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

Characterization of myeloproliferative neoplasms based on genetics only and prognostication of transformation to blast phase

Myeloproliferative neoplasms (MPN) are a heterogeneous group of clonal disorders characterized by aberrant hematopoietic proliferation and an intrinsic risk of progression to blast phase. The WHO classification 2022 identifies chronic myeloid leukemia and the BCR::ABL1 negative MPNs polycythemia vera, primary myelofibrosis and essential thrombocythemia as individual entities. However, overlaps, borderline findings or transitions between MPN subtypes occur and incomplete clinical data often complicates diagnosis. By conducting a thorough genetic analysis, we've developed a model that relies on 12 genetic markers to accurately stratify MPN patients. The model can be simplified into a decision tree for routine use. Comparing samples at chronic and blast phase revealed, that one third of patients lost their MPN driver-gene mutation, while mutations in splicing and chromatin modifying genes were stable, indicating a shared founder clone of chronic and blast phase with different driver mutations and therefore different progressing capacities. This was further supported by gain of typical de novo AML gene mutations, accompanied by gain of complex karyotypes and RAS pathway gene mutations. Our data suggest to perform a broader genetic screening at diagnosis and also at clinical progression, as driver mutations may change and the MPN-driver mutations present at diagnosis may disappear.

Germline genetic variants that predispose to myeloproliferative neoplasms and hereditary myeloproliferative phenotypes

Epidemiological evidence of familial predispositions to myeloid malignancies and myeloproliferative neoplasms (MPN) has long been recognised, but recent studies have added to knowledge of specific germline variants in multiple genes that contribute to the familial risk. These variants may be common risk alleles in the general population but have low penetrance and cause sporadic MPN, such as the JAK2 46/1 haplotype, the variant most strongly associated with MPN. Association studies are increasingly identifying other MPN susceptibility genes such as TERT, MECOM, and SH2B3, while some common variants in DDX41 and RUNX1 appear to lead to a spectrum of myeloid malignancies. RBBP6 and ATM variants have been identified in familial MPN clusters and very rare germline variants such as chromosome 14q duplication cause hereditary MPN with high penetrance. Rarely, there are hereditary non-malignant diseases with an MPN-like phenotype. Knowledge of those genes and germline genetic changes which lead to MPN or diseases that mimic MPN helps to improve accuracy of diagnosis, aids with counselling regarding familial risk, and may contribute to clinical decision-making. Large scale population exome and genome sequencing studies will improve our knowledge of both common and rare germline genetic contributions to MPN.

Exploring hematological alterations and genetics linked to SNV rs10974944 in myeloproliferative neoplasms among Amazon patients

BCR::ABL1-negative myeloproliferative neoplasms are hematopoietic disorders characterized by panmyelosis. JAK2 V617F is a frequent variant in these diseases and often occurs in the 46/1 haplotype. The G allele of rs10974944 has been shown to be associated with this variant, specifically its acquisition, correlations with familial cases, and laboratory alterations. This study evaluated the association between the 46/1 haplotype and JAK2 V617F in patients with myeloproliferative neoplasms in a population from the Brazilian Amazon. Clinical, laboratory and molecular sequencing analyses were considered. Carriers of the G allele of rs10974944 with polycythemia vera showed an increase in mean corpuscular volume and mean corpuscular hemoglobin, while in those with essential thrombocythemia, there was an elevation in red blood cells, hematocrit, and hemoglobin. Associations were observed between rs10974944 and the JAK2 V617F, in which the G allele (OR 3.4; p < 0.0001) and GG genotype (OR 4.9; p = 0.0016) were associated with JAK2 V617F + and an increase in variant allele frequency (GG: OR 15.8; p =  < 0.0001; G: OR 6.0; p = 0.0002). These results suggest an association between rs10974944 (G) and a status for JAK2 V617F, JAK2 V617F + _VAF ≥ 50%, and laboratory alterations in the erythroid lineage.

The molecular landscape of myeloproliferative neoplasms associated with splanchnic vein thrombosis: Current perspective

BCR::ABL1-negative myeloproliferative neoplasms (MPNs) are classically represented by polycythemia vera, essential thrombocythemia, and primary myelofibrosis. BCR::ABL1-negative MPNs are significantly associated with morbidity and mortality related to an increased risk of thrombo-hemorrhagic events. They show a consistent association with splanchnic vein thrombosis (SVT), either represented by the portal, mesenteric or splenic vein thrombosis, or Budd-Chiari Syndrome. SVT is also a frequent presenting manifestation of MPN. MPNs associated with SVT show a predilection for younger women, high association with JAK2V617F mutation, low JAK2V617F variant allele frequency (generally <10 %), and low rates of CALR, MPL, or JAK2 exon 12 mutations. Next-Generation Sequencing techniques have contributed to deepening our knowledge of the molecular landscape of such cases, with potential diagnostic and prognostic implications. In this narrative review, we analyze the current perspective on the molecular background of MPN associated with SVT, pointing as well future directions in this field.

Iron homeostasis governs erythroid phenotype in polycythemia vera

Polycythemia vera (PV) is a myeloproliferative neoplasm driven by activating mutations in JAK2 that result in unrestrained erythrocyte production, increasing patients' hematocrit and hemoglobin concentrations, placing them at risk of life-threatening thrombotic events. Our genome-wide association study of 440 PV cases and 403 351 controls using UK Biobank data showed that single nucleotide polymorphisms in HFE known to cause hemochromatosis are highly associated with PV diagnosis, linking iron regulation to PV. Analysis of the FinnGen dataset independently confirmed overrepresentation of homozygous HFE variants in patients with PV. HFE influences the expression of hepcidin, the master regulator of systemic iron homeostasis. Through genetic dissection of mouse models of PV, we show that the PV erythroid phenotype is directly linked to hepcidin expression: endogenous hepcidin upregulation alleviates erythroid disease whereas hepcidin ablation worsens it. Furthermore, we demonstrate that in PV, hepcidin is not regulated by expanded erythropoiesis but is likely governed by inflammatory cytokines signaling via GP130-coupled receptors. These findings have important implications for understanding the pathophysiology of PV and offer new therapeutic strategies for this disease.

Study of the Janus kinase 2 (JAK2) gene haplotype 46/1 association with driver mutations of chronic Ph-negative myeloproliferative neoplasms

Introduction. Haplotype JAK2 46/1 is associated with more frequent development of Ph-negative myeloproliferative neoplasms (MPN) and with an increased detection rate of the JAK2 V617F mutation. At the same time, the molecular mechanisms of such associations remain unclear. Previously, there were no studies of regional, age and gender aspects of the predictive value of carriage of the 46/1 JAK2 haplotype, which could assess this relationship in some observations.

Aim — to analyze the degree of association between 46/1 haplotype and the V617F mutation of the JAK2 gene depending on the sex, age, and place of residence of patients examined for suspected MPN.

Methods. The study included 949 DNA samples from patients with suspected MPN. Samples of 150 volunteers and blood donors were included in the control group. Haplotype 46/1 (rs10974944), V617F mutation in the JAK2 gene, mutations in the CALR gene (type 1: c.1092_1143del; L367fs*46, COSV57116546; type 2: c.1154_1155insTTGTC; K385fs*47, COSV57116551) and in the MPL gene (W515K, W515L) were determined for all samples using real-time polymerase chain reaction (PCR-RT).

Results. The 46/1 JAK2 haplotype were shown to be associated with a clinically significant level (> 2 %) of the allelic burden of the JAK2 V617F mutation. The odds ratio of the risk of developing a V617F positive MPN when carrying this haplotype variant did not depend on the main place of residence of the patients and was found to be most pronounced in men under 50 years of age. The odds ratio of the risk did not depend on the age of the examined women.

Conclusion. The association of 46/1 haplotype with the presence of other drivers of MPN mutations in the CALR or MPL genes was also statistically significant, which confirms the hypothesis of “favorable soil” rather than “hypermutability” of the JAK2 gene.

The Contribution of JAK2 46/1 Haplotype in the Predisposition to Myeloproliferative Neoplasms

Haplotype 46/1 (GGCC) consists of a set of genetic variations distributed along chromosome 9p.24.1, which extend from the Janus Kinase 2 gene to Insulin like 4. Marked by four jointly inherited variants (rs3780367, rs10974944, rs12343867, and rs1159782), this haplotype has a strong association with the development of BCR-ABL1-negative myeloproliferative neoplasms (MPNs) because it precedes the acquisition of the JAK2V617F variant, a common genetic alteration in individuals with these hematological malignancies. It is also described as one of the factors that increases the risk of familial MPNs by more than five times, 46/1 is associated with events related to inflammatory dysregulation, splenomegaly, splanchnic vein thrombosis, Budd-Chiari syndrome, increases in RBC count, platelets, leukocytes, hematocrit, and hemoglobin, which are characteristic of MPNs, as well as other findings that are still being elucidated and which are of great interest for the etiopathological understanding of these hematological neoplasms. Considering these factors, the present review aims to describe the main findings and discussions involving the 46/1 haplotype, and highlights the molecular and immunological aspects and their relevance as a tool for clinical practice and investigation of familial cases.

JAK2 rs10974944 is associated with both V617F-positive and negative myeloproliferative neoplasms in a Vietnamese population: A potential genetic marker

The JAK2 gene encodes for a non‐receptor tyrosine kinase that plays a key role in the JAK/STAT signaling transfer pathway. Genetic polymorphisms of this gene have been indicated to be associated with myeloproliferative neoplasm‐associated thrombosis in recent studies. This research aimed to evaluate the association between the variant rs10974944 and different types of Myeloproliferative neoplasms disorders in the Vietnamese population. DNA samples were obtained from 172 essential thrombocythemia patients, 14 primary myelofibrosis patients, 76 polycythemia vera patients, and 192 healthy controls. The JAK2 rs10974944 and V617F genotypes were identified by the polymerase chain reaction‐restriction fragment length polymorphism genotyping and Sanger sequencing methods. Results showed that there was a strong association between rs10974944 and Myeloproliferative neoplasms phenotype (p < .0001) and the most significant association was observed in the recessive model of the mutant allele (G). The G allele carriers had a 1.74, 2.86, and 3.03 higher risk of getting essential thrombocythemia, primary myelofibrosis, and polycythemia vera, respectively. Interestingly, this effect of rs10974944 seemed to be independent of the JAK2 V617F genotype. The distribution of rs10974944 genotypes were significantly different between V617F‐positive and negative groups (p = .008). Moreover, the GG genotype of rs10974944 was observed to be associated with the risk of getting Myeloproliferative neoplasms both in JAK2 V617F‐positive group, and for the first time in JAK2 V617F‐negative patients. A systematic meta‐analysis in different populations strengthened the evidence regarding the correlation between rs10974944 and myeloproliferative neoplasm disorders. To sum up, our results suggested that rs10974944 can be used as a predisposition screening marker for predicting Myeloproliferative neoplasms susceptibility.

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.

The Genetic Makeup of Myeloproliferative Neoplasms: Role of Germline Variants in Defining Disease Risk, Phenotypic Diversity and Outcome

Myeloproliferative neoplasms are hematologic malignancies typified by a substantial heritable component. Germline variants may affect the risk of developing a MPN, as documented by GWAS studies on large patient cohorts. In addition, once the MPN occurred, inherited host genetic factors can be responsible for tuning the disease phenotypic presentation, outcome, and response to therapy. This review covered the polymorphisms that have been variably associated to MPNs, discussing them in the functional perspective of the biological pathways involved. Finally, we reviewed host genetic determinants of clonal hematopoiesis, a pre-malignant state that may anticipate overt hematologic neoplasms including MPNs.

TET2 rs1548483 SNP Associating with Susceptibility to Molecularly Annotated Polycythemia Vera and Primary Myelofibrosis

Background: The complexity of myeloproliferative neoplasms (MPNs) cannot be characterized by acquired somatic mutations alone. Individual genetic background is thought to contribute to the development of MPNs. The aim of our study was to assess the association between the TET2 rs1548483 single nucleotide polymorphism (SNP) and the susceptibility to polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF) or chronic myeloid leukemia (CML). Methods: We evaluated the TET2 rs1548483 SNP through real-time PCR in 1601 MPN patients out of which 431 with PV, 688 with TE, 233 with PMF, 249 with CML and 197 controls. We included only patients with a molecularly proven driver mutation, such as JAK2 V617F, CALR or BCR-ABL1. Results: Significant association between TET2 rs154843 variant allele and JAK2 V617F-positive PV and PMF (OR = 1.70; 95% CI: 1.01–2.91; p-value = 0.046, and OR = 2.04; 95% CI: 1.10–3.77; p-value = 0.024, respectively), and type 2 CALR-positive PMF (OR = 2.98; 95% CI: 1.12–7.93; p-value = 0.035) was noted. Conclusions: The TET2 rs1548483 SNP is associated with the susceptibility to molecularly annotated PV and PMF.

Cytokine Profiling in Myeloproliferative Neoplasms: Overview on Phenotype Correlation, Outcome Prediction, and Role of Genetic Variants

Among hematologic malignancies, the classic Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are considered a model of inflammation-related cancer development. In this context, the use of immune-modulating agents has recently expanded the MPN therapeutic scenario. Cytokines are key mediators of an auto-amplifying, detrimental cross-talk between the MPN clone and the tumor microenvironment represented by immune, stromal, and endothelial cells. This review focuses on recent advances in cytokine-profiling of MPN patients, analyzing different expression patterns among the three main Philadelphia-negative (Ph-negative) MPNs, as well as correlations with disease molecular profile, phenotype, progression, and outcome. The role of the megakaryocytic clone as the main source of cytokines, particularly in myelofibrosis, is also reviewed. Finally, we report emerging intriguing evidence on the contribution of host genetic variants to the chronic pro-inflammatory state that typifies MPNs.

Cytokine Profiling in Myeloproliferative Neoplasms: Overview on Phenotype Correlation, Outcome Prediction, and Role of Genetic Variants

Among hematologic malignancies, the classic Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are considered a model of inflammation-related cancer development. In this context, the use of immune-modulating agents has recently expanded the MPN therapeutic scenario. Cytokines are key mediators of an auto-amplifying, detrimental cross-talk between the MPN clone and the tumor microenvironment represented by immune, stromal, and endothelial cells. This review focuses on recent advances in cytokine-profiling of MPN patients, analyzing different expression patterns among the three main Philadelphia-negative (Ph-negative) MPNs, as well as correlations with disease molecular profile, phenotype, progression, and outcome. The role of the megakaryocytic clone as the main source of cytokines, particularly in myelofibrosis, is also reviewed. Finally, we report emerging intriguing evidence on the contribution of host genetic variants to the chronic pro-inflammatory state that typifies MPNs.

The germline JAK2 GGCC (46/1) haplotype and survival among 414 molecularly-annotated patients with primary myelofibrosis

JAK2 mutations in myeloproliferative neoplasms (MPNs) are associated with the germline GGCC (46/1) haplotype. In 2010, we reported an association between shortened survival in primary myelofibrosis (PMF) and nullizygosity for the JAK2 46/1 haplotype. In the current study, we have increased the number of informative cases from 130 to 414 (median age 63 years; 63% males), in order to revisit with the phenotypic and prognostic relevance of the JAK2 46/1 haplotype in PMF. JAK2 46/1 haplotype was documented in 69% of the study patients, including 25% in homozygous and 44% in heterozygous state. Driver mutation frequency in patients homozygous/heterozygous/nullizygous for the 46/1 haplotype was 78%/60%/56% JAK2, 10%/20%/18% type 1-like CALR, 3%/2%/5% type 2-like CALR, 4%/8%/7% MPL, and 6%/10%/14% triple-negative (P = .02). In univariate analysis, nullizygosity for the JAK2 46/1 haplotype was associated with inferior overall survival (HR 1.5, 95% CI 1.1-1.9), most pronounced in JAK2 (P <.001), as opposed to CALR/MPL mutated (P = .48) or triple-negative cases (P = .27). Multivariable analysis that included karyotype, driver mutational status and high-molecular risk mutations confirmed the independent prognostic contribution of nullizygosity for the 46/1 haplotype (P = .02; HR 1.4, 95% CI 1.1-1.8). Nullizygosity for 46/1 also remained significant in the context of the genetically-inspired GIPSS risk model (P = .04), but not in the context of the integrated genetics-clinical MIPSS70+ version 2.0 model (P = .4). Leukemia-free survival was not affected by the 46/1 haplotype (P = .6). The current study confirms the association of nullizygosity for the JAK2 GGCC (46/1) haplotype with inferior survival in JAK2-mutated PMF.