Familial polycythemia caused by a novel mutation in the beta globin gene: essential role of P50 in evaluation of familial polycythemia

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.

JAK2 unmutated erythrocytosis: 2023 Update on diagnosis and management

DISEASE OVERVIEW

JAK2 unmutated or non-polycythemia vera (PV) erythrocytosis encompasses a heterogenous spectrum of hereditary and acquired entities.

DIAGNOSIS

Foremost in the evaluation of erythrocytosis is the exclusion of PV through JAK2 (inclusive of exons 12-15) mutation screening. Initial assessment should also include gathering of previous records on hematocrit (Hct) and hemoglobin (Hgb) levels, in order to streamline the diagnostic process by first distinguishing longstanding from acquired erythrocytosis; subsequent subcategorization is facilitated by serum erythropoietin (Epo) measurement, germline mutation screening, and review of historical data, including comorbid conditions and medication list. Hereditary erythrocytosis constitutes the main culprit in the context of longstanding erythrocytosis, especially when associated with a positive family history. In this regard, a subnormal serum Epo level suggests EPO receptor mutation. Otherwise, considerations include those associated with decreased (high oxygen affinity Hgb variants, 2,3-bisphosphoglycerate deficiency, PIEZO1 mutations, methemoglobinemia) or normal oxygen tension at 50% Hgb saturation (P50). The latter include germline oxygen sensing pathway (HIF2A-PHD2-VHL) and other rare mutations. Acquired erythrocytosis commonly results from central (e.g., cardiopulmonary disease, high-altitude habitat) or peripheral (e.g., renal artery stenosis) hypoxia. Other noteworthy conditions associated with acquired erythrocytosis include Epo-producing tumors (e.g., renal cell carcinoma, cerebral hemangioblastoma) and drugs (e.g., testosterone, erythropoiesis stimulating agents, sodium-glucose cotransporter-2 inhibitors). Idiopathic erythrocytosis is an ill-defined terminology that presumes the existence of an increased Hgb/Hct level without an identifiable etiology. Such classification often lacks accounting for normal outliers and is marred by truncated diagnostic evaluation.

MANAGEMENT

Current consensus treatment guidelines are not supported by hard evidence and their value is further undermined by limited phenotypic characterization and unfounded concerns for thrombosis. We are of the opinion that cytoreductive therapy and indiscriminate use of phlebotomy should be avoided in the treatment of non-clonal erythrocytosis. However, it is reasonable to consider therapeutic phlebotomy if one were to demonstrate value in symptom control, with frequency determined by symptoms rather than Hct level. In addition, cardiovascular risk optimization and low dose aspirin is often advised.

FUTURE DIRECTIONS

Advances in molecular hematology might result in better characterization of "idiopathic erythrocytosis" and expansion of the repertoire for germline mutations in hereditary erythrocytosis. Prospective controlled studies are needed to clarify potential pathology from JAK2 unmutated erythrocytosis, as well as to document the therapeutic value of phlebotomy.

Attenuated cardiac autonomic function in humans with high-affinity hemoglobin and compensatory polycythemia

During hypoxic exposure, humans with high-affinity hemoglobin (and compensatory polycythemia) have blunted increases in heart rate compared with healthy humans with typical oxyhemoglobin dissociation curves. This response may be associated with altered autonomic control of heart rate. Our hypothesis-generating study aimed to investigate cardiac baroreflex sensitivity and heart rate variability among nine humans with high-affinity hemoglobin [6 females, O2 partial pressure at 50% [Formula: see text] (P50) = 16 ± 1 mmHg] compared with 12 humans with typical affinity hemoglobin (6 F, P50 = 26 ± 1 mmHg). Participants breathed normal room air for a 10-min baseline, followed by 20 min of isocapnic hypoxic exposure, designed to lower the arterial partial pressure O2 ([Formula: see text]) to ∼50 mmHg. Beat-by-beat heart rate and arterial blood pressure were recorded. Data were averaged in 5-min periods throughout the hypoxia exposure, beginning with the last 5 min of baseline in normoxia. Spontaneous cardiac baroreflex sensitivity and heart rate variability were determined using the sequence method and the time and frequency domain analyses, respectively. Cardiac baroreflex sensitivity was lower in humans with high-affinity hemoglobin than controls at baseline and during isocapnic hypoxic exposure (normoxia: 7 ± 4 vs. 16 ± 10 ms/mmHg, hypoxia minutes 15-20: 4 ± 3 vs. 14 ± 11 ms/mmHg; group effect: P = 0.02, high-affinity hemoglobin vs. control, respectively). Heart rate variability calculated in both the time (standard deviation of the N-N interval) and frequency (low frequency) domains was lower in humans with high-affinity hemoglobin than in controls (all P < 0.05). Our data suggest that humans with high-affinity hemoglobin may have attenuated cardiac autonomic function.

JAK2 unmutated erythrocytosis: current diagnostic approach and therapeutic views

JAK2 unmutated or non-polycythemia vera (PV) erythrocytosis encompasses both hereditary and acquired conditions. A systematic diagnostic approach begins with documentation of historical hematocrit (Hct)/hemoglobin (Hgb) measurements and classification of the process as life-long/unknown duration or acquired. Further investigation in both categories is facilitated by determination of serum erythropoietin level (EPO). Workup for hereditary/congenital erythrocytosis requires documentation of family history and laboratory screening for high-oxygen affinity hemoglobin variants, 2, 3 biphosphoglycerate deficiency, and germline mutations that are known to alter cellular oxygen sensing (e.g., PHD2, HIF2A, VHL) or EPO signaling (e.g., EPOR mutations); the latter is uniquely associated with subnormal EPO. Acquired erythrocytosis is often elicited by central or peripheral hypoxia resulting from cardiopulmonary disease/high-altitude dwelling or renal artery stenosis, respectively; EPO in the former instance is often normal (compensated by negative feed-back). Other conditions associated with acquired erythrocytosis include EPO-producing tumors and the use of drugs that promote erythropoiesis (e.g., testosterone, erythropoiesis stimulating agents). "Idiopathic erythrocytosis" loosely refers to an otherwise not explained situation. Historically, management of non-PV erythrocytosis has been conflicted by unfounded concerns regarding thrombosis risk, stemming from limited phenotypic characterization, save for Chuvash polycythemia, well-known for its thrombotic tendency. In general, cytoreductive therapy should be avoided and phlebotomy is seldom warranted where frequency is determined by symptom control rather than Hct threshold. Although not supported by hard evidence, cardiovascular risk optimization and low-dose aspirin use are often advised. Application of modern genetic tests and development of controlled therapeutic intervention trials are needed to advance current clinical practice.

Bisphosphoglycerate Mutase Deficiency Protects against Cerebral Malaria and Severe Malaria-Induced Anemia

The replication cycle and pathogenesis of the Plasmodium malarial parasite involves rapid expansion in red blood cells (RBCs), and variants of certain RBC-specific proteins protect against malaria in humans. In RBCs, bisphosphoglycerate mutase (BPGM) acts as a key allosteric regulator of hemoglobin/oxyhemoglobin. We demonstrate here that a loss-of-function mutation in the murine Bpgm (Bpgm^L166P) gene confers protection against both Plasmodium-induced cerebral malaria and blood-stage malaria. The malaria protection seen in Bpgm^L166P mutant mice is associated with reduced blood parasitemia levels, milder clinical symptoms, and increased survival. The protective effect of Bpgm^L166P involves a dual mechanism that enhances the host's stress erythroid response to Plasmodium-driven RBC loss and simultaneously alters the intracellular milieu of the RBCs, including increased oxyhemoglobin and reduced energy metabolism, reducing Plasmodium maturation, and replication. Overall, our study highlights the importance of BPGM as a regulator of hemoglobin/oxyhemoglobin in malaria pathogenesis and suggests a new potential malaria therapeutic target.

[A new case of rare erythrocytosis due to EGLN1 mutation with review of the literature]

INTRODUCTION

The origin of polycythemia is often simple to detect. Sometimes it is necessary to look for hereditary forms, the decisive parameters being the dosage of erythropoietin and the measurement of the oxygen dissociation curve (P50). These rare diseases are related to high oxygen-affinity haemoglobins, abnormalities of the erythropoietin receptor or dysfunction of the HIF (hypoxia-inducible factor) pathway.

CASE REPORT

We report the case of a 56-year-old patient with unexplained polycythemia associated with normal serum erythropoietin and normal P50, in whom the never previously described mutation c.400C>T(p.Gln134*) on exon 1 in the EGLN1 gene (encoding PHD2) was found.

CONCLUSION

In the face of an unexplained polycythemia a good cooperation between clinicians and biologists is necessary to be able to characterize rare hereditary pathologies.

Mild erythrocytosis as a presenting manifestation of PIEZO1 associated erythrocyte volume disorders

Piezo1, encoded by the gene PIEZO1, is an erythrocytic cellular membrane mechanoactivated cation channel. Mutations have been implicated in erythrocyte volume disorders (EVDs)-especially hereditary xerocytosis (HX)/dehydrated stomatocytosis (DHS). We identified three patients, all with novel PIEZO1 mutations, but only one displaying the HX/DHS phenotype. Retrospective review of three cases. Osmotic gradient red cell deformability (Osmoscan) was assessed via the Technicon Ektacytometer. Red cell band 3 content was estimated using Eosin-5'-Maleimide staining. Patient 1 was evaluated for polycythemia. Osmoscans suggested mild spherocytosis; a novel PIEZO1 mutation (p.Thr1589Ile, exon 35) was identified, causing mild erythrocytosis without hemolytic anemia. Patient 2 was evaluated for macrocytosis/reticulocytosis, normal-to-high hemoglobin, and indirect hyperbilirubinemia. Osmoscans suggested increased cellular hydration; a second novel PIEZO1 mutation (p.Arg1728Cys, exon 37) was identified, resulting in overhydrated stomatocytosis with well-compensated hemolysis. Patient 3 was evaluated for indirect hyperbilirubinemia only. Osmoscans suggested dehydrated stomatocytosis (DHS, xerocytosis); a third novel PIEZO1 mutation (p.Arg2279Cys, exon 47) was identified. All three patients' blood smears demonstrated stomatocytes and spherocytes. EVDs may be underdiagnosed due to the lack of "expected" anemia in a hemolytic disorder; two of three patients had high hemoglobin and red cell counts and one had high normal values for both parameters and the presence of stomatocytes/dehydrated cells lead to identification of causative PIEZO1 mutations. PIEZO1-associated EVDs may be more common than previously suspected and should be included in the diagnostic algorithms for mild erythrocytosis/unexplained jaundice.

Heterozygous Hemoglobin Sherwood Forest Causing Polycythemia

Hemoglobin (Hb) Sherwood Forest is a rare high-affinity hemoglobin first described in 1977, arising from an Arg to Thr substitution at codon 104 of the beta chain. This hemoglobin variant has been identified in few individuals and has been associated with a compensatory erythrocytosis in the homozygous state. Prior scarce case reports have noted that heterozygotes for this variant are phenotypically normal. Here we present a patient who was evaluated in our hematology clinic for chronic erythrocytosis and was found to be heterozygous for Hb Sherwood Forest. No other primary or secondary cause of his polycythemia was identified. This is the first described case of heterozygous Hemoglobin Sherwood Forest causing erythrocytosis.

Hb San Cataldo [β144(HC1)Lys→Thr; HBB: C.434A > C]: A New Hemoglobin Variant with Increased Affinity for Oxygen

A 59-year-old Italian woman came to our center for revaluation of a previous diagnosis of polycythemia vera. The patient presented with a lifelong history of polycythemia, no increase in white blood cells (WBCs) and platelets, and a negative bone marrow biopsy. Analysis of hemoglobin (Hb) fractions showed an abnormal fast moving Hb component. We aimed to determine if this variant was the cause of polycythemia in this patient. A complete blood count (CBC) was performed by an automated cell counter and Hb fractions were determined by high performance liquid chromatography (HPLC). Standard stability tests and oxygen affinity evaluation were also performed. Genomic DNA was extracted from peripheral blood leukocytes using the phenol chloroform method and the entire β-globin gene was analyzed by direct sequencing. At the hematological level, no anemia or hemolysis was observed but an abnormal Hb fraction was detected using cation exchange HPLC. Molecular analysis of the β-globin gene showed heterozygosity for an AAG > ACG substitution at codon 144, resulting in a Lys→Thr amino acid replacement. We demonstrated that this is a new Hb variant with increased oxygen affinity. Its altered physiology is caused by the reduction of 2,3-diphosphoglycerate (2,3-DPG) effects, due to an amino acid substitution in the central pocket near the C-terminal of the β chain. We called this new variant Hb San Cataldo for the native city of proband.

Raised HIF1α during normoxia in high altitude pulmonary edema susceptible non-mountaineers

High altitude pulmonary edema (HAPE) susceptibility is associated with EGLN1 polymorphisms, we hypothesized that HAPE-susceptible (HAPE-S, had HAPE episode in past) subjects may exhibit abnormal HIF1α levels in normoxic conditions. We measured HIF1α levels in HAPE-S and HAPE resistant (HAPE-R, no HAPE episode) individuals with similar pulmonary functions. Hemodynamic responses were also measured before and after normobaric hypoxia (Fi02 = 0.12 for 30 min duration at sea level) in both groups. . HIF1α was higher in HAPE-S (320.3 ± 267.5 vs 58.75 ± 33.88 pg/ml, P < 0.05) than HAPE-R, at baseline, despite no significant difference in baseline oxygen saturations (97.7 ± 1.7% and 98.8 ± 0.7). As expected, HAPE-S showed an exaggerated increase in pulmonary artery pressure (27.9 ± 6 vs 19.3 ± 3.7 mm Hg, P < 0.05) and a fall in peripheral oxygen saturation (66.9 ± 11.7 vs 78.7 ± 3.8%, P < 0.05), when exposed to hypoxia. HIF1α levels at baseline could accurately classify members of the two groups (AUC = 0.87). In a subset of the groups where hemoglobin fractions were additionally measured to understand the cause of elevated hypoxic response at baseline, two of four HAPE-S subjects showed reduced HbA. In conclusion, HIF 1 α levels during normoxia may represent an important marker for determination of HAPE susceptibility.

[Inherited primitive and secondary polycythemia]

Myeloproliferative disorders and secondary polycythemia cover most of the polycythemia cases encountered in daily practice. Inherited polycythemias are rare entities that have to be suspected when the classical causes of acquired polycythemia have been ruled out. Recent advances were made in the understanding of these pathologies, which are still little known to the physicians. This review reports the state of knowledge and proposes an algorithm to follow when confronted to a possible case of inherited polycythemia.

GLUT1 reductions exacerbate Alzheimer's disease vasculo-neuronal dysfunction and degeneration

The glucose transporter GLUT1 at the blood-brain barrier (BBB) mediates glucose transport into the brain. Alzheimer's disease is characterized by early reductions in glucose transport associated with diminished GLUT1 expression at the BBB. Whether GLUT1 reduction influences disease pathogenesis remains, however, elusive. Here we show that GLUT1 deficiency in mice overexpressing amyloid β-peptide (Aβ) precursor protein leads to early cerebral microvascular degeneration, blood flow reductions and dysregulation and BBB breakdown, and to accelerated amyloid β-peptide (Aβ) pathology, reduced Aβ clearance, diminished neuronal activity, behavioral deficits, and progressive neuronal loss and neurodegeneration that develop after initial cerebrovascular degenerative changes. We also show that GLUT1 deficiency in endothelium, but not in astrocytes, initiates the vascular phenotype as shown by BBB breakdown. Thus, reduced BBB GLUT1 expression worsens Alzheimer's disease cerebrovascular degeneration, neuropathology and cognitive function, suggesting that GLUT1 may represent a therapeutic target for Alzheimer's disease vasculo-neuronal dysfunction and degeneration.

A Japanese Family with Congenital Erythrocytosis Caused by Haemoglobin Bethesda

We herein present a case of congenital erythrocytosis caused by haemoglobin (Hb) Bethesda in a Japanese family. A 55-year-old asymptomatic man was referred to our hospital for the investigation of erythrocytosis, which was present in other members of his family. The patient's serum erythropoietin level was normal, and the JAK2 V617F mutation was not detected. His P50 value was mildly decreased, thus we suspected the presence of an Hb variant with a high oxygen affinity. The high-performance liquid chromatography analysis showed an abnormal Hb, and by direct sequencing we identified the Hb Bethesda variant in this patient. For the differential diagnosis, we recommend the estimation of the P50 value as a practical and useful test.

A new high affinity variant Hb Aurillac (β141Leu→Val)

Hemoglobin (Hb) variant β141(H19)Leu→Val (HBB:c.424C>G), one of the two mutations defining Hb Kochi [the other one being β144(HC1)Lys-Tyr-His→0 (HBB:c.433A>T)], was found as an isolated mutation. In contrast to what was suggested for Hb Kochi, the new variant was not clinically silent. It displayed increased oxygen affinity and was associated with mild erythrocytosis.

Familial secondary erythrocytosis due to increased oxygen affinity is caused by destabilization of the T state of hemoglobin Brigham (α₂β₂(Pro100Leu))

Hemoglobin Brigham (β Pro100 to Leu) was first reported in a patient with familial erythrocytosis. Erythrocytes of an affected individual from the same family contain both HbA and Hb Brigham and exhibit elevated O₂ affinity compared with normal cells (P₅₀ = 23 mm Hg vs. 31 mmHg at pH 7.4 at 37°C). O₂ affinities measured for hemolysates were sensitive to changes in pH or chloride concentrations, indicating little change in the Bohr and Chloride effects. Hb Brigham was separated from normal HbA by nondenaturing cation exchange liquid chromatography, and the amino acid substitution was verified by mass spectrometry. The properties of Hb Brigham isolated from the patient's blood were then compared with those of recombinant Hb Brigham expressed in Escherichia coli. Kinetic experiments suggest that the rate constants for ligand binding and release in the high (R) and low (T) affinity quaternary states of Hb Brigham are similar to those of native hemoglobin. However, the Brigham mutation decreases the T to R equilibrium constant (L) which accelerates the switch to the R state during ligand binding to deoxy-Hb, increasing the rate of association by approximately twofold, and decelerates the switch during ligand dissociation from HbO₂, decreasing the rate approximately twofold. These kinetic data help explain the high O₂ affinity characteristics of Hb Brigham and provide further evidence for the importance of the contribution of Pro100 to intersubunit contacts and stabilization of the T quaternary structure.

Benign Familial Polycythaemia in a Young Male

Polycythaemia has been reported rarely as a familial condition. There is evidence to suggest transmission as a Mendelian dominant trait, but recessive inheritance has also been described. We present here a case of benign familial polycythaemia in a 25-year-old male with similar presentation in his family members. Our patient presented with reddish discolouration of the eyes, early satiety , weight loss and itching at intervals, for four years. An additional examination revealed red beefy tongue and Grade III clubbing. The importance of presenting this case lies in the fact that the prognosis appears to be good in these patients, but regular observation is necessary as Kiladjian and colleagues have mentioned that there is a risk of leukaemia, thrombosis and myelofibrosis in these patients later on, as the idiopathic erythrocytosis group contains a certain number of polycythaemia patients.

Blood p50 evaluation enhances diagnostic definition of isolated erythrocytosis

BACKGROUND

High oxygen-affinity haemoglobin variants and 2,3-diphosphoglycerate (2,3-DPG) deficiency are inherited diseases generating low tissue oxygen tension and erythropoietin-driven erythrocytosis, that characterizes the clinical phenotype of patients. Level of blood p50 (the oxygen tension at which haemoglobin is 50% saturated) is used to recognize these conditions.

OBJECTIVES

To define the clinical utility of blood p50 measurement in the diagnosis of isolated erythrocytosis.

SUBJECTS AND DESIGN

Venous blood p50 measurement was included in the diagnostic work-up of 102 consecutive patients with isolated erythrocytosis besides blood cell count, arterial oxygen saturation, serum erythropoietin measurement and screening for JAK2 mutations.

SETTING

Haematological Outpatient Section at University Hospital.

RESULTS

Seven patients had relative erythrocytosis. Among 95 patients with absolute erythrocytosis, 4 (4.2%) had decreased p50 level. The extended study of family members revealed a familial inheritance. Two families had haemoglobin variants already described as Haemoglobin Malmö and Haemoglobin San Diego. In one family, the proband had a new high oxygen-affinity haemoglobin variant (Haemoglobin Safi) resulting from the transversion C-->A at codon 81 of the alpha2-globin gene. In the last family, a deficiency of 2,3-DPG was found. Within the 91 patients with normal p50 values, 46 (51%) had secondary erythrocytosis, 13 (14%) polycythemia vera and 32 (35%) idiopathic erythrocytosis.

CONCLUSIONS

This study suggests that the investigation of blood p50 level may be useful to define diagnosis in patients with isolated erythrocytosis.