Primary Familial Polycythemia Due to EPO Receptor Mutation (EPOR-related ECYT1/PFCP): Research Report

Verification status. I ran three web searches. Only three PMIDs came back with a source I could read, and I marked those [verified]. Everything else is from my background knowledge and is marked [unverified]. Under this repository's rules, an unverified item is a lead only. Run just fetch-reference PMID:<id> and check the snippet before it becomes evidence. I did not read any abstract in full, so I give no direct quotes except short fragments from the search results. The MONDO ID given in the template (MONDO:0007572) and every HPO, GO, CL, UBERON and NCIT ID below also need an OAK lookup before binding. I wrote none of them from a lookup.

1. Disease information

• What it is. An autosomal dominant erythrocytosis. The red cell mass is raised because of a germline EPOR mutation, and serum erythropoietin (EPO) is low or low-normal. It is called "primary" because the defect is intrinsic to erythroid progenitors, not to oxygen sensing or EPO production.
• Identifiers.
• OMIM #133100, "Erythrocytosis, familial, 1 (ECYT1)", with primary familial and congenital polycythemia (PFCP) as an alternative title (OMIM mirror).
• Orphanet ORPHA:90042 (reached through the PhenoDis mirror).
• MedGen C4551637 (MedGen).
• GARD and NORD pages exist (GARD, NORD MONDO page).
• I have not checked MONDO, ICD-10/11 or MeSH.
• Synonyms. Primary familial and congenital polycythemia (PFCP); familial erythrocytosis type 1; familial benign erythrocytosis; EPOR-related erythrocytosis.
• Source level. The resources above are aggregated disease-level records. The primary papers are family and cohort reports.

2. Etiology

• Cause. Heterozygous germline EPOR mutations. "All mutations so far described lead to the truncation of the C-terminal receptor sequence that contains negative regulatory domains" (Pasquier et al. 2017, [PMID:29269524] [verified]). The mutations are nonsense or frameshift variants, mostly in the last exon, exon 8.
• Example. An EPOR G1251T change (a premature stop codon at residue 393) in one family, with a 20-fold rise in circulating endothelial precursors (PLoS ONE 2010; PMID not retrieved) [unverified].
• Frequency among cases. One source says EPOR mutations explain roughly 12–15% of PFCP. A screen of 270 cases found EPOR mutations in only 1.1% of them. These figures conflict, probably because the cohorts were selected differently. Most erythrocytosis cases have no identified cause. Both figures are unverified.
• Modifiers. Kralovics et al. (J Clin Invest 1998) described an affected child with a unique EPOR mutation who did not develop polycythemia even though their erythroid progenitors were hypersensitive to EPO. The authors suggested unidentified environmental or genetic modifiers may suppress disease. The abstract was not fetched, so I did not use its wording. Penetrance of the biochemical defect is therefore not equal to penetrance of the clinical phenotype.
• Environmental and protective factors. None established. Carriers of a gain-of-function EPOR variant may be more sensitive to hypoxia (altitude, smoking, sleep apnea) [unverified, inferred].

3. Phenotypes

Suggested HPO terms need lookup before binding.

• Onset. Congenital or childhood, with variable penetrance. Many carriers are found by family screening.
• Quality of life. I found no quantitative data.
• Frequencies. I did not retrieve per-feature frequencies.

4. Genetic and molecular information

• Gene. EPOR, 19p13.2. The HGNC ID is not looked up; this repository writes it as lowercase hgnc:<n>.
• Variant class. Nonsense or frameshift variants that truncate the cytoplasmic C-terminus. This removes negative regulatory domains, including the binding site for SHP-1 (a phosphatase) and the residues needed for receptor internalization and degradation [unverified, standard mechanism].
• Functional consequence. Gain of function through loss of negative regulation. Huang et al. 2010 ([PMID:20096014] [verified]) reviewed several lines of evidence for a causal role of the truncated receptor. They note that truncated PFCP EpoRs are not properly down-regulated upon stimulation.
• Different variants act by different mechanisms. Pasquier 2017 concludes that mutation types act through distinct mechanisms. A frameshift variant reported in Haematologica (PMID not retrieved) showed "a strong gain-of-function mutation, which induces major erythropoietin hypersensitivity in primary erythroid progenitors", with persistent JAK2 and STAT5 activation [unverified].
• Origin. Germline. Population frequency, ClinVar classification and modifier genes were not checked.
• Epigenetics and chromosomal abnormalities. Not applicable and not researched.

5. Environmental information

None established. Cardiovascular risk factors such as smoking probably add to thrombotic risk [inferred]. No infectious agents are involved.

6. Mechanism and pathophysiology

Causal chain

1. A germline nonsense or frameshift variant in the last EPOR exon causes truncation of the cytoplasmic C-terminus. (Demonstrated.)
2. The truncated receptor lacks negative regulatory domains. These include the docking site for negative regulators (SHP-1) and the signals for internalization and degradation. (Demonstrated for some variants; the exact domain varies.)
3. The receptor is not properly down-regulated after ligand binding, so it persists on the cell surface. (Demonstrated for the G1251T variant in the PLoS ONE report.)
4. JAK2 and STAT5 activation is prolonged after EPO binding. (Demonstrated for at least one frameshift variant.)
5. Erythroid progenitors (BFU-E and CFU-E) become hypersensitive to EPO and grow with very little or no added EPO. (Demonstrated.)
6. Red cell production rises despite low EPO, and erythrocytosis results. Low EPO is the expected feedback response to the raised red cell mass. (Demonstrated.)
7. Raised hematocrit increases blood viscosity and may lead to thrombotic and cardiovascular events. (Inferred from clinical association; the strength of the effect is uncertain.)

Branch. Some variants may not simply be hyperactive. They may act by distinct mechanisms (Pasquier 2017), so the chain above is the common case, not a universal one.

Candidate GO and CL terms (to verify) - Erythrocyte differentiation. - Erythropoietin-mediated signaling pathway. - JAK-STAT cascade. - Negative regulation of receptor signaling. - Erythroid progenitor cell (CL), erythrocyte (CL).

Not researched. Omics, single-cell and CRISPR screens.

7. Anatomical structures affected

• Bone marrow is the primary site. Blood is where the erythrocytosis shows. The vasculature is affected secondarily through hyperviscosity.
• Cell types are the erythroid progenitor and the erythrocyte. The PLoS ONE report also found raised circulating endothelial precursors [unverified].
• Subcellular site: the plasma membrane receptor and its cytoplasmic domain, with downstream JAK2/STAT5 signaling in the cytoplasm and nucleus.
• No lateralization.

8. Temporal development

• Congenital or early onset, chronic and lifelong. Whether it progresses was not established. Complications probably accumulate with age.
• No spontaneous remission is known. I found no data on critical periods.

9. Inheritance and population

• Inheritance. Autosomal dominant. Penetrance of the clinical phenotype is incomplete (Kralovics 1998 report of a non-polycythemic carrier child).
• Prevalence. Very rare. No reliable prevalence figure retrieved.
• Founder effect. A study titled "Benefit of phlebotomy and low-dose aspirin in the prevention of vascular events in patients with EPOR primary familial polycythemia on the island of New Caledonia" (PMID not retrieved) suggests a large regional cluster [unverified]. I did not read it.
• Sex ratio, ancestry and consanguinity. Not researched.

10. Diagnostics

• Laboratory findings. Raised hemoglobin and hematocrit, low or low-normal EPO, normal white cell and platelet counts.
• Exclusion of other causes. Rule out JAK2 V617F and exon 12 variants (polycythemia vera). Also rule out secondary causes: hypoxia, renal disease and EPO-secreting tumors. Check other familial erythrocytosis genes (VHL, EGLN1, EPAS1, HBB and others) [standard practice, unverified here].
• Genetic testing. EPOR sequencing, with exon 8 as the hot spot, or an erythrocytosis gene panel. Family history and a typical pattern of dominant inheritance support the diagnosis.
• Bone marrow culture. Endogenous erythroid colonies and EPO hypersensitivity can be shown in vitro, but this is not routine.

11. Outcome and prognosis

• Survival and life expectancy data are not retrieved.
• The main risks are thrombosis and cardiovascular events, linked to hematocrit [inferred].
• Cardiovascular outcomes are not uniform. Reports describe both families with early events and families with a benign course [inferred, unverified].

12. Treatment

• Phlebotomy. Used periodically to relieve symptoms or keep hematocrit near normal. The target hematocrit in this disease is debated. It is not firmly established, and the polycythemia vera targets may not transfer [unverified].
• Low-dose aspirin. The New Caledonia study above addresses phlebotomy plus aspirin for preventing vascular events. I did not retrieve its results.
• Cytoreduction and JAK2 inhibition. My searches did not find any evidence on ruxolitinib or hydroxyurea in EPOR-related disease. The pathway is JAK2-dependent, so a JAK2 inhibitor is a plausible hypothesis. It is not an established treatment. Do not curate it as one.
• Cardiovascular risk-factor management applies.
• NCIT terms: phlebotomy and Pharmacotherapy (NCIT:C15986, taken from the CLAUDE.md list); the phlebotomy ID is not looked up.
• No clinical trials were identified.

13. Prevention

• Genetic counseling and cascade testing of relatives.
• Tertiary prevention: control of hematocrit and of cardiovascular risk factors, and avoiding dehydration.
• No primary prevention or vaccination applies.

14. Other species and natural disease

No naturally occurring animal disease was identified. OMIA was not searched.

15. Model organisms

• Human truncated EPOR knock-in mouse. Divoky et al. 2001 ([PMID:11158582] [verified]) replaced the murine gene with the mutant human EPOR. The mice became polycythemic. A later report says the phenotype appeared at 3 to 6 weeks of age but not at birth, mirroring the human disease (J Mol Med 2015; PMID not retrieved).
• Truncated mouse EpoR. Mice carrying the truncated mouse receptor were not polycythemic, so the phenotype depended on the human receptor. The authors noted that erythropoiesis differs between mice and humans. This is a possible HUMAN_MODEL_MISMATCH discussion in the KB. The details need confirmation from the full papers.
• Limitation. Consequences in non-erythroid tissues were unknown in the 2001 paper.

Gaps to close before curation

1. Fetch and verify PMIDs for Kralovics 1998, the PLoS ONE 2010 G1251T paper, the Haematologica frameshift paper, the J Mol Med 2015 mouse paper, and the New Caledonia study.
2. Confirm the GeneReviews and Orphanet content. GeneReviews did not surface in my searches.
3. Look up every MONDO, HP, GO, CL, UBERON and NCIT ID above with OAK. Check that the stub's MONDO ID matches this entity.
4. Find data on prevalence, thrombosis frequency, and treatment outcome, including ruxolitinib, if any exists.

Sources

• PMC Pasquier et al. (PMID:29269524), via search results
• Huang et al. review (PMID:20096014), via search results
• JCI Kralovics 1998 (full text PDF)
• PLoS ONE 2010 G1251T report (DOAJ)
• Haematologica 2018 (flipbook page)
• OMIM #133100 mirror
• MedGen C4551637
• PhenoDis (Orphanet mirror)
• GARD
• NORD MONDO page

Reference Validation

Checked with linkml-reference-validator 0.3.0.

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• HP:0001899 (1 mention) - the report calls it "Core feature"; HP calls it Increased hematocrit

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.

3 of 4 terms resolved to a current term; the rest could not be looked up either way.