The C allele of JAK2 rs4495487 is an additional candidate locus that contributes to myeloproliferative neoplasm predisposition in the Japanese population

<p>Abstract</p> <p>Background</p> <p>Polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) are myeloproliferative neoplasms (MPNs) characterized in most cases by a unique somatic mutation, <it>JAK2 </it>V617F. Recent studies revealed that <it>JAK2 </it>V617F occurs more frequently in a specific <it>JAK2 </it>haplotype, named <it>JAK2 </it>46/1 or GGCC haplotype, which is tagged by rs10974944 (C/G) and/or rs12343867 (T/C). This study examined the impact of single nucleotide polymorphisms (SNPs) of the <it>JAK2 </it>locus on MPNs in a Japanese population.</p> <p>Methods</p> <p>We sequenced 24 <it>JAK2 </it>SNPs in Japanese patients with PV. We then genotyped 138 MPN patients (33 PV, 96 ET, and 9 PMF) with known <it>JAK2 </it>mutational status and 107 controls for a novel SNP, in addition to two SNPs known to be part of the 46/1 haplotype (rs10974944 and rs12343867). Associations with risk of MPN were estimated by odds ratios and their 95% confidence intervals using logistic regression.</p> <p>Results</p> <p>A novel locus, rs4495487 (T/C), with a mutated T allele was significantly associated with PV. Similar to rs10974944 and rs12343867, rs4495487 in the <it>JAK2 </it>locus is significantly associated with <it>JAK2</it>-positive MPN. Based on the results of SNP analysis of the three <it>JAK2 </it>locus, we defined the "GCC genotype" as having at least one minor allele in each SNP (G allele in rs10974944, C allele in rs4495487, and C allele in rs12343867). The GCC genotype was associated with increased risk of both <it>JAK2 </it>V617F-positive and <it>JAK2 </it>V617F-negative MPN. In ET patients, leukocyte count and hemoglobin were significantly associated with <it>JAK2 </it>V617F, rather than the GCC genotype. In contrast, none of the <it>JAK2 </it>V617F-negative ET patients without the GCC genotype had thrombosis, and splenomegaly was frequently seen in this subset of ET patients. PV patients without the GCC genotype were significantly associated with high platelet count.</p> <p>Conclusions</p> <p>Our results indicate that the C allele of <it>JAK2 </it>rs4495487, in addition to the 46/1 haplotype, contributes significantly to the occurrence of <it>JAK2 </it>V617F-positive and <it>JAK2 </it>V617F-negative MPNs in the Japanese population. Because lack of the GCC genotype represents a distinct clinical-hematological subset of MPN, analyzing <it>JAK2 </it>SNPs and quantifying <it>JAK2 </it>V617F mutations will provide further insights into the molecular pathogenesis of MPN.</p

Germline and somatic JAK2 mutations and susceptibility to chronic myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are a group of closely related stem-cell-derived clonal proliferative diseases. Most cases are sporadic but first-degree relatives of MPN patients have a five- to seven-fold increased risk for developing an MPN. The tumors of most patients carry a mutation in the Janus kinase 2 gene (JAK2V617F). Recently, three groups have described a strong association of JAK2 germline polymorphisms with MPN in patients positive for JAK2V617F. The somatic mutation occurs primarily on one particular germline JAK2 haplotype, which may account for as much as 50% of the risk to first-degree relatives. This finding provides new directions for unraveling the pathogenesis of MPN

IDH1 and IDH2 mutation studies in 1473 patients with chronic-, fibrotic- or blast-phase essential thrombocythemia, polycythemia vera or myelofibrosis

In a multi-institutional collaborative project, 1473 patients with myeloproliferative neoplasms (MPN) were screened for isocitrate dehydrogenase 1 (IDH1)/IDH2 mutations: 594 essential thrombocythemia (ET), 421 polycythemia vera (PV), 312 primary myelofibrosis (PMF), 95 post-PV/ET MF and 51 blast-phase MPN. A total of 38 IDH mutations (18 IDH1-R132, 19 IDH2-R140 and 1 IDH2-R172) were detected: 5 (0.8%) ET, 8 (1.9%) PV, 13 (4.2%) PMF, 1 (1%) post-PV/ET MF and 11 (21.6%) blast-phase MPN (P<0.01). Mutant IDH was documented in the presence or absence of JAK2, MPL and TET2 mutations, with similar mutational frequencies. However, IDH-mutated patients were more likely to be nullizygous for JAK2 46/1 haplotype, especially in PMF (P=0.04), and less likely to display complex karyotype, in blast-phase disease (P<0.01). In chronic-phase PMF, JAK2 46/1 haplotype nullizygosity (P<0.01; hazard ratio (HR) 2.9, 95% confidence interval (CI) 1.7–5.2), but not IDH mutational status (P=0.55; HR 1.3, 95% CI 0.5–3.4), had an adverse effect on survival. This was confirmed by multivariable analysis. In contrast, in both blast-phase PMF (P=0.04) and blast-phase MPN (P=0.01), the presence of an IDH mutation predicted worse survival. The current study clarifies disease- and stage-specific IDH mutation incidence and prognostic relevance in MPN and provides additional evidence for the biological effect of distinct JAK2 haplotypes

Different molecular mechanisms causing 9p21 deletions in acute lymphoblastic leukemia of childhood

Deletion of chromosome 9p21 is a crucial event for the development of several cancers including acute lymphoblastic leukemia (ALL). Double strand breaks (DSBs) triggering 9p21 deletions in ALL have been reported to occur at a few defined sites by illegitimate action of the V(D)J recombination activating protein complex. We have cloned 23 breakpoint junctions for a total of 46 breakpoints in 17 childhood ALL (9 B- and 8 T-lineages) showing different size deletions at one or both homologous chromosomes 9 to investigate which particular sequences make the region susceptible to interstitial deletion. We found that half of 9p21 deletion breakpoints were mediated by ectopic V(D)J recombination mechanisms whereas the remaining half were associated to repeated sequences, including some with potential for non-B DNA structure formation. Other mechanisms, such as microhomology-mediated repair, that are common in other cancers, play only a very minor role in ALL. Nucleotide insertions at breakpoint junctions and microinversions flanking the breakpoints have been detected at 20/23 and 2/23 breakpoint junctions, respectively, both in the presence of recombination signal sequence (RSS)-like sequences and of other unspecific sequences. The majority of breakpoints were unique except for two cases, both T-ALL, showing identical deletions. Four of the 46 breakpoints coincide with those reported in other cases, thus confirming the presence of recurrent deletion hotspots. Among the six cases with heterozygous 9p deletions, we found that the remaining CDKN2A and CDKN2B alleles were hypermethylated at CpG islands

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

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

Mathematical Modelling as a Proof of Concept for MPNs as a Human Inflammation Model for Cancer Development

<p><b>Left:</b> Typical development in stem cells (top panel A) and mature cells (bottom panel B). Healthy hematopoietic cells (full blue curves) dominate in the early phase where the number of malignant cells (stipulated red curves) are few. The total number of cells is also shown (dotted green curves). When a stem cell mutates without repairing mechanisms, a slowly increasing exponential growth starts. At a certain stage, the malignant cells become dominant, and the healthy hematopoietic cells begin to show a visible decline. Finally, the composition between the cell types results in a takeover by the malignant cells, leading to an exponential decline in hematopoietic cells and ultimately their extinction. The development is driven by an approximately exponential increase in the MPN stem cells, and the development is closely followed by the mature MPN cells. <b>Right:</b> B)The corresponding allele burden (7%, 33% and 67% corresponding to ET, PV, and PMF, respectively) defined as the ratio of MPN mature cells to the total number of mature cells.</p

Inherited and acquired genetic factors in myeloproliferative neoplasms

Myeloproliferative Neoplasien (MPN) stellen eine heterogene Gruppe maligner myeloischer Erkrankungen dar, denen klonale Hämatopoiese als gemeinsamer pathogenetischer Faktor zu Grunde liegt. Erworbene Gendefekte stehen bekanntlich in Zusammenhang mit abnormer Zellproliferation und klonalem Auswuchs hämatopoietischer Zellen. Die Zielsetzung dieser Arbeit war neue Erkenntnisse über die Rolle rekurrenter genetischer Anomalien in der Pathogenese der MPN zu gewinnen. Deletionen des langen Arms von Chromosom 13 (del13q) wurden in myeloischen Neoplasien bereits beschrieben, wobei ihre genaue Häufigkeit sowie pathogenetische Bedeutung weitgehend unbekannt ist. Mittels hochauflösender Mikromatrix-Genkartierungsanalysen konnten wir insgesamt 16 Patienten mit del13q identifizieren und eine del13q-Häufigkeit von etwa 3% in unserer MPN-Patientenkohorte definieren. Die Zusammenstellung dieser Chromosomenabschnitte lies eine neue minimale deletierte Region von etwa 850 kb erkennen, welche 7 Gene - einschliesslich dem Retinoblastoma 1 (RB1) Tumorsuppressorgen - beinhaltete. Genetische und funktionelle Analysen zeigten jedoch keinen pathogenetischen Effekt eines RB1-Allelverlustes in MPN. Daten aus klonalen Analysen hämatopoietischer Vorläuferzellen legten nahe, dass die JAK2-V617F Mutation in einigen Patienten mehr als nur ein Mal erworben wurde. In einer PCR-basierten Untersuchung konnten wir zeigen, dass etwa 3% aller MPN-Patienten die JAK2-V617F Mutation mindestens zweimal erworben hatten. Zudem zeigte sich, dass ein bestimmtes JAK2-Genallel anfälliger für V617F als auch Exon 12 Mutationen des JAK2-Gens ist. Wir konnten einen Haplotyp identifzieren, der das JAK2-Gen beinhaltet und ein höheres Risiko für JAK2 Mutation-positive MPN birgt. Um zu eruieren, ob dieser vererbbare genetische Faktor der familiären Häufung von MPN zugrunde liegt, führten wir eine Untersuchung familiärer MPN-Fälle durch. Diese zeigte, dass der JAK2 GGCC Haplotyp auch hier ein höheres Risiko für JAK2-Mutationen mit sich bringt, aber nicht die familiäre Häufung in MPN erklärt. Unsere Daten weisen allerdings darauf hin, dass andere maligne Erkrankungen in familiären MPN häufiger mit dem JAK2 GGCC Haplotyp vergesellschaftet sind. Zusammenfassend zeigt diese Arbeit, dass vererbbare genetische Faktoren die erworbene Mutagenität beeinflussen können. Der genaue genetische Hintergrund dieses pathogenetischen Mechanismus bleibt jedoch aufzuklären.Myeloproliferative neoplasms (MPN) are a heterogeneous group of myeloid malignancies that share the main pathogenetic feature of clonal hematopoiesis. Acquired genetic defects such as point mutations or chromosomal deletions have been implicated in aberrant proliferation and clonal outgrowth of hematopoietic cells. In this study, we aimed to elucidate the role of recurrent genetic aberrations in disease pathogenesis of MPN. Although deletions of the long arm of chromosome 13 (del13q) have previously been reported in myeloid neoplasms, their actual frequency and pathogenetic impact in MPN remains unknown. Using high-resolution microarray mapping analysis, we identified a total number of 16 patients with del13q and determined a frequency of about 3% in MPN. The delineation of the deleted regions revealed a novel common deleted region of about 850 kb that contains 7 genes, including the Retinoblastoma 1 (RB1) tumor suppressor gene. Further genetic and functional analysis did not show a role for the monoallelic loss of RB1 in MPN pathogenesis. However, data obtained from the analysis of clonal hierarchies of del13q and other genetic defects in hematopoietic progenitor cells did suggest that the JAK2-V617F mutation could be acquired multiple times in the same individual. Further evidence for multiple acquisitions of JAK2-V617F could be gained by a PCR-based assay, revealing that about 3% of MPN patients acquired the JAK2-V617F mutation at least two times. This analysis further showed that a certain allele of the JAK2 gene was more susceptible to acquire the V617F as well as exon 12 mutations. Subsequently, we identified a common haplotype - the JAK2 GGCC haplotype - that harbors the JAK2 gene and confers susceptibility to JAK2 mutation-positive MPN. To test the hypothesis that this inherited genetic factor underlies familial clustering in MPN, we performed association analysis of the GGCC haplotype in familial MPN patients. As a result, we could show that the GGCC haplotype confers susceptibility to JAK2 mutations in familial MPN cases, but does not cause familial clustering. Interestingly, we gained evidence that malignancies other than MPN were more frequent in familial MPN patients who carried the JAK2 GGCC haplotype. Taken all together, our findings indicate that inherited genetic factors can influence somatic mutability - probably not only in MPN, but as well in other malignant disorders. The exact genetic mechanisms underlying this pathogenetic effect remain yet to be identified.submitted by Damla Olcaydu KraucherAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Med. Univ., Diss., 2013OeBB(VLID)171489