Tibetans do not exhibit increased hemoglobin concentration at high altitude. We describe a high-frequency missense mutation in the EGLN1 gene, which encodes prolyl hydroxylase 2 (PHD2), that contributes to this adaptive response. We show that a variant in EGLN1, c.[12C>G; 380G>C], contributes functionally to the Tibetan high-altitude phenotype. PHD2 triggers the degradation of hypoxia-inducible factors (HIFs), which mediate many physiological responses to hypoxia, including erythropoiesis. The PHD2 p.[Asp4Glu; Cys127Ser] variant exhibits a lower Km value for oxygen, suggesting that it promotes increased HIF degradation under hypoxic conditions. Whereas hypoxia stimulates the proliferation of wild-type erythroid progenitors, the proliferation of progenitors with the c.[12C>G; 380G>C] mutation in EGLN1 is significantly impaired under hypoxic culture conditions. We show that the c.[12C>G; 380G>C] mutation originated ~8,000 years ago on the same haplotype previously associated with adaptation to high altitude. The c.[12C>G; 380G>C] mutation abrogates hypoxia-induced and HIF-mediated augmentation of erythropoiesis, which provides a molecular mechanism for the observed protection of Tibetans from polycythemia at high altitude.
To better understand the underlying molecular basis of polycythemia vera (PV), we performed whole-exome sequencing and DNA copy-number analysis of 31 JAK2V617F-positive patients and further investigated the evolution of somatic mutations using longitudinal samples. In addition to JAK2V617F and 9pUPD, we identified frequent recurrent somatic mutation in ASXL1, TET2, DNMT3A, SF3B1 and NF1. Forty two percent of patients had a somatic mutation in at least one epigenetic modifier gene. In 4 of 31 patients, variant allele abundance suggested mutation of JAK2V617F was preceded by other somatic mutations including ASXL1, DNMT3A and SF3B1. Strikingly, in 7 patients, apparent germline variants were detected at COSMIC codons in one or more PV-related genes in which we had also discovered somatic mutations across the cohort, suggesting that some pre-JAK2V617F mutations contribute to substantial T-lymphocyte progeny. This study contributes to novel understanding of the complexity of PV pathogenesis.
High altitude exerts selective evolutionary pressure primarily due to its hypoxic environment, resulting in multiple adaptive responses. High hemoglobin-oxygen affinity is postulated to be one such adaptive change, which has been reported in Sherpas of the Himalayas. Tibetans have lived on the Qinghai-Tibetan plateau for thousands of years and have developed unique phenotypes, such as protection from polycythemia which has been linked to PDH2 mutation, resulting in downregulation of HIF pathway. In order to see if Tibetans also developed high hemoglobin-oxygen affinity as a part of their genetic adaptation, we conducted this study assessing hemoglobin-oxygen affinity and their fetal hemoglobin levels in Tibetan subjects from 3 different altitudes. We found normal hemoglobin-oxygen affinity in all subjects, fetal hemoglobin levels were normal in all except one and no hemoglobin variants in any of the subjects. We conclude that increased hemoglobin-oxygen affinity or increased fetal hemoglobin are not adaptive phenotypes of the Tibetan highlanders.
Hypoxia; Hemoglobin-oxygen affinity; P50; fetal hemoglobin
A fraction of polycythemia vera (PV) & essential thrombocythemia (ET) cases will, in time, undergo myelofibrotic transformation. In such cases, fibrosis may mask the diagnostic histological features of the original underlying myeloproliferative neoplasm (MPN). Thus confidently differentiating postfibrotic PV/ET from primary myelofibrosis (PMF) histologically may not be possible.
It is controversial whether post PV/ET myelofibrosis (MF) differs clinicopathologically from PMF, or if these entities are biologically, clinically, and prognostically indistinguishable. To answer this question, we compared multiple candidate biologic, morphologic, and prognostic parameters between 19 postfibrotic ET/PV individuals and 18 PMF individuals. The postfibrotic ET/PV and PMF cases did not differ in regards to clinical outcome, cytogenetic abnormalities, serum lactate dehydrogenase (LDH) level, peripheral blast count, bone marrow morphology, or grade of reticulin fibrosis. Only JAK2 allele burden differed between the two groups, which was higher in the postfibrotic PV/ET population (p=0.011).
Cardinal morphologic features of PMF (i.e. marrow cellularity, intrasinusoidal hematopoiesis, osteosclerosis, etc.) were commonly observed in post-PV/ET MF marrow biopsies and only a minority of post-PV/ET MF marrow biopsies retained diagnostic features of the primary MPN (panmyelosis in PV and megakaryocytic hyperplasia in ET). Our study indicates that PMF and post-PV/ET MF are clinically and biologically indistinguishable.
Myelofibrotic transformation; polycythemia; myelofibrosis; thrombocythemia
Polycythemia vera (PV) is a chronic myeloproliferative neoplasm (MPN) characterized by excessive production of red blood cells. Patients with PV are at a risk of thrombosis, bleeding, and transformation to myelofibrosis or acute myeloid leukemia. Therapy for PV is based on the use of phlebotomy, aspirin, and in high-risk patients, cytoreductive agents such as hydroxyurea. Anecdotal evidence suggests that imatinib mesylate, a selective tyrosine kinase inhibitor of ABL1, ARG, PDGFR, and KIT kinases has activity in PV. We conducted an open-label phase II clinical trial of imatinib at the standard dose of 400 mg daily in 24 patients with PV. The median duration of imatinib therapy was 5.1 months (range 0.2–86.4). Overall, 4 (17%) patients responded: one had a complete and three partial hematological response. The median time to response was 17.5 months (range 6–28), and the median duration of response was 17 months (range 9–68). No significant changes in JAK2V617F mutation burden were noted during imatinib therapy when compared with pre-treatment values (P = 0.46). Therapy with imatinib was generally well tolerated. Our data indicate that imatinib has minimal clinical activity in PV.
Imatinib mesylate; Polycythemia vera; JAK2 mutation
Polycythemia vera (PV) is an acquired blood disorder, with variable increase of clonal myeloid cells (erythrocytes, granulocytes and platelets) and mostly normal polyclonal T lymphocytes. Most patients have a somatic V617F gain-of-function mutation in JAK2 associated with acquired uniparental disomy (UPD) on chromosome 9p. Yet, the JAK2 V617F mutation is not a PV-initiating event and the family clustering of PV suggests a contribution of inherited genetic events. Using whole-genome SNP arrays, we assayed 34 T-cells and 66 granulocytes (including 32 pairs from the same patients), and identified multiple SNPs around JAK2 that are associated with PV susceptibility (rs11999802, P=1.8×10−8, OR=4.4). We also developed a quantitative measure of the fraction of somatic single nucleotide variants (SNVs) based on allele-specific PCR, and a quantitative measure of somatic UPD based on “fractional copy-neutral loss-of-heterozygosity (LOH)” on SNP arrays. Somatic genomic changes in granulocytes revealed strong genetic heterogeneity, including 9p UPD and chromosomal gain. The magnitude of somatic 9p UPD was strongly associated with V617F dosage (r2=0.74, P=4.8×10−12), suggesting that UPD preferentially increases the V617F subclone. In granulocytes with heterozygous rs11999802 genotypes, UPD increased the relative fraction of germline risk alleles (P=0.03). Thus, germline risk variants at JAK2 predispose to somatic point mutations within JAK2, whose allelic dosage can be further increased by a serial subclonal expansion of allele-specific UPD or copy number alteration, contributing to PV pathogenesis. We argue that PV represents a unique disease model to study the interplay between germline risk variants and convergent mechanisms of somatic mutations.
We postulated that the hypoxic response in sickle cell disease (SCD) contributes to altered gene expression and pulmonary hypertension, a complication associated with early mortality.
Methods and Results
To identify genes regulated by the hypoxic response and not other effects of chronic anemia, we compared expression variation in peripheral blood mononuclear cells from 13 SCD subjects with hemoglobin SS genotype and 15 Chuvash polycythemia subjects (VHLR200W homozygotes with constitutive up-regulation of hypoxia inducible factors in the absence of anemia or hypoxia). At 5% false discovery rate, 1040 genes exhibited >1.15 fold change in both conditions; 297 were up-regulated and 743 down-regulated including MAPK8 encoding a mitogen-activated protein kinase important for apoptosis, T-cell differentiation and inflammatory responses. Association mapping with a focus on local regulatory polymorphisms in 61 SCD patients identified expression quantitative trait loci (eQTL) for 103 of these hypoxia response genes. In a University of Illinois SCD cohort the A allele of a MAPK8 eQTL, rs10857560, was associated with pre-capillary pulmonary hypertension defined as mean pulmonary artery pressure ≥25 and pulmonary capillary wedge pressure ≤15 mm Hg at right heart catheterization (allele frequency=0.66; OR=13.8, P=0.00036, n=238). This association was confirmed in an independent Walk-PHaSST cohort (allele frequency=0.65; OR=11.3, P=0.0025, n=519). The homozygous AA genotype of rs10857560 was associated with decreased MAPK8 expression and present in all 14 identified pre-capillary pulmonary hypertension cases among the combined 757 patients.
Our study demonstrates a prominent hypoxic transcription component in SCD and a MAPK8 eQTL associated with pre-capillary pulmonary hypertension.
sickle cell disease; MAPK8; hypoxic response; expression quantitative trait loci; association mapping; pre-capillary pulmonary hypertension
In congenital Chuvash polycythemia (CP), VHLR200W homozygosity leads to elevated hypoxia inducible factor (HIF) levels at normoxia. CP is often treated by phlebotomy resulting in iron deficiency, permitting us to examine the separate and synergistic effects of iron deficiency and HIF signaling on gene expression. We compared peripheral blood mononuclear cell gene expression profiles of eight VHLR200W homozygotes with 17 wildtype individuals with normal iron status and found 812 up-regulated and 2120 down-regulated genes at false discovery rate 0.05. Among differential genes we identified three major gene regulation modules involving induction of innate immune responses, alteration of carbohydrate and lipid metabolism, and down-regulation of cell proliferation, stress-induced apoptosis and T-cell activation. These observations suggest molecular mechanisms for previous observations in CP of lower blood sugar without increased insulin and low oncogenic potential. Studies including 16 additional VHLR200W homozygotes with low ferritin indicated that iron deficiency enhanced the induction effect of VHLR200W for 50 genes including hemoglobin synthesis loci but suppressed the effect for 107 genes enriched for HIF-2 targets. This pattern is consistent with potentiation of HIF-1α protein stability by iron deficiency but a trend for down-regulation of HIF-2α translation by iron deficiency overriding an increase in HIF-2α protein stability.
polycythaemia; erythrocytosis; mutations; molecular haematology; genetics
Disease-specific induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity to establish novel disease models and accelerate drug development using distinct tissue target cells generated from isogenic iPSC lines with and without disease-causing mutations. To realize the potential of iPSCs in modeling acquired diseases which are usually heterogeneous, we have generated multiple iPSC lines including two lines that are JAK2-wild-type and four lines homozygous for JAK2-V617F somatic mutation from a single polycythemia vera (PV) patient blood. In vitro differentiation of the same patient-derived iPSC lines have demonstrated the differential contributions of their parental hematopoietic clones to the abnormal erythropoiesis including the formation of endogenous erythroid colonies. This iPSC approach thus may provide unique and valuable insights into the genetic events responsible for disease development. To examine the potential of iPSCs in drug testing, we generated isogenic hematopoietic progenitors and erythroblasts from the same iPSC lines derived from PV patients and normal donors. Their response to three clinical JAK inhibitors, INCB018424 (Ruxolitinib), TG101348 (SAR302503), and the more recent CYT387 was evaluated. All three drugs similarly inhibited erythropoiesis from normal and PV iPSC lines containing the wild-type JAK2 genotype, as well as those containing a homozygous or heterozygous JAK2-V617F activating mutation that showed increased erythropoiesis without a JAK inhibitor. However, the JAK inhibitors had less inhibitory effect on the self-renewal of CD341 hematopoietic progenitors. The iPSC-mediated disease modeling thus underlies the ineffectiveness of the current JAK inhibitors and provides a modeling system to develop better targeted therapies for the JAK2 mutated hematopoiesis.
Induced pluripotent stem cells; Hematopoietic progenitor cells; Erythropoiesis; Preclinical drug evaluation; Hematopoietic malignancies
The occurrence of ≥ two distinct types of tumors, one of them paraganglioma (PGL), is unusual in an individual patient, except in hereditary cancer syndromes.
Patients and Methods
Four unrelated patients were investigated, with thorough clinical evaluation. Plasma and tissue catecholamines and metanephrines were measured by high-performance liquid chromatography. Anatomic and functional imaging were performed for tumor visualization. Germline and tumor tissue DNA were analyzed for hypoxia-inducible factor 2 alpha (HIF2A) mutations. The prolyl hydroxylation and stability of the mutant HIF2α protein, transcriptional activity of mutant HIF2A, and expression of hypoxia-related genes were also investigated. Immunohistochemical staining for HIF1/2α was performed on formalin-fixed, paraffin-embedded tumor tissue.
Patients were found to have polycythemia, multiple PGLs, and duodenal somatostatinomas by imaging or biochemistry with somatic gain-of-function HIF2A mutations. Each patient carried an identical unique mutation in both types of tumors but not in germline DNA. The HIF2A mutations in these patients were clustered adjacent to an oxygen-sensing proline residue, affecting HIF2α interaction with the prolyl hydroxylase domain 2–containing protein, decreasing the hydroxylation of HIF2α, and reducing HIF2α affinity for the von Hippel–Lindau protein and its degradation. An increase in the half-life of HIF2α was associated with upregulation of the hypoxia-related genes EPO, VEGFA, GLUT1, and END1 in tumors.
Our findings indicate the existence of a new syndrome with multiple PGLs and somatostatinomas associated with polycythemia. This new syndrome results from somatic gain-of-function HIF2A mutations, which cause an upregulation of hypoxia-related genes, including EPO and genes important in cancer biology.
Congenital polycythemias have diverse etiologies, including mutations in the hypoxia sensing pathway. These include HIF2A at exon 12, VHL gene (Chuvash polycythemia), and PHD2 mutations, which in one family was also associated with recurrent pheochromocytoma/paraganglioma (PHEO/PGL). Over the past two decades, we have studied seven unrelated patients with sporadic congenital polycythemia who subsequently developed PHEO/PGL with, until now, no discernible molecular basis. We now report a polycythemic patient with a novel germline HIF2AF374Y (exon 9) mutation, inherited from his mother, who developed PHEO/PGL.
We show that this is a gain-of-function mutation and demonstrate no loss-of-heterozygosity or additional somatic mutation of HIF2A in the tumor, indicating HIF2AF374Y may be predisposing rather than causative of PHEO/PGL. This report, in view of 2 other concomitantly reported PHEO/PGL patients with somatic mutations of HIF2A and polycythemia, underscores the PHEO/PGL promoting potential of mutations of HIF2A that alone are not sufficient for PHEO/PGL development.
HIF2A; Paraganglioma; Familial erythrocytosis
The simultaneous occurrence of polycythemia vera (PV) and chronic lymphocytic leukemia (CLL) is a rare event that offers a possibility to study their common origin. PV originates from self-renewing hematopoietic stem cells (HSC) with both lymphoid and myeloid potential(1–3). It has been reported that CLL also originates from self-renewing HSC with a potential for both lymphoid and myeloid differentiation(4, 5). We report 3 females with concomitant CLL and PV whose X-chromosome inactivation patterns of the neoplastic cells revealed that granulocytes/platelets and B-lymphocytes used different X-chromosome alleles. These data indicate that both PV and CLL have arisen independently and from different HSC.
PV; CLL; JAK2 V617F; clonality
Self-tumor Ags that elicit antitumor immune responses in responses to IFN-α stimulation remain poorly defined. We screened a human testis cDNA library with sera from three polycythemia vera patients who responded to IFN-α and identified a novel Ag, MPD6. MPD6 belongs to the group of cryptic Ags without conventional genomic structure and is encoded by a cryptic open reading frame located in the 3′-untranslated region of myotrophin mRNA. MPD6 elicits IgG Ab responses in a subset of polycythemia vera patients, as well as patients with chronic myelogenous leukemia and prostate cancer, suggesting that it is broadly immunogenic. The expression of myotrophin-MPD6 transcripts was upregulated in some tumor cells, but only slightly increased in K562 cells in response to IFN-α treatment. By using bicistronic reporter constructs, we showed that the translation of MPD6 was mediated by a novel internal ribosome entry site (IRES) upstream of the MPD6 reading frame. Furthermore, the MPD6-IRES-mediated translation, but not myotrophin-MPD6 transcription, was significantly upregulated in response to IFN-α stimulation. These findings demonstrate that a novel IRES-mediated mechanism may be responsible for the translation of unconventional self-Ag MPD6 in responsive to IFN-α stimulation. The eliciting antitumor immune response against unconventional Ag MPD6 in patients with myeloproliferative diseases suggests MPD6 as a potential target of novel immunotherapy.
In Chuvash polycythemia, a homozygous 598C>T mutation in the von Hippel-Lindau gene (VHL) leads to an R200W substitution in VHL protein, impaired degradation of α-subunits of hypoxia inducible factor (HIF)-1 and HIF-2, and augmented hypoxic responses during normoxia. Chronic hypoxia of high altitude is associated with decreased serum glucose and insulin concentrations. Other investigators reported that HIF-1 promotes cellular glucose uptake by increased expression of GLUT1 and increased glycolysis by increased expression of enzymes such as PDK. On the other hand, inactivation of Vhl in murine liver leads to hypoglycemia associated with a HIF-2-related decrease in the expression of the gluconeogenic enzymes genes Pepck, G6pc, and Glut2. We therefore hypothesized that glucose concentrations are decreased in individuals with Chuvash polycythemia. We found that 88 Chuvash VHLR200W homozygotes had lower random glucose and glycosylated hemoglobin A1c levels than 52 Chuvash subjects with wildtype VHL alleles. Serum metabolomics revealed higher glycerol and citrate levels in the VHLR200W homozygotes. We expanded these observations in VHLR200W homozygote mice and found that they had lower fasting glucose values and lower glucose excursions than wild-type control mice but no change in fasting insulin concentrations. Hepatic expression of Glut2 and G6pc but not Pdk2 was decreased and skeletal muscle expression of Glut1, Pdk1 and Pdk4 was increased. These results suggest that both decreased hepatic gluconeogenesis and increased skeletal uptake and glycolysis contribute to the decreased glucose concentrations. Further study is needed to determine whether pharmacologically manipulating HIF expression might be beneficial for treatment of diabetic patients.
VHL; hypoxia inducible factors; glucose; insulin; glycolysis; gluconeogenesis
The author of this lecture has been especially honored to be selected to deliver the Ernest Beutler Memorial Lecture at the Acute Leukemia Forum 2012 and to write this overview. Ernest Beutler was the pivotal influence in my introduction to academic life, and his contribution to hematology in the last 5 decades was unsurpassed. Taking a cue from Ernie’s example, I have elected in the keynote speech and this brief treatise, to start with an unconventional introduction and to expand on some discoveries made in my laboratory. Then I will extend these findings to the focus of the Acute Leukemia Forum to address potentially new approaches to therapies of acute leukemias. Somatic and germline mutations of acute leukemias are unfortunately caused by arrays of somatic and germline mutations. Simultaneous targeting of so many mutations makes it not possible to efficiently target all for cure. Albeit we should be aware that we should not in the near future ignore targeted therapy of those functionally important genetic and epigenetic events that are either initiating or contributing to aggressivity of acute leukemia, as these may be ameliorated by targeted intervention against one, or even a few together, of these defined molecular lesions. Yet, leukemic cells, like other cancer cells, have the unique metabolic feature to generate energy, referred as the Warburg effect, which can potentially be targeted to suppress or even eradicate cancer.
Acute Leukemia Forum; Beutler; cancer cell metabolism; glycolysis; hypoxia-inducible factor; HIF; HIF-1; HIF-2; HIF-3; IDH1; IDH2; isocitrate dehydrogenase; leukemia; polycythemia; tumorigenesis; von Hippel-Lindau; Warburg
Ruxolitinib, a Janus kinase 1 and 2 inhibitor, demonstrated improvements in spleen volume, symptoms, and survival over placebo and best available therapy in intermediate-2 or high-risk myelofibrosis patients with baseline platelet counts ≥100 × 109/L in phase III studies. The most common adverse events were dose-dependent anemia and thrombocytopenia, which were anticipated because thrombopoietin and erythropoietin signal through JAK2. These events were manageable, rarely leading to treatment discontinuation. Because approximately one-quarter of MF patients have platelet counts <100 × 109/L consequent to their disease, ruxolitinib was evaluated in this subset of patients using lower initial doses. Interim results of a phase II study of ruxolitinib in myelofibrosis patients with baseline platelet counts of 50-100 × 109/L are reported.
Ruxolitinib was initiated at a dose of 5 mg twice daily (BID), and doses could be increased by 5 mg once daily every 4 weeks to 10 mg BID if platelet counts remained adequate. Additional dosage increases required evidence of suboptimal efficacy. Assessments included measurement of spleen volume by MRI, MF symptoms by MF Symptom Assessment Form v2.0 Total Symptom Score [TSS]), Patient Global Impression of Change (PGIC); EORTC QLQ-C30, and safety/tolerability.
By week 24, 62% of patients achieved stable doses ≥10 mg BID. Median reductions in spleen volume and TSS were 24.2% and 43.8%, respectively. Thrombocytopenia necessitating dose reductions and dose interruptions occurred in 12 and 8 patients, respectively, and occurred mainly in patients with baseline platelet counts ≤75 × 109/L. Seven patients experienced platelet count increases ≥15 × 109/L. Mean hemoglobin levels remained stable over the treatment period. Two patients discontinued for adverse events: 1 for grade 4 retroperitoneal hemorrhage secondary to multiple and suspected pre-existing renal artery aneurysms and 1 for grade 4 thrombocytopenia.
Results suggest that a low starting dose of ruxolitinib with escalation to 10 mg BID may be appropriate in myelofibrosis patients with low platelet counts.
Janus kinase inhibitor; Myelofibrosis; Phase II; Platelet count; Ruxolitinib; Spleen volume; Total symptom score
Thromboses represent a major cause of morbidity and mortality in Polycythemia Vera (PV) but the contributing mechanisms are not fully described.
Patients and methods
To evaluate whether environmental conditions such as altitude/hypoxia could impact thromboses history, we retrospectively analyzed thrombosis history in 71 PV patients living at an elevation of 5,000 feet or more in the SLC area (SLC) and 166 PV patients living near sea level in the Baltimore area (BLM). The SLC cohort was older with a longer disease duration. No significant differences in type of anticoagulation therapy or prothrombotic factors were present between the two cohorts. After adjusting for age, sex and disease duration, SLC patients experienced an estimated 3.9-fold increase in the odds of a history of thromboses compared to BLM patients (95% confidence interval 1.8-7.6; p = 0.0004). A history of cardiovascular event was present in 58% of the SLC patients compared to 27% of the BLM patients (p<0.0001). Before diagnosis thromboses occurred in 18% and 4% of the SLC and BLM groups respectively (p =0.003). No correlation between JAK2V617F allele burden and thrombosis was observed in this study.
This retrospective study suggests that even moderate hypoxia associated with 5,000 feet elevation should be considered as independent prothrombotic risk factor. This observation needs to be confirmed by prospective studies.
Recent studies have identified genes involved in high-altitude adaptation in Tibetans. Genetic variants/haplotypes within regions containing three of these genes (EPAS1, EGLN1, and PPARA) are associated with relatively decreased hemoglobin levels observed in Tibetans at high altitude, providing corroborative evidence for genetic adaptation to this extreme environment. The mechanisms that afford adaptation to high-altitude hypoxia, however, remain unclear. Considering the strong metabolic demands imposed by hypoxia, we hypothesized that a shift in fuel preference to glucose oxidation and glycolysis at the expense of fatty acid oxidation would improve adaptation to decreased oxygen availability. Correlations between serum free fatty acids and lactate concentrations in Tibetan groups living at high altitude and putatively selected haplotypes provide insight into this hypothesis. An EPAS1 haplotype that exhibits a signal of positive selection is significantly associated with increased lactate concentration, the product of anaerobic glycolysis. Furthermore, the putatively advantageous PPARA haplotype is correlated with serum free fatty acid levels, suggesting a possible decrease in the activity of fatty acid oxidation. Although further studies are required to assess the molecular mechanisms underlying these patterns, these associations suggest that genetic adaptation to high altitude involves alteration in energy utilization pathways.
Organismal response to hypoxia is essential for critical regulation of erythropoiesis, other physiological functions and survival. There is an evidence of individual variation in response to hypoxia as some but not all of the affected individuals develop polycythemia, and or pulmonary and cerebral edema. A significant population difference in response to hypoxia exist as many Tibetans, Ethiopian and Andean natives developed an adaptive mechanisms to extreme hypoxia. A proportion of any non-adapted individuals exposed to high altitude develop pulmonary edema (HAPE), pulmonary hypertension, cerebral edema and extreme polycythemia. The isolation of causative gene(s) responsible for HAPE and other extreme hypoxia complications would provide a rational basis for specific targeted therapy of HAPE, allow its targeted prevention for at-risk populations, and clarification of its, and pathophysiology of other hypoxic maladaptations. As today, the only suggested linkage in unrelated individual with HAPE has been with endothelial nitric oxide synthase (eNOS) gene. Here we describe a family with multiple members affected with HAPE in three generations. Families with multiple affected members with HAPE have not been described. We first ruled out linkage of HAPE with eNOS gene. We then performed analysis of the whole genome using high-density SNP arrays (Affymetrix v5.0) and assuming a single gene causation of HAPE ruled out a linkage with 34 other candidate genes. Only HIF2A haplotype was shared by individuals who exhibit the HAPE phenotype, and the work on their possible causative role in HAPE is in progress. Clearly a small size of our family does not provide sufficient power for a conclusive analysis of linkage; we hope that collaboration with other investigators referring us more HAPE patients in effort to increase sample size would lead to identification of gene(s) responsible for HAPE and possibly other maladaptive hypoxic complications.
Hypoxia; Erythropoietin; High Altitude Pulmonary Edema (HAPE); Endothelial Nitric Oxide (eNOS); Hypoxia Inducible Factor (HIF)
Hypoxia inducible factors (HIFs) are transcription factors controlling energy, iron metabolism, erythropoiesis, and development, and, when dysregulated, contribute to tumorigenesis, cancer progression, and invasion. However, HIFα mutations have not previously been identified in any cancer. Here we report two novel somatic gain-of-function HIF2α mutations in two patients, one presenting with a paraganglioma and a second with both paraganglioma and somatostatinoma. Both mutations were shown to confer increased HIF2α activity and protein half-life. While germline mutations of regulators of HIFα, including VHL and EGLN1, have been reported in pheochromocytomas/paragangliomas, this is the first report of a somatic gain-of-function mutation in HIF.
HIF2α; paraganglioma; somatostatinoma; polycythemia
Congenital methemoglobinemia due to NADH-cytochrome b5 reductase 3 (CYB5R3) deficiency is an autosomal recessive disorder that occurs sporadically worldwide, although endemic clusters of this disorder have been identified in certain ethnic groups. It is present as two distinct phenotypes, type I and type II. Type I methemoglobinemia is characterized by CYB5R3 enzyme deficiency restricted to erythrocytes and is associated with benign cyanosis. The less frequent type II methemoglobinemia is associated with generalized CYB5R3 deficiency affecting all cells and is lethal in early infancy. Here we describe the molecular basis of type I methemoglobinemia due to CYB5R3 deficiency in four patients from three distinct ethnic backgrounds, Asian Indian, Mexican and Greek.
The CYB5R3 gene of three probands with type I methemoglobinemia and their relatives were sequenced revealing several putative causative mutations; in one subject multiple mutations were present. Two novel mutations, S54R and F157C, were identified and the previously described A179T, V253M mutations were also identified. All these point mutations mapped to the NADH binding domain and or the FAD binding domain. Each has the potential to sterically hinder cofactor binding causing instability of the CYB5R3 protein. Wild type CYB5R3 as well as two of these novel mutations, S54R and F157C, were amplified, cloned, and purified recombinant peptide obtained. Kinetic and thermodynamic studies of these proteins show that the above mutations lead to decreased thermal stability.
methemoglobinemia; NADH-cytochrome b5 reductase 3; gene mutation; cyanosis; protein structure
We analysed the results of haematopoietic cell transplantation (HCT) in 30 patients aged 60–78 (median 65) years, with primary myelofibrosis or myelofibrosis evolving from antecedent polycythaemia vera or essential thrombocythaemia. Donors were human leucocyte antigen (HLA)-identical siblings (N = 15) or unrelated individuals (N = 15). Various conditioning regimens were used, ranging from very low intensity (fludarabine plus 2 Gy total body irradiation) to high dose (busulfan plus cyclophosphamide). Stem cell sources were granulocyte colony-stimulating factor mobilized peripheral blood progenitor cells in 29 patients and marrow in one patient. Sustained engraftment was documented in 27 of 30 patients. Day -100 mortality was 13%. With a median follow-up of 22 (range 0.5–69) months, 3-year overall survival and progression-free survival were 45% and 40%, respectively. Currently, 13 patients are surviving. Seven patients died with disease progression at 0.5–22 months, and 10 patients died from other causes at 1.5–37.5 months after HCT. While the selection of older patients for transplantation was probably biased, the present results are encouraging. Motivated older patients with myelofibrosis without substantial comorbid conditions should be offered the option of allogeneic HCT.
myelofibrosis, older patients; haematopoietic cell transplantation
Evaluation of bone marrow fibrosis and osteosclerosis in myeloproliferative neoplasms (MPN) is subject to interobserver inconsistency. Performance data for currently utilized fibrosis grading systems are lacking, and classification scales for osteosclerosis do not exist. Digital imaging can serve as a quantification method for fibrosis and osteosclerosis. We used digital imaging techniques for trabecular area assessment and reticulin-fiber quantification. Patients with all Philadelphia negative MPN subtypes had higher trabecular volume than controls (p ≤0.0015). Results suggest that the degree of osteosclerosis helps differentiate primary myelofibrosis from other MPN. Numerical quantification of fibrosis highly correlated with subjective scores, and interobserver correlation was satisfactory. Digital imaging provides accurate quantification for osteosclerosis and fibrosis.
bone marrow fibrosis; digital imaging; myeloproliferative neoplasms; osteosclerosis