Spectrum of Mutations Associated with Hereditary Erythrocytosis
Bibliographic record
Abstract
Abstract Background: Mechanisms of hereditary erythrocytosis have been elucidated recently. These include high oxygen affinity (HOA) hemoglobin (Hb) variants, bisphosphoglycerate mutase (BPGM) deficiency, abnormalities in the erythropoietin receptor (EPOR) and oxygen-sensing pathway (OSP) proteins prolyl hydroxylase domain-2 (PHD2), hypoxia-inducible factor-2 alpha subunit (HIF2A), and von Hippel-Lindau (VHL). We present our experience with these disorders. Methods: Evaluation of erythrocytosis patients' blood samples for HOA Hb variants by protein or DNA sequencing methods has been performed in our laboratory for over 30 years. Testing has included alkaline/acid electrophoresis, isoelectric focusing, capillary electrophoresis, high performance liquid chromatography, mass spectrometry and Sanger sequencing. BPGM deficiency was determined by enzyme activity assay and/or genetic testing. Since 2012 we have evaluated the EPOR, EGLN1 (PHD2), EPAS1(HIF2A), and VHL genes. Reflexive evaluations, which include testing for p50 and pertinent Sanger sequencing of HBB, HBA1, HBA2, EPOR (exon 8), EGLN1 (exons 1-5), EPAS1 (exon 12) and VHL, have been performed on a subset of cases. Genetic results were correlated with clinical and phenotypic data. Results: Retrospective database review identified 62 confirmed HOA Hb variants (48β, 14α) with clinical erythrocytosis (Table 1). Multiple Hb variants were silent on at least one protein method but showed decreased p50 values. One homozygous BPGM mutation case was identified. Of the 394 cases evaluated for EPOR and OSP abnormalities, 39 cases (10%) contained genetic alterations. Of these, 11 were known pathogenic mutations and 28 were novel alterations including 4 pathogenic, 12 likely pathogenic and 12 variants of unknown significance (VUS). Eighteen EGLN1, 10 EPAS1, and 7 EPOR alterations were detected, all heterozygous. Four VHL mutation cases were identified: 3 homozygous/compound heterozygous known mutations and one novel heterozygous VUS (p.R200Q). All EPOR mutations resulted in a premature stop codon. Most of the EPAS1 alterations were located near proline 531, although two predicted splice site disturbances were found. The EGLN1 alterations were novel, variable, and affect the enzyme's catalytic domain. All 4 VHL cases involved the R200 amino acid position in at least one allele. Serum Epo levels varied: decreased in EPOR (5/5); normal in PHD2 (11/11) and most HIF2A (6/7) and VHL (3/4) cases; increased in 1 HIF2A and 1 VHL case. p50 was normal in EPOR and OSP cases (31/31 tested). Conclusion: A spectrum of abnormalities was identified. Salient points include: 1) Diagnostically, a high index of suspicion for HOA Hb variants is required as they can give false negative results by routine protein detection methods. p50 and Epo levels were useful for triage. 2) Phenotypically, serum Epo levels were low in EPOR and normal in PHD2 and HIF2A cases. Unexpectedly, the two classic Chuvash polycythemia VHL cases were associated with normal Epo levels. 3) Mechanistically, the alterations were truncating in EPOR, variable and scattered in EGLN1 and clustered near proline 531 in EPAS1. VHL mutations were rare and consistently affected the R200 amino acid position in at least one allele. Novel alterations were frequent, especially in EGLN1. 4) Clinically, many patients were asymptomatic but a subset demonstrated recurrent headaches and one had chest pain. Clotting complications included cerebrovascular accident in one EPAS1 and EGLN1 case each and portal vein thrombosis in one EGLN1 case. Table 1. Clinically significant high oxygen affinity Hb variants at Mayo Clinic n Beta Alpha >30 Malmo Tarrant 10 - 20 Bethesda, San Diego, Andrew-Minneapolis, M-Saskatoon, Olympia, Syracuse, Abruzzo Dallas 5 - 10 Ty Gard, Ypsilanti, Alberta, Coimbra, North Chicago J-Cape Town 2 - 4 Brigham, Kempsey, Little Rock, Puttelange, Wood, Brisbane, Cowtown, Creteil, Linkoping, Osler, Potomac, Providence, Ranier, Sparta, Vanderbilt, Heathrow, Helsinki, Hiroshima, Homozygous HPFH, McKees-Rocks, Pierre Benite, Regina Chesapeake, Ethiopia, Chiapas, Columbia Missouri, Burlington, Legnano 1 Alcorn County*, Bologna-St. Orsola, Bunbury, Cambridge-MA, Cardarelli, Chandigarh, Johnstown, Nantes, Nebraska, Olomouc, Palmerston North, Pitie-Salpetriere, Saint-Jacques, South Milwaukee Linwood, Longview*, Milledgeville, Sarasota Springs, Voorhees * novel Disclosures Pardanani: Stemline: Research Funding.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".