Discordant distribution of JAK2V617F mutation in siblings with familial myeloproliferative disorders

Hereditary Predisposition to Hematopoietic Neoplasms: When Bloodline Matters for Blood Cancers

With the advent of precision genomics, hereditary predisposition to hematopoietic neoplasms- collectively known as hereditary predisposition syndromes (HPS)-are being increasingly recognized in clinical practice. Familial clustering was first observed in patients with leukemia, which led to the identification of several germline variants, such as RUNX1, CEBPA, GATA2, ANKRD26, DDX41, and ETV6, among others, now established as HPS, with tendency to develop myeloid neoplasms. However, evidence for hereditary predisposition is also apparent in lymphoid and plasma--cell neoplasms, with recent discoveries of germline variants in genes such as IKZF1, SH2B3, PAX5 (familial acute lymphoblastic leukemia), and KDM1A/LSD1 (familial multiple myeloma). Specific inherited bone marrow failure syndromes-such as GATA2 haploinsufficiency syndromes, short telomere syndromes, Shwachman-Diamond syndrome, Diamond-Blackfan anemia, severe congenital neutropenia, and familial thrombocytopenias-also have an increased predisposition to develop myeloid neoplasms, whereas inherited immune deficiency syndromes, such as ataxia-telangiectasia, Bloom syndrome, Wiskott Aldrich syndrome, and Bruton agammaglobulinemia, are associated with an increased risk for lymphoid neoplasms. Timely recognition of HPS is critical to ensure safe choice of donors and/or conditioning-regimen intensity for allogeneic hematopoietic stem-cell transplantation and to enable direction of appropriate genomics-driven personalized therapies. The purpose of this review is to provide a comprehensive overview of HPS and serve as a useful reference for clinicians to recognize relevant signs and symptoms among patients to enable timely screening and referrals to pursue germline assessment. In addition, we also discuss our institutional approach toward identification of HPS and offer a stepwise diagnostic and management algorithm.

Experimental Modeling of Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPN) are genetically very complex and heterogeneous diseases in which the acquisition of a somatic driver mutation triggers three main myeloid cytokine receptors, and phenotypically expresses as polycythemia vera (PV), essential thrombocytosis (ET), and primary myelofibrosis (PMF). The course of the diseases may be influenced by germline predispositions, modifying mutations, their order of acquisition and environmental factors such as aging and inflammation. Deciphering these contributory elements, their mutual interrelationships, and their contribution to MPN pathogenesis brings important insights into the diseases. Animal models (mainly mouse and zebrafish) have already significantly contributed to understanding the role of several acquired and germline mutations in MPN oncogenic signaling. Novel technologies such as induced pluripotent stem cells (iPSCs) and precise genome editing (using CRISPR/Cas9) contribute to the emerging understanding of MPN pathogenesis and clonal architecture, and form a convenient platform for evaluating drug efficacy. In this overview, the genetic landscape of MPN is briefly described, with an attempt to cover the main discoveries of the last 15 years. Mouse and zebrafish models of the driver mutations are discussed and followed by a review of recent progress in modeling MPN with patient-derived iPSCs and CRISPR/Cas9 gene editing.

Advances in understanding the pathogenesis of familial myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are generally acquired as a result of a somatic stem cell mutation leading to clonal expansion of myeloid precursors. In addition to sporadic cases, familial MPN occurs when one or several MPN affect different relatives of the same family. MPN driver mutations (JAK2, CALR, MPL) are somatically acquired also in familial cases, so a genetic predisposition to acquire one of the MPN driver mutations would be inherited, even though the causative germline mutations underlying familial MPN remain largely unknown. Recently some germline variants [ATG2B and GSKIP duplication, RBBP6 mutations, SH2B3 (LNK) mutations], which can cause familial MPN, have been reported but these mutations are rare and do not explain most familial cases. Patients with familial MPN show the same clinical features and suffer the same complications as those with sporadic disease. This review aims to offer up-to-date information regarding the genetics of familial MPN.

The expression of Death Inducer-Obliterator (DIDO) variants in Myeloproliferative Neoplasms

Chronic Myeloid Leukemia (CML), Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF) are Myeloproliferative Neoplasms (MPN) characterized by clonal myeloproliferation without cell maturation impairment. CML pathogenesis is associated with the Ph chromosome leading to BCR-ABL tyrosine-kinase constitutive expression. The Ph negative MPN (PV, ET and PMF) are characterized by the mutation JAK2(V617F) of the JAK2 protein in the auto-inhibitory JH2 domain, which is found in most PV patients and in approximately half of ET and PMF patients. Considerable effort is being made to understand the role of JAK2(V617F) at the MPN initiation and to clarify the pathogenesis and apoptosis resistance in CML, PV, ET and PMF patients. In the present investigation, we evaluated the Death Inducer-Obliterator (DIDO) (variants DIDO 1, 2 and 3) levels in CML, PV, ET and PMF patients. Our data reported the DIDO 1, 2 and 3 differential expressions in Myeloproliferative Neoplasms.

Back to biology: new insights on inheritance in myeloproliferative disorders

The myeloproliferative disorders (MPDs) are a group of hematologic diseases with significant overlap in both clinical phenotype and genetic etiology. While most often caused by acquired somatic mutations in hematopoietic stem cells, the presence of familial clustering in MPD cases suggests that inheritance is an important factor in the etiology of this disease. Though far less common than sporadic disease, inherited MPDs can be clinically indistinguishable from sporadic disease. Recently, germline mutations in Janus kinase 2 (JAK2) and MPL, two genes frequently mutated in sporadic MPD, have been shown to cause inherited thrombocytosis. Study of the function of these mutant proteins has led to a new understanding of the biological mechanisms that produce myeloproliferative disease. In this review, we summarize the data regarding inherited mutations that cause or predispose to MPDs, with a focus on the biological effects of mutant proteins. We propose that defining inherited MPDs in this manner has the potential to simplify diagnosis in a group of disorders that can be difficult to differentiate clinically.

Gastrointestinal stromal tumors in the setting of multiple tumor syndromes

PURPOSE OF REVIEW

Knowledge related to gastrointestinal stromal tumor (GIST) in the setting of nonhereditary and hereditary multiple tumor syndromes continues to expand. This review describes associations between sporadic GIST and second malignancies, as well as new contributions to our knowledge about hereditary GIST multiple tumor syndromes.

RECENT FINDINGS

Sporadic GIST patients have increased risk of developing synchronous/metachronous cancers, including nonhematologic and hematologic malignancies. Data suggest these associations are nonrandom, more prevalent in men and increase with age. New adrenal tumors have also been associated with nonhereditary Carney's triad. Meanwhile, understanding of the molecular basis of heritable GIST syndromes has improved. Several new familial GIST kindreds have been reported, including those with germline KIT and PDGFRα mutations. Knowledge about succinate dehydrogenase (SDH) deficiency and mutations in hereditary GIST syndromes has expanded. It is now known that neurofibromatosis-1-associated GISTs are SDHB-positive, whereas Carney-Stratakis syndrome-associated GISTs are SDHB-deficient with underlying germline mutations in SDH subunits A-D.

SUMMARY

Recognition and early diagnosis of GIST syndromes allows for improved comprehensive medical care. With additional understanding of the molecular pathogenesis of GIST multiple tumor syndromes, we can refine our screening programs and management of these patients and their families.

Genetic and epigenetic alterations of myeloproliferative disorders

The classical BCR-ABL negative myeloproliferative neoplasms (MPN) polycythemia vera, essential thrombocythemia, and primary myelofibrosis are clonal hematopoietic disorders characterized by excessive production of terminally differentiated myeloid cells. In MPN patients, the disease can progress to secondary myelofibrosis or acute myeloid leukemia. Clonal hematopoiesis, disease phenotype, and progression are caused by somatically acquired genetic lesions of genes involved in cytokine signaling, RNA splicing, as well as epigenetic regulation. This review provides an overview of point mutations and cytogenetic lesions associated with MPN and addresses the role of these somatic lesions in MPN disease progression.

Long term follow up of 93 families with myeloproliferative neoplasms: life expectancy and implications of JAK2V617F in the occurrence of complications

The long-term evolution of familial myeloproliferative neoplasms was studied in 93 families with 227 subjects including 97 with polycythemia vera (PV), 105 essential thrombocythemia (ET), 14 primary myelofibrosis (PMF) and 11 chronic myeloid leukemia (CML). In PV patients, with 12years of median follow-up, overall survival was 83% at 10years and 37% at 20years. A high JAK2(V617F) allele burden was correlated with the transformation to myelofibrosis (p<0.0001), but not with the transformation to acute leukemia. Among the 105 ET, with 8years of median follow-up, overall survival was 83% at 10years and 57% at 20years. Progression to acute leukemia and progression to myelofibrosis were 10% and 13%. There was a trend toward a more frequent evolution to myelofibrosis when the JAK2(V617F) mutated allele burden was >50% (p=0.09), but not to AML. Hematologic transformation of the MPN was responsible for 69% of the deaths, cerebral stroke for 7% and 4% died of myocardial infarction. Eleven JAK2(V617F) mutated patients developed 13 deep splanchnic thromboses in PV and ET. Finally whereas patients with familial PV and ET have a comparable prognosis to non-familial MPN, the JAK2(V617F) mutation was associated with a more frequent occurrence of thrombosis in the entire population.

Mouse models of myeloproliferative neoplasms: JAK of all grades

In 2005, several groups identified a single gain-of-function point mutation in the JAK2 kinase that was present in the majority of patients with myeloproliferative neoplasms (MPNs). Since this discovery, much effort has been dedicated to understanding the molecular consequences of the JAK2V617F mutation in the haematopoietic system. Three waves of mouse models have been produced recently (bone marrow transplantation, transgenic and targeted knock-in), which have facilitated the understanding of the molecular pathogenesis of JAK2V617F-positive MPNs, providing potential platforms for designing and validating novel therapies in humans. This Commentary briefly summarises the first two types of mouse models and then focuses on the more recently generated knock-in models.

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.

Increased risks of polycythemia vera, essential thrombocythemia, and myelofibrosis among 24,577 first-degree relatives of 11,039 patients with myeloproliferative neoplasms in Sweden

Previous small studies have reported familial clustering of myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). We identified 6217 PV, 2838 ET, 1172 MF, and 812 MPN unclassifiable (NOS) patients diagnosed in Sweden, 43 550 controls, and first-degree relatives of cases (n = 24 577) and controls (n = 99 542). Using a marginal survival model, we calculated relative risks (RRs) and 95% confidence intervals as measures of familial aggregation. Relatives of MPN patients had significantly increased risks of PV (RR = 5.7; 3.5-9.1), ET (RR = 7.4; 3.7-14.8), and MPN NOS (RR = 7.5; 2.7-20.8). Analyses stratified by type of first-degree relative revealed consistently higher risks for siblings, compatible with a model of recessive genetic inheritance, which can be confirmed only by identifying the susceptibility gene(s). Mean age at MPN diagnosis was not different (P = .20) for affected relatives of cases (57.5 years) versus controls (60.6 years), and risk of MPN by age was not different for parents versus offspring of MPN cases (P = .10), providing no support for anticipation. Relatives of MPN patients had a borderline increased risk of chronic myeloid leukemia (CML; RR = 1.9; 0.9-3.8; P = .09). Our findings of 5- to 7-fold elevated risk of MPNs among first-degree relatives of MPN patients support the hypothesis that common, strong, shared susceptibility genes predispose to PV, ET, MF, and possibly CML.

Host genetic variation contributes to phenotypic diversity in myeloproliferative disorders

JAK2V617F is an acquired mutation associated with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). We tested the hypothesis that the paradox of a single disease allele associated with 3 distinctive clinical phenotypes could be explained in part by host-modifying influences. We screened for genetic variation within 4 candidate genes involved in JAK-STAT signaling, including receptors for erythropoietin (EPOR), thrombopoietin (MPL), and granulocyte colony-stimulating factor (GCSFR), and JAK2. We genotyped 32 linkage disequilibrium tag single nucleotide polymorphism (SNP) loci in 179 white patients: 84 had PV, 58 had PMF, and 37 had ET. Genotype-phenotype analysis showed 3 JAK2 SNPs (rs7046736, rs10815148, and rs12342421) to be significantly but reciprocally associated with PV (P < .001 for all; odds ratio = 0.16, 2.72, and 2.46, respectively) and ET (P < .001 for all; odds ratio = 3.05, 0.29, and 0.30, respectively) but not with PMF. Three additional JAK2 SNPs (rs10758669, rs3808850, and rs10974947) and a single EPOR SNP (rs318699) were also significantly associated with PV but not with ET or PMF. Finally, intragene haplotypes in JAK2 were significantly associated with PV only. Thus, host genetic variation may contribute to phenotypic diversity among myeloproliferative disorders, including in the presence of a shared disease allele.

Somatic mutations of JAK2 exon 12 in patients with JAK2 (V617F)-negative myeloproliferative disorders

We searched for JAK2 exon 12 mutations in patients with JAK2 (V617F)-negative myeloproliferative disorders. Seventeen patients with polycythemia vera (PV), including 15 sporadic cases and 2 familial cases, carried deletions or duplications of exon 12 in circulating granulocytes but not in T lymphocytes. Two of the 8 mutations detected were novel, and the most frequent ones were N542-E543del and E543-D544del. Most patients with PV carrying an exon 12 mutation had isolated erythrocytosis at clinical onset, unlike patients with JAK2 (V617F)-positive PV, most of whom had also elevations in white blood cell and/or platelet counts. Both patients with familial PV carrying an exon 12 mutation had an affected sibling with JAK2 (V617F)-positive PV. Thus, several somatic mutations of JAK2 exon 12 can be found in a myeloproliferative disorder that is mainly characterized by erythrocytosis. Moreover, a genetic predisposition to acquisition of different JAK2 mutations is inherited in families with myeloproliferative disorders.

Advances in the molecular characterization of Philadelphia-negative chronic myeloproliferative disorders

PURPOSE OF REVIEW

The identification and characterization of somatic disease alleles have greatly improved our understanding of the molecular pathogenesis of myeloproliferative disorders. This review focuses on recent studies investigating the role of activated tyrosine kinase signaling in the Philadelphia chromosome negative myeloproliferative disorders.

RECENT FINDINGS

Previously identified tyrosine kinase mutations in chronic myeloid leukemia and other myeloproliferative disorders suggested the possibility that polycythemia vera, essential thrombocythemia and primary myelofibrosis are also caused by activated tyrosine kinases. Recent studies identified an activating mutation in the JAK2 tyrosine kinase (JAK2V617F) in most patients with polycythemia vera and in approximately half of those with essential thrombocythemia and primary myelofibrosis. More recently, activating mutations in the thrombopoietin receptor and in JAK2 exon 12 have been identified in JAK2V617F negative myeloproliferative disorders.

SUMMARY

The discovery of activated tyrosine kinases in the majority of patients with polycythemia vera, essential thrombocythemia and primary myelofibrosis has diagnostic and pathogenetic implications. Subsequent studies are needed to elucidate the cause of myeloproliferative disorders without known disease alleles and to determine if inhibition of JAK2 signaling has therapeutic efficacy in the treatment of polycythemia vera, essential thrombocythemia and primary myelofibrosis.

Familial chronic myeloproliferative disorders: clinical phenotype and evidence of disease anticipation

PURPOSE

Chronic myeloproliferative disorders (CMDs) have sporadic occurrence. However, familial clustering is reported. The purpose of this study was to assess the prevalence and the clinical phenotype of familial CMDs, and to study the anticipation of disease onset in successive generations.

PATIENTS AND METHODS

Among 458 patients with apparently sporadic CMDs, an interview-based investigation of family history was performed to identify familial cases. The clinical phenotype of familial CMDs was compared with that of sporadic CMDs. Anticipation was studied evaluating age at diagnosis and telomere length in successive generations.

RESULTS

Among 458 patients with apparently sporadic CMDs, the prevalence of familial cases was 7.6% (35 pedigrees; 75 patients). Kolmogorov-Smirnov and two-tailed Fisher's exact tests did not demonstrate significant differences in clinical presentation between patients with familial and sporadic CMDs. Within 544 person-years of follow-up, patients with familial CMDs developed similar complications and disease evolutions as those with sporadic CMDs. The comparison of second-generation and first-generation patients showed a significantly younger age at diagnosis (Wilcoxon matched-pair test, P = .001) and a significantly higher age-dependent hazard of CMD onset (Nelson-Aalen method, P < .001) in patients of the second generation. A significant shortening of telomere length was highlighted in offspring compared with parent (P = .043).

CONCLUSION

This study indicates that a thorough investigation of family history should be part of the initial work-up of patients with CMDs. Patients with familial CMDs show the same clinical features and suffer the same complications as patients with sporadic disease. Age distribution between parent and offspring and telomere length shortening provide evidence of disease anticipation.

Extending Jak2V617F and MplW515 mutation analysis to single hematopoietic colonies and B and T lymphocytes

JAK2V617F and MPLW515L/K are myeloproliferative disorder (MPD)-associated mutations. We genotyped 552 individual hematopoietic colonies obtained by CD34+ cell culture from 16 affected patients (13 JAK2V617F and 3 MPLW515L/K) to determine (a) the proportion of colonies harboring a particular mutation in the presence or absence of cytokines, (b) the lineage distribution of endogenous colonies for each mutation, and (c) the differences (if any) in the pattern of mutation among the various MPDs, as established by genotyping of individual colonies. Genotyping analysis revealed cohabitation of mutation-negative and mutation-positive endogenous colonies in polycythemia vera as well as other MPDs. Culture of progenitor cells harboring MPLW515L/K yielded virtually no endogenous erythroid colonies in contrast to JAK2V617F-harboring progenitor cells. The mutation pattern (i.e., relative distribution of homozygous, heterozygous, or wild-type colonies) was not a distinguishing feature among the MPDs, and MPLW515 mutations were detected in B and/or T lymphocytes in all three patients tested. These observations suggest that clonal myelopoiesis antedates acquisition of JAK2V617F or MPLW515L/K mutations and that the latter is acquired in a lympho-myeloid progenitor cell.

MPL515 mutations in myeloproliferative and other myeloid disorders: a study of 1182 patients

Recently, a gain-of-function MPL mutation, MPLW515L, was described in patients with JAK2V617F-negative myelofibrosis with myeloid metaplasia (MMM). To gain more information on mutational frequency, disease specificity, and clinical correlates, genomic DNA from 1182 patients with myeloproliferative and other myeloid disorders and 64 healthy controls was screened for MPL515 mutations, regardless of JAK2V617F mutational status: 290 with MMM, 242 with polycythemia vera, 318 with essential thrombocythemia (ET), 88 with myelodysplastic syndrome, 118 with chronic myelomonocytic leukemia, and 126 with acute myeloid leukemia (AML). MPL515 mutations, either MPLW515L (n = 17) or a previously undescribed MPLW515K (n = 5), were detected in 20 patients. The diagnosis of patients with mutant MPL alleles at the time of molecular testing was de novo MMM in 12 patients, ET in 4, post-ET MMM in 1, and MMM in blast crisis in 3. Six patients carried the MPLW515L and JAK2V617F alleles concurrently. We conclude that MPLW515L or MPLW515K mutations are present in patients with MMM or ET at a frequency of approximately 5% and 1%, respectively, but are not observed in patients with polycythemia vera (PV) or other myeloid disorders. Furthermore, MPL mutations may occur concurrently with the JAK2V617F mutation, suggesting that these alleles may have functional complementation in myeloproliferative disease.

JAK2 (V617F) as an acquired somatic mutation and a secondary genetic event associated with disease progression in familial myeloproliferative disorders

BACKGROUND

A somatic gain-of-function mutation of the Janus kinase 2 (JAK2) gene has been identified in chronic myeloproliferative disorders, which appear to have a sporadic occurrence in most individuals. The authors studied the biologic significance of the JAK2 (V617F) mutation in familial myeloproliferative disorders.

METHODS

Twenty pedigrees with familial chronic myeloproliferative disorders were identified through an investigation of family history in 264 patients with sporadic myeloproliferative disorders. A quantitative real-time polymerase chain reaction (qRT-PCR)-based allelic discrimination assay was employed for the detection of the V617F mutation in circulating granulocytes and T lymphocytes. An analysis of X-chromosome inactivation pattern was performed in female patients.

RESULTS

Fourteen families had homogeneous phenotypes, and 6 families had mixed phenotypes. By using a qRT-PCR-based allelic discrimination assay, the JAK2 (V617F) mutation was detected in circulating granulocytes from 20 of 31 patients, but the mutation was not detected in T lymphocytes. Granulocyte mutant alleles ranged from 2.1% to 91.5% and, on average, increased with time. Discordant distribution of the JAK2 (V617F) mutation was observed in siblings with polycythemia vera. The proportion of granulocytes that carried the JAK2 (V617F) mutation was lower than the proportion of clonal granulocytes, as determined in an analysis of X-chromosome inactivation patterns in female patients.

CONCLUSIONS

The current findings indicated that the JAK2 (V617F) mutation represents an acquired somatic mutation in patients with familial chronic myeloproliferative disorders and probably occurs as a secondary genetic event in the background of preexisting clonal hematopoiesis. Thus, a genetic predisposition to acquisition of JAK2 (V617F) is inherited in families with myeloproliferative disorders.