JAK2 unmutated erythrocytosis: 2023 Update on diagnosis and management

Diagnostic Approaches to Investigate JAK2-Unmutated Erythrocytosis Based on a Single Tertiary Center Experience

INTRODUCTION

Erythrocytosis is attributed to various clinical and molecular factors. Many cases of JAK2-unmutated erythrocytosis remain undiagnosed. We investigated the characteristics and causes of JAK2-unmutated erythrocytosis.

METHODS

We assessed the clinical and laboratory results of patients with erythrocytosis without JAK2 mutations and performed targeted next-generation sequencing (NGS) panels for somatic and germline mutations.

RESULTS

In total, 117 patients with JAK2-unmutated erythrocytosis were included. The median hemoglobin and hematocrit levels were 17.9 g/dL and 53.4%, respectively. Erythropoietin levels were not below the reference range. Thrombotic events were reported in 17 patients (14.5%). Among JAK2-unmutated patients, 44 had undergone targeted panel sequencing consisting of myeloid neoplasm-related genes, and 16 had one or more reportable variants in ASXL1 (5/44), TET2, CALR, FLT3, and SH2B3 (2/44). Additional testing for germline causes revealed eight variants in seven genes in eight patients, including NF1, BPGM, EPAS1, PIEZO1, RHAG, SH2B3, and VHL genes. One NF1 pathogenic, one BPGM likely pathogenic, and six variants of undetermined significance were detected.

CONCLUSION

Somatic and germline mutations were identified in 36.4% and 33.3 % of the JAK2-unmutated group; most variants had unknown clinical significance. Not all genetic causes have been identified; comprehensive diagnostic approaches are crucial for identifying the cause of erythrocytosis.

Erythrocytosis: Diagnosis and investigation

An absolute erythrocytosis is present when the red cell mass is greater than 125% of the predicted. This is suspected when the hemoglobin or hematocrit is above the normal range. An erythrocytosis can be classified as primary or secondary and congenital or acquired. The commonest primary acquired disorder is polycythemia vera. The diagnostic criteria for PV have evolved over time and this is the main diagnosis managed in hematology clinics. There are a variety of rare congenital causes both primary and secondary. In particular in young patients and/or those with a family history a congenital cause is suspected. There remains a larger cohort with acquired erythrocytosis mainly with non-hematological pathology. In order to explore for a cause of erythrocytosis, measurement of the erythropoietin level is a first step. A low erythropoietin level indicates a primary cause and a normal or elevated level indicates a secondary etiology. Further investigation is then dictated by initial findings and includes mutational testing with PCR and NGS for those in whom a congenital cause is suspected. Following this possibly bone marrow biopsy, scans, and further investigation as indicated by history and initial findings. Investigation is directed toward the identification of those with a hematological disorder which would be best managed following guidelines in hematology clinics and referral elsewhere in those for whom there are non-hematological reasons for the elevated hemoglobin.

Zebrafish mutants in egln1 display a hypoxic response and develop polycythemia

AIMS

Prolyl hydroxylase domain 2 (PHD2), encoded by the Egln1 gene, serves as a pivotal regulator of the hypoxia-inducible factor (HIF) pathway and acts as a cellular oxygen sensor. Somatic inactivation of Phd2 in mice results in polycythemia and congestive heart failure. However, due to the embryonic lethality of Phd2 deficiency, its role in development remains elusive. Here, we investigated the function of two egln1 paralogous genes, egln1a and egln1b, in zebrafish.

MAIN METHODS

The egln1 null zebrafish were generated using the CRISPR/Cas9 system. Quantitative real-time PCR assays and Western blot analysis were employed to detect the effect of egln1 deficiency on the hypoxia signaling pathway. The hypoxia response of egln1 mutant zebrafish were assessed by analyzing heart rate, gill agitation frequency, and blood flow velocity. Subsequently, o-dianisidine staining and in situ hybridization were used to investigate the role of egln1 in zebrafish hematopoietic function.

KEY FINDINGS

Our data show that the loss of egln1a or egln1b individually has no visible effects on growth rate. However, the egln1a; egln1b double mutant displayed significant growth retardation and elevated mortality at around 2.5 months old. Both egln1a-null and egln1b-null zebrafish embryo exhibited enhanced tolerance to hypoxia, systemic hypoxic response that include hif pathway activation, increased cardiac activity, and polycythemia.

SIGNIFICANCE

Our research introduces zebrafish egln1 mutants as the first congenital embryonic viable systemic vertebrate animal model for PHD2, providing novel insights into hypoxic signaling and the progression of PHD2- associated disease.

Erythrocytosis and CKD: A Review

Erythrocytosis or polycythemia is defined as an increase in red blood cell concentration above the age- and sex-specific normal levels. Unlike anemia, which is very common in patients with chronic kidney disease (CKD), erythrocytosis is less frequent but requires specific understanding by health care professionals in order to provide the best care. Erythrocytosis, especially when undiagnosed and untreated, can lead to serious thrombotic events and higher mortality. Classic causes of erythrocytosis associated with CKD include cystic kidney diseases, kidney or other erythropoietin-secreting neoplasms, high-altitude renal syndrome, overdosage of erythropoietin-stimulating agents, androgen therapy, heavy smoking, chronic lung disease, obstructive sleep apnea, IgA nephropathy, post-kidney transplant erythrocytosis, renal artery stenosis, and congenital etiologies. After ruling out the common acquired causes of erythrocytosis and/or in the presence of suggestive parameters, primary erythrocytosis or polycythemia vera (PV) should be considered, and patients should be screened for JAK2V617F somatic mutation. The newest entity inducing erythrocytosis is linked to the use of sodium/glucose cotransporter 2 (SGLT2) inhibitors that hypothetically activate hypoxia-inducible factor 2α (HIF-2α) and in some cases unmask PV. This Review focuses on the pathogenesis, renal manifestations and management of PV, the pathophysiology of erythrocytosis induced by SGLT2 inhibitors and the relevance of timely JAK2 mutation screening in these patients.

Predictors of Progression in a Series of 81 Adult Patients Surgically Managed for an Intracranial Hemangioblastoma: Implications for the Postoperative Follow-Up

The aim was to identify predictors of progression in a series of patients managed for an intracranial hemangioblastoma, in order to guide the postoperative follow-up modalities. The characteristics of 81 patients managed for an intracranial hemangioblastoma between January 2000 and October 2022 were retrospectively analyzed. The mean age at diagnosis was of 48 ± 16 years. Eleven (14%) patients had von Hippel-Lindau disease. The most frequent tumor location was the cerebellar hemispheres (n = 51, 65%) and 11 (14%) patients had multicentric hemangioblastomas. A gross total resection was achieved in 75 (93%) patients. Eighteen (22%) patients had a local progression, with a median progression-free survival of 56 months 95% CI [1;240]. Eleven (14%) patients had a distant progression (new hemangioblastoma and/or growth of an already known hemangioblastoma). Local progression was more frequent in younger patients (39 ± 14 years vs. 51 ± 16 years; p = 0.005), and those with von Hippel-Lindau disease (n = 8, 44% vs. n = 3, 5%, p < 0.0001), multiple cerebral locations (n = 3, 17% vs. n = 2, 3%, p = 0.02), and partial tumoral resection (n = 4, 18% vs. n = 1, 2%, p = 0.0006). Therefore, it is advisable to propose a postoperative follow-up for at least 10 years, and longer if at least one predictor of progression is present.

TNF-α is a predictive marker in distinguishing myeloproliferative neoplasm and idiopathic erythrocytosis/thrombocytosis: development and validation of a non-invasive diagnostic model

Purpose

Philadelphia-chromosome negative myeloproliferative neoplasms (MPN) exhibit phenotypic similarities with JAK/STAT-unmutated idiopathic erythrocytosis and thrombocytosis (IE/IT). We aimed to develop a clinical diagnostic model to discern MPN and IE/IT.

Methods

A retrospective study was performed on 77 MPN patients and 32 IE/IT patients in our center from January 2018 to December 2023. We investigated the role of hemogram, cytokine and spleen size in differentiating MPN and IE/IT among newly onset erythrocytosis and thrombocytosis patients. Independent influencing factors were integrated into a nomogram for individualized risk prediction. The calibration and discrimination ability of the model were evaluated by concordance index (C-index), calibration curve.

Results

MPN had significantly higher TNF-α level than IE/IT, and the TNF-α level is correlated with MF-grade. Multivariable analyses revealed that TNF-α, PLT count, age, size of spleen were independent diagnostic factors in differentiating MPN and IE/IT. Nomograms integrated the above 4 factors for differentiating MPN and IE/IT was internally validated and had good performance, the C-index of the model is 0.979.

Conclusion

The elevation of serum TNF-α in MPN patients is of diagnostic significance and is correlated with the severity of myelofibrosis. The nomogram incorporating TNF-α with age, PLT count and spleen size presents a noteworthy tool in the preliminary discrimination of MPN patients and those with idiopathic erythrocytosis or thrombocytosis. This highlights the potential of cytokines as biomarkers in hematologic disorders.

Idiopathic erythrocytosis: A diagnostic and management challenge with emerging areas for exploration

Despite published algorithms for approaching the work-up of erythrocytosis, a significant proportion of patients are left with uncertainty as to its aetiology and prognosis. The term 'idiopathic erythrocytosis' (IE) is applied when known primary and secondary aetiologies have been ruled out. However, the assignment of secondary aetiologies is not always straightforward or evidence based, which can lead to misdiagnosis and heterogeneity in cohort studies. Furthermore, new studies have identified germline or somatic mutations that may affect prognosis. Epidemiological and cohort data are inconsistent as to whether IE increases the risk for complications such as arterial and venous thromboembolism, clonal transformation or comorbid conditions. Randomized trials assessing the role of phlebotomy for long-term management of IE have not been performed, so treatment remains a vexing problem for clinicians. Standardization of terminology and testing strategies, including comprehensive genetic screening in clinical research, are key to refining our understanding of IE.

Polycythemia vera: 2024 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) is a JAK2-mutated myeloproliferative neoplasm characterized by clonal erythrocytosis; other features include leukocytosis, thrombocytosis, splenomegaly, pruritus, constitutional symptoms, microcirculatory disturbances, and increased risk of thrombosis and progression into myelofibrosis (post-PV MF) or acute myeloid leukemia (AML).

DIAGNOSIS

A working diagnosis is considered in the presence of a JAK2 mutation associated with hemoglobin/hematocrit levels of >16.5 g/dL/49% in men or 16 g/dL/48% in women; morphologic confirmation by bone marrow examination is advised but not mandated.

CYTOGENETICS

Abnormal karyotype is seen in 15%-20% of patients with the most frequent sole abnormalities being +9 (5%), loss of chromosome Y (4%), +8 (3%), and 20q- (3%).

MUTATIONS

Over 50% of patients harbor DNA sequence variants/mutations other than JAK2, with the most frequent being TET2 (18%) and ASXL1 (15%). Prognostically adverse mutations include SRSF2, IDH2, RUNX1, and U2AF1, with a combined incidence of 5%-10%.

SURVIVAL AND PROGNOSIS

Median survival is ⁓15 years but exceeds 35 years for patients aged ≤40 years. Risk factors for survival include older age, leukocytosis, abnormal karyotype, and the presence of adverse mutations. Twenty-year risk for thrombosis, post-PV MF, or AML are ⁓26%, 16% and 4%, respectively.

RISK FACTORS FOR THROMBOSIS

Two risk categories are considered: high (age >60 years or thrombosis history) and low (absence of both risk factors). Additional predictors for arterial thrombosis include cardiovascular risk factors and for venous thrombosis higher absolute neutrophil count and JAK2V617F allele burden.

TREATMENT

Current goal of therapy is to prevent thrombosis. Periodic phlebotomy, with a hematocrit target of <45%, combined with once- or twice-daily aspirin (81 mg) therapy, absent contraindications, is the backbone of treatment in all patients, regardless of risk category. Cytoreductive therapy is reserved for high-risk disease with first-line drugs of choice being hydroxyurea and pegylated interferon-α and second-line busulfan and ruxolitinib. In addition, systemic anticoagulation is advised in patients with venous thrombosis history.

ADDITIONAL TREATMENT CONSIDERATIONS

At the present time, we do not consider a drug-induced reduction in JAK2V617F allele burden, which is often incomplete and seen not only with peg-IFN but also with ruxolitinib and busulfan, as an indicator of disease-modifying activity, unless accompanied by cytogenetic and independently-verified morphologic remission. Accordingly, we do not use the specific parameter to influence treatment choices. The current review also includes specific treatment strategies in the context of pregnancy, splanchnic vein thrombosis, pruritus, perioperative care, and post-PV MF.

Contribution of lowered hemoglobin threshold value in the diagnosis of polycythemia vera: Comparison of 2016 and 2008 WHO criteria

Polycythemia vera (PV) diagnosis remains a difficult task despite various updates in the 2016 World Health Organization (WHO) diagnostic criteria compared to 2008 criteria. This study aimed to examine the biochemical and clinical features of patients diagnosed with PV using the WHO 2016 criteria but would have been missed by the WHO 2008 criteria, and to ascertain the impact of the lowered thresholds on PV diagnosis. A total of 229 patients with suspected myeloproliferative neoplasms were included in this cross sectional study. The study group was divided with regard to hemoglobin values. Group A consisted of 126 patients with hemoglobin values of ≤ 18.5 g/dL in males and ≤ 16.5 g/dL in females. Group B comprised 103 patients with hemoglobin values of > 18.5 g/dL in males and > 16.5 g/dL in females. The number of PV diagnoses increased to 145 from 87 (increased by 66.67%) when the 2016 diagnostic criteria were employed rather that the 2008 criteria. Mean age and the frequency of female subjects were lower in Group A compared to Group B. The groups were similar in terms of chronic obstructive pulmonary disease/obstructive sleep apnea syndrome, spleen status, smoking status, and mean corpuscular volume, white blood count, neutrophil, eosinophil and platelet values. red blood cells and lactate dehydrogenase values were significantly higher, while lymphocyte counts were significantly lower in Group B. With the introduction of WHO 2016 criteria, we found a significant increase in the number of patients who were candidates for PV testing and were ultimately diagnosed with PV. These findings support the diagnostic value of the 2016 WHO criteria, and by extension, the lowered thresholds for detection of patients requiring further analysis.

Germline JAK2 E846D Substitution as the Cause of Erythrocytosis?

The discovery in 2005 of the JAK2 V617F gain-of-function mutation in myeloproliferative neoplasms and more particularly in polycythemia vera has deeply changed the diagnostic and therapeutic approaches to polycythemia. More recently, the use of NGS in routine practice has revealed a large number of variants, although it is not always possible to classify them as pathogenic. This is notably the case for the JAK2 E846D variant for which for which questions remain unanswered. In a large French national cohort of 650 patients with well-characterized erythrocytosis, an isolated germline heterozygous JAK2 E846D substitution was observed in only two cases. For one of the patients, a family study could be performed, without segregation of the variant with the erythrocytosis phenotype. On the other hand, based on the large UK Biobank resource cohort including more than half a million UK participants, the JAK2 E846D variant was found in 760 individuals, associated with a moderate increase in hemoglobin and hematocrit values, but with no significant difference to the mean values of the rest of the studied population. Altogether, our data as well as UK Biobank cohort analyses suggest that the occurrence of an absolute polycythemia cannot be attributed to the sole demonstration of an isolated JAK2 E846D variant. However, it must be accompanied by other stimuli or favoring factors in order to generate absolute erythrocytosis.