Importance of Sequencing HBA1, HBA2 and HBB Genes to Confirm the Diagnosis of High Oxygen Affinity Hemoglobin

High oxygen affinity hemoglobin (HOAH) is the main cause of constitutional erythrocytosis. Mutations in the genes coding the alpha and beta globin chains (HBA1, HBA2 and HBB) strengthen the binding of oxygen to hemoglobin (Hb), bringing about tissue hypoxia and a secondary erythrocytosis. The diagnosis of HOAH is based upon the identification of a mutation in HBA1, HBA2 or HBB in specialized laboratories. Phenotypic studies of Hb are also useful, but electrophoretic analysis can be normal in 1/3 of cases. The establishment of the dissociation curve of Hb can be used as another screening test, a shift to the left indicating an increased affinity for Hb. The direct measurement of venous P50 using a Hemox Analyzer is of great importance, but due to specific analytic conditions, it is only available in a few specialized laboratories. Alternatively, an estimated measurement of the P50 can be obtained in most of the blood gas analyzers on venous blood. The aim of our study was therefore to determine whether a normal venous P50 value could rule out HOAH. We sequenced the HBB, HBA1 and HBA2 genes of 75 patients with idiopathic erythrocytosis. Patients had previously undergone an exhaustive medical check-up after which the venous P50 value was defined as normal. Surprisingly, sequencing detected HOAH in three patients (Hb Olympia in two patients, and Hb St Nazaire in another). A careful retrospective examination of their medical files revealed that (i) one of the P50 samples was arterial; (ii) there was some air in another sample; and (iii) the P50 measurement was not actually done in one of the patients. Our study shows that in real life conditions, due to pre-analytical contingencies, a venous P50 value that is classified as being normal may not be sufficient to rule out a diagnosis of HOAH. Therefore, we recommend the systematic sequencing of the HBB, HBA1 and HBA2 genes in the exploration of idiopathic erythrocytosis.

Single Centre Analysis of JAK2 V617F and Exon 12 Negative Idiopathic Erythrocytosis

Introduction The molecular categorisation of myeloproliferative neoplasms (MPNs) has changed the landscape of diagnosis and treatment. Polycythaemia vera (PV) is characterised by red blood cell proliferation and JAK2 V617F or Exon 12 mutations in up to 98% of patients 1. However, some patients without such mutations have an arduous diagnostic course with varying management and prognostic outcomes 2. We present our experience in managing this challenging cohort and aim to illuminate a potential diagnostic pathway for patients. Method We searched electronic records of patients attending haematology clinics over the last 20 years at University College Hospital with a prior diagnosis of PV / erythrocytosis (presenting with raised Haemoglobin (Hb) &/ Haematocrit (Hct)) with no evidence of JAK2 exon 12 or 14 mutations on bone marrow or peripheral blood molecular analysis (multiplex PCR sensitivity 0.1%). We reviewed their diagnostic workup, which included full blood count & where available, bone marrow myeloid (Illumina TruSight Myeloid) & erythroid next generation sequencing (NGS) panels. Results 37 patients with JAK2 V617F & Exon 12 mutation negative erythrocytosis were identified. Patients were categorised in to 3 groups 2; idiopathic erythrocytosis (IE), secondary polycythaemia (SP) & high affinity haemoglobinopathies (HAH); patient characteristics are summarised in Table 1. The median age of IE & HAH was younger, their presenting Hb/Hct levels was higher compared to SP, with a male predominance. Constitutional symptoms were only reported in the IE cohort. Erythropoietin (EPO) was elevated in HAH & IE patients but within normal range in SP. Thrombotic events occurred in all cohorts, most frequently in IE. Splenomegaly was reported in 4/21 IE, 1/13 SP, but was not a feature in HAH patients. When performed, IE red cell mass (RCM) studies were raised but within normal range in SP patients. Table 2 details IE cohort erythroid mutations. Myeloid NGS only identified MPL and BCOR mutations of pathogenic significance and multiple single nucleotide polymorphisms of no known significance. No abnormalities were demonstrated in 15% of SP patients that underwent bone marrow myeloid mutational analysis. Venesections (VS) were instigated in 95% of the IE cohort, antiplatelets (AP) in 52%, anticoagulation (AC) in 14% and cytoreductive therapy (CT) in 19% due to intolerance/failure of VS. VS programme was instigated in 46% of SP patients, AP in 7% and AC in 47%. Discussion The median age of our IE cohort was 48 yrs with a 19% incidence of thrombosis. Where performed, bone marrow histology demonstrated hypercellularity but was not consistent with MPN diagnostic criteria. Myeloid NGS panel mutations such as BCOR may represent clonal haematopoieis of indeterminate potential. Heterozygous VHL C598T & C376A mutations, in keeping with Chuvash polycythaemia, were demonstrated. Mutations in EGLN1 & BPGM,were detected in our patients, however there was an absence of correlating haematological parameters or family history to support a diagnosis of congenital erythrocytosis (2). Variants of unknown significance were also detected in SH2B3, BMP6 & EGLN3 gene duplication. SP patients were older (median age 68 years) and where performed had normal RCM and no myeloid mutations identified. The initial approach adopted at our centre for diagnosing and managing JAK2 V617F & Exon 12 negative erythocytosis begins with clinical evaluation for secondary causes. This is followed by assessment of EPO level, RCM study, extended molecular mutational analysis involving screening for high affinity haemoglobins, congenital erythrocytosis and bone marrow histology. Where patients are symptomatic or considered at high risk for thrombosis, we venesect to a personalised target and patients are offered AP and/or AC. CT is instigated where VS is not tolerated or ineffective, however this approach is not corroborated in the literature. Our experience highlights the clinical heterogeneity of JAK2 negative erythrocytosis and the need to develop a robust and systematic diagnostic and treatment algorithm with further clarification of the role of molecular profiling. 1. William W, Kralovics R. Genetic basis and molecular pathophysiology of classical myeloproliferative neoplasms. Blood. 2017 Feb; 129(6):667-679 2. McMullin MF. Idiopathic erythrocytosis: a disappearing entity. Hematology Am Soc Educ Program. 2009; 2009(1):629-635 Figure 1 Figure 1. Disclosures Sekhar: Novartis: Consultancy, Research Funding.

Idiopathic Erythrocytosis: Vascular Complications

Idiopathic Erythrocytosis (IE) is a diagnosis of exclusion once primary and secondary causes have been eliminated; yet IE remains an enigmatic disorder. Published series from decades ago (Modan & Modan J. Hematol [1968] 14:375; Pearson & Wetherly-Mein, Clin.Lab Hematol. [1974] 1:189) have reported high rates of vascular complications (46%) and advise phlebotomy to keep the hematocrit to less than 45%. A More recent series (McMullin B.J. Hematol. [2005] 130:174) advise no need for phlebotomy in patients with no co-morbidities such as vascular disease, diabetes, or hypertension. In an attempt to determine some practice guidelines, we undertook a retrospective analysis of patients identified with IE within our practice and to quantify the rates of vascular complications, if any. From January 1, 2016 to December 31. 2020 99 patients were referred because of erythrocytosis. Twenty of these 99 patients had polycythemia rubra vera and 77 had secondary erythrocytosis ( 64 males, 13 females, median age 61 years). Of these 77 patients with secondary erythrocytosis, 40 had obstructive sleep apnea, 10 men abused testosterone, and 1 patient each was either post splenectomy or post kidney transplant, 1 patient had a renal cell carcinoma, and 1 patient had familial erythrocytosis. Twenty patients were identified as having IE and all 20 did not have a JAK2 mutation. There 13 males and 7 females with a median age of 63 years (range 31-76). The median hemoglobin was 17.2 gm/dl and the median hematocrit was 51.2 (range 15.0 to 18.4 and 49% to 55% respectively). The median erythropoietin level was 9.9 mu/ml (range 5-38.5). Two of the 20 patients underwent therapeutic phlebotomy and developed no vascular complications. Eighteen patients were simply followed with phlebotomy despite having comorbidities of hypertension, increased BMI, type II diabetes, and none developed vascular complications. IE remain an enigmatic disorder that requires uniform diagnostic criteria as well as uniform practice guidelines; however, given our retrospective review, we do not believe that therapeutic phlebotomy is justified. Disclosures No relevant conflicts of interest to declare.

Molecular Pathways Involved in the Development of Congenital Erythrocytosis

Patients with idiopathic erythrocytosis are directed to targeted genetic testing including nine genes involved in oxygen sensing pathway in kidneys, erythropoietin signal transduction in pre-erythrocytes and hemoglobin-oxygen affinity regulation in mature erythrocytes. However, in more than 60% of cases the genetic cause remains undiagnosed, suggesting that other genes and mechanisms must be involved in the disease development. This review aims to explore additional molecular mechanisms in recognized erythrocytosis pathways and propose new pathways associated with this rare hematological disorder. For this purpose, a comprehensive review of the literature was performed and different in silico tools were used. We identified genes involved in several mechanisms and molecular pathways, including mRNA transcriptional regulation, post-translational modifications, membrane transport, regulation of signal transduction, glucose metabolism and iron homeostasis, which have the potential to influence the main erythrocytosis-associated pathways. We provide valuable theoretical information for deeper insight into possible mechanisms of disease development. This information can be also helpful to improve the current diagnostic solutions for patients with idiopathic erythrocytosis.

Congenital erythrocytosis – A condition behind recurrent thromboses: A case report and literature review

Congenital erythrocytosis (CE) is an extremely rare disease and an infrequent cause of heamoglobin and haematocrit elevation. Genetic testing of CE is not widely available. Patients in whom a cause of erythrocytosis is not identified are classified as idiopathic erythrocytosis (IE) patients. In some types of CE thrombotic events have been reported but there is little hard evidence to advise on management in asymptomatic patients. Similarly is true for patients with IE. We describe a young patient who suffered several thromboembolic complications before the diagnosis of CE type 4 was established.

Postoperative Pharmacologic Anticoagulation following Temporal Lobe Resection of a Gliosarcoma in a Hypercoagulable Patient

Gliosarcomas are a rare subtype of glioblastomas associated with high rates of malignancy-associated venous thromboembolism (VTE). VTE risk is further increased in hypercoagulable patients upon discontinuing pharmacologic anticoagulation for surgery. We present a 60-year old obese male with history of hypercoagulability on apixaban who developed extensive thrombosis following resection of a gliosarcoma. Prior to temporal lobe resection, apixaban was discontinued and an IVC filter placed. On postoperative day 4, imaging revealed thrombosis above the IVC filter extending to the bilateral common, internal and external iliac, and femoral veins, requiring immediate anticoagulation and suction thrombectomy. Clinicians must balance the risk of VTE and intracerebral hemorrhage following neurosurgical. While withholding pharmacologic VTE is standard, hypercoagulable patients may benefit from pharmacologic prophylaxis postoperatively. Patients with multiple risk factors including malignancies with high rates VTE, like gliosarcomas, medical and hematological conditions, including idiopathic erythrocytosis, and history of VTE may benefit from earlier pharmacologic prophylaxis.

Clinical Features of Idiopathic Erythrocytosis in a Racially Diverse Population

Background: Idiopathic erythrocytosis (IE) is an entity characterized by a persistently elevated hemoglobin, variable erythropoietin (EPO) level, absence of janus kinase 2 (JAK2) mutations suggestive of polycythemia vera (PV) and no identifiable secondary cause. Previous studies have compared IE to PV, showing a lower incidence of venous thrombosis and leukemic transformation in IE but similar incidence of arterial events. PV is known to be associated with constitutional symptoms and splenomegaly, while hereditary erythrocytosis can be associated with recurrent headaches and fatigue. A comprehensive assessment of clinical features including symptoms in IE has not been performed. Methods: Patients signed informed consent to participate in an observational study approved by the Institutional Review Board. Enrollment criteria included: age 18 years or older; hemoglobin level greater than 16 g/dL on two occasions at least 3 months apart or greater than 15 g/dL if undergoing phlebotomy; negative testing for JAK2 mutations; and negative work up for secondary causes of erythrocytosis. Baseline assessment included history and physical exam, vital signs, pulse oximetry, and body mass index. Baseline laboratory exams included a complete blood cell count, complete metabolic panel, C-reactive protein, iron panel, ferritin, hemoglobin A1C, erythropoietin level. Abdominal ultrasound was performed to evaluate for splenomegaly. The Myeloproliferative Symptom Assessment Form (MPN-SAF) was used to assess for the presence and severity of a broad range of symptoms that may be expected to occur in patients with IE. The MPN-SAF was administered at baseline and every 6 months thereafter. Results: 35 patients had data available for analysis. Patient characteristics are shown in Table 1. The most prevalent co-morbid conditions were those known to be associated with cardiovascular disease risk and metabolic syndrome, including hepatic steatosis identified on abdominal ultrasound in 63% of patients. Three (8.6%) patients had a history of venous or arterial thrombosis. Two (5.8%) patients had a history of lymphoma (NK/T-cell and Hodgkin). Three patients (8.6%) had a first-degree relative with a myeloproliferative neoplasm (chronic myelomonocytic leukemia, essential thrombocytosis and polycythemia vera) and one patient had a son with IE and history of stroke. 16 (46%) patients were taking aspirin and 11 (31%) had undergone phlebotomy within 3 months of study enrollment. Patients reported the following symptoms on the MPN-SAF at baseline: fatigue (77%), early satiety (57%), difficulty sleeping (57%), numbness/tingling (51%), headaches (49%), concentration problems (40%), itching (40%), bone pain (37%), night sweats (37%), depression (37%), abdominal pain (37%), abdominal discomfort (37%), inactivity (37%), problems with sexual desire/function (34%), dizziness/lightheadedness (31%), cough (26%), fever (17%), and unintentional weight loss (17%). Fatigue carried the highest average symptom intensity (3.77, SD 3.17). Discussion: In this study, we describe the clinical features associated with IE in a multiracial cohort. Patients with IE are frequently symptomatic and have a high incidence of hepatic steatosis by ultrasound. Disclosures No relevant conflicts of interest to declare.