombopag in Immune Thrombocytopenia, Aplastic Anemia, and Myelodysplastic Syndrome: From Megakaryopoiesis to Immunomodulation

Eltrombopag is an orally available thrombopoietin receptor agonist indicated for the treatment of immune thrombocytopenia (ITP). Beyond the effect on megakaryopoiesis, the drug also showed a stimulating effect on the hematopoietic stem cell with consistent clinical efficacy in aplastic anemia (AA) and myelodysplastic syndromes (MDS). Eltrombopag is highly effective in ITP and less so in AA and MDS. This observation underlines the importance of residual normal hematopoiesis, which is maximal in ITP, minimal/absent in AA, and dysregulated in MDS. In ITP, the drug at 50-75 mg daily induced up to 85% responses both in clinical trials and real-life studies, with the possibility of tapering and discontinuation. In AA, eltrombopag at 150 mg daily was effective in about 40% of cases relapsed/refractory to standard immunosuppression or ineligible for bone marrow transplant. In MDS, the drug seems less effective, with responses in about a quarter of patients at various schedules. The efficacy of eltrombopag in ITP, AA, and MDS suggests the existence of common immune-pathological mechanisms in these diseases, including autoimmunity against peripheral blood cells and bone marrow precursors, as well as a possible evolution of one condition into the other. Additional mechanisms of action emerging from the clinical use of eltrombopag include modulation of T-regulatory cells, restoration of Fc-γ receptor balance in phagocytes, and an iron-mobilizing effect. In this review, we analyzed the most recent literature on eltrombopag use and efficacy in patients with ITP, AA, and MDS, exploring the basis for different dosing, combined treatments, and discontinuation in each context.

Phenotype description and response to thrombopoietin receptor agonist in DIAPH1-related disorder

DIAPH1-related disorder has a bilineage hematological phenotype of macrothrombocytopenia and neutropenia associated with hearing loss. Eltrombopag increased proplatelet formation from cultured DIAPH1-related disorder megakaryocytes and improved platelet counts in vivo.

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

Patients with inherited thrombocytopenias often require platelet transfusions to raise their platelet count before surgery or other invasive procedures; moreover, subjects with clinically significant spontaneous bleeding may benefit from an enduring improvement of thrombocytopenia. The hypothesis that thrombopoietin-mimetics can increase platelet count in inherited thrombocytopenias is appealing, but evidence is scarce. We conducted a prospective, phase II clinical trial to investigate the efficacy of the oral thrombopoietin-mimetic eltrombopag in different forms of inherited thrombocytopenia. We enrolled 24 patients affected by MYH9-related disease, ANKRD26-related thrombocytopenia, X-linked thrombocytopenia/ Wiskott-Aldrich syndrome, monoallelic Bernard-Soulier syndrome, or ITGB3-related thrombocytopenia. The average pre-treatment platelet count was 40.4 ×10⁹/L. Patients received a 3- to 6-week course of eltrombopag in a dose-escalated manner. Of 23 patients evaluable for response, 11 (47.8%) achieved a major response (platelet count >100 ×10⁹/L), ten (43.5%) had a minor response (platelet count at least twice the baseline value), and two patients (8.7%) did not respond. The average increase of platelet count compared to baseline was 64.5 ×10⁹/L (P<0.001). Four patients with clinically significant spontaneous bleeding entered a program of long-term eltrombopag administration (16 additional weeks): all of them obtained remission of mucosal hemorrhages, with the remission persisting throughout the treatment period. Treatment was globally well tolerated: five patients reported mild adverse events and one patient a moderate adverse event. In conclusion, eltrombopag was safe and effective in increasing platelet count and reducing bleeding symptoms in different forms of inherited thrombocytopenia. Despite these encouraging results, caution is recommended when using thrombopoietinmimetics in inherited thrombocytopenias predisposing to leukemia. ClinicalTrials.gov identifier: NCT02422394.

Thrombopoietin receptor agonists: ten years later

The two thrombopoietin receptor agonists (TPO-RA), eltrombopag and romiplostim, were licensed in the US for treatment of immune thrombocytopenia (ITP) in 2008 and, since then, their use has progressively increased around the world; they are currently used in more than 100 countries. The six largest randomized controlled trials conducted in ITP have used one of these two agents. All studies have demonstrated a platelet response rate between 50-90%, depending on the criteria used, with good safety and tolerability. TPO-RA were shown to be effective in reducing bleeding and the need for concomitant or rescue medication. Many other investigations of their mechanism of effect, prospective and retrospective trials, and studies focusing on toxicity have been performed widening our knowledge of these two agents. Initial concerns on issues such as myelofibrosis have not been confirmed. Only a small number of patients develop moderate-severe reticulin fibrosis and/or collagen fibrosis; however, these are usually reversed after discontinuation of TPO-RA. Studies indicate, however, that TPO-RA may increase the risk of venous thromboembolism. Both TPO-RA are currently approved in patients with chronic ITP aged >1-year who are refractory to at least one other treatment. Eltrombopag has acquired two additional indications: severe aplastic anemia refractory to first-line treatment and hepatitis C patients undergoing treatment with interferon-ribavirin. Despite these wide-ranging studies, important questions still need to be answered. This summary review on TPO-RA will summarize what is known regarding efficacy in ITP, evaluate safety concerns in more depth, and focus on the questions that remain.

MYH9-related disorders display heterogeneous kidney involvement and outcome

Background

MYH9-related diseases (MYH9-RD) are autosomal dominant disorders caused by mutations of the MYH9 gene encoding the non-muscle myosin heavy chain IIA. They are characterized by congenital thrombocytopenia, giant platelets and leucocyte inclusions. Hearing impairment, pre-senile cataract and nephropathy can also occur. We aimed to evaluate renal involvement and outcome in MYH9-RD patients followed-up by nephrologists.

Methods

We conducted a retrospective multicentre observational study of 13 patients among 9 families with MYH9 mutation diagnosed by genetic testing and immunofluorescence assay referred to nephrologists.

Results

At initial referral, median age was 30 (range 14–76) years. Median estimated glomerular filtration rate was 66 mL/min/1.73 m² (0–141) and two patients had already end-stage renal disease (ESRD). Renal presentation associated proteinuria (n = 12), haematuria (n = 6) and hypertension (n = 6). Three patients developed a rapid onset ESRD whereas five others had a relatively stable kidney function over a 3-year median follow-up (1–34). Extra-renal features varied widely, with hearing impairment in six patients, cataract in two and mild liver dysfunction in seven. Thrombocytopenia existed at referral in 11 patients. Time to diagnosis varied from 0 to 29 years (median 3 years). Initial diagnoses such as idiopathic thrombocytopenic purpura (n = 4) and focal segmental glomerulosclerosis (n = 1) led to corticosteroid administration (n = 4), intravenous immunoglobulins (n = 3), cyclophosphamide (n = 1) and splenectomy (n = 1).

Conclusions

Renal involvement and outcome in MYH9-RD are heterogeneous. The diagnosis is often delayed and misdiagnoses can lead to unnecessary treatments. MYH9-RD should be considered in any patient with glomerular involvement associated with a low or slightly decreased platelet count and/or hearing loss and liver dysfunction.

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.

MYH9: Structure, functions and role of non-muscle myosin IIA in human disease

The MYH9 gene encodes the heavy chain of non-muscle myosin IIA, a widely expressed cytoplasmic myosin that participates in a variety of processes requiring the generation of intracellular chemomechanical force and translocation of the actin cytoskeleton. Non-muscle myosin IIA functions are regulated by phosphorylation of its 20 kDa light chain, of the heavy chain, and by interactions with other proteins. Variants of MYH9 cause an autosomal-dominant disorder, termed MYH9-related disease, and may be involved in other conditions, such as chronic kidney disease, non-syndromic deafness, and cancer. This review discusses the structure of the MYH9 gene and its protein, as well as the regulation and physiologic functions of non-muscle myosin IIA with particular reference to embryonic development. Moreover, the review focuses on current knowledge about the role of MYH9 variants in human disease.