Shinshu M ed J, 63⑶ :157〜165, 2015

Gene‑gene Interaction Between EPAS1 and EGLN1 in Patientswith High‑Altitude Pulmonary Edema
Toshimichi HORIUCHI , Masao OTA , Yunden DROMA
Nobumitsu KOBAYASHI and Masayuki HANAOKA
1) The First Department of Medicine, Shinshu University School of Medicine
2) Department of Legal Medicine, Shinshu University School of Medicine

Objective:Endothelial PER‑ARNT‑SIM (PAS)domain protein 1(EPAS1,also known as HIF2α)and egl nine
homolog 1 (EFLN1), also known as prolyl hydroxylase domain protein 2 (PHD2), have key functions in the
upstream of the hypoxia‑inducible factor (HIF)pathway.In order to dissect the genetic biologyof susceptibility to high‑altitude pulmonary edema (HAPE)from the viewpoint of the HIF pathway,we identiﬁed the allelicdiscriminations of three signiﬁcant tag single‑nucleotide polymorphisms (SNPs)in EPAS1 and three tag SNPs
in EGLN1 in HAPE‑susceptible (HAPE‑s)Japanese subjects.
Methods: Alleles were determined for the six SNPs (rs13419896, rs4953354, and rs4953388 in EPAS1 ;rs1435166, rs7542797, and rs2153364 in EGLN1) by the TaqM an

SNP Genotyping Assay in a group of 59

HAPE‑s subjects and a control group of 67 HAPE resistant (HAPE‑r)subjects.In addition to the case‑control
analysis,multi‑dimensional reduction (MDR)methodology was applied to a gene‑gene interaction analysis toevaluate the association of HAPE‑s with gene‑gene interactions.
Results:The EGLN1 rs2153364(A/G)x EPAS1 rs13419896(G/A)interaction was signiﬁcantly associated with
HAPE‑s in the pairwise model (P＝0.0049)based on the balanced accuracy of 63.23% in M DR.However,nosigniﬁcance was detected for the association with HAPE‑s in the single gene model.
Conclusion :The EPAS1‑EGLN1 interaction appears to be associated with HAPE‑s in the Japanese population despite the individual genes not being associated with HAPE‑s. Shinshu Med J 63 : 157 ―165, 2015
(Received for publication January 29, 2015;accepted in revised form February 17, 2015)
Key words:hypoxia‑inducible factor, gene‑gene interaction, high‑altitude pulmonary edema

Introduction

Science Research Society (http://soukaken.com/,inJapanese). Exposure to the oxygen‑depleted envi-

M ountains cover more than one‑ﬁfth of theronment triggers the onset of a range of physiologi-

Earthʼ
s surface and are popular tourist destinations.

cal and biochemical reactions that enhance theLarge numbers of people travel to high altitudes foreﬃcacy of the bodyʼs respiratory , cardiovascular,

various reasons,including trekking,pilgrimage,andand oxygen utilization systems through the proc-

tourism. In Japan, approximately 38‑65 million

ess of acclimatization. Failure to acclimatize leads

people climb mountains (＞2,000 m above sea level)to high‑altitude pulmonary edema (HAPE), a form

for recreation each year according to the Japanof accelerated pulmonaryedema of non‑cardiogenic
origin that occurs in lowlanders who rapidly ascend

Corresponding author:Masayuki Hanaoka
The First Department of Medicine, Shinshu University
School of M edicine, 3‑1‑1 Asahi, M atsumoto, Nagano

above 2,500 m ;it has a considerably high mortality
if hypoxic exposure persists. The inception and390‑8621, Japan

progression of HAPE are governed by both genetic

E‑mail:masayuki＠shinshu-u.ac.jp

and environmental factors .

No. 3, 2015157

Horiuchi.Ota.Droma et al.

The hypoxia‑inducible factor (HIF)pathwaytrig-

rs4953354, and rs4953388) and three tag SNPs ingers downstream cascades of multiple molecular

EGLN1 (rs1435166, rs7542797, and rs2153364) inevents involving the pathophysiology of hypoxia .

HAPE‑susceptible (HAPE‑s)Japanese subjects andMore than a dozen candidate genes in the HIF

compared the results to HAPE‑resistant (HAPE‑r)pathway have been shown to contribute to theJapanese subjects in a case‑control study and gene‑

genetic adaptation to hypoxia in high‑altitude popu-

gene interaction analysis.

lations across multiple studies, including en-

Methods

dothelial PER‑ARNT‑SIM (PAS)domain protein 1(EPAS1), also known as HIF2α, and egl nine

Ethics statement

homolog 1 (EGLN1), also known as prolyl hy-

The current study was approved by the Ethics

droxylase domain protein 2 (PHD2). These two

Committee of Shinshu University School of Medi-

key genes function in the upstream of the HIF

cine (Matsumoto, Japan). The protocol was perfor-

pathway in human high‑altitude adaptation.

med in accordance with the principles outlined inSpeciﬁcally, the single‑nucleotide polymorphisms

the Declaration on Helsinki of the World M edical(SNPs) of rs13419896 (G/A), rs4953354 (A/G), andAssociation

rs4953388 (G/A)in EPAS1 were demonstrated to be

Committee of Shinshu University School of Medi-

signiﬁcantly associated with hypoxia tolerance incine (Permission numbers: 106). Written informed

indigenous high‑altitude Tibetan

consent was obtained from each subject after pro-and Sherpa

populations. Moreover, the SNPs of rs1435166 (A/G), rs7542797 (A/C), rs2153364 (A/G) in EGLN1

and was approved by the Ethics

viding them with a full explanation of the study.
Subjects

were documented to be signiﬁcantly associated with

The case‑control study included a case group

human high‑altitude adaptation in the Indo‑Aryan

with 59 HAPE‑s subjects (52 males, 7 females,

population .Obviously,the genetic contributions of

average age 34.2 years)and a control group with 67

HIF to hypoxia adaptation in indigenous high‑alti-

HAPE‑r subjects (58 males,9 females,average age

tude populations may not be applicable to the eluci-

37.0 years).All subjects were unrelated natives born

dation of genetic biology in HAPE,an acute diseasein Japan and resided at low altitudes.The HAPE‑scaused by sudden oxygen deprivation,despite high‑subjects were patients admitted to Shinshu Univer-

altitude hypoxia being a common initial element insity Hospital because of HAPE that occurred whileboth disorders. Indigenous high‑altitude popula-climbing in the Japan Alps at heights over 2,500 m

tions, such as Tibetans and Sherpas, have success-between 1971 and 2013.The diagnosis of HAPE wasfully lived and reproduced at high altitudes forbased on diagnostic criteria at the onset of thehundreds of generations with hypoxia as a constantdisorder .All patients with HAPE recovered promptly

evolutionary pressure,bringing about natural selec-

within one week of hospitalization.Related clinicaltion toward phenotypes (e.g., relatively low hemo-

examinations and cardiovascular tests were con-globin) that tend to oﬀer beneﬁcial adaptations toducted to exclude any pre‑existing cardiopulmo-

sustained hypoxia.In contrast,HAPE occurs innaryproblems.The HAPE‑r subjects wereelitemoun-lowlanders rapidly exposed to a high altitude,

taineers from the Mountaineering Association of

resulting in a failure to acclimatize to high‑altitude

Nagano Prefecture (Nagano,Japan)and the Alpine

hypoxia,which is characterized byhypoxia‑induced

Club of Shinshu University(Matsumoto,Japan)andacute pulmonary vasoconstriction

often climbed mountains higher than 3,000 m. We.

In order to dissect the genetic biology of HAPE

deﬁned these subjects as HAPE‑r due to their resis-

susceptibility from the viewpoint of the HIF path-tance to HAPE during exposure to high‑altitude

way, we identiﬁed the allelic discriminations ofenvironments.During recruitment,no HAPE‑r sub-three signiﬁcant tag SNPs in EPAS1 (rs13419896,

jects reported a history of medical problems related

158

Shinshu Med J Vol.63

EPAS1 and EGLN1 interaction in high‑altitude pulmonary edema

to altitude or cardiopulmonarydisorders in a questi-

are located in introns.

onnaire containing the components of the Lake

Selection of

Tag SNPs

Louise Score . Venous blood samples were col-The EGLN1 gene contains four coding exons andlected and frozen at ‑70 ℃ for research purposes.

maps to chromosome 1q42‑q43. Three SNPs

Selection of

Tag SNPs［rs1435166 (A/G), rs7542797 (A/C), and rs2153364

The tag SNPs act as direct proxies for all other(A/G)］were selected as tag SNPs due to an evalua-

untyped SNPs because they are highly correlatedtion of their tagging eﬃciency(r ＝1.0)for available

with one another by means of pairwise tagging .

SNPs in EGLN1 from the genotype data in the

Setting the threshold of correction coeﬃcient (r )atInternational HapMap Consortium 2005(http://hap-

1.0 resulted in a perfect correlation between the tag

map.ncbi.nlm.nih.gov/) with the JPT population

SNP and untyped SNPs, capturing the untyped(Table 2). In particular, EGLN1 rs1435166 (Table 2)

SNPs perfectly and eﬃciently.

had highly pairwise correlations with seven SNPs

The human EPAS1 gene contains 16 exons, with

reported to be signiﬁcantly associated with HAPE‑

spans of at least 120 kb, and maps to chromosome

s in the Indian population . All three SNPs are

2p21‑p16. The introns within the genomic region

located in introns.

encode the N‑terminal basic helix‑loop‑helix

Genotyping(bHLH)/PAS proteins,which are critical regulators

Genomic DNA samples from HAPE‑s and HAPE‑rof gene expression networks of transcriptional

subjects were extracted from venous blood leuko-

responses to low oxygen tension mediated by thecytes as described previously

HIF signaling pathway . Three SNPs［rs13419896

ing Assay Mix containing the forward and reverse(G, ancestral allele/A, derived allele) according toprimers and FAM

the NCBI dbSNP database, rs4953354 (A/G), andbinder‑labeled probes for the six SNPs were pur-rs4953388 (G/A)］ in EPAS1 were selected as tagchased from Applied Biosystems Inc. (Tokyo,

SNPs because they can capture (r ＝1.0) numerous

Japan). Allelic discrimination was performed using

untyped SNPs in EPAS1 from the genotype data ina pre‑designed 5′nuclease assay (TaqMan

the International HapM ap Consortium 2005 (http://

Genotyping Assay)and the Applied Biosystems 7500

hapmap.ncbi.nlm.nih.gov/)with the Japanese popu-

Fast Real‑time PCR System according to the manu-

lation from Tokyo, Japan (JPT) (Table 1). In addi-

facturerʼs instructions (Applied Biosystems Inc.,tion, these SNPs are signiﬁcantly associated with

Foster City, CA, USA). Following thermal cycling,

hypoxia tolerance in indigenous high‑altitude

genotype data were acquired automatically andTibetan and Sherpa populations

analyzed using sequence detection software (SDS

Table 1

.All three SNPs

and VIC.The SNP Genotypdye‑minor groove

SNP

Tagging eﬃciency of single nucleotide polymorphisms (SNPs) rs13419896 (G/A), rs4953354 (A/G), andrs4953388 (G/A)in EPAS1 in the Tokyo, Japan (JPT)population .
HapMap‑JPT

Test SNP

Alleles captured

rs13419896 rs4952819, rs4953342, rs4952820, and rs4953348
rs4953354 rs10187368, rs4953355, rs1868085, rs1868086, rs1868087, rs1374748, and rs13409493
rs1447563, rs4953372, rs11125075, rs1530624, rs4396767, rs12986899, rs13003074, rs2121700, rs718849,
rs4953388

rs13020043, rs13002880, rs2121698, rs4953387, rs4953390, rs13030579, rs12986653, rs13001507, rs13007688,
rs13011721, rs6544898, rs13005507, rs13024277, rs13024546, rs13025211, rs17817004, rs4953396, rs2084679,
rs13010097, rs2346414, rs2346415, rs880671, and rs4952830

Checked by tagger software based on the genotype data in the International HapM ap Consortium 2005 (http://
hapmap.ncbi.nlm.nih.gov/)with Japanese from the JPT.
The threshold of pairwise correction (r )was set at 1.0, at which all alleles are to be captured.
No. 3, 2015159

Horiuchi.Ota.Droma et al.
Table 2

Tagging eﬃciency of single nucleotide polymorphisms (SNPs) rs1435166 (A/G), rs7542797 (A/C), andrs2153364 (A/G)in EGLN1 in the Tokyo, Japan (JPT)population .
HapMap‑JPT

Test SNP

Alleles captured
rs479200,rs2486729,rs2437148,rs2808614,rs2244994,rs2486732,rs2024878,rs10489611,rs2437147,rs973254,

rs1435166

rs2472261, rs2790889, rs2486736, rs2749699, rs2808616, rs2808584, rs2808586, rs2790890, rs2486731,
rs2486742,rs2790887,rs2749710,rs480902,rs2066140,rs10489610,rs973252,rs2486727,rs2244986,rs2790879,
rs2474623,rs973253,rs2808611,rs2739513,rs2486737,rs2572263,rs1538664,rs2808580,rs2486741,rs2739511,
rs2491405, rs2491404, rs2790891, rs2790882, and rs2486745

rs7542797
rs2153364

rs7542797
rs2153364

Checked by tagger software based on the genotype data in the International HapM ap Consortium 2005 (http://
hapmap.ncbi.nlm.nih.gov/)with Japanese from the JPT.
The threshold of pairwise correction (r )was set at 1.0,at which all alleles are to be captured.The SNPs in bold werereported to be signiﬁcantly associated with HAPE‑s in the Indian population (14).

v1.3.1, Applied Biosystems Inc.).

Results

Statistical analysis
The chi‑square test was used for between‑group

Single gene modelcomparisons,but Fisherʼs exact probabilitytest was

The genotype distributions of the six SNPs con-used for comparisons when the number of subjects

formed to HWE (P＞0.05) in both the case andwas less than ﬁve. The exact test of Hardy‑Wein-control groups. No signiﬁcant diﬀerences were

berg equilibrium (HWE) was performed by thedetected between the case and control groups inMarkov chain method,which is reported to have theterms of genotype distributions or allelic fre-advantage of obtaining complete enumeration whenquencies for the six SNPs (Table 3),suggesting thatthe number of alleles and sample size are small .

these SNPs were not associated with HAPE suscep-

Therefore,the possibility of type II error due to ourtibility in the single gene model.

relatively small sample sizes was minimized.Two‑

Gene‑gene interaction analysis

tailed P‑values ＜0.05 indicated signiﬁcance. The

Because three SNPs (EPAS1 rs4953354 andcurrent genetic analysis was trustworthydespite thers4953388 and EGLN1 rs7542797) were not derived

relatively small sample sizes in both groups because

homozygous genotypes in the HAPE‑s and HAPE‑

the studied cohorts were ethnically homogenousr groups (Table 3), the EGLN1 rs2153364 (A/G) x

Japanese.

EPAS1 rs13419896 (G/A)model was the best model

Gene‑gene interactions were evaluated by multi‑of random pairwise combinations for the six SNPs

dimensional reduction (M DR,version 3.0.2)with theacross the two genes,based on a balanced accuracy

variable alleles of the SNPs in the two genes.

of 63.23% and a cross‑validation consistency of 6/

Random combinations of pairwise SNPs were anal-

10 in the performance of MDR in the whole dataset(http://www.multifactordimen-(Fig. 1). This best pairwise interaction model (Fig.

yzed by M DR

sionalityreduction.org/) to detect and characterize

1) showed a signiﬁcant association with HAPE‑s

the pairwise interactions of these SNPs across the［P＝0.0049 ;95% conﬁdence interval (CI)3.16 (1.40‑

two genes. The relative risk (RR) and 95%

7.14)］. Regarding HAPE susceptibility, the interac-conﬁdence interval (95% CI) were calculatedtion between EGLN1 rs2153364 AA (ancestralaccordingly.

genotype)and EPAS1 rs13419896 GA (heterozygous
genotype) was categorized as the most high‑risk
combination (9 subjects of HAPE‑s vs.3 subjects of

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Shinshu Med J Vol.63

EPAS1 and EGLN1 interaction in high‑altitude pulmonary edema
Table 3

Gene

Genotype distributions and allele frequencies of rs13419896, rs4953354, and rs4953388 in EPAS1 andrs1435166, rs7542797, and rs2153364 in EGLN1 in HAPE‑s (n＝59)and HAPE‑r subjects (n＝67)

dbSNP

AllelesAllele 1
Frequency

1/2

HAPE‑s HAPE‑r

Genotype distribution
P

P

11
12
22
11/
HAPE‑s HAPE‑r HAPE‑s HAPE‑r HAPE‑s HAPE‑r 12＋22

P
11＋12/
22

rs13419896
rs4953354
rs4953388

G/A
A/G
G/A

0.796
0.889
0.963

0.735
0.875
0.968

0.266
0.742
0.824

0.611
0.778
0.926

0.545
0.750
0.937

0.370
0.222
0.074

0.379
0.250
0.063

0.019
0
0

0.076
0
0

0.496
0.724
0.821

0.152
‑
‑

rs1435166
EGLN1 rs7542797
rs2153364

A/G
A/C
A/G

0.432
0.924
0.508

0.455
0.918
0.515

0.714
0.858
0.919

0.203
0.847
0.322

0.164
0.836
0.224

0.458
0.153
0.373

0.582
0.164
0.582

0.339
0
0.305

0.254
0
0.194

0.569
0.865
0.216

0.294
‑

EPAS1

0.149

n＝total number of subjects;SNP＝single nucleotide polymorphism ;HAPE‑s＝subjects susceptible to high‑altitude pulmonary edema ;HAPE‑r＝subjects resistant to high‑altitude pulmonary edema.
1/2 indicates ancestral allele/derived allele according to the NCBI dbSNP database.
Chi‑square test (2×2 contingency table).
2×2 contingency table assuming dominant mode (11/12＋22)of inheritance in HAPE‑s.
2×2 contingency table assuming recessive mode (11＋12/22) of inheritance in HAPE‑s.

Fig. 1The best model as determined bymulti‑dimensional reduction (M DR)for EPAS1 rs13419896(G/A)x EGLN1 rs2153364 (A/G). The numbers within each square represent the numbers of cases(left) and controls (right). For each square, dark‑grey shading indicates a high risk of high‑altitude pulmonary edema (HAPE), whereas light‑grey shading represents a low risk of HAPE
and white shading indicates no combination.The interaction between EGLN1 rs2153364 AA andEPAS1 rs13419896 GA was categorized as the most high‑risk combination for HAPE susceptibility［relative risk (RR)＝3.41 with 95% conﬁdence interval (95% CI)from 0.97 to 11.99 ］,whereas
the interaction between EGLN1 rs2153364 AG and EPAS1 rs13419896 AA was the most low‑risk
combination for HAPE susceptibility in the Japanese population (RR＝0.23 with 95% CI from 0.
03 to 1.89).The other high‑risk combinations were EGLN1 rs2153364 AA x EPAS1 rs13419896 GG(RR＝2.04 with 95% CI from 0.73 to 5.76) and EGLN1 rs2153364 GG x EPAS1 rs13419896 GG(RR＝1.70 with 95% CI from 0.064 to 4.50),whereas the other low‑risk combinations were EGLN1
rs2153364 AG x EPAS1 rs13419896 GG (RR＝0.70 with 95% IC from 0.39 to 1.28), EGLN1
rs2153364 AG x EPAS1 rs13419896 GA (RR＝0.71 with 95% IC from 0.25 to 2.05) and EGLN1
rs2153364 GG x EPAS1 rs13419896 GA (RR＝0.97 with 95% IC from 0.35 to 2.73).

No. 3, 2015161

Horiuchi.Ota.Droma et al.

HAPE‑r,RR＝3.41 with 95% CI from 0.97 to 11.99)

erythropoietin, among others, to challenge hypoxia

among the detected three high‑risk combinations,stress physiologically.

whereas the interaction between EGLN1 rs2153364

Over the years,a bodyof evidence has accumulat-

AG (heterozygous genotype)and EPAS1 rs13419896

ed for the genetic loci of EPAS1 and EGLN1 being

AA (ancestral genotype) was the most low‑risk

associated with human adaptation to high‑altitude

combination (1 subjects of HAPE‑s vs.5 subjects ofhypoxia through generations

HAPE‑r, RR＝0.23 with 95% CI from 0.03 to 1.89)［rs13419896 (G/A), rs4953354 (A/G), rs4953388 (G/among the four detected low‑risk combinations ofA)］ in EPAS1 are signiﬁcantly associated withgenotypes in the present Japanese population (Fig.

hypoxia tolerance in indigenous high‑altitude

1).

Tibetan and Sherpa
Discussion. The three SNPs

populations.In addition,thethree SNPs ［rs1435166 (A/G), rs7542797 (A/C),
rs2153364 (A/G)］in EGLN1 highly correlate with

The main result of the present study was the

rs479200, rs2486729, rs2486736, rs480902, rs2790879,

detection of a potential association of the interac-rs973253, and rs1538664 in EGLN1 in the Japanesetion between EPAS1 and EGLN1 with HAPE sus-

population ; these SNPs have been signiﬁcantly

ceptibility in the Japanese population.The subjects

associated with HAPE‑s subjects in the Indo‑Aryan

carrying the AA ancestral genotype of EGLN1

population . However, the present study did not

rs2153364 (A/G)and the GA heterozygous genotype

show any associations between the six SNPs andof EPAS1 rs13419896 (G/A) were at high risk for

HAPE susceptibility in the Japanese population in

HAPE.The present study provides some suggestive

the single gene model.On the other hand,the gene‑

information about the EPAS1 and EGLN1 genes ingene interaction analysis suggested a potential asso-

association with HAPE susceptibility in regards tociation of the EPAS1‑EGLN1 interaction with

the HIF signaling pathway. However, these two

HAPE susceptibility in the Japanese population.

genes did not show an association with HAPE‑s in

The adaptive physiological features of Tibetans,the Japanese population in the single gene model.

such as a low hypoxic pulmonary vasoconstrictor

EPAS1 encodes the hypoxia‑inducible‑factor‑2

response and relatively low hemoglobin levels,werealpha (HIF2A)protein,which shares 48% sequenceacquired through natural selection over generations,

identity with HIF1A .Similar to HIF1A,EPAS1 is

as the ancestors of Tibetans occupied the high‑stimulated by hypoxic conditions and heterodimer-

altitude region as early as 30,000 years ago . In

izes with HIF2B for transcriptional activation ofcontrast, the pathophysiological features of HAPE

target genes . In contrast, EGLN1 encodes prolyl

characterized by acute hypoxia‑induced pulmonaryhydroxylase domain protein 2(PHD2),which senses

vasoconstriction and permeable pulmonary vascu-

hypoxia and negatively aﬀects the activity oflar endothelium occur acutely in lowlanders rapidly

HIF2A and plays a regulatory role in mammalian

exposed to high altitudes and hypoxia

oxygen homeostasis . In normoxia, HIF2A

process of natural selection in the Tibetan adapta-

subunits are marked for the ubiquitin‑proteasometion to hypoxia is distinct from the pathogenesis ofdegradation pathway through hydroxylation ofan acute challenge to hypoxic stress in lowlanders

proline by PHD2. When exposed to hypoxia, therapidly exposed to high altitudes. Regarding the

PHD2‑dependent hydroxylation is inadequate andsigniﬁcant associations of EGLN1 loci with suscep-

HIF2A marks for ubiquitin‑proteasome degrada-

tibility to HAPE in the Indo‑Aryan population ,tion fade away, thereby enhancing the HIF signa-

the probability of replicating such results is only

ling pathway and inducing the expression of a seriesoccasional in the Japanese population because ofof genes that activate glycolytic enzymes, hemeox-

the polygenic architecture of the human genomeygenase, vascular endothelial growth factor, andand the characteristics of SNPs . Nevertheless,

162.Thus,theShinshu Med J Vol.63

EPAS1 and EGLN1 interaction in high‑altitude pulmonary edema

EGLN1 rs480902 did not show a signiﬁcant associa-

dothelial growth factor, and erythropoietin, amongtion with acute mountain sickness in the Hanothers,to participate in the pathogenesis of HAPE.

Chinese population .

Detailed investigations are expected to determine

Epistasis,or interactions between genes,is funda-

the functions of the gene‑gene interactions in thementally important to understanding both the struc-

HIF signaling pathway in the pathogenesis ofture and function of genetic pathways and the evolu-

HAPE.

tionary dynamics of complex genetic systems .

The power of the present study was inadequate

The methodology of gene‑gene interaction analysis

due to the limitations of the MDR method, which

was eventually carried out to assess the multi‑

reduced high‑dimensional genetic data into a single

dimensional relations of the EPAS1 and EGLN1

dimension so that gene‑gene interactions could begenes of the HIF signaling pathway with HAPE

detected in a sample size smaller than the original

susceptibility in the Japanese population in thesample size. HAPE is actually a relatively rare

present study,despite the fact that numerous candi-disease and occurs only in lowlanders rapidly

date genes were individually identiﬁed as being

exposed to high altitudes, so the sample size issigniﬁcantly associated with HAPE‑s populations

always smaller than other common diseases. Thus,

worldwide. The current superﬁcial results are

the present gene‑gene interaction analysis needs to

not direct evidence of the functions of and communi-

be replicated in other populations with HAPE andcations between the genetic varieties for the physio-

proven by other technical analyses of gene‑genelogical response to acute hypoxia in HAPE suscepti-

interactions, such as BOOST .

bility.However,the present results showing that the

In conclusion, the present study demonstrated aancestral homozygous AA genotype of EGLN1

potential association of the EPAS1×EGLN1 inter-rs2153364 (A/G) interacts with EPAS1 rs13419896

action with HAPE susceptibility in the Japanese(G/A)as a high‑risk genotype in HAPE‑s subjects

population, despite no associations detected in theis in agreement with the previous report by Mishar

single gene model.This ﬁnding is small,but encour-et al.; they reported a 4.55‑fold up‑regulation of

aging,and needs to be validated through replication

EGLN1 expression in HAPE‑s subjects comparedstudies with large sample sizes and diﬀerent eth-

to HAPE‑r subjects .Therefore,we proposed that

nicities to establish the global eﬃcacy of these

the up‑regulation of the negative regulator ofgenes in the HIF signaling pathway regarding

EGLN1 causes down‑regulation of proteasome deg-

hypoxic response in HAPE susceptibility.

radation of HIF‑2 in a hypoxic environment, leading to HIF‑2 accumulation and inducing over‑expressions of downstream genes that activate

The authors state that thay have no conﬂict ofinterest in the present study.

glycolytic enzymes, hemeoxygenase, vascular enReferences
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