Refractory Anemia With Ringed Sideroblasts Associated With Marked Thrombocytosis Research Articles

An MPL W515L mutation in refractory anemia with ringed sideroblasts associated with marked thrombocytosis: A case report.

The current study presents the case of a 63-year-old patient exhibiting refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T), who was positive for the MPL W515L mutation, but negative for the JAK2 V617F mutation. Following diagnosis, the patient remained asymptomatic for over three years, however, in August 2012, the patient relapsed and was administered with supportive treatment in the form of subcutaneous darbepoetin α at a dose of 300 μg/week, which resulted in an increased hemoglobin concentration, allowing the patient to remain transfusion-independent. The MPL W515L mutation has been reported in two previous cases of myelodysplastic/myeloproliferative neoplasms (MDS/MPN) with ringed sideroblasts, however, to the best of our knowledge, the current report is the first to present a case of RARS-T with an MPL W515L mutation. A clinical trial designed to evaluate the efficacy of a targeted agent against the JAK2 V617F mutation is currently ongoing, with the aim of providing a novel therapeutic strategy for treating MDS/MPN patients. As MPL is located upstream of the JAK-STAT signaling pathway, it is a possible therapeutic target in MDS/MPN patients positive for an MPL W515L mutation, but negative for a JAK2 V617F mutation.

Frequent Mutations in the Calreticulin Gene CALR in Myeloproliferative Neoplasms

The classical, BCR-ABL1 negative myeloproliferative neoplasms (MPN) are polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). The most common genetic alteration in MPN is the JAK2-V617F mutation detected in 95% of PV patients and in 50-60% of patients with ET or PMF. Mutations in exon 12 of JAK2 and in the thrombopoietin receptor gene MPL are found in an additional 5-10% of the cases. In recent years a number of other genes were shown to be affected in MPN. However, these mutations are not mutually exclusive with JAK2 and MPL mutations and are also found in other myeloid malignancies. A specific molecular marker for the remaining 40% of ET or PMF patients with wild type JAK2 and MPL is still unknown.We used whole-exome sequencing to identify novel mutations in PMF patients with wild type JAK2 and MPL. The analysis revealed recurrent somatic insertions and deletions in CALR encoding for calreticulin. All detected mutations resulted in a frameshift and clustered in the last exon (exon 9) of the gene. Following up on this finding we developed a PCR based assay to screen 1107 MPN patients for insertion/deletion mutations in exon 9 of CALR. No mutations were detected in PV. In ET and PMF CALR mutations were mutually exclusive with mutant JAK2 and mutant MPL. Of the patients with wild type JAK2 and MPL, 67% ET and 88% PMF had mutant CALR. We also tested 19 patients with wild type CALR-exon 9 for mutations in the other exons of the gene, but all were negative. Furthermore we did not find CALR-exon 9 mutations in 254 patients with de novo acute myeloid leukemia, 45 with chronic myeloid leukemia, 73 with myelodysplastic syndrome or 64 with chronic myelomonocytic leukemia. Out of 24 patients with refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T), 3 patients carried CALR mutations. These patients were wild type for JAK2 and MPL.In total we detected 36 different types of mutations in CALR. A 52 bp deletion and a 5 bp insertion were the most prominent types found in 53% and 32% of all cases with mutant CALR. All 36 types of mutations result in a frameshift to the same alternative reading frame, generating a novel C-terminus of the mutated protein. The wild type C-terminal region of CALR contains a high-capacity calcium-binding domain and is highly negatively charged. As a consequence of the frameshift mutations the negatively charged amino acids are replaced by both neutral and positively charged amino acids. In addition, an endoplasmic reticulum retention signal present in the wild type protein is lost in the mutant variants. Expression in HEK cells showed that wild type CALR localizes in the endoplasmic reticulum, whereas this localization is less prominent in cells expressing mutant CALR. This observation is in line with the loss of the endoplasmic reticulum retention signal in the mutant protein.Overexpression of the most common CALR mutation (a 52 bp deletion) in interleukin-3 (IL-3) dependent Ba/F3 cells led to IL-3-independent growth and hypersensitivity to IL-3. Cells overexpressing the mutant were sensitive to the JAK-family kinase inhibitor SAR302503 and showed elevated STAT5 phosphorylation in absence of IL-3. This indicates that JAK-STAT signaling is involved in the observed cytokine independent growth of mutant CALR expressing Ba/F3 cells.ET and PMF patients with mutant CALR present with lower white blood cell counts (P<0.001 for ET, P=0.027 for PMF) and elevated platelet levels (P<0.001 in both entities) compared to patients with mutant JAK2. In both disease entities patients with mutant CALR show significantly better overall survival than patients with mutant JAK2 (P=0.043 in ET, P<0.001 in PMF). ET patients with mutant CALR had a lower risk of thrombosis in comparison to those with mutant JAK2 (P=0.003).Mutant CALR is a novel, specific molecular marker detected in the majority of MPN patients negative for JAK2 and MPL mutations. Use of this marker in the clinic is expected to improve diagnostic and therapeutic decision-making in MPN. Disclosures:No relevant conflicts of interest to declare.

Pathway Mutations in the Splicing Machinery in Myeloid Neoplasms

AbstractAbstract SCI-14During the past decade, significant progress has been made in our understanding of the molecular pathogenesis of myelodysplastic syndromes (MDS) and related myeloid neoplasms, in which one of the major findings was frequent mutations of genes in epigenetic regulation, such as DNA methylation (DNMT3A, TET2, and IDH1/2) and chromatin modifications (ASXL1, EZH2, EED, and SUZ12). They are also found in comparable or even higher fractions of other myeloid neoplasms, underscoring the common impact of deregulated epigenetic regulation on myeloid leukemogenesis. On the other hand, a new class of pathway mutations has been uncovered recently that commonly involve the RNA splicing machinery (1, 2, 3). Thus, at least eight different components of the machinery, invariably engaged in the 3' splice site recognition, have been reported to be mutated in as high as 45 percent to 85 percent of cases with different subtypes of MDS and related myeloid neoplasms mostly in a mutually exclusive manner. This indicates that the 3' splice site recognition is the functional target of these mutations. There exist discrete mutational hotspots in three out of four major targets, including SF3B1, SRSF2, U2AF35, and ZRSR2, and these mutant alleles can induce abnormal RNA splicing, indicating the gain-of-function nature of the mutations (2). Splicing factor mutations are largely specific to myelodysplasia phenotypes but relatively rare in acute myeloid leukemia and myeloproliferative neoplasms (2), suggesting their primary roles in the pathogenesis of myelodysplasia. The genotype-phenotype association is especially prominent in the case of SF3B1 mutations, which were found in 76 percent to 83 percent of cases of refractory anemia with ringed sideroblasts (RARS), refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T), and refractory cytopenia with multilineage dysplasia and ringed sideroblasts (RCMD-RS) (1, 2). In this session, the updated findings on the spliceosome mutations found in myelodysplasia, including their clinical and functional aspects, will be discussed. Disclosures:No relevant conflicts of interest to declare.

Outcome of Refractory Anemia with Ringed Sideroblasts Associated with Marked Thrombocytosis (RARS-T) In a Large Cohort of Patients

AbstractAbstract 4113 Introduction:Most of the data related to RARS-T, a rare disorder, involve small cohorts of patients. We aimed to analyze more patients also considering a variety of myelodysplastic or myeloproliferative disorders. Objective:To compare a large cohort of patients with RARS-T to refractory anemia with ringed sideroblasts (RARS), refractory anemia with ringed sideroblasts and multilineage dysplasia (RARS-MD) or essential thrombocythemia (ET) at the time of diagnosis and during disease evolution, in terms of survival and complications. Materials:Data of a European multi-center study was used including 199 cases of RARS-T 173 cases of RARS, 102 cases of RARS-MD and 431 cases of ET. Results:At baseline, compared to RARS and RARS-MD patients, RARS-T patients had similar hemoglobin concentration, but a higher white blood count. The JAK2V617F mutation was observed in 43%, 12% and 5% in RARS-T, RARS and RARS-MD patients, respectively. When separated in 2 groups (450,000<platelet count <600,000 and platelet count >600,000 × 109/l), RARS-T patients were comparable for sex, age, hemoglobin level and survival. However, patients with platelet count > 600,000 × 109/l had higher WBC (11 ×109/l versus 7.5 ×109/l, p<0.001). Similarly, no difference was noted in the survival in the JAK2 positive and negative RARS-T patients. The age and sex standardised overall survival of RARS-T patients was similar to RARS and RARS-MD patients, but lower than ET patients (p<0.001). This was despite a higher risk of transformation in acute leukemia, relative to RARS-T afflicted individuals, of 2.4 and 3.5 in RARS-MD and RARS patients, respectively. Conclusion:According to our results, the outcome in RARS-T more closely mimics myelodysplastic syndromes rather than myeloproliferative neoplasms. Our results agree with the WHO 2008 classification that considers RARS-T as a separate disorder. Disclosures:Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Gattermann:Novartis: Honoraria, Research Funding. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Acquired Mutation of the Tyrosine Kinase JAK2V617F in Egyptian Patients with Myeloid Disorders

Janus Kinase 2 (JAK2) is a member of a family of four Janus Kinases, 2, and 3 and tyrosine kinase 2. Mutated JAK2 (V617F) has the ability to activate downstream signal transducer and activator of transcription (STAT)-mediated transcription in the absence of the ligand erythropoietin. The autoinhibitory activity of JAK2 is disrupted by the presence of the V617F mutation. Somatic mutation in JAK2 (V617F) gene has been reported in myeloid disorders. This study reports the prevalence of JAK2V617F using amplification refractory mutation system (ARMS)-polymerase chain reaction in 246 Egyptian patients with different myeloid disorders and studied the relationship between the JAK2V617F mutation and parameters in peripheral blood. The mutation was detected among 88 patients (35.8%) with different myeloid disorders. JAK2V617F was found among 81.4% of polycythemia vera (PV), 50% of essential thrombocythemia, 46.1% of primary myelofibrosis (PMF), 33.3% of philadelphia (Ph)-negative chronic myeloid leukemia, 33.3% of myelodysplastic syndrome (MDS)/myeloproliferative neoplasm (MPN), and 50% of refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T) patients. Hemoglobin and white blood cells were significantly higher in the mutated group of MPN including PV, essential thrombocythemia, and PMF, whereas platelet counts were higher among the mutated PV, PMF, RARS-T, and MDS/MPN group. The identification of JAK2V617F mutations has raised the prospect of developing specific JAK2V617F inhibitors to treat mutated patients.

Mutational Status of TET2, JAK2, and MPL in Refractory Anemia with Ringed Sideroblasts Associated with Marked Thrombocytosis.

Abstract 418According to the WHO classification, myelodysplastic/myeloproliferative neoplasms include chronic myelomonocytic leukemia, atypical chronic myeloid leukemia (BCR-ABL1 negative), juvenile myelomonocytic leukemia, and myelodysplastic/myeloproliferative neoplasms, unclassifiable (MDS/MPN, U). The best characterized of these latter conditions is the provisional entity defined as refractory anemia with ringed sideroblasts (RARS) associated with marked thrombocytosis (RARS-T); up to 60% of RARS-T patients harbor the JAK2 (V617F) mutation. Somatic mutations of TET2 have been recently described in myeloid neoplasms, where they appear to be associated with the amplification of the mutated clone at the early stages of hematopoietic differentiation [N Engl J Med. 2009 May 28;360(22):2355-7]. In order to gain a deeper insight into the pathophysiology of RARS-T, we studied a cohort of 187 patients with myeloid neoplasms and investigated the relationship between ringed sideroblasts, thrombocytosis, and mutational status of TET2, JAK2 and MPL. RARS-T was defined according to the following WHO criteria: i) refractory anemia associated with erythroid dysplasia and ringed sideroblasts ≥ 15%; ii) < 5% blasts in the bone marrow; iii) platelet count ≥ 450 × 109/L; iv) presence of large atypical megakaryocytes similar to those observed in BCR/ABL1-negative myeloproliferative neoplasms; v) absence of del(5q), t(3;3)(q21;q26) or inv(3)(q21q26). The combination of ringed sideroblasts ≥ 15% and platelet count ≥ 450 × 109/L was found in 19 subjects fulfilling the diagnostic criteria for RARS-T, while 24 patients had RARS without thrombocytosis. JAK2 and MPL mutations were detected in circulating granulocytes and bone marrow CD34+ cells - but not in T-lymphocytes - from 11 out of 19 (58%) RARS-T patients. Three RARS patients, who initially had low to normal platelet counts, progressed to RARS-T, and two of them acquired JAK2 (V617F) at this time. Somatic mutations of TET2 were found in three of the 15 RARS-T patients studied, and the presence of multiple mutant genes allowed analysis of subclones in two of them. One of these patients carried the following three somatic mutations: TET2 (C1271Y), JAK2 (V617F) and MPL (W515L). Analysis of genomic DNA from circulating granulocytes showed 50% TET2 (C1271Y) mutant alleles but smaller proportions of JAK2 (V617F) and MPL (W515L) mutant alleles (5.8% and 20% respectively). We then analyzed five BFU-E grown from peripheral blood mononuclear cells obtained from this patient. All these five colonies were heterozygous for TET2 (C1271Y), while three of them were heterozygous also for MPL (W515L) and the remaining two were heterozygous also for JAK2 (V617F), clearly indicating that erythroid progenitors carrying JAK2 or MPL mutants belonged to subclones of the dominant TET2 (C1271Y) clone. A woman with the TET2 (S1612LfsX4) mutation (50% granulocyte mutant alleles) and fully clonal hematopoiesis as indicated by X-chromosome inactivation patterns, carried 28% JAK2 (V617F) mutant alleles in circulating granulocytes, indicating that granulocytes harboring JAK2 mutant alleles belonged to a subclone of the initial TET2 (S1612LfsX4) mutant clone. Over a 5-year period, in fact, the initial TET2 mutant clone was completely replaced by the TET2/JAK2 mutant subclone. In other two female patients with RARS-T and no somatic mutation of TET2, granulocytes carrying JAK2 (V617F) represented only a fraction (11 to 22%) of clonal granulocytes as determined by X-chromosome inactivation patterns (96 to 100%). Somatic mutations of TET2 were detected also in a significant proportion of patients with RARS without thrombocytosis, while no JAK2 or MPL mutation was identified in these individuals. These observations suggest that the occurrence of a TET2 mutation may represent the initial event determining clonal dominance of hematopoietic cells both in RARS and RARS-T patients, while the subsequent occurrence of JAK2 and/or MPL mutations likely generates myelodysplastic/myeloproliferative subclones in RARS-T patients. In conclusion, RARS-T is indeed a myeloid neoplasm with both myelodysplastic and myeloproliferative features at the molecular and clinical level, and it may develop from RARS through the acquisition of somatic mutations of JAK2, MPL or other as-yet-unknown genes on the background of clonal hematopoiesis caused by somatic mutations of TET2 or other similar (as-yet-unknown) mutant genes. Disclosures:No relevant conflicts of interest to declare.

Molecular and clinical features of refractory anemia with ringed sideroblasts associated with marked thrombocytosis

AbstractWe studied patients with myeloid neoplasm associated with ringed sideroblasts and/or thrombocytosis. The combination of ringed sideroblasts 15% or greater and platelet count of 450 × 109/L or greater was found in 19 subjects fulfilling the diagnostic criteria for refractory anemia with ringed sideroblasts (RARS) associated with marked thrombocytosis (RARS-T), and in 3 patients with primary myelofibrosis. JAK2 and MPL mutations were detected in circulating granulocytes and bone marrow CD34+ cells, but not in T lymphocytes, from 11 of 19 patients with RARS-T. Three patients with RARS, who initially had low to normal platelet counts, progressed to RARS-T, and 2 of them acquired JAK2 (V617F) at this time. In female patients with RARS-T, granulocytes carrying JAK2 (V617F) represented only a fraction of clonal granulocytes as determined by X-chromosome inactivation patterns. RARS and RARS-T patient groups both consistently showed up-regulation of ALAS2 and down-regulation of ABCB7 in CD34+ cells, but several other genes were differentially expressed, including PSIP1 (LEDGF), CXCR4, and CDC2L5. These observations suggest that RARS-T is indeed a myeloid neoplasm with both myelodysplastic and myeloproliferative features at the molecular and clinical levels and that it may develop from RARS through the acquisition of somatic mutations of JAK2, MPL, or other as-yet-unknown genes.

Refractory Anemia with Ringed Sideroblasts Associated with Marked Thrombocytosis (RARS-t): A Clinicopathological Entity with Questionable Pathogenesis

Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-t) is a clinicopathological entity with features of both myelodysplastic syndrome and myeloproliferative disorder. The cases of RARS-t reported in literature are few and do not confirm whether this disease represents a variant of Refractory anemia with ringed sideroblasts (RARS), a variant of Essential Thrombocythemia (ET), or the simultaneous occurrence of two separate disorders (RARS and ET). Because of this ambiguity, RARS-t has been assigned to MDS/MPD- Unclassifiable subcategory as a provisional entity in the WHO (2001) classification. Recent studies have demonstrated association of RARS-t with JAK2 V617F mutation in up to 67% of cases, suggesting its proximity to MPD. In a few studies, presence of JAK2 mutation was related with better prognosis. Based on this evidence, there are chances that this provisional entity may be clubbed with the group of MPD disorders in the revised WHO classification. We present here 4 cases of RARS-t diagnosed within a period of 1 year (2007–2008) at our institution. Clinicopathological features of these cases are mentioned in the attached table (Table-1). Two of these cases were not associated with anemia at the time of presentation, however could be diagnosed as RARS-t based on the presence of dyserythropoetic features and >15% ringed sideroblasts in marrow on iron stains. Other causes of reactive ring sideroblasts and thrombocytosis were ruled out in these cases. 2/4 cases were positive for JAK2 V617F mutation, however no correlation was found between the JAK2 positivity and the clinicopathological features including prognosis. All the 4 patients were given hydroxyurea and pyridoxine therapy. In contrast to other studies, one of our JAK2 positive cases had to be maintained on the transfusion support alone due to the multiple treatment failures. Our data adds to the literature supporting the association of RARS-t with JAK2 mutation. However, we do not agree with the notion that JAK2 positivity renders a better prognosis. Also, lack of any correlation of clinicopathological features in our cases with the JAK2 mutation drives us to think that it might be only a secondary association rather a primary pathogenesis event. Review of the literature reminds us that the pathogenetic events resulting in myelodysplastic component of this overlap syndrome have only been rarely addressed. In future, more studies focusing on the mutations responsible for genesis of ringed sideroblasts such as ALAS2, ABCB7, FECH and gene expression profiles of bone marrow progenitor cells are required for better understanding of this common but under reported entity.Table 1CaseAgeSexHb. (g/dL)Hct.MCV (fL)RS%Platelet (× 109/L)WBC (× 109/L)JAK2mutationOther cytogeneticsFibrosisOrganomegalyCase#184F12.938.994.6>15%7098.3Negativenormal karyotype1+ reticulinAbsentCase#285M10.328.3131>15%10727.2Negativenormal karyotype1+ reticulinAbsentCase#368M6.925101.3>15%6345.4Positivenormal karyotype1+ reticulinAbsentCase#463M13.741.578.7>15%127217.7Positivenormal karyotype1+reticulinAbsent

SNP Arrays in Patients with Myelodysplastic Syndromes and Ringed Sideroblasts: A Karyotypic and Disease Association Analysis

Introduction: The myelodysplastic syndromes (MDS) are a heterogeneous group of clonal hematopoietic stem cell disorders. Ringed sideroblasts (RS) are found in the following subclasses of MDS: refractory anemia with ringed sideroblasts (RARS), refractory cytopenia with multilineage dysplasia and ringed sideroblasts (RCMD-RS), and refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T). The objective of this study was to evaluate the use of single nucleotide polymorphism (SNP) arrays (SNP-A) in patients with MDS and RS and specificallyto compare chromosomal abnormalities detected by metaphase karyotyping (MC) with those detected using high-resolution SNP based karyotyping (which can detect unbalanced genomic lesions in addition to copy-neutral loss of heterozygozity) andto conduct a disease association analysis using the SNP-A.Methods: We reviewed the electronic records of patients with MDS and RS seen at our institution between 2002 and 2008. DNA was extracted using the Puregene DNA Purification Kit. Gene Chip Mapping 250K Assay Kit (Affymetrix) was used. Signal intensity and genotype calls were analyzed using CNAG v.3.0. For the disease association analysis, the Fisher's p-value was used to compare SNPs found in patients with MDS and RS versus 150 normal controls.Results: 83 patients with MDS who have RS were identified. 40 (48%) had RARS, 25 (30%) had RCMD-RS, and 18 (22%) had RARS-T. The mean age of these patients was 70.7 years, 53 patients (64%) were males, and 70 (84%) were Caucasian. Of those 83 patients, 45 had available DNA for SNP analysis, 23 (51%) of whom had RARS, 11 (24%) had RCMD-RS, and 11 (24%) had RARS-T. The mean age of these 45 patients was 69.9 years, 29 (64%) were males, and 39 (87%) were Caucasian. By MC, 20/45 (44.5%) patients had abnormal karyotypes and 25/45 (55.5%) patients had normal karyotypes. Using SNP-A, chromosomal abnormalities including UPD were identified in 29/45 (64.5%) of patients. Of the 25 pts who had normal karyotypes by MC, 11 (44%) had abnormal karyotypes by SNP-A. The chromosomal distributions of the lesions detected by MC were as follows: chromosome 5 (18.4%), chromosome 7 (15.8%), chromosome 8 (13.1%), chromosome 17, 18, 19, 20, 21 (5.2% in each), and others (26.3 % in total). The distribution of chromosomal lesions detected by SNP-array analysis (excluding UPD) was as follows: chromosome 8 (18.7 %), chromosome 5 (14.6%), chromosome 7 (12.5%), chromosome 17 (10.4%), chromosome 20 (8.3%), chromosome 4 (6.2%), chromosomes 2, 3, 13, 22 (4.1% each), and others (12.5% in total). UPD was found in 12/45 (26.7%) patients mostly affecting chromosome 1 (27.8%). A large number of SNPs were found to be significantly more prevalent in patients with MDS with RS than in controls (with p-value < 0.0001). Genes within 50 kb from these SNPs were scrutinized. At least 11 of those genes (RP1, LIMD1, CHL1, ATP6V1F, TEAD2, SPTLC2, CDH13, DIAPH2, DLEU2, FAM10A4, TRPM8) are known to be related to cancer in the literature. Given that karyotypic abnormalities were more prevalent in chromosomes 8, 5, and 7, we looked specifically at the SNPs in those chromosomes which were significantly associated with disease (rs 409429, rs 446153, rs 453186 and rs 509273 in chromosome 8; rs6891109 in chromosome 5; and rs6970371 in chromosome 7). The genes within 50 kb of these SNPs that are known to be associated with cancer are: RP1 in chromosome 8 (colon cancer), and ATP6V1F in chromosome 7 (prostate cancer).Conclusion: This study shows that SNP-A based karyotyping is a useful tool for karyotyping and can detect more chromosomal abnormalities than MC (64.5 versus 44.5%, odds ratio 1.45). We also found that about half of the patients who had normal karyotypes by MC were found to have karyotypic abnormalities by SNP-A. In addition, we show multiple candidate genes that could be important in the pathogenesis of MDS with RS.

Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T), another myeloproliferative condition characterized by JAK2 V617F mutation

Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T), another myeloproliferative condition characterized by JAK2 V617F mutation

Granulocyte JAK2 (V617F) Mutation Status in Myeloid Neoplasms with Ringed Sideroblasts.

The most common type of acquired sideroblastic anemia is the myelodysplastic syndrome (MDS) defined as refractory anemia with ringed sideroblasts (RARS). We have previously demonstrated that mitochondrial iron accumulation in this condition is in the form of mitochondrial ferritin (MtF). A gain-of-function mutation of JAK2 is found in most patients with chronic myeloproliferative disorders. A high frequency of this mutation has been also reported in RARS associated with marked thrombocytosis (RARS-T), a provisional entity characterized by marked increase in platelet count, hypercellular marrow with increased megakaryocytes, and ringed sideroblasts. In this study, we investigated the granulocyte JAK2 (V617F) mutation status in 73 patients receiving a diagnosis of myeloid malignancy with ringed sideroblasts at the Division of Hematology, University of Pavia Medical School & IRCCS Policlinico San Matteo Pavia, Italy between 2001 and 2006. According to the WHO classification of the myeloid neoplasms, 23 patients had RARS, 17 had refractory cytopenia with multilineage dysplasia and ringed sideroblasts (RCMD-RS), 16 had refractory anemia with blasts excess, four had MDS with isolated del(5q), and 13 fulfilled the criteria for RARS-T. JAK2 (V617F) mutation status was analyzed on peripheral blood granulocytes through a quantitative real time PCR-based allelic discrimination assay. We compared clinical and biological features of patients with RARS-T with those of patients with refractory anemia or cytopenia with ringed sideroblasts, and found that RARS-T patients had higher neutrophil and platelet counts, lower frequency of cytogenetic abnormalities and higher incidence of the JAK2 (V617F) mutation (P values ranging from <.001 to .02). JAK2 (V617F) was detected in six out of 63 evaluable cases (9.5%), one being diagnosed as MDS with isolated del(5q) and five as RARS-T, resulting in an incidence of mutation in the latter group of 45%. The proportion of mutant alleles ranged between 2.8% and 18.4%, values commonly observed by us in essential thrombocythemia [Blood. 2006 May 1;107(9):3676–82]. Focusing the analysis on RARS-T, a significantly higher hemoglobin level at diagnosis was found in mutated (median value 11.2 g/dL, range 10.1–15.4) compared with non mutated patients (median value 9 g/dL, range 6–9.9) (P=.009). JAK2-positive patients also showed a significantly lower percentage of ringed sideroblasts in the bone marrow (P=.01), and an increased marrow reticulin fibrosis (P=.03). We then evaluated the clonality of hematopoiesis in female patients through analysis of X-chromosome inactivation patterns (XCIPs) in circulating granulocytes and bone marrow CD34-positive cells. Twenty-one out of 23 informative female patients with ringed sideroblasts (91%), as well as 5/6 RARS-T (83%) displayed a clonal pattern of X-chromosome inactivation. These observations suggest that refractory anemia with ringed sideroblasts with marked thrombocytosis is a clonal stem cell disorder significantly associated with the JAK2 (V617F) mutation. This disorder shows both dysplastic and proliferative features, the presence of the mutation being associated with a predominant myeloproliferative phenotype. The recognition of a heterogeneous genetic background in myeloid neoplasms with ringed sideroblasts suggests that different mechanisms might be involved in the induction of mitochondrial ferritin expression in these disorders.

Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T), another myeloproliferative condition characterized by JAK2 V617F mutation

AbstractJAK2 V617F mutation recently was identified as a pathogenic factor in typical chronic myeloproliferative diseases (CMPD). Some forms of myelodysplastic syndromes (MDS) show a significant overlap with CMPD (classified as MDS/MPD), but the diagnostic assignment may be challenging. We studied blood or bone marrow from 270 patients with MDS, MDS/MPD, and CMPD for the presence of JAK2 V617F mutation using polymerase chain reaction, sequencing, and melting curve analysis. The detection rate of JAK2 V617F mutants for polycythemia vera, chronic idiopathic myelofibrosis, and essential thrombocythemia (n = 103) was similar to the previously reported results. In typical forms of MDS (n = 89) JAK2 V617F mutation was very rare (n = 2). However, a higher prevalence of this mutation was found in patients with MDS/MPD-U (9 of 35). Within this group, most of the patients harboring JAK2 V617F mutation showed features consistent with the provisional MDS/MPD-U entity refractory anemia with ringed sideroblasts and thrombocytosis (RARS-T). Among 9 RARS-T patients, 6 showed the presence of JAK2 V617F mutation, and in 1 patient without mutation, aberrant, positive phospho-STAT5 staining was seen that is typically present in association with JAK2 V617F mutation. In summary, we found that RARS-T reveals a high frequency of JAK2 V617F mutation and likely constitutes another JAK2 mutation-associated form of CMPD.