Aleukemic Chronic Myeloid Leukemia Without Neutrophilia and Thrombocytosis: A Report From the BCR::ABL1 Pathology Group

Chronic myeloid leukemia (CML) is characterized by leukocytosis with left-shifted neutrophilia, basophilia, eosinophilia, and variable thrombocytosis. However, extremely rare cases of patients with CML without significant leukocytosis and thrombocytosis (aleukemic phase [ALP] CML, or CML-ALP) have been reported. Due to its rarity and limited awareness, there remains a significant knowledge gap concerning the pathologic diagnosis, disease progression, and optimal patient management and outcomes. In this multi-institutional study, we investigated 31 patients with CML-ALP. Over half (54.8%) of patients had a history of or concurrent hematopoietic or nonhematopoietic malignancies. At time of diagnosis of CML-ALP, approximately 26.7% of patients exhibited neutrophilia, 56.7% had basophilia, and 13.3% showed eosinophilia. The median number of metaphases positive for t(9;22)(q34;q11.2) was 15, with a median of 38.5% of interphase nuclei positive for BCR::ABL1 by fluorescence in situ hybridization. The median BCR::ABL1 level was 26.14%. Remarkably, 14 (45.2%) patients were initially misdiagnosed or not diagnosed before karyotype or fluorescence in situ hybridization information for BCR::ABL1 became available. Twenty-five patients received tyrosine kinase inhibitors (TKIs). One patient developed blast crisis while on TKI treatment 8 months after initial diagnosis. With a median follow-up time of 46.1 months, 20 of 22 patients who received TKI therapy and had detailed follow-up information achieved complete cytogenetic remission or deeper, 15 achieved major molecular remission or deeper, and 10 achieved molecularly undetectable leukemia. In conclusion, given the frequent occurrence of prior or concurrent malignancies, aleukemic presentation, and low level of t(9;22)(q34;q11.2)/BCR::ABL1, misdiagnosis or delayed diagnosis is common among these patients. While these patients generally respond well to TKIs, rare patients may develop blastic transformation. It is therefore important for pathologists and hematologists to be aware of this highly unusual presentation of CML to ensure timely diagnosis and appropriate management.

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.

Hereditary thrombocythemia due to splicing donor site mutation of THPO in a Japanese family

Thrombopoietin (THPO) is an essential factor for platelet production. Hereditary thrombocythemia (HT) is caused by a germline mutation of THPO, MPL, or JAK2 and is inherited in an autosomal-dominant manner. We identified a Japanese family with HT due to a point mutation of the splicing donor site of the THPO gene (THPO c.13 + 1G > A). Bone marrow biopsy showed increased megakaryocytes mimicking essential thrombocythemia. One affected family member developed chronic myeloid leukemia. We cloned the mutation and developed mutated and wild type THPO expression vectors. Molecular analysis showed that the mutation causes an exon 3 skipping transcript of THPO that abrogates a suppressive untranslated upstream open reading frame. Although the transcript levels of THPO mRNA were comparable, mutated transcripts were more efficiently translated and THPO protein expression was significantly higher than that of the wild type.

Idiopathic Thrombocytosis in Alpha Thalassemia Trait Patient

Platelet count increases are typically a reactionary response to one of a variety of pathophysiological events. We present here a case of microcytic hypochromic red blood cells and thrombocytosis in an adolescent female that we have monitored for three years. The patient was positive for alpha thalassemia trait; negative for mutation in Janus kinase 2, calreticulin, or myeloproliferative leukemia virus oncogene; and negative for reactive causes of thrombocytosis. Noticeably, a variant in atypical chemokine receptor 1 (ACKR1) (c.-67T>C, rs2814778) was found to be homozygous. Accordingly, the case was diagnosed as idiopathic thrombocytosis, and treatment was given to restore platelet levels to normal. Our findings highlight the possibility of an unknown association between alpha thalassemia trait and idiopathic thrombocytosis in the presence of ACKR1 mutation, which could be implicated in disease pathogenesis.

JAK2 R683S Mutation Resulting in Dual Diagnoses of Chronic Eosinophilic Leukemia and Myelodysplastic/Myeloproliferative Overlap Syndrome

A 66-year-old male presented with hypereosinophilia, thrombocytosis, extensive thrombosis refractory to direct oral anticoagulant therapy, and evidence of end-organ damage, including rash, splenic infarcts, and pulmonary infiltrates. Bone marrow biopsy revealed myeloid malignancy consistent with both chronic eosinophilic leukemia and myelodysplastic/myeloproliferative neoplasms (MDS/MPN) with SF3B1 mutation and thrombocytosis. Next-generation sequencing of the patient's eosinophils and neutrophil compartments revealed pathologic variants in EZH2 and SF3B1 in addition to a noncanonical JAK2 R683S mutation that has not been previously described in myeloproliferative disorders or other chronic myeloid neoplasms. These mutations were not present in the patient's lymphoid cell fraction, suggesting that the hematopoietic malignancy arose in a myeloid-committed progenitor cell. Based on this case and previous work from our group, we propose that noncanonical JAK2 mutations may permit signal transduction that biases toward eosinophilic differentiation in chronic myeloid neoplasms. Although the patient's blood counts initially responded to ruxolitinib and hydroxyurea, the response was not durable. Early referral for allogenic bone marrow transplant appears necessary to prevent long-term complications and disease progression in myeloid neoplasms with clonal hypereosinophilia driven by noncanonical JAK2 mutations.

Atypical chronic myeloid leukemia and myelodysplastic/myeloproliferative neoplasm, not otherwise specified: 2023 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Atypical chronic myeloid leukemia (aCML) and myelodysplastic/myeloproliferative (MDS/MPN) neoplasms, not otherwise specified (NOS), are MDS/MPN overlap neoplasms characterized by leukocytosis, in the absence of monocytosis and eosinophilia, with <20% blasts in the blood and bone marrow.

DIAGNOSIS

aCML, previously known as aCML, BCR::ABL1 negative, was renamed as aCML by the ICC classification, and as MDS/MPN with neutrophilia by the 5th edition of the WHO classification. This entity is characterized by dysplastic neutrophilia with immature myeloid cells comprising ≥10% of the white blood cell count, with prominent dysgranulopoiesis. MDS/MPN-NOS consists of MDS/MPN overlap neoplasms not meeting criteria for defined categories such as chronic myelomonocytic leukemia (CMML), MDS/MPN-ring sideroblasts-thrombocytosis (MDS/MPN-RS-T), and aCML.

MUTATIONS AND KARYOTYPE

Cytogenetic abnormalities are seen in 40-50% of patients in both categories. In aCML, somatic mutations commonly encountered include ASXL1, SETBP1, ETNK1, and EZH2 whereas MDS/MPN-NOS can be further stratified by mutational profiles into CMML-like, MDS/MPN-RS-T-like, aCML-like, TP35-mutated, and "others", respectively.

RISK STRATIFICATION

The Mayo Clinic aCML model stratifies patients based on age >67 years, hemoglobin <10 g/dl, and the presence of TET2 mutations into low-risk (0-1 points) and high-risk (>2 points) groups, with median survivals of 18 and 7 months, respectively. MDS/MPN-NOS patients have traditionally been risk stratified using MDS risk models such as IPSS and IPSS-R.

TREATMENT

Leukocytosis and anemia are managed like lower risk MPN and MDS. DNMT inhibitors have been used in both entities with suboptimal response rates. Allogeneic stem cell transplant remains the only curative strategy but is associated with high morbidity and mortality.

Clinical Application for Diagnosis of Myelodysplatic/Myeloproliferative Neoplasm with Ring Sideroblasts and Thrombocytosis

BACKGROUND

Myelodysplastic/myeloproliferative neoplasm with ring sideroblasts and thrombocytosis (MDS/ MPN-RS-T) was newly introduced as a full entity in the 2016 revision of the WHO classification. In this study, we investigated the morphologic, laboratory, and clinical features of MDS/MPN-RS-T.

METHODS

We reviewed the bone marrow and genetic studies of patients whose diagnoses were coded as "refractory anemia with ring sideroblasts (RARS)" or "MDS/MPN, unclassifiable" between January 2008 and April 2018.

RESULTS

A total of 8 cases fulfilled the criteria for a diagnosis of MDS/MPN-RS-T. All of them had no specific symptoms. Half of the cases had less than 450 × 109/L platelet counts by an automated hematology analyzer; however, all platelet counts exceeded 450 × 109/L when performed manually. JAK2 mutation tests were performed in 7 cases, and a heterozygous mutation was detected in 1 case. SF3B1 mutations were present in 3 of the 4 cases tested.

CONCLUSIONS

When RARS is suspected in patients without thrombocytopenia, manual platelet counts should be performed. For patients with suspected essential thrombocythemia, RS evaluation through careful observation of an iron-stained slide is crucial. Since the independent evaluation of RS was reflected in the revised classification, the ambiguous disease classification becomes clearer and more consistent.

Genetic alterations in patients with chronic leucocytosis and persistent thrombocytosis

To elucidate the relevance of genetic alterations, we analysed 17 genes known to be involved in haematological neoplasms in patients with chronic leucocytosis and patients with persistent thrombocytosis. Mutations of the JAK2, SETBP1 and ASXL1 genes were found in 1/13, 1/13, and 2/13 patients with leucocytosis, respectively. Mutations of the JAK2, CALR, SETBP1 and ASXL1 genes were found in 1/5, 1/5, 1/5 and 2/5 patients with thrombocytosis, respectively. One leucocytosis patient with a JAK2 V617F mutation developed polycythaemia vera. Another leucocytosis patient developed Philadelphia chromosome-negative chronic myeloid leukaemia (Ph(-) CML) accompanied by t(9;12)(q34.1;p13.?3) (Mori et al. 2016). Another leucocytosis patient with mutations of the SETBP1 and ASXL1 genes progressed to blast crisis of Ph(-) CML accompanied by i(17)(q10). Chronic leucocytosis patients who had genetic alterations tended to develop haematological neoplasms, while thrombocytosis unexpectedly resolved in two persistent thrombocytosis patients with genetic alterations.

Distinct effects of V617F and exon12-mutated JAK2 expressions on erythropoiesis in a human induced pluripotent stem cell (iPSC)-based model

Activating mutations affecting the JAK-STAT signal transduction is the genetic driver of myeloproliferative neoplasms (MPNs) which comprise polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis. The JAK2p.V617F mutation can produce both erythrocytosis in PV and thrombocytosis in ET, while JAK2 exon 12 mutations cause only erythrocytosis. We hypothesized that these two mutations activated different intracellular signals. In this study, the induced pluripotent stem cells (iPSCs) were used to model JAK2-mutated MPNs. Normal iPSCs underwent lentiviral transduction to overexpress JAK2p.V617F or JAK2p.N542_E543del (JAK2exon12) under a doxycycline-inducible system. The modified iPSCs were differentiated into erythroid cells. Compared with JAK2V617F-iPSCs, JAK2exon12-iPSCs yielded more total CD71⁺GlycophorinA⁺ erythroid cells, displayed more mature morphology and expressed more adult hemoglobin after doxycycline induction. Capillary Western immunoassay revealed significantly higher phospho-STAT1 but lower phospho-STAT3 and lower Phospho-AKT in JAK2exon12-iPSCs compared with those of JAK2V617F-iPSCs in response to erythropoietin. Furthermore, interferon alpha and arsenic trioxide were tested on these modified iPSCs to explore their potentials for MPN therapy. Both agents preferentially inhibited proliferation and promoted apoptosis of the iPSCs expressing mutant JAK2 compared with those without doxycycline induction. In conclusion, the modified iPSC model can be used to investigate the mechanisms and search for new therapy of MPNs.

Thrombocytosis and Effects of IL-6 Knock-Out in a Colitis-Associated Cancer Model

There is an increasing number of studies showing that thrombocytosis—accompanying a variety of solid tumors including colorectal cancer (CRC)—is associated with shorter survival and earlier development of metastases. The mechanisms of cancer-associated thrombocytosis are not completely understood yet. The aim of our study was to evaluate the role of IL-6 in tumor development and thrombocytosis in mice with inflammation-induced CRC, using a CRISPR/cas9 IL-6 knockout (KO) strain. Adult male FB/Ant mice (n = 39) were divided into four groups: (1) IL-6 KO controls (n = 5); (2) IL-6 KO CRC model group (n = 18); (3) Wild-type (WT) controls (n = 6); and (4) WT CRC model group (n = 10). CRC model animals in (2) and (4) received azoxymethane (AOM)/dextran sodium sulfate (DSS) treatment to induce inflammation-related CRC. Plasma and liver tissues were obtained to determine platelet counts, IL-6 and thrombopoietin-1 (TPO) levels. In 1 WT and 2 IL-6 KO mice in vivo confocal endomicroscopy and 18F-fluorodeoxyglucose (FDG) PET/MRI examinations were performed to evaluate the inflammatory burden and neoplastic transformation. At the end of the study, tumorous foci could be observed macroscopically in both CRC model groups. Platelet counts were significantly elevated in the WT CRC group compared to the IL-6 KO CRC group. TPO levels moved parallelly with platelet counts. In vivo fluorescent microscopy showed signs of disordered and multi-nuclear crypt morphology with increased mucus production in a WT animal, while regular mucosal structure was prominent in the IL-6 KO animals. The WT animal presented more intense and larger colonic FDG uptake than IL-6 KO animals. Our study confirmed thrombocytosis accompanying inflammation-related CRC and the crucial role of IL-6 in this process. Significantly higher platelet counts were found in the WT CRC group compared to both the control group and the IL-6 KO group. Concomitantly, the tumor burden of WT mice was also greater than that of IL-6 KO mice. Our findings are in line with earlier paraneoplastic IL-6 effect suggestions.

Diagnostic workflow for hereditary erythrocytosis and thrombocytosis

In the patient presenting with an elevated blood count who does not have an acquired clonal disorder causing a myeloproliferative neoplasm, hereditary erythrocytosis or hereditary thrombocytosis needs to be considered as a possible explanation. A young patient and/or those with a family history of myeloproliferative neoplasm should specifically raise this possibility. Among the causes of hereditary erythrocytosis are mutations in the genes in the oxygen sensing pathway and high-affinity hemoglobins. Hereditary thrombocytosis has been shown to be accounted for by mutations in THPO, MPL, and JAK2 genes. In those who have a possible hereditary erythrocytosis or thrombocytosis, the investigative pathway includes specific investigation to rule out the more common acquired clonal disorders, and, if indicated, other secondary causes, measurement of specific cytokines as indicated, and search for specific identified molecular lesions that have been shown to cause these hereditary disorders. There remain individuals who appear to have a hereditary disorder in whom a genetic lesion cannot currently be identified.

Mutant calreticulin knockin mice develop thrombocytosis and myelofibrosis without a stem cell self-renewal advantage

Somatic mutations in the endoplasmic reticulum chaperone calreticulin (CALR) are detected in approximately 40% of patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF). Multiple different mutations have been reported, but all result in a +1-bp frameshift and generate a novel protein C terminus. In this study, we generated a conditional mouse knockin model of the most common CALR mutation, a 52-bp deletion. The mutant novel human C-terminal sequence is integrated into the otherwise intact mouse CALR gene and results in mutant CALR expression under the control of the endogenous mouse locus. CALRdel/+ mice develop a transplantable ET-like disease with marked thrombocytosis, which is associated with increased and morphologically abnormal megakaryocytes and increased numbers of phenotypically defined hematopoietic stem cells (HSCs). Homozygous CALRdel/del mice developed extreme thrombocytosis accompanied by features of MF, including leukocytosis, reduced hematocrit, splenomegaly, and increased bone marrow reticulin. CALRdel/+ HSCs were more proliferative in vitro, but neither CALRdel/+ nor CALRdel/del displayed a competitive transplantation advantage in primary or secondary recipient mice. These results demonstrate the consequences of heterozygous and homozygous CALR mutations and provide a powerful model for dissecting the pathogenesis of CALR-mutant ET and PMF.

Splicing factor mutations in MDS RARS and MDS/MPN-RS-T

Spliceosomal mutations, especially mutations in SF3B1, are frequently (>80%) identified in patients with refractory anemia with ringed sideroblasts (RARS) and myelodysplastic/myeloproliferative neoplasms with ringed sideroblasts and thrombocytosis (MDS/MPN-RS-T; previously known as RARS-T), and SF3B1 mutations have a high positive predictive value for disease phenotype with ringed sideroblasts. These observations suggest that SF3B1 mutations play important roles in the pathogenesis of these disorders and formation of ringed sideroblasts. Here we will review recent insights into the molecular mechanisms of mis-splicing caused by mutant SF3B1 and the pathogenesis of RSs in the context of congenital sideroblastic anemia as well as RARS with SF3B1 mutations. We will also discuss therapy of SF3B1 mutant MDS, including novel approaches.

Prevalence of the frequency of JAK2 (V617F) mutation in different myeloproliferative disorders in Egyptian patients

BACKGROUND AND OBJECTIVES

Detection of chromosomal abnormalities in myeloproliferative disorders is important for proper diagnosis of these disorders. This study has investigated the presence of JAK2 mutation (V617F) in Egyptian patients with myeloproliferative disorders referred to National Cancer institute, Cairo University.

METHODS

The study involved 110 cases of Philadelphia negative Myeloproliferative diseases (MPDs), 70 cases with Polycythemia Vera (PV), 24 cases with Essential Thrombocytosis (ET) and 16 cases with Idiopathic Myelofibrosis (IMF) and 20 cases as a control group which represented as; (10 cases with secondary erythrocytosis, 1 case with reactive thrombocytosis, 4 cases as normal control and 5 as Philadelphia positive Chronic Myeloid Leukemia cases), they were collected from National Cancer Institute (NCI) over 3 years. We used ARMS technique for mutation detection.

RESULTS

The frequency of the V617F JAK2 mutation was highest in patients with PV where 56 out of 70 cases (80%) carried the mutation, followed by ET with 6 of 24 (25) and IMF with 2 of 16 (12.5%) . None of the cases with secondary Erythrocytosis, reactive thrombocytosis, the normal controls or Philadelphia positive CML cases carried the mutation.

CONCLUSIONS

Our results are concordant with international published results for detection of this mutation. It is unequivocal now that V617F is met in many MPDs especially PRV. Finding this mutation in those patients is thought to have a big impact on the diagnosis and treatment of these disorders.

Increased expression of HIF2α during iron deficiency-associated megakaryocytic differentiation

BACKGROUND

Iron deficiency is associated with reactive thrombocytosis; however, the mechanisms driving this phenomenon remain unclear. We previously demonstrated that this occurs alongside enhanced megakaryopoiesis in iron-deficient rats, without alterations in the megakaryopoietic growth factors thrombopoietin, interleukin-6, or interleukin-11.

OBJECTIVES

The aim of this study was to evaluate megakaryocyte differentiation under iron deficiency in an in vitro model and to investigate potential genes involved in this process.

METHODS

Human erythroleukemia and megakaryoblastic leukemia cell lines, as well as cord-blood derived hematopoietic stem cells were cultured under iron deficiency. Cell morphology, ploidy, expression of CD41, CD61, and CD42b, and proplatelet formation were assessed in iron-deficient cultures. Polymerase chain reaction arrays were used to identify candidate genes that were verified using real-time polymerase chain reaction. Hypoxia-inducible factor 1, α subunit (HIF2α) protein expression was assessed in bone marrow sections from iron-deficient rats and vascular endothelial growth factor (VEGF)-A in culture supernatants.

RESULTS AND CONCLUSIONS

Iron deficiency enhanced megakaryoid features in cell lines, increasing ploidy and initiating formation of proplatelet-like structures. In cord blood cell cultures, iron deficiency increased the percentage of cells expressing megakaryopoietic markers and enhanced proplatelet formation. HIF2α and VEGF were identified as potential pathways involved in this process. HIF2α protein expression was increased in megakaryocytes from iron-deficient rats, and VEGF-A concentration was higher in iron-deficient culture supernatants. Addition of VEGF-A to cell cultures increased percentage expression of megakaryocyte CD41. In conclusion, the data demonstrate that iron deficiency augments megakaryocytic differentiation and proplatelet formation and a potential role of HIF2α in megakaryopoiesis.

[New disease markers within the chronic myeloproliferative neoplasms]

The chaperone and calcium storing protein calreticulin is coded by CALR, and newly identified mutations in CALR are found in respectively 49-70% and 56-88% of JAK2- and MPL-negative patients with essential thrombocytaemia (ET) and primary myelofibrosis (PMF). A total of 41 mutations have been identified, all located to exon 9 which codes the protein's C-terminal. CALR mutations are present only in myeloid malignancies and confer a more indolent disease than JAK2-mutated ET and PMF. CALR mutations as a diagnostic and prognostic tool are promising and the mutations are potential targets for immune therapy.

Complex patterns of chromosome 11 aberrations in myeloid malignancies target CBL, MLL, DDB1 and LMO2

Exome sequencing of primary tumors identifies complex somatic mutation patterns. Assignment of relevance of individual somatic mutations is difficult and poses the next challenge for interpretation of next generation sequencing data. Here we present an approach how exome sequencing in combination with SNP microarray data may identify targets of chromosomal aberrations in myeloid malignancies. The rationale of this approach is that hotspots of chromosomal aberrations might also harbor point mutations in the target genes of deletions, gains or uniparental disomies (UPDs). Chromosome 11 is a frequent target of lesions in myeloid malignancies. Therefore, we studied chromosome 11 in a total of 813 samples from 773 individual patients with different myeloid malignancies by SNP microarrays and complemented the data with exome sequencing in selected cases exhibiting chromosome 11 defects. We found gains, losses and UPDs of chromosome 11 in 52 of the 813 samples (6.4%). Chromosome 11q UPDs frequently associated with mutations of CBL. In one patient the 11qUPD amplified somatic mutations in both CBL and the DNA repair gene DDB1. A duplication within MLL exon 3 was detected in another patient with 11qUPD. We identified several common deleted regions (CDR) on chromosome 11. One of the CDRs associated with de novo acute myeloid leukemia (P=0.013). One patient with a deletion at the LMO2 locus harbored an additional point mutation on the other allele indicating that LMO2 might be a tumor suppressor frequently targeted by 11p deletions. Our chromosome-centered analysis indicates that chromosome 11 contains a number of tumor suppressor genes and that the role of this chromosome in myeloid malignancies is more complex than previously recognized.

Refractory anemia with ringed sideroblasts and thrombocytosis without JAK2 V617F mutation: report of three cases

In the WHO classification, there is a provisional entity called Myelodysplastic/Myeloproliferative Neoplasm, Unclassifiable (MDS/MPN, U). Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T) was included in this category. Recently published studies report a small percentage of patients with RARS-T. Sixty percent of these have JAK2 V617F mutation, which can suggest the coexistence of two pathological conditions (MDS and MPN). In this paper, we analyzed three patients diagnosed with RARS-T in the Department of Hematology, "Fundeni" Clinical Institute, Bucharest, Romania, during the period 2005-2011. The patients were investigated with cytogenetic exam and molecular biology. In these three cases were identified morphological features of multilineage dysplasia (two-lineage dysplasia in two cases and three-lineage dysplasia in one case). In two cases, thrombocytosis was under 1000×10(3)/μL and clinical evolution was similar to the myelodysplastic syndrome (transfusion dependent anemia with response to administration of erythropoietin). In the third case, the platelets were over 1000×10(3)/μL and with response to the treatment with Hydrea, which improved anemia. JAK2 V617F mutation was not identified in any case. RARS-T remains a provisional entity and requires a complex investigation of patients for the correct diagnosis of these patients. Therapeutic options should be personalized to each case in part because there is not yet a standardized treatment of these patients.

c-Myb and GATA-1 alternate dominant roles during megakaryocyte differentiation

BACKGROUND

Transcription factors are essential for blood cell formation. Mice expressing low levels of c-Myb (c-Myb(low)) have an increased number of bone marrow megakaryocytes (MKs) and corresponding thrombocytosis. In contrast, mice engineered to express low levels of GATA-1 (GATA-1(low)) in the megakaryocytic lineage exhibit aberrant megakaryocytopoiesis with hyperproliferation of progenitors and defective terminal differentiation leading to thrombocytopenia. These seemingly opposite roles may affect platelet turnover and thus be of clinical relevance.

OBJECTIVE

To determine how these two transcription factors act together to control megakaryocytopoiesis and platelet formation.

METHODS

We used a combination of cellular and molecular in vitro assays to examine the ability of bone marrow cells from mice expressing low levels of both c-Myb and GATA-1 (referred to as double(low)) to produce MKs and platelets.

RESULTS

Double(low) cells, or those with low GATA-1 levels in which c-Myb is conditionally deleted, lack the hyperproliferative capacity of GATA-1(low) cells, allowing the cells to proceed towards more committed MKs that are, however, impaired in their capacity to produce fully differentiated cells, as confirmed by the abundance of morphologically aberrant cells that lack the ability to form proplatelets.

CONCLUSION

c-Myb and GATA-1 act in concert to achieve correct megakaryocytic differentiation. GATA-1 regulates both the proliferation of megakaryocytic progenitors and their terminal maturation. c-Myb also acts at the level of the progenitor by influencing its commitment to differentiation, but in contrast to GATA-1 it does not have any effect on the process of terminal differentiation.

Refractory anaemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T) with superimposed 5q-syndrome

Refractory anaemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T) is a rare entity belonging to myeloproliferative/myelodysplastic syndromes. Myelodysplastic syndrome (MDS) with isolated del(5q) is a category of MDS characterized by better prognosis and specific morphology. Herein we describe a 69-year-old male with anaemia and thrombocytosis presenting with coexisting features of both these rare diseases. After the description of the clinical data, we summarize the histopathologic, cytogenetic and molecular findings, as well as introduced treatment. Next, we discuss possible diagnostic options with reference to the relevant literature.

Genetic origins and clinical phenotype of familial and acquired erythrocytosis and thrombocytosis

Familial and acquired erythrocytosis and thrombocytosis are characterized by myeloid lineage hyperproliferation, which is either single or multi-lineage in origin. The single lineage disorders exhibit Mendelian inheritance with polyclonal hematopoiesis and often arise from a single genetic defect. In contrast, the multi-lineage disorders exhibit complex patterns of inheritance with multi-genetic origins and clonal hematopoiesis. They have the potential to acquire JAK2 somatic mutations, but this is not the primary event. Identification of the disease-causing genes will enable better classification of familial and acquired erythrocytosis and thrombocytosis. Furthermore, it will provide an insight into the mechanisms regulating myeloid cell proliferation.

Thrombocytosis

Major progress in understanding the pathogenesis in patients with thrombocytosis has been made by identifying mutations in the key regulators of thrombopoietin: the thrombopoietin receptor MPL and JAK2. Together, these mutations can be found in 50% to 60% of patients with essential thrombocythemia or primary myelofibrosis and in 10% to 20% of hereditary thrombocytosis. A decrease in expression of the Mpl protein can cause thrombocytosis even in the absence of mutations in the coding sequence, due to a shift in the balance between stimulation of signaling in megakaryopoiesis and removal of thrombopoietin by receptor mediated internalization in platelets. When present in a heterozygous state the JAK2-V617F mutation preferentially stimulates megakaryopoiesis and in most cases manifests as essential thrombocythemia (ET), whereas homozygous JAK2-V617F reduces megakaryopoiesis in favor of increased erythropoiesis, resulting in polycythemia vera and/or myelofibrosis. In 30% to 40% of patients with ET or primary myelofibrosis (PMF) and in 80% to 90% of pedigrees with hereditary thrombocytosis the disease-causing gene remains unknown. Ongoing genetic and genomic screens have identified genes that, when mutated, can cause thrombocytosis in mouse models. A more complete picture of the pathways that regulate megakaryopoisis and platelet production will be important for finding new ways of controlling platelet production in patients with thrombocytosis.

Extreme thrombocytosis associated with transient myeloproliferative disorder with Down Syndrome with t(11;17)(q13;q21)

A female patient with Down Syndrome (DS) had neonatal thrombocytosis with platelet counts exceeding 2,000 x 10(3)/microL and transient myeloproliferative disorder (TMD). Platelet counts remained elevated the first 2 months of life. A translocation located between chromosomes 17 and 11 was observed. We describe a patient with thrombocytosis and TMD showing an 11q13 translocation. The leukocytosis and thrombocytosis improved after an exchange transfusion.

Most pediatric patients with essential thrombocythemia show hypersensitivity to erythropoietin in vitro, with rare JAK2 V617F-positive erythroid colonies

Essential thrombocythemia (ET), a Philadelphia (Ph) chromosome negative chronic myeloproliferative disorder, is usually a disease of middle age and it is extremely rare in pediatric patients. In this report we studied 12 children diagnosed with ET and one child with thrombocytosis and family history of ET. We failed to detect JAK2 V617F mutation either in peripheral blood leukocytes or in separated platelets and granulocytes. Monoclonal hematopoiesis was noted in only one female patient. Erythroid progenitors of most of the patients displayed hypersensitivity to erythropoietin (Epo) in vitro; Epo-independent erythroid colonies (EECs) were detected in seven patients. Among EECs of three patients we observed rare colonies heterozygous or homozygous for the JAK2 V617F mutation. Our data suggest that childhood ET patients could bear minor JAK2 V617F-positive subclones.

The role of JAK2 mutations in RARS and other MDS

Acquired sideroblastic anemia with unilineage dysplasia (WHO RARS) is a clonal stem cell disorder characterized by erythroid dysplasia, mitochondrial accumulation of mitochondrial ferritin, defective erythroid maturation and anemia. A fraction of these patients also show elevated platelet counts; since 2001 this has been defined as RARS with marked thrombocytosis (RARS-T). It has recently been described that around half of RARS-T patients, along with a small subset of other MDS and mixed myelodysplastic/ myeloproliferative disorders, carry the JAK2 mutation, and that MPL mutations are found in single patients. Clinically, RARS-T patients show features of both RARS, essential thrombocythmia (ET) and to some extent also myelofibrosis. However, the degree of anemia and overall survival is more similar to RARS than myeloproliferative disorders. The occurrence of JAK2 mutations and features of ET in RARS is too frequent to be the result of chance only, and it is possible that this link may provide a key to an increased understanding of the genetic abnormalities causing ring sideroblast formation.

The JAK2V617F mutation in polycythemia vera and other myeloproliferative disorders: one mutation for three diseases?

The discovery of the JAK2V617F mutation has made the diagnosis of polycythemia vera (PV) much easier, but the pathogenesis of PV is still incompletely understood. In particular, it is not yet elucidated how a single mutation can be found in multiple myeloproliferative disorders (MPD) and myelodysplastic syndromes with ring sideroblasts and whether the sole JAK2V617F is sufficient to induce a MPD in humans. Several hypotheses are under investigation such as differences in the targeted hematopoietic stem cells (HSC), host modifier polymorphisms, intensity of JAK2V617F signaling, presence of other somatic mutations, or the presence of a pre-JAK2 event that may vary according to the MPD phenotype. Multiple studies have provided some evidence for and against each hypothesis, but it now seems possible to reconcile these hypotheses into a model that will need to be tested using newly developed tools. Recent investigations have also led to new treatment modalities that could benefit patients with PV.

Detection of the JAK2V617F mutation in patients with slightly elevated platelets or hemoglobin without a secondary cause

Recently, an activating somatic mutation of Janus kinase 2 (JAK2V617F) was identified in the myeloproliferative disorders (MPDs). In this study, we investigated the occurrence of JAK2V617F in patients with slightly elevated platelets or hemoglobin without a secondary cause, who did not meet the criteria of polycythemia vera or essential thrombocythemia. Six out of 18 patients (33%) were positive for the JAK2 mutation, and five of these six patients had a history of thrombosis. These findings suggest that apart from thrombocytosis/erythrocytosis, other mechanisms exist that cause thrombosis, and more patients with a latent form of MPD are likely to exist. Future studies will have to elucidate how to treat these patients.

Bortezomib is an effective agent for MDS/MPD syndrome with 5q− anomaly and thrombocytosis

Thrombocytosis is not a frequent event in myelodysplasia (MDS) and is observed mainly in 5q- syndrome and MDS/myeloproliferative (MPD) overlap syndromes. The pathogenetic mechanism of thrombocytosis in 5q- has not been fully elucidated to-date. Bortezomib is a proteasome inhibitor which seems to be effective in MDS. We present here the first case in the literature with MDS/MPD syndrome, sole 5q- anomaly and thrombocytosis in which bortezomib administration normalized platelet count, produced a major erythroid response, and reduced levels of interleukin-6 (IL-6) and TNF-alpha while increased levels of IL-4 in the bone marrow plasma. The study of such cases will reveal the exact role of bortezomib in the management of MDS/MPD.

Role of the activating mutation Val617Phe of Janus kinase 2 gene in myeloproliferative diseases and significance of its detection

The Val617Phe point mutation of Janus kinase 2 gene is believed to participate in the pathogenesis of myeloproliferative syndrome characterised by the clonal alteration of hematopoetic stem cells. According to current results, the frequency of Val617Phe activating mutation is around 80% in polycythaemia vera, 35% in essential thrombocythaemia, and 50% in chronic idiopathic myelofibrosis. The diagnoses of polycythaemia vera, essential thrombocythaemia and idiopathic myelofibrosis were so far based on the exclusion of secondary factors as well as bone marrow biopsy histology. The goal of the present work was to establish simple molecular genetic techniques for the routine testing of Janus kinase 2 gene Val617Phe mutation, and to compare the clinical phenotypes of Val617Phe mutation positive and negative myeloproliferative syndromes. We employed the allele specific polymerase chain technique for detection of Val617Phe mutation in 252 patients with myeloproliferative syndrome. We measured Val617Phe frequency as 85,4% (117/137) in polycytaemia vera, 56,6% (56/99) in essential thrombocythaemia, and 87,5% (14/16) in idiopathic myelofibrosis. We found significantly elevated hemoglobin levels and white blood cell counts (measured at the time of diagnosis) in Val617Phe-positive polycythaemia vera and essential thrombocythaemia patient groups compared to Val617Phe-negative patients. However, the frequencies of splenomegaly and other complications (thrombosis, bleeding, transformation to acute leukemia) were not significantly different between the mutation-positive and negative groups. In conclusion, the non-invasive mutation analysis of the Janus kinase 2 Val617Phe is suitable for routine laboratory application and helps the differential diagnosis of myeloproliferative syndrome. Althought the exact role of Val617Phe mutation testing has not yet been identified on the basis of a broad professional consensus, the testing is suggested in cases of erythrocytoses and thrombocytoses of unknown origin.

Haematological characteristics of MYH9 disorders due to MYH9 R702 mutations

OBJECTIVE

MYH9 disorders are characterised by giant platelets, thrombocytopenia, and Döhle body-like cytoplasmic granulocyte inclusion bodies that result from mutations in MYH9, the gene for non-muscle myosin heavy chain-IIA (NMMHC-IIA). MYH9 R702 mutations are highly associated with Alport manifestations and result in Epstein syndrome. The aim of our study was to determine the haematological characteristics of MYH9 disorders as a result of R702 mutations to aid in making a proper diagnosis.

PATIENTS AND METHODS

Platelet size of patients with MYH9 disorders was determined as platelet diameter by microscopic observation of 200 platelets on stained peripheral blood smears. Double in situ hybridisation using a biotinylated oligo(dT) probe and immunofluorescence analysis of neutrophil NMMHC-IIA was performed on peripheral blood smears.

RESULTS

Patients carrying R702 mutations had significantly larger platelets than those with other MYH9 mutations. Although granulocyte inclusion bodies were mostly invisible on stained blood smears, immunofluorescence analysis for NMMHC-IIA showed an abnormal type II localisation in all neutrophils. We first showed that poly(A)+ RNA coincided with accumulated NMMHC-IIA at inclusion bodies in patients with MYH9 disorders. However, no condensation of poly(A)+ RNA at inclusion bodies was observed in patients with R702 mutations.

CONCLUSION

Our study shows that R702 mutations result in especially large platelets and inclusion bodies being faint and mostly invisible on conventionally stained blood smears. We further demonstrated that poly(A)+ RNA content but not NMMHC-IIA accumulation is responsible for the morphological appearance/stainability of inclusion bodies on stained blood smears and the amount of poly(A)+ RNA is decreased in those with R702 mutations.

Thrombocytosis and thrombosis

The aim of this review is to discuss current diagnostic approaches to, and classification of, patients presenting with thrombocytosis, in light of novel information derived from the discovery of specific molecular abnormalities in chronic myeloproliferative disorders (CMPD), which represent the most common cause of primary thrombocytosis. The JAK2V617F and the MPLW515L/K mutations have been found in patients with essential thrombocythemia, polycythemia vera, and primary myelofibrosis, and less frequently in other myeloproliferative disorders complicated by thrombocytosis. However, neither mutation is disease specific nor is it universally present in patients with elevated platelet counts due to a CMPD; therefore, distinguishing between reactive and primary forms of thrombocytosis, as well as among the different clinical entities that constitute the CMPD, still requires a multifaceted diagnostic approach that includes as a key step the accurate evaluation of bone marrow histology. The role of elevated platelet counts in thrombosis, which represent the predominant complication of CMPD,significantly affecting prognosis and quality of life as well as, paradoxically, in the pathogenesis of the hemorrhagic manifestations, will be discussed. Established and novel potential risk factors for thrombosis, including the clinical relevance of the JAK2V617F mutation, and current management strategies for thrombocytosis are also briefly discussed.