Advances in understanding the pathogenesis of familial myeloproliferative neoplasms

Hereditary chronic neutrophilic leukemia in a four-generation family without transformation to acute leukemia

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative neoplasm (MPN) characterized by peripheral blood neutrophilia, marrow granulocyte hyperplasia, hepatosplenomegaly, and driver mutations in the colony-stimulating factor 3 receptor (CSF3R). Designation of activating CSF3R mutations as a defining genomic abnormality for CNL has led to increased recognition of the disease. However, the natural history of CNL remains poorly understood with most patients reported being of older age, lacking germline data, and having poor survival, in part due to transformation to acute leukemia. CSF3R driver mutations in most patients with CNL have been reported to be acquired, although rare cases of germline mutations have been described. Here, we report the largest pedigree to date with familial CNL, spanning four generations with affected family members ranging in age from 4 to 53 years, none of whom have transformed to acute leukemia. A heterozygous T618I CSF3R mutation was identified in peripheral blood and mesenchymal stromal cells from the proband and in all affected living family members, while the unaffected family members tested were homozygous wild type. We show that the T618I mutation also confers a survival advantage to neutrophils in an MCL1-dependent manner. Collectively, these data provide additional insights into the natural history of familial CNL arising from T618I CSF3R mutations and suggest that enhanced neutrophil survival also contributes to the high neutrophil count observed in patients with CNL.

Germline MPL mutations may be a rare cause of "triple-negative" thrombocytosis

Hereditary thrombocytosis (HT) is a rare inherited disorder with clinical features resembling those of sporadic essential thrombocythemia. This study included 933 patients with persistent isolated thrombocytosis for whom secondary reactive causes were excluded. Of 933 patients screened, 567 were JAK2-mutated, 255 CALR-mutated, 41 MPL-mutated, 2 double-mutated, and 68 were triple-negative. Two patients carried germline non-canonical mutations in exon 10: MPL W515* and MPL V501A. One triple-negative patient carried another germline non-canonical MPL mutation outside exon 10: MPL R102P. As germline MPL mutations may be underlying causes of HT, we recommend screening patients with triple-negative isolated thrombocytosis for non-canonical MPL mutations. Although clear evidence concerning HT treatment is still lacking, individuals with HT should probably be excluded from cytoreductive treatment. Thus, an accurate diagnosis is pivotal in avoiding unnecessary treatments.

Essential Thrombocythemia and Post-Essential Thrombocythemia Myelofibrosis: Updates on Diagnosis, Clinical Aspects, and Management

Although several decades have passed since the description of myeloproliferative neoplasms (MPN), many aspects of their pathophysiology have not been elucidated. In this review, we discuss the mutational landscape of patients with essential thrombocythemia (ET), prognostic scores and salient pathology, and clinical points. We discuss also the diagnostic challenges of differentiating ET from prefibrotic MF. We then focus on post-essential thrombocythemia myelofibrosis (post-ET MF), a rare subset of MPN that is usually studied in conjunction with post-polycythemia vera MF. The transition of ET to post-ET MF is not well studied on a molecular level, and we present available data. Patients with secondary MF could benefit from allogenic hematopoietic stem cell transplantation, and we present available data focusing on post-ET MF.

Haematological malignancies in relatives of patients affected with myeloproliferative neoplasms

In a cohort of 3131 patients with myeloproliferative neoplasms (MPNs), we identified 200 patients (6.4%) who reported a second case of haematological malignancies (HM) in first‐ or second‐degree relatives. The occurrence of a second HM in the family was not influenced by MPN subtype, sex or driver mutation, while it was associated with age at MPN diagnosis: 8.5% of patients diagnosed with MPN younger than 45 years had a second relative affected with HM compared to 5.5% of those diagnosed at the age of 45 years or older (p = 0.003), thus suggesting a genetic predisposition to HM with early onset.

Second Cancer Onset in Myeloproliferative Neoplasms: What, When, Why?

The risk of developing a solid cancer is a major issue arising in the disease course of a myeloproliferative neoplasm (MPN). Although the connection between the two diseases has been widely described, the backstage of this complex scenario has still to be explored. Several cellular and molecular mechanisms have been suggested to link the two tumors. Sometimes the MPN is considered to trigger a second cancer but at other times both diseases seem to depend on the same source. Increasing knowledge in recent years has revealed emerging pathways, supporting older, more consolidated theories, but there are still many unresolved issues. Our work aims to present the biological face of the complex clinical scenario in MPN patients developing a second cancer, focusing on the main cellular and molecular pathways linking the two diseases.

Familial essential thrombocythemia: 6 cases from a mono‐institutional series

Rarely essential thrombocythemia (ET) is diagnosed in more than one person within a family. Familial myeloproliferative neoplasms are underdiagnosed. In this report, we describe 6 couples of familial ET, evaluating the heterogeneity of the mutational state and the clinical presentation.

Familial essential thrombocythemia (ET) is very rare, also due to underdiagnosis. The collection of the cases could be useful to find out familial MPN diseases. Performing a complete blood count in relatives of patients with ET may lead to a suspicion of diagnosis of familial cases.

Identification and prioritization of myeloid malignancy germline variants in a large cohort of adult patients with AML

Inherited predisposition to myeloid malignancies is more common than previously appreciated. We analyzed the whole-exome sequencing data of paired leukemia and skin biopsy samples from 391 adult patients from the Beat AML 1.0 consortium. Using the 2015 American College of Medical Genetics and Genomics (ACMG) guidelines for variant interpretation, we curated 1547 unique variants from 228 genes. The pathogenic/likely pathogenic (P/LP) germline variants were identified in 53 acute myeloid leukemia (AML) patients (13.6%) in 34 genes, including 6.39% (25/391) of patients harboring P/LP variants in genes considered clinically actionable (tier 1). 41.5% of the 53 patients with P/LP variants were in genes associated with the DNA damage response. The most frequently mutated genes were CHEK2 (8 patients) and DDX41 (7 patients). Pathogenic germline variants were also found in new candidate genes (DNAH5, DNAH9, DNMT3A, and SUZ12). No strong correlation was found between the germline mutational rate and age of AML onset. Among 49 patients who have a reported history of at least one family member affected with hematological malignancies, 6 patients harbored known P/LP germline variants and the remaining patients had at least one variant of uncertain significance, suggesting a need for further functional validation studies. Using CHEK2 as an example, we show that three-dimensional protein modeling can be one of the effective methodologies to prioritize variants of unknown significance for functional studies. Further, we evaluated an in silico approach that applies ACMG curation in an automated manner using the tool for assessment and (TAPES) prioritization in exome studies, which can minimize manual curation time for variants. Overall, our findings suggest a need to comprehensively understand the predisposition potential of many germline variants in order to enable closer monitoring for disease management and treatment interventions for affected patients and families.

Characterization of a genomic region 8 kb downstream of GFI1B associated with myeloproliferative neoplasms

A genomic locus 8 kb downstream of the transcription factor GFI1B (Growth Factor Independence 1B) predisposes to clonal hematopoiesis and myeloproliferative neoplasms. One of the most significantly associated polymorphisms in this region is rs621940-G. GFI1B auto-represses GFI1B, and altered GFI1B expression contributes to myeloid neoplasms. We studied whether rs621940-G affects GFI1B expression and growth of immature cells. GFI1B ChIP-seq showed clear binding to the rs621940 locus. Preferential binding of various hematopoietic transcription factors to either the rs621940-C or -G allele was observed, but GFI1B showed no preference. In gene reporter assays the rs621940 region inhibited GFI1B promoter activity with the G-allele having less suppressive effects compared to the C-allele. However, CRISPR-Cas9 mediated deletion of the locus in K562 cells did not alter GFI1B expression nor auto-repression. In healthy peripheral blood mononuclear cells GFI1B expression did not differ consistently between the rs621940 alleles. Long range and targeted deep sequencing did not detect consistent effects of rs621940-G on allelic GFI1B expression either. Finally, we observed that myeloid colony formation was not significantly affected by either rs621940 allele in 193 healthy donors. Together, these findings show no evidence that rs621940 or its locus affect GFI1B expression, auto-repression or growth of immature myeloid cells.

Philadelphia-Negative MPN: A Molecular Journey, from Hematopoietic Stem Cell to Clinical Features

Philadelphia negative Myeloproliferative Neoplasms (MPN) are a heterogeneous group of hematopoietic stem cell diseases. MPNs show different risk grades of thrombotic complications and acute myeloid leukemia evolution. In the last couple of decades, from JAK2 mutation detection in 2005 to the newer molecular trademarks studied through next generation sequencing, we are learning to approach MPNs from a deeper perspective. Here, we intend to elucidate the important factors affecting MPN clonal advantage and the reasons why some patients progress to more aggressive disease. Understanding these mechanisms is the key to developing new treatment approaches and targeted therapies for MPN patients.

Targets in MPNs and potential therapeutics

Philadelphia-negative classical Myeloproliferative Neoplasms (MPNs), including Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF), are clonal hemopathies that emerge in the hematopoietic stem cell (HSC) compartment. MPN driver mutations are restricted to specific exons (14 and 12) of Janus kinase 2 (JAK2), thrombopoietin receptor (MPL/TPOR) and calreticulin (CALR) genes, are involved directly in clonal myeloproliferation and generate the MPN phenotype. As a result, an increased number of fully functional erythrocytes, platelets and leukocytes is observed in the peripheral blood. Nevertheless, the complexity and heterogeneity of MPN clinical phenotypes cannot be solely explained by the type of driver mutation. Other factors, such as additional somatic mutations affecting epigenetic regulators or spliceosomes components, mutant allele burdens and modifiers of signaling by driver mutants, clonal architecture and the order of mutation acquisition, signaling events that occur downstream of a driver mutation, the presence of specific germ-line variants, the interaction of the neoplastic clone with bone marrow microenvironment and chronic inflammation, all can modulate the disease phenotype, influence the MPN clinical course and therefore, might be useful therapeutic targets.

Germline variants in DNA repair genes, including BRCA1/2, may cause familial myeloproliferative neoplasms

The molecular causes of myeloproliferative neoplasms (MPNs) have not yet been fully elucidated. Approximately 7% to 8% of the patients carry predisposing genetic germline variants that lead to driver mutations, which enhance JAK-STAT signaling. To identify additional predisposing genetic germline variants, we performed whole-exome sequencing in 5 families, each with parent-child or sibling pairs affected by MPNs and carrying the somatic JAK2 V617F mutation. In 4 families, we detected rare germline variants in known tumor predisposition genes of the DNA repair pathway, including the highly penetrant BRCA1 and BRCA2 genes. The identification of an underlying hereditary tumor predisposition is of major relevance for the individual patients as well as for their families in the context of therapeutic options and preventive care. Two patients with essential thrombocythemia or polycythemia vera experienced progression to acute myeloid leukemia, which may suggest a high risk of leukemic transformation in these familial MPNs. Our study demonstrates the relevance of genetic germline diagnostics in elucidating the causes of MPNs and suggests novel therapeutic options (eg, PARP inhibitors) in MPNs. Furthermore, we uncover a broader tumor spectrum upon the detection of a germline mutation in genes of the DNA repair pathway.

Thrombocytosis in children and adolescents-classification, diagnostic approach, and clinical management

Secondary thrombocytosis is a frequent secondary finding in childhood infection and inflammation. Primary hereditary thrombocytosis may be caused by germline mutations within the genes encoding key regulators of thrombopoiesis, i.e., thrombopoietin (THPO) and its receptor c-MPL (MPL) or the receptor's effector kinase Januskinase2 (JAK2). Furthermore, somatic mutations in JAK2, MPL, and in the gene-encoding calreticulin (CALR) have been described to act as driver mutations within the so-called Philadelphia-negative myeloproliferative neoplasms (MPNs), namely essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF). Increasing knowledge on the molecular mechanisms and on the clinical complications of these diseases is reflected by the WHO diagnostic criteria and European LeukemiaNet (ELN) recommendations on the management of adult MPN. However, data on childhood thrombocytosis are rare, and no consensus guidelines for pediatric thrombocytosis exist. Current literature has highlighted differences in the epidemiology and molecular pathogenesis of childhood thrombocytosis as compared to adults. Furthermore, age-dependent complications and pharmacological specificities suggest that recommendations tailored to the pediatric population are necessary in clinical practice. Here we summarize literature on classification, diagnostics, and clinical management of childhood thrombocytosis.

New progress in the study of germline susceptibility genes of myeloid neoplasms

In 2016, the World Health Organization incorporated ‘myeloid neoplasms with germline predisposition’ into its classification of tumors of hematopoietic and lymphoid tissues, revealing the important role of germline mutations in certain myeloid neoplasms, particularly myelodysplastic syndrome and acute myeloid leukemia. The awareness of germline susceptibility has increased, and some patients with myeloid neoplasms present with a preexisting disorder or organ dysfunction. In such cases, mutations in genes including CCAAT enhancer binding protein α (CEBPA), DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 (DDX41), RUNX family transcription factor 1 (RUNX1), GATA binding protein 2 (GATA2), Janus kinase 2 (JAK2) and ETS variant transcription factor 6 (ETV6) have been recognized. Moreover, with the application of advanced technologies and reports of more cases, additional germline mutations associated with myeloid neoplasms have been identified and provide insights into the formation, prognosis and therapy of myeloid neoplasms. The present review discusses the well-known CEBPA, DDX41, RUNX1, GATA2, JAK2 and ETV6 germline mutations, and other mutations including those of lymphocyte adapter protein/SH2B adapter protein 3 and duplications of autophagy related 2B, GSK3B interacting protein αnd RB binding protein 6, ubiquitin ligase, that remain to be confirmed or explored. Recommendations for the management of diseases associated with germline mutations are also provided.

Epidemiology of the Philadelphia Chromosome-Negative Classical Myeloproliferative Neoplasms

Polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) comprise the BCR-ABL-negative classical myeloproliferative neoplasms (MPNs). These clonal myeloid diseases are principally driven by well-described molecular events; however, factors leading to their acquisition are not well understood. Beyond increasing age, male sex, and race/ethnicity differences, few consistent risk factors for the MPNs are known. PV and ET have an incidence of 0.5 to 4.0 and 1.1 to 2.0 cases per 100,000 person-years, respectively, and predict similar survival. PMF, which has an incidence of about 0.3 to 2.0 cases per 100,000 person-years, is associated with the shortest survival of the MPNs.

A Rare Association Between Prostate Cancer and Polycythemia Vera

The association of polycythemia vera (PV) and localized prostate cancer is uncommon. PV is one of the myeloproliferative neoplasms that is characterized by an increased red cell mass and uncontrolled formation of blood cells owing to an acquired mutation in Janus kinase-2. PV has numerous complications and could raise the hazard of other tumors. Here, we report an extremely rare association of localized prostate cancer in a 62-year-old male with PV. He was treated by CyberKnife surgery and completed four doses of goserelin and radiotherapy, his follow up Magnetic Resonance Imaging (MRI) four months after completion of treatment showed no recurrence, and the PV was treated with hydroxyurea 500 mg twice per day and repeated phlebotomies, when needed, to keep his hematocrit level under 45%.

SH2B3 (LNK) rs3184504 polymorphism is correlated with JAK2 V617F-positive myeloproliferative neoplasms

Background: Pathogenesis and phenotypic diversity in myeloproliferative neoplasms (MPN) cannot be fully explained by the currently known acquired mutations alone. Some susceptible germline variants of different genes have been proved to be associated with the development of these diseases. The goal of our study was to evaluate the association between the rs3184504 polymorphism of SH2B3 (LNK) gene (p.R262W, c.784T>C) and the risk of developing the four typical MPN - polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), and chronic myeloid leukemia (CML).

Material and methods: We investigated the SH2B3 rs3184504 T>C polymorphism by real-time PCR in 1901 MPN patients (575 with PV, 798 with ET, 251 with PMF, and 277 with CML), all of them harboring one of the specific driver mutations - JAK2 V617F or CALR in case of PV, ET and PMF, or BCR-ABL1 in case of CML, and 359 controls.

Results: Overall, the TT homozygous genotype was significantly associated with BCR-ABL1-negative MPN (OR = 1.34; 95% CI = 1.03-1.74; crude p-value = 0.02; adjusted p-value = 0.04). The most significant association was seen in case of PV (OR = 1.54; 95% CI = 1.14-2.06; crude p-value = 0.004; adjusted p-value = 0.024). Also, SH2B3 rs3184504 correlated significantly with JAK2 V617F-positive MPN (OR = 1.36; 95% CI = 1.04-1.77; crude p-value = 0.02; adjusted p-value = 0.08), but not with those CALR-positive. ET (regardless of molecular subtype) and CML were not correlated with SH2B3 rs3184504.

Conclusions: The SH2B3 rs3184504 polymorphism is associated with risk of MPN development, especially PV. This effect is restricted to JAK2 V617F-positive PV and PMF only.

Hereditary Predisposition to Hematopoietic Neoplasms: When Bloodline Matters for Blood Cancers

With the advent of precision genomics, hereditary predisposition to hematopoietic neoplasms- collectively known as hereditary predisposition syndromes (HPS)-are being increasingly recognized in clinical practice. Familial clustering was first observed in patients with leukemia, which led to the identification of several germline variants, such as RUNX1, CEBPA, GATA2, ANKRD26, DDX41, and ETV6, among others, now established as HPS, with tendency to develop myeloid neoplasms. However, evidence for hereditary predisposition is also apparent in lymphoid and plasma--cell neoplasms, with recent discoveries of germline variants in genes such as IKZF1, SH2B3, PAX5 (familial acute lymphoblastic leukemia), and KDM1A/LSD1 (familial multiple myeloma). Specific inherited bone marrow failure syndromes-such as GATA2 haploinsufficiency syndromes, short telomere syndromes, Shwachman-Diamond syndrome, Diamond-Blackfan anemia, severe congenital neutropenia, and familial thrombocytopenias-also have an increased predisposition to develop myeloid neoplasms, whereas inherited immune deficiency syndromes, such as ataxia-telangiectasia, Bloom syndrome, Wiskott Aldrich syndrome, and Bruton agammaglobulinemia, are associated with an increased risk for lymphoid neoplasms. Timely recognition of HPS is critical to ensure safe choice of donors and/or conditioning-regimen intensity for allogeneic hematopoietic stem-cell transplantation and to enable direction of appropriate genomics-driven personalized therapies. The purpose of this review is to provide a comprehensive overview of HPS and serve as a useful reference for clinicians to recognize relevant signs and symptoms among patients to enable timely screening and referrals to pursue germline assessment. In addition, we also discuss our institutional approach toward identification of HPS and offer a stepwise diagnostic and management algorithm.

Epidemiology of the classical myeloproliferative neoplasms: The four corners of an expansive and complex map

The classical myeloproliferative neoplasms (MPNs), specifically chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF), represent clonal myeloid disorders whose pathogenesis is driven by well-defined molecular abnormalities. In this comprehensive review, we summarize the epidemiological literature and present our own analysis of the most recent the Surveillance, Epidemiology, and End Results (SEER) program data through 2016. Older age and male gender are known risk factors for MPNs, but the potential etiological role of other variables is less established. The incidences of CML, PV, and ET are relatively similar at 1.0-2.0 per 100,000 person-years in the United States, while PMF is rarer with an incidence of 0.3 per 100,000 person-years. The availability of tyrosine kinase inhibitor therapy has dramatically improved CML patient outcomes and yield a life expectancy similar to the general population. Patients with PV or ET have better survival than PMF patients.

Emerging translational science discoveries, clonal approaches, and treatment trends in chronic myeloproliferative neoplasms

The 60th American Society of Hematology (ASH) held in San Diego in December 2018 was followed by the 13th Post-ASH chronic myeloproliferative neoplasms (MPNs) workshop on December 4 and 5, 2018. This closed annual workshop, first introduced in 2006 by Goldman and Mughal, was organized in collaboration with Alpine Oncology Foundation and allowed experts in preclinical and clinical research in the chronic MPNs to discuss the current scenario, including relevant presentations at ASH, and address pivotal open questions that impact translational research and clinical management. This review is based on the presentations and deliberations at this workshop, and rather than provide a resume of the proceedings, we have selected some of the important translational science and treatment issues that require clarity. We discuss the experimental and observational evidence to support the intimate interaction between aging, inflammation, and clonal evolution of MPNs, the clinical impact of the unfolding mutational landscape on the emerging targets and treatment of MPNs, new methods to detect clonal heterogeneity, the challenges in managing childhood and adolescent MPN, and reflect on the treatment of systemic mastocytosis (SM) following the licensing of midostaurin.

Colony-Forming Cell Assay Detecting the Co-Expression of JAK2V617F and BCR-ABL1 in the Same Clone: A Case Report

BCR-ABL1-negative myeloproliferative disorders and chronic myeloid leukaemia are haematologic malignancies characterised by single and mutually exclusive genetic alterations. Nevertheless, several patients co-expressing the JAK2V617F mutation and the BCR-ABL1 transcript have been described in the literature. We report the case of a 61-year-old male who presented with an essential thrombocythaemia phenotype and had a subsequent diagnosis of chronic phase chronic myeloid leukaemia. Colony-forming assays demonstrated the coexistence of 2 different haematopoietic clones: one was positive for the JAK2V617F mutation and the other co-expressed both JAK2V617F and the BCR-ABL1 fusion gene. No colonies displayed the BCR-ABL1 transcript alone. These findings indicate that the JAK2V617F mutation was the founding genetic alteration of the disease, followed by the acquisition of the BCR-ABL1 chimeric oncogene. Our data support the hypothesis that a heterozygous JAK2V617F clone may have favoured the bi-clonal nature of this myeloproliferative disorder, generating clones harbouring a second transforming genetic event.

Challenges in the introduction of next-generation sequencing (NGS) for diagnostics of myeloid malignancies into clinical routine use

Given the vast phenotypic and genetic heterogeneity of acute and chronic myeloid malignancies, hematologists have eagerly awaited the introduction of next-generation sequencing (NGS) into the routine diagnostic armamentarium to enable a more differentiated disease classification, risk stratification, and improved therapeutic decisions. At present, an increasing number of hematologic laboratories are in the process of integrating NGS procedures into the diagnostic algorithms of patients with acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), and myeloproliferative neoplasms (MPNs). Inevitably accompanying such developments, physicians and molecular biologists are facing unexpected challenges regarding the interpretation and implementation of molecular genetic results derived from NGS in myeloid malignancies. This article summarizes typical challenges that may arise in the context of NGS-based analyses at diagnosis and during follow-up of myeloid malignancies.

[Targeted sequencing analysis of hyper-eosinophilic syndrome and chronic eosinophilic leukemia]

Objective: Analysis of the molecular characteristics of eosinophilia. Methods: Targeting sequence to 24 patients with chronic eosinophilic leukemia (CEL) with rearrangement of PDGFRA, PDGFRB, or FGFR1 and 62 patients with hyper-eosinophilic syndrome (HES). Mutation annotation and analysis of amino acid mutation using authoritative databases to speculate on possible pathogenic mutation. Results: Thirty-seven kinds of clonal variant were detected from 17 patients with CEL, no recurrent mutation site and hot spot region were found. No pathogenic mutation was detected in 19 patients with PDGFRA rearrangement, but pathogenic mutations of ASXL1, RUNX1 and NRAS were detected from 2 patients with FGFR1 rearrangement who progressed to acute myeloid leukemia and 1 patient with PDGFRB rearrangement who progressed to T lymphoblastic lymphoma, respectively. One hundred and two kinds of clonal abnormalities were detected in 49 patients with HES. The main hot spot mutation regions included: CEBPA Exon1, TET2 Exon3, ASXL1 Exon12, IDH1 Y208C, and FGFR3 L164V. CRRLF2 P224L and PDGFRB R370C point mutations were detected separately in 2 patients with HES who treated with imatinib monotherapy and achieved hematologic remission. Conclusion: The pathogenesis of CEL with PDGFRA, PDGFRB or FGFR1 rearrangement is usually single, and the progression of the disease may involve other driver mutation. A variety of genes with hot mutation regions may be involved in the pathogenesis of HES, and some mutation sites are sensitive to tyrosine kinase inhibitors.

The JAK2 GGCC (46/1) Haplotype in Myeloproliferative Neoplasms: Causal or Random?

The germline JAK2 haplotype known as “GGCC or 46/1 haplotype” (haplotype^GGCC_46/1) consists of a combination of single nucleotide polymorphisms (SNPs) mapping in a region of about 250 kb, extending from the JAK2 intron 10 to the Insulin-like 4 (INLS4) gene. Four main SNPs (rs3780367, rs10974944, rs12343867, and rs1159782) generating a “GGCC” combination are more frequently indicated to represent the JAK2 haplotype. These SNPs are inherited together and are frequently associated with the onset of myeloproliferative neoplasms (MPN) positive for both JAK2 V617 and exon 12 mutations. The association between the JAK2 haplotype^GGCC_46/1 and mutations in other genes, such as thrombopoietin receptor (MPL) and calreticulin (CALR), or the association with triple negative MPN, is still controversial. This review provides an overview of the frequency and the role of the JAK2 haplotype^GGCC_46/1 in the pathogenesis of different myeloid neoplasms and describes the hypothetical mechanisms at the basis of the association with JAK2 gene mutations. Moreover, possible clinical implications are discussed, as different papers reported contrasting data about the correlation between the JAK2 haplotype^GGCC_46/1 and blood cell count, survival, or disease progression.

Myeloproliferative neoplasms: from origins to outcomes

Substantial progress has been made in our understanding of the pathogenetic basis of myeloproliferative neoplasms. The discovery of mutations in JAK2 over a decade ago heralded a new age for patient care as a consequence of improved diagnosis and the development of therapeutic JAK inhibitors. The more recent identification of mutations in calreticulin brought with it a sense of completeness, with most patients with myeloproliferative neoplasm now having a biological basis for their excessive myeloproliferation. We are also beginning to understand the processes that lead to acquisition of somatic mutations and the factors that influence subsequent clonal expansion and emergence of disease. Extended genomic profiling has established a multitude of additional acquired mutations, particularly prevalent in myelofibrosis, where their presence carries prognostic implications. A major goal is to integrate genetic, clinical, and laboratory features to identify patients who share disease biology and clinical outcome, such that therapies, both existing and novel, can be better targeted.

Myeloproliferative neoplasms: from origins to outcomes

Substantial progress has been made in our understanding of the pathogenetic basis of myeloproliferative neoplasms. The discovery of mutations in JAK2 over a decade ago heralded a new age for patient care as a consequence of improved diagnosis and the development of therapeutic JAK inhibitors. The more recent identification of mutations in calreticulin brought with it a sense of completeness, with most patients with myeloproliferative neoplasm now having a biological basis for their excessive myeloproliferation. We are also beginning to understand the processes that lead to acquisition of somatic mutations and the factors that influence subsequent clonal expansion and emergence of disease. Extended genomic profiling has established a multitude of additional acquired mutations, particularly prevalent in myelofibrosis, where their presence carries prognostic implications. A major goal is to integrate genetic, clinical, and laboratory features to identify patients who share disease biology and clinical outcome, such that therapies, both existing and novel, can be better targeted.

Buccal epithelial cells display somatic, bone marrow-derived CALR mutation

Buccal epithelial cells harbor an MPN-associated CALR mutation in a patient with CALR-mutant essential thrombocytosis, Ph⁺ CML, and no germ line CALR mutation.

Effects of vascular endothelial growth factors and their receptors on megakaryocytes and platelets and related diseases

It is well known that vascular endothelial growth factors (VEGFs) and their receptors (vascular endothelial growth factor receptors, VEGFRs) are expressed in different tissues, and VEGF-VEGFR loops regulate a wide range of responses, including metabolic homeostasis, cell proliferation, migration and tubuleogenesis. As ligands, VEGFs act on three structurally related VEGFRs (VEGFR1, VEGFR2 and VEGFR3 [also termed FLT1, KDR and FLT4, respectively]) that deliver downstream signals. Haematopoietic stem cells (HSCs), megakaryocytic cell lines, cultured megakaryocytes (MKs), primary MKs and abnormal MKs express and secrete VEGFs. During the development from HSCs to MKs, VEGFR1, VEGFR2 and VEGFR3 are expressed at different developmental stages, respectively, and re-expressed, e.g., VEGFR2, and play different roles in commitment, differentiation, proliferation, survival and polyplodization of HSCs/MKs via autocrine, paracrine and/or even intracrine loops. Moreover, VEGFs and their receptors are abnormally expressed in MK-related diseases, including myeloproliferative neoplasms, myelodysplastic syndromes and acute megakaryocytic leukaemia (a rare subtype of acute myeloid leukaemia), and they lead to the disordered proliferation/differentiation of bone marrow cells and angiogenesis, indicating that they are closely related to these diseases. Thus, targeting VEGF-VEGFR loops may be of potential therapeutic value.