Loss-of-function Additional sex combs like 1 mutations disrupt hematopoiesis but do not cause severe myelodysplasia or leukemia

Current findings for recurring mutations in acute myeloid leukemia

The development of acute myeloid leukemia (AML) is a multistep process that requires at least two genetic abnormalities for the development of the disease. The identification of genetic mutations in AML has greatly advanced our understanding of leukemogenesis. Recently, the use of novel technologies, such as massively parallel DNA sequencing or high-resolution single-nucleotide polymorphism arrays, has allowed the identification of several novel recurrent gene mutations in AML. The aim of this review is to summarize the current findings for the identification of these gene mutations (Dnmt, TET2, IDH1/2, NPM1, ASXL1, etc.), most of which are frequently found in cytogenetically normal AML. The cooperative interactions of these molecular aberrations and their interactions with class I/II mutations are presented. The prognostic and predictive significances of these aberrations are also reviewed.

New mutations and pathogenesis of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are clonal disorders characterized by excessive production of mature blood cells. In the majority of classic MPN—polycythemia vera, essential thrombocythemia, and primitive myelofibrosis—driver oncogenic mutations affecting Janus kinase 2 (JAK2) or MPL lead to constitutive activation of cytokine-regulated intracellular signaling pathways. LNK, c-CBL, or SOCSs (all negative regulators of signaling pathways), although infrequently targeted, may either drive the disease or synergize with JAK2 and MPL mutations. IZF1 deletions or TP53 mutations are mainly found at transformation phases and are present at greater frequency than in de novo acute myeloid leukemias. Loss-of-function mutations in 3 genes involved in epigenetic regulation, TET2, ASXL1, and EZH2, may be early events preceding JAK2V617F but may also occur late during disease progression. They are more frequently observed in PMF than PV and ET and are also present in other types of malignant myeloid diseases. A likely hypothesis is that they facilitate clonal selection, allowing the dominance of the JAK2V617F subclone during the chronic phase and, together with cooperating mutations, promote blast crisis. Their precise roles in hematopoiesis and in the pathogenesis of MPN, as well as their prognostic impact and potential as a therapeutic target, are currently under investigation.

Mutational spectrum analysis of chronic myelomonocytic leukemia includes genes associated with epigenetic regulation: UTX, EZH2, and DNMT3A

Chronic myelomonocytic leukemia (CMML), a myelodysplastic/myeloproliferative neoplasm, is characterized by monocytic proliferation, dysplasia, and progression to acute myeloid leukemia. CMML has been associated with somatic mutations in diverse recently identified genes. We analyzed 72 well-characterized patients with CMML (N = 52) and CMML-derived acute myeloid leukemia (N = 20) for recurrent chromosomal abnormalities with the use of routine cytogenetics and single nucleotide polymorphism arrays along with comprehensive mutational screening. Cytogenetic aberrations were present in 46% of cases, whereas single nucleotide polymorphism array increased the diagnostic yield to 60%. At least 1 mutation was found in 86% of all cases; novel UTX, DNMT3A, and EZH2 mutations were found in 8%, 10%, and 5.5% of patients, respectively. TET2 mutations were present in 49%, ASXL1 in 43%, CBL in 14%, IDH1/2 in 4%, KRAS in 7%, NRAS in 4%, and JAK2 V617F in 1% of patients. Various mutant genotype combinations were observed, indicating molecular heterogeneity in CMML. Our results suggest that molecular defects affecting distinct pathways can lead to similar clinical phenotypes.

JAK inhibitors in myeloproliferative neoplasms: rationale, current data and perspective

JAK-STAT is an appealing but also problematic drug target in BCR-ABL1-negative myeloproliferative neoplasms (MPN) - it is appealing because the majority of patients with MPN harbor gain-of-function JAK2 or MPL mutations - it is problematic because currently available JAK inhibitors do not distinguish between oncogenic and physiologic JAK-STAT activation. Furthermore, JAK-STAT-relevant mutations in MPN do not always constitute the predominant or ancestral mutant clone. Such complexities undermine the value of JAK-STAT as a robust drug target in MPN and partly explain the hitherto lack of histologic or molecular remissions associated with currently available JAK inhibitors. Most of these drugs were, however, effective in alleviating constitutional symptoms and reducing spleen size; the mechanism of action in this instance includes drug-induced down-regulation of inflammatory cytokine activity. In addition, non-specific myelosuppression contributes to both their salutary and detrimental effects on peripheral blood count. Non-hematologic side effects include gastrointestinal disturbances, asymptomatic elevation of liver and pancreatic enzymes, peripheral neuropathy and hyperacute relapse of symptoms during treatment interruption. It is our impression that many more JAK inhibitors need to be evaluated in order to identify the best-in-class in terms of efficacy, toxicity and suitability for future combination treatment programs.

Epigenetic abnormalities in myeloproliferative neoplasms: a target for novel therapeutic strategies

The myeloproliferative neoplasms (MPNs) are a group of clonal hematological malignancies characterized by a hypercellular bone marrow and a tendency to develop thrombotic complications and to evolve to myelofibrosis and acute leukemia. Unlike chronic myelogenous leukemia, where a single disease-initiating genetic event has been identified, a more complicated series of genetic mutations appear to be responsible for the BCR-ABL1-negative MPNs which include polycythemia vera, essential thrombocythemia, and primary myelofibrosis. Recent studies have revealed a number of epigenetic alterations that also likely contribute to disease pathogenesis and determine clinical outcome. Increasing evidence indicates that alterations in DNA methylation, histone modification, and microRNA expression patterns can collectively influence gene expression and potentially contribute to MPN pathogenesis. Examples include mutations in genes encoding proteins that modify chromatin structure (EZH2, ASXL1, IDH1/2, JAK2V617F, and IKZF1) as well as epigenetic modification of genes critical for cell proliferation and survival (suppressors of cytokine signaling, polycythemia rubra vera-1, CXC chemokine receptor 4, and histone deacetylase (HDAC)). These epigenetic lesions serve as novel targets for experimental therapeutic interventions. Clinical trials are currently underway evaluating HDAC inhibitors and DNA methyltransferase inhibitors for the treatment of patients with MPNs.

Uses and abuses of JAK2 and MPL mutation tests in myeloproliferative neoplasms a paper from the 2010 William Beaumont hospital symposium on molecular pathology

JAK2V617F is sufficiently prevalent in BCR-ABL1-negative myeloproliferative neoplasms (MPNs) to be useful as a clonal marker. JAK2V617F mutation screening is indicated for the evaluation of erythrocytosis, thrombocytosis, splanchnic vein thrombosis, and otherwise unexplained BCR-ABL1-negative granulocytosis. However, the mutation does not provide additional value in the presence of unequivocal morphologic diagnosis, and its presence does not necessarily distinguish one MPN from another or provide useful prognostic information. In general, quantitative cell-based JAK2V617F mutation assays are preferred because the additional information obtained on mutant allele burden enhances diagnostic certainty and facilitates monitoring of response to treatment. JAK2 exon 12 mutation screening is indicated only in the presence of JAK2V617F-negative erythrocytosis that is associated with a subnormal serum erythropoietin level. MPL mutations are neither frequent nor specific enough to warrant their routine use for MPN diagnosis, but they may be useful in resolving specific diagnostic problems. The practice of en bloc screening for JAK2V617F, JAK2 exon 12, and MPL mutations is scientifically irrational and economically irresponsible.

Clinical effect of point mutations in myelodysplastic syndromes

BACKGROUND

Myelodysplastic syndromes are clinically heterogeneous disorders characterized by clonal hematopoiesis, impaired differentiation, peripheral-blood cytopenias, and a risk of progression to acute myeloid leukemia. Somatic mutations may influence the clinical phenotype but are not included in current prognostic scoring systems.

METHODS

We used a combination of genomic approaches, including next-generation sequencing and mass spectrometry-based genotyping, to identify mutations in samples of bone marrow aspirate from 439 patients with myelodysplastic syndromes. We then examined whether the mutation status for each gene was associated with clinical variables, including specific cytopenias, the proportion of blasts, and overall survival.

RESULTS

We identified somatic mutations in 18 genes, including two, ETV6 and GNAS, that have not been reported to be mutated in patients with myelodysplastic syndromes. A total of 51% of all patients had at least one point mutation, including 52% of the patients with normal cytogenetics. Mutations in RUNX1, TP53, and NRAS were most strongly associated with severe thrombocytopenia (P<0.001 for all comparisons) and an increased proportion of bone marrow blasts (P<0.006 for all comparisons). In a multivariable Cox regression model, the presence of mutations in five genes retained independent prognostic significance: TP53 (hazard ratio for death from any cause, 2.48; 95% confidence interval [CI], 1.60 to 3.84), EZH2 (hazard ratio, 2.13; 95% CI, 1.36 to 3.33), ETV6 (hazard ratio, 2.04; 95% CI, 1.08 to 3.86), RUNX1 (hazard ratio, 1.47; 95% CI, 1.01 to 2.15), and ASXL1 (hazard ratio, 1.38; 95% CI, 1.00 to 1.89).

CONCLUSIONS

Somatic point mutations are common in myelodysplastic syndromes and are associated with specific clinical features. Mutations in TP53, EZH2, ETV6, RUNX1, and ASXL1 are predictors of poor overall survival in patients with myelodysplastic syndromes, independently of established risk factors. (Funded by the National Institutes of Health and others.).

Disruption of the ASXL1 gene is frequent in primary, post-essential thrombocytosis and post-polycythemia vera myelofibrosis, but not essential thrombocytosis or polycythemia vera: analysis of molecular genetics and clinical phenotypes

BACKGROUND

The myeloproliferative neoplasms, essential thrombocytosis, polycythemia vera and primary myelofibrosis, share the same acquired genetic lesion, but the concept of JAK2 V617F serving as the sole lesion responsible for these neoplasms is under question, and there has been interest in identifying additional mutations that may contribute to disease pathogenesis. Because ASXL1 lesions have been increasingly identified in myeloid neoplasms, we examined the relationships of ASXL1 mutation or deletion to both clinical phenotype and associated molecular features in 166 patients with myeloproliferative neoplasms.

DESIGN AND METHODS

Exon 12 of ASXL1 was amplified from neutrophil genomic DNA and bidirectionally sequenced in 77 patients with myelofibrosis (including patients with primary and post-essential thrombocytosis or post-polycythemia myelofibrosis), 42 patients with polycythemia vera, 41 with essential thrombocytosis and 6 with post-myelofibrosis acute myeloid leukemia. Pyrosequencing assays were designed to determine the allele percentages of JAK2 V617F (G5073770T), ASXL1 2475dupA, and ASXL1 2846_2847del in neutrophil genomic DNA samples. Clinical and laboratory characteristics of patients with wild-type and ASXL1 mutations were then compared.

RESULTS

We identified nonsense mutations or hemizygous deletion of ASXL1 in 36% of the patients with myelofibrosis, but very rarely among those with polycythemia vera or essential thrombocytosis. Among the patients with myelofibrosis, those with ASXL1 lesions were not distinguished from their wild-type counterparts with regard to JAK2 V617F status, exposure to chemotherapy or evolution to leukemia. Myelofibrosis patients with ASXL1 lesions were more likely to have received anemia-directed therapy compared to those without lesions [15/26 (58%) versus 11/39 (23%); P=0.02]. Using serial banked samples and quantitative ASXL1 mutant allele burden assays, we observed the acquisition and accumulation of ASXL1 mutations over time in two patients with post-essential thrombocytosis myelofibrosis.

CONCLUSIONS

ASXL1 haploinsufficiency is associated with a myelofibrosis phenotype in the context of other known and unknown lesions, and disruption of ASXL1 function may contribute to the disease pathogenesis of myelofibrosis.

Mouse models of diseases of megakaryocyte and platelet homeostasis

Platelets are the small anuclear blood cells that are the product of megakaryocytopoiesis, the process of hematopoietic stem cell commitment to megakaryocyte production and the differentiation and maturation of these cells for platelet release. Deregulation or disruption of megakaryocytopoiesis can result in platelet deficiencies, the thrombocytopenias, with attendant risk of hemorrhage or thrombocytosis, a pathological excess of platelet numbers. Mouse models, particularly those engineered to carry genetic alterations modeling mutations associated with human disease, have provided important insights into megakaryocytopoiesis and deregulation of this process in disease. This review focuses on mouse models of diseases of altered megakaryocyte and platelet number, illustrating the profound contribution of these models in validating suspected roles of disease-associated genetic alterations, promoting discovery of new links between genetic mutations and specific diseases, and providing unique tools for better understanding of disease pathophysiology and progression, as well as resources to define drug action or develop new therapeutic strategies.

Genetics of the myeloproliferative neoplasms

PURPOSE OF REVIEW

Since the discovery of the JAK2V617F mutation in 2005, an increasing number of somatic and germline genetic events responsible for myeloproliferative neoplasm (MPN) pathogenesis have been uncovered. The purpose of this review is to outline the most recent discoveries of the genetic alterations found in patients with MPNs.

RECENT FINDINGS

In addition to the JAK2V617F mutation, additional mutations in the JAK–STAT pathway have been discovered including a series of mutations in exon 12 of JAK2, the thrombopoietic receptor gene MPL, and in the gene encoding the JAK–STAT inhibitory adaptor protein LNK. Additionally, mutations in genes which appear to affect the epigenome of MPN patients have been discovered including mutations in TET2, IDH1/ 2, EZH2, and ASXL1. Lastly, some insights into the genetic events which contribute to transformation of a chronic MPN phenotype to acute myeloid leukemia have been elucidated, including deletion of the transcription factor Ikaros.

SUMMARY

The spectrum of genetic abnormalities found in the classic MPNs has increased over the last 6 years and somatic mutations in JAK2, MPL, LNK, TET2, EZH2, ASXL1, and IDH1/2 have all been described. Despite this, the initiating genetic events responsible for the development of MPNs is still not totally understood.

The nuclear deubiquitinase BAP1 is commonly inactivated by somatic mutations and 3p21.1 losses in malignant pleural mesothelioma

Malignant pleural mesotheliomas (MPMs) often show CDKN2A and NF2 inactivation, but other highly recurrent mutations have not been described. To identify additional driver genes, we used an integrated genomic analysis of 53 MPM tumor samples to guide a focused sequencing effort that uncovered somatic inactivating mutations in BAP1 in 23% of MPMs. The BAP1 nuclear deubiquitinase is known to target histones (together with ASXL1 as a Polycomb repressor subunit) and the HCF1 transcriptional co-factor, and we show that BAP1 knockdown in MPM cell lines affects E2F and Polycomb target genes. These findings implicate transcriptional deregulation in the pathogenesis of MPM.

Prognostic significance of ASXL1 mutations in patients with myelodysplastic syndromes

PURPOSE

To study the incidence and prognostic impact of mutations in Additional sex comb-like 1 (ASXL1) in a large cohort of patients with myelodysplastic syndrome (MDS).

PATIENTS, MATERIALS, AND METHODS

Overall, 193 patients with MDS and 65 healthy volunteers were examined for ASXL1 mutations by direct sequencing and for expression levels of ASXL1. The prognostic impact of ASXL1 mutation and expression levels was evaluated in the context of other clinical and molecular prognostic markers.

RESULTS

Mutations in ASXL1 occurred with a frequency of 20.7% in MDS (n = 40 of 193) with 70% (n = 28) of mutations being frameshift mutations and 30% (n = 12) being heterozygous point mutations leading to translational changes. ASXL1 mutations were correlated with an intermediate-risk karyotype (P = .002) but not with other clinical parameters. The presence of ASXL1 mutations was associated with a shorter overall survival for frameshift and point mutations combined (hazard ratio [HR], 1.744; 95% CI, 1.08 to 2.82; P = .024) and for frameshift mutations only (HR, 2.06; 95% CI, 1.21 to 3.50; P = .008). ASXL1 frameshift mutations were associated with a reduced time to progression of acute myeloid leukemia (AML; HR 2.35; 95% CI, 1.17 to 4.74; P = .017). In multivariate analysis, when considering karyotype, transfusion dependence, and IDH1 mutation status, ASXL1 frameshift mutations remained an independent prognostic marker in MDS (overall survival: HR, 1.85; 95% CI, 1.03 to 3.34; P = .040; time to AML progression: HR, 2.39; 95% CI, 1.12 to 5.09; P = .024).

CONCLUSION

These results suggest that ASXL1 mutations are frequent molecular aberrations in MDS that predict an adverse prognostic outcome. Screening of patients for ASXL1 mutations might be useful for clinical risk stratification and treatment decisions in the future.

Mouse models of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are hematopoietic malignancies characterized by peripheral cytopenias in the face of normo- or hypercellular, dysplastic bone marrow that arise from mutations in the hematopoietic stem/progenitor cell (HSPC). The disease is characterized by multiple cytogenetic and molecular defects, which result in an extremely heterogeneous phenotype. Recently, significant efforts have been made to develop appropriate mouse models to study this complex disease. Because of the heterogeneity of MDS, no single model is able to capture the MDS phenotype in its entirety. In this review, we describe several MDS mouse models and discuss the advances made in our understanding of the different disease mechanisms within the malignant clone and the marrow microenvironment. In addition, we describe progress in xenotransplantation models of MDS and discuss questions that remain to be answered.

Mutations with epigenetic effects in myeloproliferative neoplasms and recent progress in treatment: Proceedings from the 5th International Post-ASH Symposium

Immediately following the 2010 annual American Society of Hematology (ASH) meeting, the 5th International Post-ASH Symposium on Chronic Myelogenous Leukemia and BCR-ABL1-Negative Myeloproliferative Neoplasms (MPNs) took place on 7–8 December 2010 in Orlando, Florida, USA. During this meeting, the most recent advances in laboratory research and clinical practice, including those that were presented at the 2010 ASH meeting, were discussed among recognized authorities in the field. The current paper summarizes the proceedings of this meeting in BCR-ABL1-negative MPN. We provide a detailed overview of new mutations with putative epigenetic effects (TET oncogene family member 2 (TET2), additional sex comb-like 1 (ASXL1), isocitrate dehydrogenase (IDH) and enhancer of zeste homolog 2 (EZH2)) and an update on treatment with Janus kinase (JAK) inhibitors, pomalidomide, everolimus, interferon-α, midostaurin and cladribine. In addition, the new ‘Dynamic International Prognostic Scoring System (DIPSS)-plus' prognostic model for primary myelofibrosis (PMF) and the clinical relevance of distinguishing essential thrombocythemia from prefibrotic PMF are discussed.

Annual Clinical Updates in Hematological Malignancies: a continuing medical education series: polycythemia vera and essential thrombocythemia: 2011 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms primarily characterized by erythrocytosis and thrombocytosis, respectively. Other disease features include leukocytosis, splenomegaly, thrombohemorrhagic complications, vasomotor disturbances, pruritus, and a small risk of disease progression into acute leukemia or myelofibrosis.

DIAGNOSIS

Diagnosis is based on JAK2 mutation status (PV and ET), serum erythropoietin (Epo) level (PV), and bone marrow histopathology (ET). The presence of a JAK2 mutation and subnormal serum Epo level confirm a diagnosis of PV. Differential diagnosis in ET should include chronic myelogenous leukemia and prefibrotic myelofibrosis.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk-age > 60 years or presence of thrombosis history; low-risk-absence of both of these two risk factors. Presence of extreme thrombocytosis (platelet count > 1,000 x 10⁹/L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding. Risk factors for shortened survival in both PV and ET include age > 60 years, leukocytosis, history of thrombosis, and anemia.

RISK-ADAPTED THERAPY

Survival is near-normal in ET and reasonably long in PV. The 10-year risk of leukemic/fibrotic transformation is < 1%/1% in ET and < 5%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV), and hydroxyurea (high risk PV and ET). Treatment with busulfan or interferon-a is usually effective in hydroxyurea failures.

CBL, CBLB, TET2, ASXL1, and IDH1/2 mutations and additional chromosomal aberrations constitute molecular events in chronic myelogenous leukemia

Progression of chronic myelogenous leukemia (CML) to accelerated (AP) and blast phase (BP) is because of secondary molecular events, as well as additional cytogenetic abnormalities. On the basis of the detection of JAK2, CBL, CBLB, TET2, ASXL1, and IDH1/2 mutations in myelodysplastic/myeloproliferative neoplasms, we hypothesized that they may also contribute to progression in CML. We screened these genes for mutations in 54 cases with CML (14 with chronic phase, 14 with AP, 20 with myeloid, and 6 with nonmyeloid BP). We identified 1 CBLB and 2 TET2 mutations in AP, and 1 CBL, 1 CBLB, 4 TET2, 2 ASXL1, and 2 IDH family mutations in myeloid BP. However, none of these mutations were found in chronic phase. No cases with JAK2V617F mutations were found. In 2 cases, TET2 mutations were found concomitant with CBLB mutations. By single nucleotide polymorphism arrays, uniparental disomy on chromosome 5q, 8q, 11p, and 17p was found in AP and BP but not involving 4q24 (TET2) or 11q23 (CBL). Microdeletions on chromosomes 17q11.2 and 21q22.12 involved tumor associated genes NF1 and RUNX1, respectively. Our results indicate that CBL family, TET2, ASXL1, and IDH family mutations and additional cryptic karyotypic abnormalities can occur in advanced phase CML.

Unraveling the molecular pathophysiology of myelodysplastic syndromes

Somatically acquired genetic abnormalities lead to the salient features that define myelodysplastic syndromes (MDS): clonal hematopoiesis, aberrant differentiation, peripheral cytopenias, and risk of progression to acute myeloid leukemia. Although specific karyotypic abnormalities have been linked to MDS for decades, more recent findings have demonstrated the importance of mutations within individual genes, focal alterations that are not apparent by standard cytogenetics, and aberrant epigenetic regulation of gene expression. The spectrum of genetic abnormalities in MDS implicates a wide range of molecular mechanisms in the pathogenesis of these disorders, including activation of tyrosine kinase signaling, genomic instability, impaired differentiation, altered ribosome function, and changes in the bone marrow microenvironment. Specific alterations present in individual patients with MDS may explain much of the heterogeneity in clinical phenotype associated with this disease and can predict prognosis and response to therapy. Elucidation of the full complement of genetic causes of MDS promises profound insight into the biology of the disease, improved classification and prognostic scoring schemes, and the potential for novel targeted therapies with molecular predictors of response.

How I treat myelofibrosis

It is currently assumed that myelofibrosis (MF) originates from acquired mutations that target the hematopoietic stem cell and induce dysregulation of kinase signaling, clonal myeloproliferation, and abnormal cytokine expression. These pathogenetic processes are interdependent and also individually contributory to disease phenotype-bone marrow stromal changes, extramedullary hematopoiesis, ineffective erythropoiesis, and constitutional symptoms. Molecular pathogenesis of MF is poorly understood despite a growing list of resident somatic mutations that are either functionally linked to Janus kinase (JAK)-signal transducer and activator of transcription hyperactivation (eg JAK2, MPL, and LNK mutations) or possibly involved in epigenetic dysregulation of transcription (TET2, ASXL1, or EZH2 mutations). Current prognostication in primary MF is based on the Dynamic International Prognostic Scoring System-plus model, which uses 8 independent predictors of inferior survival to classify patients into low, intermediate 1, intermediate 2, and high-risk disease groups; corresponding median survivals are estimated at 15.4, 6.5, 2.9, and 1.3 years. Such information is used to plan a risk-adapted treatment strategy for the individual patient, which might include observation alone, conventional or investigational (eg, JAK inhibitors, pomalidomide) drug therapy, allogenic stem cell transplantation with reduced- or conventional-intensity conditioning, splenectomy, or radiotherapy. I discuss these treatment approaches in the context of who should get what and when.

Polycomb group proteins: multi-faceted regulators of somatic stem cells and cancer

Polycomb Group (PcG) proteins are transcriptional repressors that epigenetically modify chromatin and participate in the establishment and maintenance of cell fates. These proteins play important roles in both stem cell self-renewal and in cancer development. Our understanding of their mechanism of action has greatly advanced over the past 10 years, but many unanswered questions remain. In this review, we present the currently available experimental data that connect PcG protein function with some of the key processes which govern somatic stem cell activity. We also highlight recent studies suggesting that a delicate balance in PcG gene dosage is crucial for proper stem cell homeostasis and prevention of cancer stem cell development.

Combined mutations of ASXL1, CBL, FLT3, IDH1, IDH2, JAK2, KRAS, NPM1, NRAS, RUNX1, TET2 and WT1 genes in myelodysplastic syndromes and acute myeloid leukemias

Background

Gene mutation is an important mechanism of myeloid leukemogenesis. However, the number and combination of gene mutated in myeloid malignancies is still a matter of investigation.

Methods

We searched for mutations in the ASXL1, CBL, FLT3, IDH1, IDH2, JAK2, KRAS, NPM1, NRAS, RUNX1, TET2 and WT1 genes in 65 myelodysplastic syndromes (MDSs) and 64 acute myeloid leukemias (AMLs) without balanced translocation or complex karyotype.

Results

Mutations in ASXL1 and CBL were frequent in refractory anemia with excess of blasts. Mutations in TET2 occurred with similar frequency in MDSs and AMLs and associated equally with either ASXL1 or NPM1 mutations. Mutations of RUNX1 were mutually exclusive with TET2 and combined with ASXL1 but not with NPM1. Mutations in FLT3 (mutation and internal tandem duplication), IDH1, IDH2, NPM1 and WT1 occurred primarily in AMLs.

Conclusion

Only 14% MDSs but half AMLs had at least two mutations in the genes studied. Based on the observed combinations and exclusions we classified the 12 genes into four classes and propose a highly speculative model that at least a mutation in one of each class is necessary for developing AML with simple or normal karyotype.

The genetic basis of myelodysplastic syndromes

Myelodysplastic syndrome (MDS) disorders are clonal diseases that often carry stereotypic chromosomal abnormalities. A smaller proportion of cases harbor point mutations that activate oncogenes or inactivate tumor suppressor genes. New technologies have accelerated the pace of discovery and are responsible for the identification of novel genetic mutations associated with MDS and other myeloid neoplasms. These discoveries have identified novel mechanisms in the pathogenesis of MDS. This article touches on the better known genetic abnormalities in MDS and explains in greater detail those that have been discovered more recently. Understanding how mutations lead to MDS and how they might cooperate with each other has become more complicated as the number of MDS-associated genetic abnormalities has grown. In some cases, these mutations have prognostic significance that could improve upon the various prognostic scoring systems in common clinical use.

Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1

Myeloproliferative neoplasms (MPNs) originate from genetically transformed hematopoietic stem cells that retain the capacity for multilineage differentiation and effective myelopoiesis. Beginning in early 2005, a number of novel mutations involving Janus kinase 2 (JAK2), Myeloproliferative Leukemia Virus (MPL), TET oncogene family member 2 (TET2), Additional Sex Combs-Like 1 (ASXL1), Casitas B-lineage lymphoma proto-oncogene (CBL), Isocitrate dehydrogenase (IDH) and IKAROS family zinc finger 1 (IKZF1) have been described in BCR-ABL1-negative MPNs. However, none of these mutations were MPN specific, displayed mutual exclusivity or could be traced back to a common ancestral clone. JAK2 and MPL mutations appear to exert a phenotype-modifying effect and are distinctly associated with polycythemia vera, essential thrombocythemia and primary myelofibrosis; the corresponding mutational frequencies are approximately 99, 55 and 65% for JAK2 and 0, 3 and 10% for MPL mutations. The incidence of TET2, ASXL1, CBL, IDH or IKZF1 mutations in these disorders ranges from 0 to 17%; these latter mutations are more common in chronic (TET2, ASXL1, CBL) or juvenile (CBL) myelomonocytic leukemias, mastocytosis (TET2), myelodysplastic syndromes (TET2, ASXL1) and secondary acute myeloid leukemia, including blast-phase MPN (IDH, ASXL1, IKZF1). The functional consequences of MPN-associated mutations include unregulated JAK-STAT (Janus kinase/signal transducer and activator of transcription) signaling, epigenetic modulation of transcription and abnormal accumulation of oncoproteins. However, it is not clear as to whether and how these abnormalities contribute to disease initiation, clonal evolution or blastic transformation.

Spectrum of molecular defects in juvenile myelomonocytic leukaemia includes ASXL1 mutations

Mutations in NF1, PTPN11, NRAS, KRAS and CBL have been reported to play a pathogenetic role in juvenile myelomonocytic leukaemia (JMML), a rare myelodyplastic/myeloproliferative neoplasm occurring in children. Recently, mutations in ASXL1 were identified in chronic myelomonocytic leukaemia and other myeloid malignancies. We sequenced exon 12 of ASLX1 in 49 JMML patients, and found 2 novel heterozygous (nonsense and frameshift) mutations, one occurring as a sole lesion, the other was in conjunction with a PTPN11 mutation. ASXL1 cooperates with KDM1A in transcriptional repression and thereby ASXL1 mutations may synergize with or mimic other JMML-related mutations.

New clues to the molecular pathogenesis of myelodysplastic syndromes

During the past few years our understanding of the genetic basis for the myelodysplastic syndromes (MDS) has improved significantly. A few subgroups have been studied in detail and the genetic alterations are now to a great extent revealed. In 5q- syndrome haploinsufficiency of the ribosomal gene RPS14 appears to cooperate with loss of two micro-RNAs miR-145 and miR-146 to induce key features of the disease. Some mutations are specific for certain categories of MDS while others, such as TET2 seem to occur across the various categories. JAK2 mutations are mainly found in patients with myeloproliferative characteristics. The prognostic implications of most of the novel mutations are not yet fully understood, moreover, functional studies are required in order to understand the interplay between the different lesions; how they give rise to the disease and how some may lead to disease evolution including leukemic transformation. An improved understanding of the pathophysiology of MDS may lead to the identification of suitable targets for future drug development.

Molecular aspects of myeloproliferative neoplasms

During these past 5 years several studies have provided major genetic insights into the pathogenesis of the so-called classical myeloproliferative neoplasms (MPNs): polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The discovery of the JAK2V617F mutation first, then of the JAK2 exon 12 and MPLW515 mutations, have modified the understanding of these diseases, their diagnosis, and management. Now it is established that almost 100% of PV patients present a JAK2 mutation. Nearly 60% of ET patients and 50% of patients with PMF have the JAK2V617F mutation. The MPLW515 mutations are also present in a small proportion of ET and PMF patients. These mutations are oncogenic events that cause these disorders; however, they do not explain the heterogeneity of the entities in which they occur. Genetic defects have not been yet identified in around 40% of ET and PMF. There are likely additional somatic genetic factors important for the MPN phenotype like the recently described TET2, ASXL1, and CBL mutations. Moreover, polymorphisms in the JAK2 gene have been recently described as associated with MPN. Additional studies of large cohorts are required to dissect the genetic events in MPNs and the mechanisms of these oncogenic cooperations.

Treatment of chronic immune thrombocytopenic purpura: the patients? perspective

BACKGROUND

The 1996 ASH guidelines recommend glucocorticoids and splenectomy as standard treatment of chronic immune thrombocytopenic purpura (ITP). We sought to find out how many German ITP-patients were treated according to these guidelines and whether high-cost treatments were offered to the patients.

METHODS

We handed out a questionnaire at two self-help group meetings in 2004 and 2005 and to all patients who contacted the ITP self-help group until the end of 2005.

RESULTS

Eighty-five questionnaires were evaluated. Age (median 34 yr) and gender distribution (38% male, 62% female) were similar to other surveys. Median duration of disease was 5.2 yr. Seventy-five percent had platelets <20,000/microL at the time of diagnosis. Twenty-four percent still had <20,000 platelets/microL at the time of this survey. Forty-two percent had oropharyngeal mucosal bleeds, 28% gastrointestinal or urological bleeds, 11% bleedings in the eye with visual impairment or intracerebral bleeds. 96% had received a trial of glucocorticoid therapy. Seventy-five percent of the patients treated with glucocorticoids perceived this treatment as particularly bothersome. Seventy-five percent of the patients with low platelet count still had their spleen. Complementary and alternative medical treatments had been used by 46% of the patients. Only 33% of the patients had ever heard of rituximab.

CONCLUSION

Despite literature suggesting that patients wish to be well informed this survey shows that chronic ITP patients know little about their disease and the various treatment modalities. This and the frequent use of complementary and alternative medicines reflects inadequate communication between doctors and ITP patients.