Academic literature on the topic 'JAK2 46/1 haplotype'

Abstract The 46/1 JAK2 haplotype predisposes to V617F-positive myeloproliferative neoplasms, but the underlying mechanism is obscure. We analyzed essential thrombocythemia patients entered into the PT-1 studies and, as expected, found that 46/1 was overrepresented in V617F-positive cases (n = 404) versus controls (n = 1492, P = 3.9 × 10−11). The 46/1 haplotype was also overrepresented in cases without V617F (n = 347, P = .009), with an excess seen for both MPL exon 10 mutated and V617F, MPL exon 10 nonmutated cases. Analysis of further MPL-positive, V617F-negative cases confirmed an excess of 46/1 (n = 176, P = .002), but no association between MPL mutations and MPL haplotype was seen. An excess of 46/1 was also seen in JAK2 exon 12 mutated cases (n = 69, P = .002), and these mutations preferentially arose on the 46/1 chromosome (P = .029). No association between 46/1 and clinical or laboratory features was seen in the PT-1 cohort either with or without V617F. The excess of 46/1 in JAK2 exon 12 cases is compatible with both the “hypermutability” and “fertile ground” hypotheses, but the excess in MPL-mutated cases argues against the former. No difference in sequence, splicing, or expression of JAK2 was found on 46/1 compared with other haplotypes, suggesting that any functional difference of JAK2 on 46/1, if it exists, must be relatively subtle.

Abstract Background: JAK2 GGCC 46/1 haplotype can be represented by four main SNPs (rs3780367, rs10974944, rs12343867, and rs1159782) which replace one cytosine and three thymidines by two guanosines and two cytosines, generating a "GGCC" combination. These four SNPs located on JAK2 introns 10, 12, 14, and 15, respectively, and are always inherited together, being in complete linkage disequilibrium. The 46/1 component of the name came from Jones et al. study where the haplotype structure of the JAK2 gene was mapped using 14 SNPs genotyped by the Wellcome Trust Case Control Consortium (WTCCC) in 1500 healthy blood donors. Two haplotypes (numbers 46 and 1) were found to be identical except for one SNP, and they have a combined frequency of 0.24 in healthy individuals. Numerous observational studies associate this haplotype with myeloproliferative neoplasms (MPNs), as well as splanchnic vein thrombosis (SVT) and non-splanchnic vein thrombosis (non-SVT). In contrast to 24% frequency noted in healthy population, the frequency goes up to 40-80% in JAK2 V617F mutated MPN, and in 64% of those with JAK2 exon 12 mutations (Anelli et al. IJMS, 2018). We herein report our study of JAK2 GGCC (46/1) Haplotype in unprovoked Venous Thrombotic Events (VTE) in patients with negative thrombophilia workup, including negative JAK2 V617F mutation. Methods: We retrospectively identified patients positive for one of the two SNPs (rs12343867 and rs10974900) and unprovoked venous thrombotic among adult patients with negative thrombophilia workup (including JAK2 mutation) treated at tertiary care center from January 2018 to January 2021. Results: We have identified 8 patients, Table (1), that were positive for JAK2 46/1 haplotype SNPs, of whom 62.5% were homozygous 2/2, 25% heterozygous 1/2, while only 12.5% harbor homozygous 1/1 (a normal variant of JAK2 haplotype). The median age 48.5 years (23-65), and the majority (87.5%) were females. Thrombosis site was noted to be SVT in half of the patients, while non-SVT was noted in the other half (12.5% had cerebral vein thrombosis, 12.5% had deep venous thrombosis, 12.5% had a pulmonary embolism, and 12.5% had jugular vein thrombosis). Half of the patients had more than one site venous thrombosis and the other half had only one site. Around 37.50% of the patients had recurrent venous thrombosis on top of therapeutic anticoagulation. Two patients (25%) had high hemoglobin (17.4/16.7) g/dl, but did not fulfill the criteria for polycythemia vera diagnosis (of whom one is a male smoker and one was a female). None of the patients had leukocytosis or thrombocytosis. By imaging, one patient had mild splenomegaly which could be related to SVT. Conclusion: We report on a potential correlation between unprovoked thrombotic events, mainly venous thrombotic events, with JAK2 46/1 haplotype in patients with a negative thrombophilia workup, a finding that merit further investigation. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Abstract Epidemiological data and family studies have indicated that inherited factors may predispose to the development of myeloproliferative neoplasms (MPN). It has also been suggested that single nucleotide polymorphisms (SNPs) within JAK2 are associated with specific MPN subtypes. To explore the role of inherited factors in more detail, we initially performed quantitative analysis of a series of JAK2 SNPs in homozygous PV cases (%V617F >50%; n=73). Most mutant haplotypes could be read directly from the distorted allele ratios brought about by expansion of the homozygous clone. In many cases with 50–90% V617F, the residual wild type haplotype could also be read. Strikingly, of the 144 V617F alleles that could be determined, 111 (77%) had an identical core haplotype (subsequently designated 46/1) whereas only 9/76 (12%) residual wild type alleles were 46/1 (P = 1.9e-21, Fisher’s exact test). To explore this observation in more detail we first determined the haplotype structure of JAK2 using 14 SNPs genotyped by the Wellcome Trust Case Control Consortium (WTCCC) in 1500 UK blood donors. Nine haplotypes were inferred using the program PHASE that accounted for 94% of alleles, with a frequency of 0.24 for haplotype 46/1. Haplotype inference and tag SNP analysis revealed that 46/1 was also more frequent in heterozygous V617F positive MPD cases (135/354 alleles) compared to 188 locally sourced healthy controls (92/376 alleles; P = 0.0001) as well as the WTCCC cohort (P = 3.3e-8). Haplotype 46/1 was more frequent in all V617F positive disease entities compared to controls: PV (n=203; P=1.2e-16), ET (n=81; P=1.2e-9) and MF (n=41; P=8.0e-5) however there was no difference in the frequency of 46/1 between controls and V617F negative MPD / idiopathic erythrocytosis (n=123). To determine if heterozygous V617F also preferentially arose on a 46/1 allele as seen for homozygous cases, we developed an allele specific PCR between V617F and a SNP that tags this haplotype. In an analysis of 67 informative heterozygous V617F cases, 50 V617F alleles were 46/1 compared to only 17 residual wild type alleles (P=9.4e-9). We conclude that the 46/1 JAK2 haplotype is a strong predisposition factor for development of V617F associated MPDs (RR=2.6; 95% CI 2.3–2.9). The reason for this predisposition is currently unknown but it is likely that 46/1 is in linkage disequilibrium with an unknown constitutional functional variant that interacts with V617F JAK2.

Abstract Abstract 433 A common constitutional JAK2 haplotype termed 46/1 (also known as GGCC) predisposes to V617F JAK2-positive myeloproliferative neoplasms (MPN) but the underlying mechanism is obscure. Two hypotheses have been postulated: (i) ‘hypermutability' of JAK2 on 46/1 compared to other haplotypes and (ii) a functional difference of JAK2 on 46/1 that positively interacts with V617F and thus provides ‘fertile ground' for development of an MPN. To investigate these possibilities we analyzed patients with essential thrombocythemia entered into the PT-1 studies. As expected, 46/1 was highly overrepresented in V617F positive cases (n=404) compared to population controls (n=1492; P=3.9×10-11) and in informative individuals V617F preferentially arose on the 46/1 chromosome (P<0.0001). This haplotype was also overrepresented in cases without V617F (n=347, P=0.009), with an excess seen for individuals with MPL exon 10 mutations as well as those who were V617F and MPL exon 10 negative. Analysis of further MPL-positive, V617F negative cases confirmed an excess of 46/1 alleles (n=176, P=0.004) however we found no association between MPL mutations and MPL haplotype. An excess of 46/1 was also seen in cases with JAK2 exon 12 mutations (n=69, P=0.002) and in informative individuals these mutations preferentially arose on the 46/1 chromosome (P=0.029). No association between 46/1 and clinical or laboratory features was seen in the PT-1 cohort either with or without V617F. An excess of 46/1 in JAK2 exon 12 mutated cases is compatible with both the hypermutability and fertile ground hypotheses, but the excess in MPL mutated cases argues against the former. However, on analysis of peripheral blood leukocytes we detected no difference in sequence, splicing or expression of JAK2 on 46/1 compared to JAK2 on other haplotypes suggesting that any functional difference of JAK2 on 46/1, if it exists, must be relatively subtle. Finally, since 46/1 is seen at comparable frequencies in different MPN subtypes it does not explain the phenotypic diversity associated with V617F JAK2. In an analysis of 138 MPL mutated cases (ET, n=99; MF, n=36; other MPN, n=3) we found that the median W515K/L mutation levels as determined by pyrosequencing in ET (21%) were significantly lower than those seen in MF (46%; P<0.0001). However we were unable to confirm previously reported differences in SNP frequencies (rs1524395 at 7p11, rs2279784 at 3q21 and rs12500918 at 4q31) between cases with ET (n=763) and PV (n=163). In summary, our data provide further evidence for the fertile ground hypothesis whereby a proposed subtle functional difference of JAK2 on 46/1 makes the development of an MPN more likely when a JAK2 mutation arises on this haplotype, or when JAK2 46/1 is present with a MPL exon 10 mutation. JAK2 and MPL mutation levels, but not 46/1 status, are related to disease phenotype. Disclosures: Schnittger: MLL Munich Leukemia Laboratory: Equity Ownership. Green:Bristol Myers Squibb: Consultancy; Shire: Consultancy; Incyte: Consultancy; Astex Therapeutics: Consultancy, Research Funding.

Abstract Abstract 2805 Background: Adequate expression and function of Jak2 in hematopoietic progenitors is critical for normal myelopoiesis. The JAK2 46/1 (GGCC) haplotype, a congenital particularity, predisposes to myeloproliferative neoplasm (MPN) both independently and through mutation of the JAK2 gene. The JAK2 V617F mutation and acquired homozygous status for JAK2 V617F are frequent in MPN. JAK2 V617F homozygosity is currently explained acquisition of the JAK2 V617F mutation followed by mitotic homologous recombination (HR) of JAK2 occurred between wild-type and mutant alleles, leading to uniparental disomy (UPD) of chromosome 9p (9pUPD). Here we report the cases of 2 PV patients (Na1061 and Na1253) with acquired homozygous status for the JAK2 46/1 haplotype yet their granulocytes carried <20% JAK2 V617F. Aim: To determine whether HR of JAK2 can precede the V617F mutation in MPN. Methods: Granulocyte DNA and CD3+ lymphocyte DNA were examined in parallel with qPCR assays specific for the wild type and 46/1 haplotypes using rs12343867, a JAK2 intron 14 marker, as well as 4 other single nucleotide polymorphisms (SNP) on chromosome 9p. 9pUPD clonality and length were determined using SNP array studies. Results: For both patients, lymphocytes were heterozygous for the 46/1 haplotype, confirming that granulocyte 46/1 homozygosity was acquired. Direct sequencing of the JAK2 and GNE genes and SNP array analyses revealed homologous recombination of part of the JAK2 gene (exons 6–19, patient Na1061) and of the complete 46/1 JAK2 haplotype (patient Na1253). Furthermore, for both patients, full length sequencing of JAK2 cDNA revealed no additional mutation. In both cases, HR of wild-type JAK2 was associated with growth advantage and high expression of recombined JAK2. For both patients, further SNP array analyses revealed partial 9pUPD concerning <30% cells, which correlated with %JAK2 V617F and was consistent with 9pUPD having occurred after JAK2 V617F (Figure 1). The distortion of SNP allelic differences was higher at the telomeric end than in the centromeric region of chr. 9p. This indicated 2 distinct partial 9pUPDs for Na1061 and 1 partial 9pUPD for Na1253. Conclusion: Homologous recombination involving wild type JAK2 can precede JAK2 mutation and 9pUPD in MPN. Thus multiple paths and diverse alterations of the JAK2 gene can lead to MPN in individuals carrying the JAK2 GGCC haplotype. We propose a new model with JAK2 HR as early event, followed or not by JAK2 mutation, or/and JAK2 mutation(s) facilitating subsequent recombination resulting in 9pUPD and JAK2 V617F homozygosity. Disclosures: No relevant conflicts of interest to declare.

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.

Abstract Abstract 4212 Primary Budd-Chiari syndrome (BCS) and non-malignant, non-cirrhotic portal vein thrombosis (PVT) are rare disorders with a considerable overlap in etiology. Myeloproliferative neoplasms (MPN) are the most frequent underlying prothrombotic factor in both entities. The JAK2 V617F mutation (VF) has been identified in over half of the individuals with MPN. Recently, a JAK2 haplotype, designated ‘46/1’, has been described. Previous studies suggest that the JAK2 46/1 haplotype represents a disease susceptibility to MPN, independent of VF status. The aim of this study was to determine the role of the JAK2 46/1 haplotype in the etiology of BCS and PVT. Patients were recruited from the EN-Vie cohort, consisting of 163 BCS and 138 PVT patients, consecutively enrolled in nine European countries between October 2003 and October 2005. DNA was available from 116 BCS patients (50 males and 66 females; median age 38.1), 97 PVT patients (47 males and 50 females; median age 49.8) and 104 healthy controls (43 males and 61 females; median age 36.8). The JAK2 46/1 haplotype was tagged by the rs12343867 single nucleotide polymorphism. Frequency of the JAK2 haplotype 46/1 was higher in BCS (36%, p=0.06) compared to controls (27%), while similar in PVT patients (28%, p=0.89). When stratified for VF status, haplotype 46/1 frequency was higher in VF positive BCS (44%, p=0.01) and VF positive PVT patients (40%, p=0.06) compared to controls. Haplotype 46/1 frequency was similar in VF negative BCS (33%, p=0.29) and PVT patients (24%, p=0.47) compared to controls. VF negative BCS patients with a proven MPN also showed increased frequency of the 46/1 haplotype (56%, p=0.07). Logistic regression, adjusted for age and sex, showed an association between the 46/1 haplotype and risk of VF positive BCS (OR: 2.10; 1.16–3.80), VF positive PVT (OR 2.07; 0.95–4.52) and VF negative BCS patients with a proven MPN (OR 3.04; 1.02–9.06). We conclude that the JAK2 46/1 haplotype may be associated with BCS and that this was limited to patients with a proven MPN, independent of VF status. In PVT, the 46/1 haplotype was only associated with patients who were VF positive. This study was carried out on behalf of the European Network for Vascular Disorders of the Liver (EN-Vie). Disclosures: No relevant conflicts of interest to declare.

Abstract The germline JAK2 46/1 haplotype has been associated with the development of JAK2V617F-positive as well as JAK2V617F-negative myeloproliferative neoplasms (MPNs). In this study we examined the role of the 46/1 haplotype in the etiology and clinical presentation of patients with splanchnic vein thrombosis (SVT), in which MPNs are the most prominent underlying etiological factor. The single-nucleotide polymorphism rs12343867, which tags 46/1, was genotyped in 199 SVT patients. The 46/1 haplotype was overrepresented in JAK2V617F-positive SVT patients compared with controls (P < .01). Prevalence of the 46/1 haplotype in JAK2V617F-negative SVT patients did not differ from prevalence in the controls. However, JAK2V617F-negative SVT patients with a proven MPN also exhibited an increased frequency of the 46/1 haplotype (P = .06). Interestingly, 46/1 was associated with increased erythropoiesis in JAK2V617F-negative SVT patients. We conclude that the 46/1 haplotype is associated with the development of JAK2V617F-positive SVT. In addition, our findings in JAK2V617F-negative SVT patients indicate an important role for the 46/1 haplotype in the etiology and diagnosis of SVT-related MPNs, independent of JAK2V617F, that requires further exploration.

Abstract Background: We have long introduced the concept of host genetic variations in the phenotypic diversity of myeloproliferative neoplasms (MPN) (Blood 2008;111:2785). Previous studies have established an association between JAK2 mutations in myeloproliferative neoplasms (MPN) and the germline GGCC (46/1) haplotype, which constitutes a string of single nucleotide polymorphisms (SNPs) near the JAK2 gene that are inherited together on chromosome 9p (reviewed recently;Int J Mol Sci. 2018; 19: 1152). In 2010, we reported an association between shortened survival in primary myelofibrosis (PMF) and nullizygosity for the JAK2 46/1 haplotype (Leukemia 2010; 24:105), although our findings were not confirmed in another study (Leukemia 2010; 24:1533). Others have reported an association with splanchnic vein thrombosis, that was not accounted for by JAK2 mutations (Ann Hematol 2014;93:1845). In the current study, we have increased the number of informative cases to 414 (from 130 reported in 2010), in order to revisit with the phenotypic and prognostic relevance of the JAK2 46/1 haplotype in PMF. Methods : Study patients were recruited from the Mayo Clinic, Rochester, MN, USA. Diagnoses PMF and its leukemic transformation were confirmed by both clinical and bone marrow examinations, in line with the 2016 World Health Organization criteria (Blood. 2016;127:2391). Screening for the JAK2 46/1 haplotype included rs12343867 SNP genotyping, as previously detailed (Leukemia 2010; 24:105), and using a commercially available TaqMan SNP genotyping assay (Applied Biosystems Inc., Foster City, CA, USA). Statistical analyses considered clinical and laboratory data collected at the time of initial PMF diagnosis or Mayo Clinic referral point. Conventional statistics was used for confirming phenotypic associations and calculation of overall (OS) and leukemia-free (LFS) survival. The JMP® Pro 13.0.0 software from SAS Institute, Cary, NC, USA, was used for all calculations. Results: 414 patients with PMF (median age 63 years; 63% males) were included in the current study; among 324 evaluable cases, MIPSS70+ version 2.0 risk distribution was 18% very high risk, 41% high risk, 19% intermediate risk, 18% low risk and 4% very low risk. Driver mutation distribution was 63% JAK2, 17% type 1-like CALR, 3% type 2-like CALR, 7% MPL and 10% triple-negative. 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=0.02). The three 46/1 haplotype groups were phenotypically mostly similar, with the exception of platelet count (p=0.02) and leukocyte count (p=0.003), which were both higher with homozygous 46/1 haplotype. 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; figure 1a); this survival effect was most pronounced in JAK2 mutated cases (figure 1b; p<0.001), as opposed to CALR/MPL mutated cases (figure 1c; p=0.48) or triple-negative cases (figure 1d; p=0.27). Multivariable analysis that included age and other genetic risk factors, including karyotype, driver mutational status and presence of high molecular risk mutations, such as ASXL1 and SRSF2, confirmed the independent prognostic contribution of nullizygosity for the 46/1 haplotype (p=0.02; HR 1.4, 95% CI 1.1-1.8). Nullizygosity for 46/1 also remained significant in the context of the recently unveiled genetics-based prognostic model, GIPSS (genetically-inspired prognostic scoring system) (p=0.04) (Leukemia.2018 doi: 10.1038/s41375-018-0107-z), but not in the context of MIPSS70+ version 2.0 (karyotype and mutation-enhanced international prognostic scoring system for transplant-age patients) (p=0.4). (JClinOncol.2018 doi: 10.1200/JCO.2018.78.9867). Leukemia-free survival was not affected by the 46/1 haplotype (p=0.6). Conclusions: The current study confirms the association of nullizygosity for the JAK2 GGCC (46/1) haplotype with inferior survival in PMF, primarily in JAK2-mutated cases; the observed survival effect was independent of currently acknowledged genetic risk factors, including karyotype and high molecular risk mutations. Disclosures No relevant conflicts of interest to declare.

This work concerns malignant myeloid hemopathies called classical BCR-ABL-negative Myeloproliferative Neoplasms (MPN) and include Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF). They result from the transformation of a multipotent hematopoietic stem cell (HSC) with hyperproliferation but no blockade of differentiation. The most common molecular defect is the acquired point mutation JAK2V617F resulting into the activation of the cytokine receptor/JAK2 pathway. We have developed a mouse constitutive and a conditional JAK2V617F knock-in (KI) mouse models. These animals developed a disease mimicking human PV evolving into secondary MF. They also displayed an age dependent increase in the total numbers of early hematopoietic cells (phenotype LK, LSK and SLAM: LSK/CD48-/CD150+). Using In vivo competitive repopulation assays we demonstrated that cells from KI origin outcompeted their WT counterparts and that a low number of JAK2V617F KI SLAM cells propagates the disease. These results show that the sole JAK2V617F mutation, without any additional mutations, is sufficient for disease phenotype and emergence. Using this KI mouse model, we tested the effect of interferon-a (IFNa) treatment on MPN development. We found that IFNa treats the disease phenotype by blocking the propagation of early JAK2V617F cells and eradicates disease-initiating cells, showing that IFNα could cure the disease in mice, as shown in some PV patients. Finally, we developed a new method combining the measurement of 46/1 SNPs and JAK2V617F allele burdens in blood predicting the frequency of normal, heterozygous and homozygous JAK2V617F clones in PV patients. This study suggested that IFNa preferentially targets the homozygous JAK2V617F clone in PV patients suggesting a link between the levels of JAK2 signaling and the success of the IFNa response.