Hereditary erythrocytosis caused by a novel EGLN1 gene mutation: a case report

Investigating the genetic basis of adaptation to environmental stresses, such as hypoxia, can enhance our understanding of human biology and resilience. High-altitude adaptation provides a valuable model for studying the genetic mechanisms of the hypoxic response. Indeed, most known loci associated with hypoxic adaptation have been identified in indigenous mountain populations; however, research on elite climbers remains limited. In our previous study, we conducted exome sequencing of experienced mountaineers and identified two pathogenic variants in the RTEL1 and COL6A1 genes, both of which are linked to respiratory failure. These findings encouraged this study, which conducted exome sequencing to explore genetic variation in a larger cohort. We performed exome sequencing for a cohort of 114 mountaineers with varying levels of experience. Variant calling was performed in the sequencing data using a pipeline based on the Genome Analysis Toolkit (GATK) v.4.1.9. Annotated variants were used to identify rare and common variants with possible effects on high-altitude adaptation. The analysis did not identify any common adaptive variants in these individuals; however, nine variants were identified as potentially relevant to high-altitude adaptation and climbing performance. These included novel variants in the EPAS1 and EGLN1 genes, which may have a positive effect under hypoxic conditions, as well as variants in TCAP, F5, GP1BA, and other genes involved in muscle activity and blood coagulation. This study identified rare variants in the EPAS1 and EGLN1 genes, which had previously been associated with high-altitude adaptation. Additionally, we describe several potentially pathogenic variants in genes not previously linked to hypoxia, highlighting the value of studying elite mountaineers as a unique cohort for broader interpretation of genetic variation.

The heritability of salt-sensitive hypertension suggests an origin in early life. The normal response to salt stress in salt-resistant individuals is inhibition of prolyl hydroxylase domain-containing proteins 2 (PHD2), which leads to an increase in the production of hypoxia-inducible factor-1 alpha (HIF-1α) and activation of its target antihypertensive genes (nitric oxide synthase (NOS-3) and heme oxygenase-1 (HO-1)) and consequently, the prevention of hypertension. However, this adaptive mechanism is impaired in salt-sensitive hypertension. To investigate the effects of perinatal maternal high salt diet (HSD) on vascular oxygen-sensing mechanisms in weanling offspring, female Dahl salt-resistant (SR) and salt-sensitive (SS) rats were mated with corresponding SR and SS males and were placed on either 0.3% NaCl normal salt diet (NSD) or 8% NaCl HSD post-positive mating for the duration of pregnancy and lactation. Trunk blood was collected from sacrificed 4-week-old weanling offspring (100-120g) for biochemical assays of plasma direct (DB) and total bilirubin (TB), nitric oxide (NO) and Asymmetric Dimethyl Arginine (ADMA). Tissue RNA in abdominal aorta extracted with Qiagen miniprep was converted to cDNA, and NOS3 (eNOS), HMOX-1 (HO-1), HIF-1α, and EGLN1 (PHD2) gene expression were measured using real-time quantitative PCR (rt-qPCR) methods. Perinatal HSD reduced DB (1.43±0.15 vs. 0.128±0.05 mg/dL; p<0.01) and TB (14.8±2.16 vs. 9.42±0.43 mg/dL; p<0.01) concentrations in SR rats. However, DB was elevated in SS HSD compared to SR HSD (0.128±0.05 vs. 0.93±0.27 p<0.0.01). TB concentrations were reduced in SS NSD (14.8±2.16 vs. 7.79±1.39 p<0.01) and SS HSD (14.8±2.16 vs. 4.49±0.26 p<0.001) when compared with SR NSD (control). NO concentration was higher in SR HSD compared with SR NSD (14.3±1.42 vs. 21.5±1.5 nmol/L; p<0.05); however, NO concentration was lower in SS HSD when compared with SR HSD (21.5±1.53 vs. 14.0±0.76 p<0.05). Perinatal HSD increased ADMA concentrations in both SR (359±29.8 vs. 626±47.2 µmol/L; p<0.01) and SS (501±35.1 vs. 787±68.5, p<0.001). Changes in gene expression are presented as fold changes compared to the control group (SR NSD). There was a decrease in vascular NOS3 gene expression in both SS NSD (1.57±0.39 vs. 0.36± 0.11, p<0.01) and SS HSD (1.57±0.39 vs. 0.72± 0.11, p<0.05). HOMX-1 gene expression was reduced in SS HSD (1.43±0.29 vs. 0.04±0.02, p<0.01). The HIF-1α gene expression in SR HSD was higher (2.11±0.16 vs. 5.12±0.85, p<0.001). However, there was a decrease in expression of vascular HIF-1α gene in SS NSD (2.11±0.16 vs. 0.25±0.13, p<0.01) and SS HSD (2.11±0.16 vs. 0.014+0.009, p<0.001). Likewise, expression of the ENGL1 gene in SS NSD (6.89±0.96vs.1.33±0.62 p<0.001) and SS HSD (6.89±0.96 vs. 0.02±0.003, p<0.0001) were reduced. Findings of this study reveal that perinatal maternal HSD diet dysregulates vascular oxygen-sensing mechanisms in offspring revealing that this mechanism is involved in the fetal programming of salt-sensitive hypertension. This study is supported by the Fogarty International Center of the National Institutes of Health under Award Number K43TW011009. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Recent studies have shown an association between the rs1614148 polymorphism of Egl-9 family hypoxia-inducible factor 1 (EGLN1) gene and maximum oxygen consumption (VO2max) in untrained individuals. The association of this polymorphism with aerobic performance in athletes and with haematological parameters has not been previously studied. The purpose of this research was to study the association of the polymorphic marker rs1614148 of the EGLN1 gene with aerobic performance and haematological parameters in athletes of different specializations and qualifications. The study involved 1309 athletes specialized in different sports (538 females 21.9 ± 4.1 years old and 771 males 22.4 ± 4.8 years old). At the time of the survey, 132 athletes had the qualification of Honored Master of Sports (HMS), 331 were qualified as International Master of Sports (IMS), 444 as Master of Sports (MS), 257 as Candidate Master of Sports (CMS), and 145 had popular sports categories. The control group consisted of 284 non-athletes (44.5 ± 4.1 years). DNA was isolated from buccal epithelial cells or from venous blood leukocytes. Genotyping was performed by real-time PCR or microarray analysis. Athletes were assessed for aerobic performance using spiroergometry (n = 259) and haematological parameters were determined (n = 240). A predominance of the rs1614148*A allele has been found both in highly qualified athletes and in the general group of endurance athletes compared to speed–strength athletes (26.3% vs. 15.8%, χ2 = 3.81, odds ratio (OR) = 1.90, p = 0.025). An association of the rs1614148 AA genotype of the EGLN1 gene with higher VO2max (p = 0.047) was observed in the IMS and HMS group, which is consistent with the literature data. No effect of the EGLN1 gene polymorphism on haematological parameters has been found. Therefore, the rs1614148*A allele predominates in the group of endurance athletes, which may be explained by its association with high aerobic capacity.

Background: Pulmonary arterial hypertension (PAH) is a disastrous disease that is characterized by high blood pressure in the pulmonary arteries which has the potential to lead to heart failure over time. Previously, our lab found that endothelial-specific knockout of Egln1, encoding prolyl 4-hydroxylase-2 (PHD2), induced spontaneous pulmonary hypertension (PH). Recently, we elucidated that Tmem100 is a lung-specific endothelial gene using Tmem100CreERT2 mice. We reason that lung endothelial-specific deletion of Egln1 could lead to the development of PH without affecting other organs’ Egln1 gene expression and defect. Methods: Tmem100-CreERT2 mice were crossed with Egln1flox/flox mice to generate Egln1f/f; Tmem100 CreERT2 (LiCKO) mice. Western blot and immunofluorescent staining were performed to verify the knockout efficacy of Egln1 in multiple organs of LiCKO mice. PH phenotypes including hemodynamics, right heart size and function, and pulmonary vascular remodeling were evaluated by right heart catheterization and echocardiography measurement. Results: Tamoxifen treatment induced Egln1 deletion in the lung ECs but no other organs in adult LiCKO mice. LiCKO mice exhibited an increase in right ventricular systolic pressure (RVSP, ~35 mmHg) and right heart hypertrophy. Echocardiography measurement showed right heart hypertrophy and cardiac and pulmonary arterial dysfunction. Pulmonary vascular remodeling including pulmonary wall thickness and muscularization of distal pulmonary arterials was enhanced in LiCKO mice compared to wild-type mice. Conclusions: Tmem100 promoter-mediated lung endothelial knockout of Egln1 in mice develops spontaneous PH. LiCKO mice could be a novel mouse model for PH to study lung and other organ crosstalk.

MPN-150 Variant of Unknown Significance in the EGLN-1 Gene Associated With Familial Erythrocytosis

Variant of Unknown Significance in the EGLN-1 Gene Associated With Familial Erythrocytosis

In the beginning there was no oxygen (O2) on planet Earth, today the atmosphere hosts 21%, after considerable oscillations of it through millions of years. Over time, living organisms evolved by mounting mechanisms to detect and respond to fluctuations in O2 concentration in their internal environment. Oxygen sensors in the carotid body, and the HIF system in all cells, play a crucial role in maintaining O2 homeostasis at the organism and cellular level. Therefore, in normoxia, HIFs are rapidly synthesized and destroyed, but in hypoxia, their degradation is inhibited. HIFs, regulate protein expression to compensate for hypoxia, increasing O2 delivery to tissues, and reducing O2 consumption. Millions of people live at high altitudes, such as in the Andean and Tibetan plateaus. Newborns in these regions weigh less than those in the lowlands, but this difference in Tibetans is smaller than in the Andeans. There is a greater increase in utero­placental blood flow in Andean and Tibetan women compared to pregnancies in Europeans, at the same altitude. These increases are due to synthesis in NO and PGI2, generated by HIFs. The Andean populations display Chronic Mountain Sickness (CMS), characterized by increase in hemoglobin concentration, diminution of PO2 and pulmonary hypertension. In contrast, the Tibetans do not have these conditions due to polymorphisms of two genes, the EPAS-1 that encodes for HIF-2a, expressing polymorphisms with loss-of-function and the EGLN-1 gene that encodes for prolyl hydroxylase-2, with gain-of-function polymorphisms, thus reducing HIFs tasks, decreasing hemoglobin concentration and pulmonary arterial hypertension.

JAK2-unmutated erythrocytosis or non-polycythemia vera erythrocytosis is a rare condition comprising both acquired and hereditary forms. Although acquired erythrocytosis has been well-studied, hereditary erythrocytosis remains poorly studied. Genetic alterations associated with hereditary erythrocytosis include mutations in erythropoietin receptor and erythropoietin (EPO), altered oxygen affinity mutations, and variants associated with the oxygen-sensing pathway. We established a molecular diagnostic approach based on these genes and retrospectively evaluated. Peripheral blood from 56 erythrocytosis patients, lacking JAK2 mutation, were screened for oxygen-sensing pathway abnormalities. Two novel mutations were identified in the EGLN1 gene: NM_022051.2:c.712G > C (p.Gly238Arg) and NM_022051.2:c.122A > C (p.Tyr41Ser) in two patients separately. Notably, both reported heterozygous mutations were absent in the population database. Predictions using multiple computer software indicated that these two missense mutations were harmful and induced a highly conserved amino acid change in EGLN1. Patients with the two mutations exhibited normal serum EPO levels and high hemoglobin and hematocrit levels. Additionally, three other variants of genes were identified in the oxygen-sensing pathway, including endothelial PAS domain protein 1 (EPAS1) rs184760160(2/56), and EGLN1 rs186996510(2/56), rs555121182(2/56). These variants were categorized as benign or likely benign. Our findings provide a framework for etiological research and highlight the importance of screening for genetic mutations associated with erythrocytosis in clinical practice.

Sheep were domesticated in the Fertile Crescent and then spread globally, where they have been encountering various environmental conditions. The Tibetan sheep has adapted to high altitudes on the Qinghai-Tibet Plateau over the past 3000 years. To explore genomic variants associated with high-altitude adaptation in Tibetan sheep, we analyzed Illumina short-reads of 994 whole genomes representing ∼ 60 sheep breeds/populations at varied altitudes, PacBio High fidelity (HiFi) reads of 13 breeds, and 96 transcriptomes from 12 sheep organs. Association testing between the inhabited altitudes and 34,298,967 variants was conducted to investigate the genetic architecture of altitude adaptation. Highly accurate HiFi reads were used to complement the current ovine reference assembly at the most significantly associated β-globin locus and to validate the presence of two haplotypes A and B among 13 sheep breeds. The haplotype A carried two homologous gene clusters: (1) HBE1, HBE2, HBB-like, and HBBC, and (2) HBE1-like, HBE2-like, HBB-like, and HBB; while the haplotype B lacked the first cluster. The high-altitude sheep showed highly frequent or nearly fixed haplotype A, while the low-altitude sheep dominated by haplotype B. We further demonstrated that sheep with haplotype A had an increased hemoglobin-O2 affinity compared with those carrying haplotype B. Another highly associated genomic region contained the EGLN1 gene which showed varied expression between high-altitude and low-altitude sheep. Our results provide evidence that the rapid adaptive evolution of advantageous alleles play an important role in facilitating the environmental adaptation of Tibetan sheep.

Zebrafish mutants in egln1 display a hypoxic response and develop polycythemia

The present study investigated two single nucleotide polymorphisms (SNPs)—rs479200 and rs516651 in the host EGLN1/PHD2 gene for their association with COVID-19 severity. A retrospective cohort of 158 COVID-19 patients from the Indian population (March 2020 to June 2021) was enrolled. Notably, the frequency of C allele (0.664) was twofold higher than T allele (0.336) in severe COVID-19 patients. Here, we report a novel finding that the C allele of rs479200 in the EGLN1 gene imparts a high risk of severe COVID-19 (odds ratio—6.214 (1.84–20.99) p = 0.003; 9.421 (2.019–43.957) p = 0.004), in additive inheritance model (adjusted and unadjusted, respectively).

Environmental and genetic factors are jointly involved in the development of chronic obstructive pulmonary disease (COPD). The EGLN1 gene is a major factor in upstream regulation of the hypoxia-inducible pathway. EGLN1 negatively regulates the hypoxia-inducible factors HIF-lα and HIF-2α by regulating the concentration of oxygen, mainly in a hypoxic environment. Hypoxia is a common physiologic condition during the progression of COPD, and several studies have identified genetic variants in EGLN1 as a key factor in the adaptation to hypoxic environments. However, it is still unclear whether there is an association between EGLN1 variants and the risk of developing COPD. A case-control study was conducted in the Gannan Tibetan Autonomous Prefecture, Gansu Province. A total of 292 COPD patients and 297 healthy controls were enrolled to assess the association of EGLN1 single nucleotide polymorphisms (SNPs) (rs41303095 A>G, rs480902 C>T, rs12097901 C>G, rs2153364 G>A) with COPD susceptibility. The EGLN1 rs41303095 A>G, rs480902 C>T, rs12097901 C>G, and rs2153364 G>A polymorphisms were not associated with COPD susceptibility (p > 0.05). The EGLN1 rs41303095 A>G, rs480902 C>T, rs12097901 C>G and rs2153364 G>A polymorphisms were found in this study not to be associated with susceptibility to COPD in Gannan Tibetans.

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by high blood pressure in the pulmonary arteries, which can potentially lead to heart failure over time. Previously, our lab found that endothelia-specific knockout of Egln1, encoding prolyl 4-hydroxylase-2 (PHD2), induced spontaneous pulmonary hypertension (PH). Recently, we elucidated that Tmem100 is a lung-specific endothelial gene using Tmem100-CreERT2 mice. We hypothesize that lung endothelial-specific deletion of Egln1 could lead to the development of PH without affecting Egln1 gene expression in other organs. Tmem100-CreERT2 mice were crossed with Egln1 flox/flox mice to generate Egln1 f/f ;Tmem100-CreERT2 (LiCKO) mice. Western blot and immunofluorescent staining were performed to verify the knockout efficacy of Egln1 in multiple organs of LiCKO mice. PH phenotypes, including hemodynamics, right heart size and function, pulmonary vascular remodeling, were evaluated by right heart catheterization and echocardiography measurements. Tamoxifen treatment induced Egln1 deletion in the lung endothelial cells (ECs) but not in other organs of adult LiCKO mice. LiCKO mice exhibited an increase in right ventricular systolic pressure (RVSP, ~35 mmHg) and right heart hypertrophy. Echocardiography measurements showed right heart hypertrophy, as well as cardiac and pulmonary arterial dysfunction. Pulmonary vascular remodeling, including increased pulmonary wall thickness and muscularization of distal pulmonary arterials, was enhanced in LiCKO mice compared to wild-type mice. Tmem100 promoter-mediated lung endothelial knockout of Egln1 in mice leads to development of spontaneous PH. LiCKO mice could serve as a novel mouse model for PH to study lung and other organ crosstalk.

Introduction. In addition to the clonal nature of the development of erythrocytosis, there are other causes, such as germinal mutations in genes of proteins responsible for the development of familial inherited erythrocytosis (EPOR, VHL, EPAS1, EGLN1, etc.).Aim. To conduct the analysis of mutations in the EPOR, VHL, EPAS1 and EGLN1 genes associated with the familial erythrocytosis ECYT1-4 among JAK2- and CALR-negative patients.Materials and methods. The study included 50 JAK2- and CALR-negative patients of Krasnoyarsk Krai with erythrocytosis of unclear etiology. Analysis of mutations in the EPOR, VHL, EPAS1 and EGLN1 genes, responsible for the development of familial erythrocytosis was conducted with the use of the Sanger sequencing. A mass parallel sequencing study was also performed for 12 patients.Results. The Sanger sequencing analysis of EPOR, VHL, EPAS1 and EGLN1 revealed any of the genetic variants in 22 of the 50 patients studied. Of all the variants identifi ed in the coding regions of the genes surveyed that result in amino acid substitutions, the following were of biggest interest: 1) two mutations in the VHL gene (rs28940298 and rs5030821) associated with the development of Chuvash polycythemia (ECYT2); 2) rs12097901 variant in the EGLN1 gene associated with altitude adaptation and increasing haemoglobin levels, but with no pathogenetic relevance for erythrocytosis according to ClinVar; and 3) one mutation in the EPOR gene not previously described in literature. According to the results of the NGS study, 12 somatic and 4 putative germinal variants were identifi ed in 5 out of 12 patients.Conclusion. The possibility of conducting a comprehensive molecular genetic study in order to identify new mutations or those already described in the literature in genes associated with familial erythrocytosis could make a signifi cant contribution to the diagnosis of patients with absolute erythrocytosis.

Hereditary erythrocytosis is a rare hematologic disorder characterized by an excess of red blood cell production. Here we describe a European collaborative study involving a collection of 2,160 patients with erythrocytosis sequenced in ten different laboratories. We focused our study on the EGLN1 gene and identified 39 germline missense variants including one gene deletion in 47 probands. EGLN1 encodes the PHD2 prolyl 4-hydroxylase, a major inhibitor of hypoxia-inducible factor. We performed a comprehensive study to evaluate the causal role of the identified PHD2 variants: (i) in silico studies of localization, conservation, and deleterious effects; (ii) analysis of hematologic parameters of carriers identified in the UK Biobank; (iii) functional studies of the protein activity and stability; and (iv) a comprehensive study of PHD2 splicing. Altogether, these studies allowed the classification of 16 pathogenic or likely pathogenic mutants in a total of 48 patients and relatives. The in silico studies extended to the variants described in the literature showed that a minority of PHD2 variants can be classified as pathogenic (36/96), without any differences from the variants of unknown significance regarding the severity of the developed disease (hematologic parameters and complications). Here, we demonstrated the great value of federating laboratories working on such rare disorders in order to implement the criteria required for genetic classification, a strategy that should be extended to all hereditary hematologic diseases.

Andean Aymara Enriched Genetic Variants Are Beneficial to High Altitude Adaptation of Andean Quechuas Living at 5000 m

BackgroundThe key pathophysiological changes in androgenetic alopecia (AGA) are limited to hair follicles (HFs) in frontal and vertex regions, sparing the occipital region.ObjectivesTo identify biological differences among HF subpopulations.MethodsPaired vertex and occipital HFs from 10 male donors with AGA were collected for RNA sequencing assay. Furthermore, HF and cell experiments were conducted on the identified key genes to reveal their roles in AGA.ResultsTranscriptome profiles revealed that 506 mRNAs, 55 microRNAs and 127 long noncoding RNAs were differentially expressed in the AGA vertex HFs. Pathway analysis of mRNAs and microRNAs revealed involvement of the hypoxia‐inducible factor (HIF)‐1, Wnt/β‐catenin, and focal adhesion pathways. Differential expression of HIF‐1 prolyl hydroxylase enzymes (EGLN1, EGLN3) and Wnt/β‐catenin pathway inhibitors (SERPINF1, SFRP2) was experimentally validated. In vitro studies revealed that reduction of EGLN1, EGLN3, SERPINF1 and SFRP2 stimulated proliferation of dermal papilla cells. Ex vivo HF studies showed that downregulation of EGLN1, EGLN3 and SERPINF1 promoted HF growth, postponed HF catagen transition, and prolonged the anagen stage, suggesting that these genes may be potentially utilized as therapeutic targets for AGA.ConclusionsWe characterized key transcriptome changes in male AGA HFs, and found that HIF‐1 pathway‐related genes (EGLN1, EGLN3) and Wnt pathway inhibitors (SERPINF1, SFRP2) may play important roles in AGA.What is already known about this topic?Multiple differentially expressed genes and signalling pathways have been found between hair follicles (HFs) in the balding area (frontal and vertex regions) and nonbalding area (occipital region) of individuals with androgenetic alopecia (AGA).A whole‐transcriptome atlas of the vertex and occipital region is lacking.What does this study add?We identified a number of differentially expressed genes and pathways between balding vertex and nonbalding occipital AGA HFs by using whole‐transcriptome analyses.We identified pathways not previously reported in AGA, such as the hypoxia‐inducible factor (HIF)‐1 signalling pathway.We verified that HIF‐1 pathway‐related genes (EGLN1, EGLN3) and Wnt pathway inhibitors (PEDF, SFRP2) played important roles in dermal papilla cell activity, hair growth and the hair cycle.What is the translational message?The EGLN1, EGLN3, SERPINF1 and SFRP2 genes may be potentially utilized as therapeutic targets for AGA.

IOX1 Fails to Reduce α-Globin and Mediates γ-Globin Silencing in Adult β0-Thalassemia/Hemoglobin E Erythroid Progenitor Cells

Novel mutations in EPO-R and oxygen-dependent degradation (ODD) domain of EPAS1 genes-a causative reason for Congenital Erythrocytosis