Lack of pathogenic mutations in the 5'-untranslated region of the thrombopoietin gene in patients with non-familial essential thrombocythaemia

Prognostic significance of mutated genes in megakaryocytic disorders

Megakaryopoiesis is a process during which platelets that play a major role in hemostasis are produced due to differentiation and maturation of megakaryocytic precursors. Several genes, including oncogenes and tumor suppressor genes, play a role in the regulation of this process. This study was conducted to investigate the oncogenes and tumor suppressor genes as well as their mutations during the megakaryopoiesis process, which can lead to megakaryocytic disorders. Relevant literature was identified by a PubMed search (1998-2019) of English language papers using the terms ‘Megakaryopoiesis’, ‘Mutation’, ‘oncogenes’, and ‘Tumor Suppressor’. According to investigations, several mutations occur in the genes implicated in megakaryopoiesis, which abnormally induce or inhibit megakaryocyte production, differentiation, and maturation, leading to platelet disorders. GATA-1 is one of the important genes in megakaryopoiesis and its mutations can be considered among the factors involved in the incidence of these disorders. Considering the essential role of these genes (such as GATA- 1) in megakaryopoiesis and the involvement of their mutations in platelet disorders, study and examination of these changes can be a positive step in the diagnosis and prognosis of these diseases.

Essential thrombocythaemia

Essential thrombocythaemia is a myeloproliferative disorder that results from the transformation of a multipotent haematopoietic progenitor. Its diagnosis can be challenging and its optimal management has been controversial, largely because of a virtual absence of randomised trials. However, this situation will be dramatically altered by two recent developments. First, the Medical Research Council Primary Thrombocythaemia 1 (PT-1) trial-the largest and most comprehensive randomised study of any myeloproliferative disorder-provides clear guidance on the management of patients with high-risk essential thrombocythaemia. Second, identification of a unique JAK2 mutation in a substantial proportion of patients with essential thrombocythaemia (and also other myeloproliferative disorders) has resulted in a powerful diagnostic tool and is likely to alter approaches to both the classification and management of the myeloproliferative disorders.

Essential thrombocythemia

Significant progress in our understanding of the molecular pathogenesis of essential thrombocythemia (ET) and the other Philadelphia (Ph) chromosome-negative myeloproliferative disorders (MPDs) has recently been achieved. Unfortunately, the diagnosis of ET still relies on a set of exclusion criteria developed years ago, as recent advances have yet to be evaluated for this purpose. The clinical course of ET is characterized by an increased incidence of thrombotic and hemorrhagic complications and an inherent tendency to progress into myelofibrosis or acute myeloid leukemia (AML). There is concern about undesirable effects of cytoreductive therapy given to prevent vascular events, particularly the risk of accelerating the rate of hematologic transformation. Thus, management involves modification of reversible vascular risk factors and further stratification according to the thrombotic risk. Myelosuppressive agents are not recommended in low-risk patients, whereas controlled studies support the therapeutic value of hydroxyurea (HU) plus aspirin in high-risk cases. Anagrelide or interferon-alpha (IFN-alpha) could be considered as second-line therapy in patients refractory or intolerant of HU. IFN-alpha is preferred in pregnant women.

Essential thrombocythaemia: challenges and evidence-based management

Essential thrombocythaemia was first described over 70 years ago. This condition is dominated by thrombotic and haemorrhagic complications and, in the long-term, by risk of transformation to myelofibrosis and/or acute leukaemia. However, it is heterogeneous both clinically and biologically. Here, a review of current concepts in disease aetiology and management is offered with reference to recent focused reviews where appropriate. In addition, five specific areas are discussed in detail: the role of the trephine biopsy, the disease entity prefibrotic myelofibrosis; the recently described Janus kinase 2 (JAK2) mutations; the leukaemogenicity of hydroxyurea (hydroxycarbamide); and lastly, the implications of the results of the Medical Research Council Primary Thrombocythaemia 1 study are explored.

Primary and secondary thrombocytosis in childhood

This review summarizes current data on the pathomechanisms and clinical aspects of primary and secondary thrombocytosis in childhood. Primary thrombocytosis is extremely rare in childhood, mostly diagnosed at the beginning of the second decade of life. As in adults, the criteria of the Polycythemia Vera Group are appropriate to diagnose primary thrombocytosis. The pathomechansims of non-familial forms are complex and include spontaneous formation of megakaryopoietic progenitors and increased sensitivity to thrombopoietin (Tpo). Familial forms can be caused by mutations in Tpo or Tpo receptor (c-mpl) genes. These mutations result in overexpression of Tpo, sustained intracellular signalling or disturbed regulation of circulating Tpo. Treatment of primary thrombocytosis is not recommended if platelet counts are <1500/nl and bleeding or thrombosis did not occur in patient's history. In severe cases, decision on treatment should weigh potential risks of treatment options (hydroxyurea, anagrelide) against expected benefits for preventing thrombosis or haemorrhage. Secondary thrombocytosis is frequent in children, in particular in the first decade of life. Hepatic Tpo production is stimulated in acute response reaction to a variety of disorders. Thrombosis prophylaxis is not required, even at platelet counts >1000/nl, except for cases with additional prothrombotic risk factors.

Classification and molecular biology of polycythemias (erythrocytoses) and thrombocytosis

In this article, polycythemic disorders are classified based on the current understanding of biology of erythropoieses and divided into primary and secondary polycythemias. Special emphasis is given to recently uncovered molecular bases of newly described congenital polycythemic disorders. This clarification of the pathophysiology of some of the congenital polycythemic states has obvious utility for more accurate diagnosis and rational prognostic determination. The molecular basis of congenital thrombocytoses is only beginning to be uncovered. In contrast, the molecular bases of polycythemia vera and essential thrombocythemia remain unknown, thus their diagnostic criteria are imprecise and their treatment remains largely empirical. The central premise of this article is that deciphering the molecular basis of human diseases leads to improved understanding of hematopoiesis, precise diagnosis, and the potential for development of a specific therapy.

Essential thrombocythemia

Essential thrombocythemia is a distinct clinical entity within the spectrum of myeloproliferative disorders. There is as yet no pathognomonic diagnostic test, and patients who currently fall into the category of essential thrombocythemia are likely to be heterogeneous. This article discusses diagnostic criteria, clinical features, prognosis, and management.

Basic sciences of the myeloproliferative diseases: pathogenic mechanisms of ET and PV

The molecular pathogenesis of ET and PV is unknown, although the relatively indolent clinical course observed in most patients suggests that the defect may be subtle and difficult to establish. Clonality analysis using X-chromosome inactivation patterns in females on purified CD34+ cells have confirmed that a defect is present in the hematopoietic stem cell. However, at least in ET, a significant proportion of patients have polyclonal hemopoiesis, and this presumably reflects the heterogeneous nature of the disorder(s). Attention has focussed on the potential disruption of the physiological regulators EPO and TPO and their respective receptors. In familial disorders, pathological mutations have been identified in some, but by no means all, cases: EPO receptor mutations in PFCP, TPO mutations in FT and, conversely, TPO receptor (c-mpl) mutations in CAMT. Equivalent ligand or receptor mutations have not been detected in ET or PV patients. However, there is evidence to suggest that c-mpl expression may be dysregulated, with low or absent c-mpl mRNA or protein reported in ET and/or PV patients. At present it is not clear whether this is the cause or consequence of the paradoxically normal/increased TPO levels found with both primary and secondary thrombocytosis. In vitro culture analysis has demonstrated both cytokine independence and hyper-sensitivity as a generalised feature of progenitor cells from many patients, but differences exist depending on the assays used and there is little understanding of the mechanism(s) underlying these responses. Two genes have recently been identified with increased mRNA expression in PV granulocytes: PRV-1, a novel cell surface receptor closely related to the uPAR/Ly6/CD59/snake toxin family of proteins, and NFI-B, a member of the nuclear factor I family which may be associated with TGF-beta resistance. Investigation of their regulation and biological effects may assist in determining the pathobiology of these elusive disorders.