Evidence for a genetic basis for altitude-related illness

Association of Pre-existing Mental Health Conditions with Acute Mountain Sickness at Everest Base Camp

Hüfner, Katharina, Fabio Caramazza, Evelyn R. Pircher Nöckler, Agnieszka E. Stawinoga, Paolo Fusar-Poli, Sanjeeb S. Bhandari, Buddha Basnyat, Monika Brodmann Maeder, Giacomo Strapazzon, Iztok Tomazin, Ken Zafren, Hermann Brugger, and Barbara Sperner-Unterweger. Association of pre-existing mental health conditions with acute mountain sickness at Everest Base Camp. High Alt Med Biol. 23:338-344, 2022. Background: Mental health disorders are common, but limited data are available regarding the number of people with a past medical history of psychiatric diagnoses going to high altitude (HA). It is also unknown whether mental health conditions are associated with an increased risk of acute mountain sickness (AMS). Methods: We analyzed data from a previous study at Everest Base Camp. Participants self-reported their past medical history and history of substance use and had a brief history taken by a physician. AMS was assessed using the self-reported 2018 Lake Louise AMS Score. Results: Eighty-five participants (66 men and 19 women, age 38 ± 9 years) were included. When questioned by a physician, 28 participants reported prior diagnoses or symptoms compatible with depression (23%), anxiety disorder (6%), post-traumatic stress disorder (1%), and psychosis/psychotic experiences (9%). The prevalence of psychiatric diagnoses in the past medical history was much lower in the self-reported data (2/85) compared to data obtained via physician assessment (28/85). Increased risks of AMS were associated with a past medical history of anxiety disorder (odds ratio [OR] 22.7; confidence interval [95% CI] 2.3-220.6; p < 0.001), depression (OR 3.6; 95% CI 1.2-11.2; p = 0.022), and recreational drug use ever (OR 7.3; 95% CI 1.5-35.5; p = 0.006). Conclusions: Many people who travel to HA have a past medical history of mental health conditions. These individuals have an increased risk of scoring positive for AMS on the Lake Louise Score compared with people without a history of mental health conditions.

Relevance of carotid bodies in COVID-19: A hypothetical viewpoint

We have considered some of the available evidence to account for the impact of SARS-CoV on the regulatory control of the autonomic nervous and respiratory systems. Apart from stimulating general interest in the subject, our hope was to provide putative explanations for some of the patients' symptoms based on described physiological and pathophysiological mechanisms seen in other diseases. Herein, we have focused on the carotid bodies. In this hypothetical viewpoint, we have discussed the plasticity of the carotid body chemoreflex and made a comparison between acute and chronic exposures to high altitude with COVID-19. From these discussions, we have postulated that the sensitivity of the hypoxic ventilatory response may well determine the outcome of disease severity and those that live at high altitude may be more resistant. We have provided insight into silent hypoxia and attempted to explain an absence of ventilatory drive and anxiety yet maintenance of consciousness. In an attempt to discover more about the mysteries of COVID-19, we conclude with questions and some hypothetical studies that may answer them.

Coping with hypoxemia: Could erythropoietin (EPO) be an adjuvant treatment of COVID-19?

A very recent epidemiological study provides preliminary evidence that living in habitats located at 2500 m above sea level (masl) might protect from the development of severe respiratory symptoms following infection with the novel SARS-CoV-2 virus. This epidemiological finding raises the question of whether physiological mechanisms underlying the acclimatization to high altitude identifies therapeutic targets for the effective treatment of severe acute respiratory syndrome pivotal to the reduction of global mortality during the COVID-19 pandemic. This article compares the symptoms of acute mountain sickness (AMS) with those of SARS-CoV-2 infection and explores overlapping patho-physiological mechanisms of the respiratory system including impaired oxygen transport, pulmonary gas exchange and brainstem circuits controlling respiration. In this context, we also discuss the potential impact of SARS-CoV-2 infection on oxygen sensing in the carotid body. Finally, since erythropoietin (EPO) is an effective prophylactic treatment for AMS, this article reviews the potential benefits of implementing FDA-approved erythropoietin-based (EPO) drug therapies to counteract a variety of acute respiratory and non-respiratory (e.g. excessive inflammation of vascular beds) symptoms of SARS-CoV-2 infection.

High Altitude Pulmonary Edema in a Mining Worker With an Abnormal Rise in Pulmonary Artery Pressure in Response to Acute Hypoxia Without Prior History of High Altitude Pulmonary Edema

High altitude pulmonary edema (HAPE) is a potentially life-threatening form of noncardiogenic pulmonary edema that may develop in otherwise healthy individuals upon ascent to high altitude. A constitutional susceptibility has been noted in some individuals, whereas others appear not to be susceptible at all. In our report, we present a case of HAPE triggered by concurrent respiratory tract infection and strenuous exercise in a mining worker with an abnormal rise in pulmonary artery pressure in response to acute hypoxia, without a prior history of HAPE during almost a year of commuting between high altitude and lowland areas.

Evidence for and Against Genetic Predispositions to Acute and Chronic Altitude Illnesses

MacInnis, Martin J., and Michael S. Koehle. Evidence for and against genetic predispositions to acute and chronic altitude illnesses. High Alt Med Biol. 17:281-293, 2016.-Humans exhibit marked variation in their responses to hypoxia, with susceptibility to acute and chronic altitude illnesses being a prominent and medically important example. Many have hypothesized that genetic differences are the cause of these variable responses to hypoxia; however, until recently, these hypotheses were based primarily on small (and sometimes anecdotal) reports pertaining to apparent differences in altitude illness susceptibility between populations, the notion that a history of altitude illness is indicative of subsequent risk, the heritability of hypoxia-related traits, and candidate gene association studies. In the past 5 years, the use of genomic techniques has helped bolster the claim that susceptibility to some altitude illnesses is likely the result of genetic variation. For each of the major altitude illnesses, we summarize and evaluate the evidence stemming from three important characteristics of a genetic trait: (1) individual susceptibility and repeatability across assessments, (2) biogeographical differences and familial aggregation, and (3) association(s) with genetic variants. Evidence to support a genetic basis for susceptibilities to acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) is limited, owing partially to the subjective and unclear phenotype of AMS and the rarity and severity of HACE. In contrast, recent genomic studies have identified genes that influence susceptibility to high-altitude pulmonary edema, chronic mountain sickness, and high-altitude pulmonary hypertension. The collection of more individual, familial, and biogeographical susceptibility data should improve our understanding of the extent to which genetic variation contributes to altitude illness susceptibility, and genomic and molecular investigations have the potential to elucidate the mechanisms that underpin altitude illness susceptibility.

Why Are High Altitude Natives So Strong at High Altitude? Nature vs. Nurture: Genetic Factors vs. Growth and Development

Among high-altitude natives there is evidence of a general hypoxia tolerance leading to enhanced performance and/or increased capacity in several important domains. These domains likely include an enhanced physical work capacity, an enhanced reproductive capacity, and an ability to resist several common pathologies of chronic high-altitude exposure. The "strength" of the high-altitude native in this regard may have both a developmental and a genetic basis, although there is better evidence for the former (developmental effects) than for the latter. For example, early-life hypoxia exposure clearly results in lung growth and remodeling leading to an increased O2 diffusing capacity in adulthood. Genetic research has yet to reveal a population genetic basis for enhanced capacity in high-altitude natives, but several traits are clearly under genetic control in Andean and Tibetan populations e.g., resting and exercise arterial O2 saturation (SaO2). This chapter reviews the effects of nature and nurture on traits that are relevant to the process of gas exchange, including pulmonary volumes and diffusion capacity, the maximal oxygen consumption (VO2max), the SaO2, and the alveolar-arterial oxygen partial pressure difference (A-aDO2) during exercise.

HIF2A Variants Were Associated with Different Levels of High-Altitude Hypoxia among Native Tibetans

Hypoxia inducible factors, including HIF1A and HIF2A, play central roles in response to high-altitude hypoxia and genetic variants of HIF1A or HIF2A were associated with high-altitude sickness or adaptation. However, it remains to determine whether they are associated with tolerance to different levels of high-altitude selection pressure among native Tibetans. We recruited 189 Tibetan subjects living at 2,700 meters (Low level of high altitude, LHA), 197 at 3,200 meters (Middle level of high altitude of high altitude, MHA), 249 at 3,700 meters (High level of high altitude, HHA) and 269 at 4,700 meters (Very high level of high altitude, VHA) and performed association analysis of twelve tSNPs (tagging SNPs) in HIF1A and HIF2A with high-altitude. We found (1) a increasing trend of HIF2A rs5621780-C(18.4%, 15.9%, 32.8% and 31.1%, respectively, in LHA, MHA, HHA and VHA)(P = 3.56E-9); (2) increasing trends of HIF2A rs6756667-A(68.7%, 73.4%, 79.9% and 89.6%), rs7589621- G(74.6%, 77.9%, 83.7%, and 92.1%) and rs1868092-A(64.1%, 67.3%, 75.1% and 84.4%) (P = 3.56E-9, 4.68E-16, 1.17E-13 and 7.09E-14, respectively); (3) a increasing trend of haplotype AG (68.7%, 73.1%, 79.9% and 89.6%) (P = 2.22E-7) which was constructed by rs6756667 and rs7589621; (4) a strong linear correlation between major alleles of rs6756667-A (R2 = 0.997, P = 0.002), rs7589621-G (R2 = 0.994, P = 0.003), rs1868092-A (R2 = 0.985, P = 0.008) and altitude by linear correlation test. The associations between HIF2A variants and different level of high altitude support that extremely high-altitude hypoxia challenge imposes selective effects on HIF2A variants among native Tibetans.

Altitude and cold weather: are they vascular risks?

PURPOSE OF REVIEW

The relationship of altitude and cold to cardiovascular risk is complex. Cold is hard to separate from altitude. This review highlights the latest information on cardiovascular disease associated with high altitude and cold; both represent unique clinical situations.

RECENT FINDINGS

Evolution and genetics are relevant to high altitude, with much new information available. Specific physiology explains some congenital heart disease at altitude. New reports of hematological changes associated with altitude and cold help clarify thrombosis, which is relevant to reports of very late in-stent thrombosis at altitude. Multiple cardiovascular risk factors are affected by altitude and cold, and an increased incidence of myocardial infarction occurs. There is new research on acute mountain sickness associated with inflammation with relevance for clinical study of pulmonary edema. Socioeconomics plays a part in altitude and cold effects on cardiovascular disease. In addition to acute disease, high altitude involves chronic mountain sickness with new knowledge of associated cardiovascular endothelial abnormalities.

SUMMARY

High altitude and cold involve acute disease, chronic disease, and public health issues. Continued research is essential to enable the best clinical management in this era of rapid worldwide travel.

Association between serum concentrations of hypoxia inducible factor responsive proteins and excessive erythrocytosis in high altitude Peru

Painschab, Matthew S., Gary E. Malpartida, Victor G. Davila-Roman, Robert H. Gilman, Todd M. Kolb, Fabiola Leon-Velarde, J. Jaime Miranda, and William Checkley. Association between serum concentrations of hypoxia inducible factor responsive proteins and excessive erythrocytosis in high altitude Peru. High Alt Med Biol 16:26-33, 2015.-Long-term residence at high altitude is associated with the development of chronic mountain sickness (CMS), which is characterized by excessive erythrocytosis (EE). EE occurs under chronic hypoxia, and a strongly selected mutation in hypoxia-inducible factor 2α (HIF2A) has been found in native Tibetans that correlates with having a normal hemoglobin at high altitude. We sought to evaluate differences in plasma levels of four HIF-responsive proteins in 20 participants with EE (hemoglobin >21 g/dL in men and >19 in women) and in 20 healthy, age- and sex-matched participants without EE living at high altitude in Puno, Peru. We performed ELISA to measure plasma levels of the four HIF-responsive proteins: vascular endothelial growth factor (VEGF), soluble VEGF receptor 1 (sVEGF-R1), endothelin-1, and erythropoietin. As a secondary aim, we evaluated the association between HIF-responsive proteins and echocardiography-estimated pulmonary artery systolic pressure (PASP) in a subset of 26 participants. sVEGF-R1 was higher in participants with vs. without EE (mean 107 pg/mL vs. 90 pg/mL; p=0.007). Although plasma concentrations of endothelin-1, VEGF, and erythropoietin were higher in participants with vs. without EE, they did not achieve statistical significance (all p>0.25). Both sVEGF-R1 (p=0.04) and erythropoietin (p=0.04) were positively associated with PASP after adjustment for age, sex, and BMI. HIF-responsive proteins may play a pathophysiological role in altitude-related, chronic diseases but our results did not show consistent changes in all measured HIF-responsive proteins. Larger studies are needed to evaluate for additional genetic and environmental risk factors.

Vascular endothelial growth factor-A is associated with chronic mountain sickness in the Andean population

A study of chronic mountain sickness (CMS) with a candidate gene--vascular endothelial growth factor A (VEGFA)--was carried out in a Peruvian population living at high altitude in Cerro de Pasco (4380 m). The study was performed by genotyping of 11 tag SNPs encompassing 2.2 kb of region of VEGFA gene in patients with a diagnosis of CMS (n = 131; 49.1 ± 12.7 years old) and unrelated healthy controls (n = 84; 47.2 ± 13.4 years old). The VEGFA tag SNP rs3025033 was found associated with CMS (p < 0.05), individuals with AG genotype have 2.5 more risk of CMS compared to those with GG genotype (p < 0.02; OR, 2.54; 95% CI: 1.10-5.88). Pairwise Fst and Nei's distance indicate genetic differentiation between Cerro de Pasco population and HapMap3 population (Fst > 0.36, p < 0.01), suggesting selection is operating on the VEGF gene. Our results suggest that VEGFA is associated with CMS in long-term residents at high altitude in the Peruvian Andes.

Myosin heavy chain 15 is associated with bovine pulmonary arterial pressure

Bovine pulmonary hypertension, brisket disease, causes significant morbidity and mortality at elevations above 2,000 m. Mean pulmonary arterial pressure (mPAP) is moderately heritable, with inheritance estimated to lie within a few major genes. Invasive mPAP measurement is currently the only tool available to identify cattle at risk of hypoxia-induced pulmonary hypertension. A genetic test could allow selection of cattle suitable for high altitude without the need for invasive testing. In this study we evaluated three candidate genes (myosin heavy chain 15 [MYH15], NADH dehydrogenase flavoprotein 2, and FK binding protein 1A) for association with mPAP in 166 yearling Angus bulls grazing at 2,182 m. The T allele (rs29016420) of MYH15 was linked to lower mPAP in a dominant manner (CC 47.2 ± 1.6 mmHg [mean ± standard error of the mean]; CT/TT 42.8 ± 0.7 mmHg; P = 0.02). The proportions of cattle with MYH15 CC, CT, and TT genotypes were 55%, 41%, and 4%, respectively. Given the high frequency of the deleterious allele, it is likely that the relative contribution of MYH15 polymorphisms to pulmonary hypertension is small, supporting previous predictions that the disease is polygenic. We evaluated allelic frequency of MYH15 in the Himalayan yak (Bos grunniens), a closely related species adapted to high altitude, and found 100% prevalence of T allele homozygosity. In summary, we identified a polymorphism in MYH15 significantly associated with mPAP. This finding may aid selection of cattle suitable for high altitude and contribute to understanding human hypoxia-induced pulmonary hypertension.

An EPAS1 haplotype is associated with high altitude polycythemia in male Han Chinese at the Qinghai-Tibetan plateau

BACKGROUND

Hemoglobin concentration at high altitude is considered an important marker of high altitude adaptation, and native Tibetans in the Qinghai-Tibetan plateau show lower hemoglobin concentrations than Han people who have emigrated from plains areas. Genetic studies revealed that EPAS1 plays a key role in high altitude adaptation and is associated with the low hemoglobin concentration in Tibetans. Three single nucleotide polymorphisms (rs13419896, rs4953354, rs1868092) of noncoding regions in EPAS1 exhibited significantly different allele frequencies in the Tibetan and Han populations and were associated with low hemoglobin concentrations in Tibetans.

METHODS

To explore the hereditary basis of high altitude polycythemia (HAPC) and investigate the association between EPAS1 and HAPC in the Han population, these 3 single nucleotide polymorphisms were assessed in 318 male Han Chinese HAPC patients and 316 control subjects. Genotyping was performed by high resolution melting curve analysis.

RESULTS

The G-G-G haplotype of rs13419896, rs4953354, and rs1868092 was significantly more frequent in HAPC patients than in control subjects, whereas no differences in the allele or genotype frequencies of the 3 single nucleotide polymorphisms were found between HAPC patients and control subjects. Moreover, genotypes of rs1868092 (AA) and rs4953354 (GG) that were not observed in the Chinese Han in the Beijing population were found at frequencies of 1.6% and 0.9%, respectively, in our study population of HAPC patients and control subjects.

CONCLUSIONS

Carriers of this EPAS1 haplotype (G-G-G, rs13419896, rs4953354, and rs1868092) may have a higher risk for HAPC. These results may contribute to a better understanding of the pathogenesis of HAPC in the Han population.

Canadian Academy of Sport and Exercise Medicine position statement: athletes at high altitude

Many sports incorporate training at altitude as a key component of their athlete training plan. Furthermore, many sports are required to compete at high altitude venues. Exercise at high altitude provides unique challenges to the athlete and to the sport medicine clinician working with these athletes. These challenges include altitude illness, alterations in training intensity and performance, nutritional and hydration difficulties, and challenges related to the austerity of the environment. Furthermore, many of the strategies that are typically utilized by visitors to altitude may have implications from an anti-doping point of view.This position statement was commissioned and approved by the Canadian Academy of Sport and Exercise Medicine. The purpose of this statement was to provide an evidence-based, best practices summary to assist clinicians with the preparation and management of athletes and individuals travelling to altitude for both competition and training.

Non-high altitude methods for rapid screening of susceptibility to acute mountain sickness

Background

Acute mountain sickness (AMS) refers to the cerebral abnormalities typically triggered by exposure to hypobaric hypoxia at high altitude. Although AMS is not often life threatening, it can seriously impact health quality and decrease productivity. Thus, detection of potential susceptibility to AMS has become important for people arriving at high-altitude plateaus for the first time, including laborers and military staff. The aim of this review was to examine techniques which efficiently assess the susceptibility to AMS prior to exposure to high altitude.

Methods

By searching online databases, we retrieved studies with associations between AMS and methods to detect the susceptible people who were not exposed to high altitudes. Studies reporting significant correlation coefficients between screening methods and AMS scores were included.

Results

Several screening techniques of AMS susceptibility were found including cold pressor test, heart rate variability, and lung functions. Of these markers, heart rate variability was positively associated with AMS scores, while the rest were negatively associated with AMS scores.

Conclusions

We identified three physiological markers that were significantly associated with the risk of AMS. Although it is well known that simple sea level tests are not really helpful in predicting AMS currently, these markers, to some degree, may be employed as references in predicting susceptibility.

AKT3, ANGPTL4, eNOS3, and VEGFA associations with high altitude sickness in Han and Tibetan Chinese at the Qinghai-Tibetan Plateau

Mountain sickness (MS) occurs among humans visiting or inhabiting high altitude environments. We conducted genetic analyses of the AKT3, ANGPTL4, eNOS3 and VEGFA genes in lowland (Han) and highland (Tibetan) Chinese. Ten single nucleotide polymorphisms (SNPs) were evaluated in Han and Tibetan patients with acute (A) and chronic (C) MS. We compared 74 patients with AMS to 79 Han unaffected with MS, as well as 48 CMS patients to 31 unaffected Tibetans. The ten SNPs studied are AKT3 (rs4590656, rs2291409), ANGPTL4 (rs1044250), eNOS3 (rs1007311, rs1799983) and VEGFA (rs79469752, rs13207351, rs28357093, rs1570360, rs3025039). Direct sequencing was used to identify individual genotypes for these SNPs. Hemoglobin (Hb), hematocrit (Hct), and red blood cell count (RBC) were found to be significantly associated with the AKT3 SNP (rs4590656), Hb was found to be associated with the eNOS3 SNP (rs1007311), and RBC was found to be significantly associated with the VEGFA SNP (rs1570360) in Tibetan patients with CMS. CMS patients were found to diverge significantly for both eNOS3 SNPs as measured by genetic distance (0.042, 0.047) and for the VEGFA SNP (rs28357093) with a genetic distance of 0.078 compared to their Tibetan control group. Heart rate (HR) was found to be significantly associated with the eNOS3 SNP (rs1799983) and arterial oxygen saturation of hemoglobin (SaO2) was found to be significantly associated with the VEGFA SNPs (rs13207351, rs1570360) in Han patients with AMS. The Han and Tibetan control groups were found to diverge significantly for the ANGPTL4 SNP and VEGFA SNP (rs28357093), as measured by genetic distances of 0.049 and 0.073, respectively. Seven of the SNPs from non-coding regions are found in the transcriptional factor response elements and their possible role in gene regulation was evaluated with regard to MS. AMS and CMS were found to be significantly associated with the four genes compared to their Han and Tibetan control groups, respectively, indicating that these nucleotide alterations have a physiological effect for the development of high altitude sickness.

EPAS1 and EGLN1 associations with high altitude sickness in Han and Tibetan Chinese at the Qinghai-Tibetan Plateau

High altitude sickness (HAS) occurs among humans visiting or inhabiting high altitude environments. Genetic differences in the EPAS1 and EGLN1 genes have been found between lowland (Han) and highland (Tibetan) Chinese. Three SNPs within EPAS1 and EGLN1 were evaluated in Han and Tibetan patients with acute mountain sickness (AMS) and chronic mountain sickness (CMS). We compared 85 patients with AMS to 79 Han unaffected with mountain sickness (MS) as well as 45 CMS patients to 34 unaffected Tibetan subjects. The three SNPs studied were EPAS1 [ch2: 46441523 (hg18], EGLN1 (rs480902) and (rs516651). Direct sequencing was used to identify individual genotypes for the three SNPs. Age was found to be significantly associated with the EPAS1 SNP in the CMS patients while heart rate (HR) and oxygen saturation level of hemoglobin (SaO(2)) were found to be significantly associated with the EGLN1 (rs480902) SNP in the Han patients with AMS. The individuals with CMS were found to diverge significantly for the EPAS1 SNP compared to their Tibetan control group as measured by genetic distance (0.123) indicating positive selection of the EPAS-G allele with age and illness. The EGLN1 (rs480902) SNP had a significant correlation with hematocrit (HCT), HR and SaO(2) in AMS patients. AMS and CMS were found to be significantly associated with the EPAS1 and EGLN1 SNPs compared to their Han and Tibetan control groups, respectively, indicating these nucleotide alterations have a physiological effect for the development of high altitude sickness.

Genetic determinants of Tibetan high-altitude adaptation

Some highland populations have genetic adaptations that enable their successful existence in a hypoxic environment. Tibetans are protected against many of the harmful responses exhibited by non-adapted populations upon exposure to severe hypoxia, including elevated hemoglobin concentration (i.e., polycythemia). Recent studies have highlighted several genes subject to natural selection in native high-altitude Tibetans. Three of these genes, EPAS1, EGLN1 and PPARA, regulate or are regulated by hypoxia inducible factor, a principal controller of erythropoiesis and other organismal functions. Uncovering the molecular basis of hypoxic adaptation should have implications for understanding hematological and other adaptations involved in hypoxia tolerance. Because the hypoxia response involves a variety of cardiovascular, pulmonary and metabolic functions, this knowledge would improve our understanding of disease mechanisms and could ultimately be translated into targeted therapies for oxygen deprivation, cardiopulmonary and cerebral pathologies, and metabolic disorders such as diabetes and obesity.

High-altitude pulmonary hypertension in cattle (brisket disease): Candidate genes and gene expression profiling of peripheral blood mononuclear cells

High-altitude pulmonary hypertension (HAPH) is a consequence of chronic alveolar hypoxia, leading to hypoxic vasoconstriction and remodeling of the pulmonary circulation. Brisket disease in cattle is a naturally occurring animal model of hypoxic pulmonary hypertension. Genetically susceptible cattle develop severe pulmonary hypertension and right heart failure at altitudes >7,000 ft. No information currently exists regarding the identity of the pathways and gene(s) responsible for HAPH or influencing severity. We hypothesized that initial insights into the pathogenesis of the disease could be discovered by a strategy of (1) sequencing of functional candidates revealed by single nucleotide polymorphism (SNP) analysis and (2) gene expression profiling of affected cattle compared with altitude-matched normal controls, with gene set enrichment analysis (GSEA) and Ingenuity pathway analysis (IPA). We isolated blood from a single herd of Black Angus cattle of both genders, aged 12-18 months, by jugular vein puncture. Mean pulmonary arterial pressures were 85.6±13 mmHg STD in the 10 affected and 35.3±1.2 mmHg STD in the 10 resistant cattle, P<0.001. From peripheral blood mononuclear cells, DNA was hybridized to an Affymetrix 10K Gene Chip SNP, and RNA was used to probe an Affymetrix Bovine genome array. SNP loci were remapped using the Btau 4.0 bovine genome assembly. mRNA data was analyzed by the Partek software package to identify sets of genes with an expression that was statistically different between the two groups. GSEA and IPA were conducted on the refined expression data to identify key cellular pathways and to generate networks and conduct functional analyses of the pathways and networks. Ten SNPs were identified by allelelic association and four candidate genes were sequenced in the cohort. Neither endothelial nitric oxide synthetase, NADH dehydrogenase, TG-interacting factor-2 nor BMPR2 were different among affected and resistant cattle. A 60-gene mRNA signature was identified that differentiated affected from unaffected cattle. Forty-six genes were overexpressed in the affected and 14 genes were downregulated in the affected cattle by at least 20%. GSEA and Ingenuity analysis identified respiratory diseases, inflammatory diseases and pathways as the top diseases and disorders (P<5.14×10(-14)), cell development and cell signaling as the top cellular functions (P<1.20×10(-08)), and IL6, TREM, PPAR, NFkB cell signaling (P<8.69×10(-09)) as the top canonical pathways associated with this gene signature. This study provides insights into differences in RNA expression in HAPH at a molecular level, and eliminates four functional gene candidates. Further studies are needed to validate and refine these preliminary findings and to determine the role of transcribed genes in the development of HAPH.

Population level determinants of acute mountain sickness among young men: a retrospective study

Background

Many visitors, including military troops, who enter highland regions from low altitude areas may suffer from acute mountain sickness (AMS), which negatively impacts workable man-hours and increases healthcare costs. The aim of this study was to evaluate the population level risk factors and build a multivariate model, which might be applicable to reduce the effects of AMS on Chinese young men traveling to this region.

Methods

Chinese highland military medical records were used to obtain data of young men (n = 3727) who entered the Tibet plateau between the years of 2006-2009. The relationship between AMS and travel profile, demographic characteristics, and health behaviors were evaluated by logistic regression. Univariate logistic models estimated the crude odds ratio. The variables that showed significance in the univariate model were included in a multivariate model to derive adjusted odds ratios and build the final model. Data corresponding to odd and even years (2 subsets) were analyzed separately and used in a simple cross-validation.

Results

Univariate analysis indicated that travel profile, prophylactic use, ethnicity, and province of birth were all associated with AMS in both subsets. In multivariate analysis, young men who traveled from lower altitude (600-800 m vs. 1300-1500 m, adjusted odds ratio (AOR) = 1.32-1.44) to higher altitudes (4100-4300 m vs. 2900-3100 m, AOR = 3.94-4.12; 3600-3700 m vs. 2900-3100 m, AOR = 2.71-2.74) by air or rapid land transport for emergency mission deployment (emergency land deployment vs. normal land deployment, AOR = 2.08-2.11; normal air deployment vs. normal land deployment, AOR = 2.00-2.20; emergency air deployment vs. normal land deployment, AOR = 2.40-3.34) during the cold season (cold vs. warm, AOR = 1.25-1.28) are at great risk for developing AMS. Non-Tibetan male soldiers (Tibetan vs. Han, AOR = 0.03-0.08), born and raised in lower provinces (eastern vs. northwestern, AOR = 1.32-1.39), and deployed without prophylaxis (prophylactic drug vs. none, AOR = 0.75-0.76), also represented a population at significantly increased risk for AMS. The predicted model was built; the area under receiver operating characteristic curve was 0.703.

Conclusion

Before a group of young men first enter a high altitude area, it is important that a health service plan should be made referring to the group's travel profile and with respect to young men's ethnicity and province of birth. Low-cost Chinese traditional prophylactic drugs might have some effect on decreasing the risk of AMS, although this needs further verification.

Evidence for a genetic basis for altitude illness: 2010 update

Altitude illness refers to a group of environmentally mediated pathophysiologies. Many people will suffer acute mountain sickness shortly after rapidly ascending to a moderately hypoxic environment, and an unfortunate few will develop potentially fatal conditions such as high altitude pulmonary edema or high altitude cerebral edema. Some individuals seem to be predisposed to developing altitude illness, suggesting an innate contribution to susceptibility. The implication that there are altitude-sensitive and altitude-tolerant individuals has stimulated much research into the contribution of a genetic background to the efficacy of altitude acclimatization. Although the effect of altitude attained and rate of ascent on the etiology of altitude illness is well known, there are only tantalizing, but rapidly accumulating, clues to the genes that may be involved. In 2006, we reviewed what was then known about the genetics of altitude illness. This article updates that review and attempts to tabulate all the available genetic data pertaining to these conditions. To date, 58 genes have been investigated for a role in altitude illness. Of these, 17 have shown some association with the susceptibility to, or the severity of, these conditions, although in many cases the effect size is small or variable. Caution is recommended when evaluating the genes for which no association was detected, because a number of the investigations reviewed in this article were insufficiently powered to detect small effects. No study has demonstrated a clear-cut altitude illness gene, but the accumulating data are consistent with a polygenic condition with a strong environmental component. The genes that have shown an association affect a variety of biological pathways, suggesting that either multiple systems are involved in altitude pathophysiology or that gene-gene interactions play a role. Although numerous studies have been performed to investigate specific genes, few have looked for evidence of heritability or familial transmission, or for epidemiological patterns that would be consistent with genetically influenced conditions. Future trends, such as genome-wide association studies and epigenetic analysis, should lead to enhanced understanding of the complex interactions within the genome and between the genome and hypoxic environments that contribute to an individual's capacity to acclimatize rapidly and effectively to altitude.

MtDNA haplogroups M7 and B in southwestern Han Chinese at risk for acute mountain sickness

We conducted a case-control study to investigate the association of mitochondrial DNA (mtDNA) haplogroups with acute mountain sickness (AMS) in Han Chinese from southwestern (SW) China. Pearson's chi-square test or Fisher's exact test revealed significant reduction of mtDNA haplogroups D and M9, while a significant increase of haplogroup M7 in AMS subjects compared with non-AMS subjects. The multivariate logistic regression analysis after adjustment for body mass index (BMI), a risk factor of AMS in the present study, showed that both D and M9 were associated with significantly decreased risk of AMS, while M7 was associated with a significantly increased risk of AMS (OR=0.605, p=0.000; OR=0.037, p=0.001, and OR=2.419, p=0.001, respectively). In addition, further analysis stratified by the AMS severities indicated that haplogroup B was correlated with a 2.41-folds increased risk of developing severe AMS (95%C.I=1.288-4.514, p=0.006). Our findings provide evidence that, in SW Han Chinese, mtDNA haplogroups D and M9 are related to individual tolerance to AMS, while haplogroups M7 and B are risk factors for AMS.

Genetic associations with mountain sickness in Han and Tibetan residents at the Qinghai-Tibetan Plateau

BACKGROUND

Acute (AMS) and chronic (CMS) mountain sicknesses are illnesses that occur among humans visiting or inhabiting high-altitude environments, respectively. Some individuals are genetically less fit than others when stressed by an extreme high-altitude environment. Seven blood physiological parameters and five genetic polymorphisms were studied in Han patients with AMS and Tibetan patients with CMS.

METHODS

We compared 98 AMS patients with 60 Han controls as well as 50 CMS patients with 36 Tibetan controls. The genetic loci studied are ACE I/D (rs4340), AGT M235T (rs699), AGTR1 A1166C (rs5186), GNB3 A(-350)G (rs2071057) and APOB A/G (rs693).

RESULTS

All physiological parameters (RBC, HCT, Hb, SaO(2), HR, and BPs/d) studied significantly changed in the CMS patients while SaO(2) and HR changed in the AMS Han patients compared to their controls. The ACE D and AGT 235M alleles were found to be significantly associated with AMS and CMS, respectively, while a significantly high incidence of the G-protein (GNB3) (-350)A allele was found in the AMS patients. ACE (I/D) was significantly associated with HR in CMS patients while the AGT M235T was significantly associated with SaO(2) and BPs/d in AMS patients. APOB A/G was significantly associated with BPs/d in AMS and HR in CMS patients.

CONCLUSION

AMS and CMS share very similar genetic results for the ACE I/D and AGT M235T polymorphisms indicating that these mutations have an effect on both illnesses.

No association between alleles of the bradykinin receptor-B2 gene and acute mountain sickness

The pathophysiological mechanism(s) of the development of acute mountain sickness (AMS) is still unclear. Although the chance of developing AMS and the severity of the condition are influenced by ascent rate and altitude attained, previous history is a reliable predictor of subsequent affliction, and some individuals and families are clearly predisposed, suggesting a genetic component to susceptibility. As the vasodilator bradykinin may be involved in acclimatization to altitude, we hypothesized that variants in genes encoding components of this pathway might play a role in AMS susceptibility. We tested this by looking for associations between two functional polymorphisms (the in/del polymorphism +9/−9 [rs5810761] and the single-nucleotide polymorphism C − 58T [rs1799722]) of BDKRB2 (the gene encoding the bradykinin receptor B2) and susceptibility to AMS in an altitude-exposed Nepalese population. Lowland attendees ( n = 233) at a religious festival at 4380 m in the Nepalese Himalaya were recruited and assessed for AMS by clinical evaluation and Lake Louise score (LLS). Those with a clinical diagnosis of AMS and an LLS ≥3 were designated AMS+ ( n = 100) and those without a diagnosis of AMS and with an LLS <3 were categorized as AMS− ( n = 117). DNA was prepared from buccal cells, genotyped for the two polymorphisms and allele frequencies compared between the two cohorts. No association was found between alleles at either polymorphism and susceptibility to AMS ( P > 0.50), although C − 58T heterozygotes were significantly more common ( P < 0.001, χ2 = 49.6) in the subjects than would be predicted if the population was in Hardy–Weinberg equilibrium. The results of our association study do not support the hypothesis that variants in BDKRB2 influence altitude tolerance in a lowland Nepalese population; however, the deviation from Hardy–Weinberg equilibrium observed for the C − 58T polymorphism could be explained by self-selection for altitude tolerance in the festival attendees.

The lack of associations between alleles at the hypoxia-inducible factor 1A C1772T loci and responses to acute hypoxia

OBJECTIVE

The aim of this study was to investigate the associations between alleles of the hypoxia-inducible factor 1A (HIF1A) C1772T polymorphism and several physiological responses to hypoxia, including the hypoxic ventilatory response (HVR), and serum erythropoietin (EPO), arterial oxygen saturation (Sao2), and acute mountain sickness (AMS) responses during 8 hours of exposure to normobaric hypoxia.

METHODS

A total of 76 males participated in the study; 52 participants completed an 8-hour exposure to 12.7% oxygen, during which time Sao2, EPO concentrations, and AMS scores were measured, while 62 individuals took part in an HVR trial (in total 38 individuals completed both protocols). DNA was obtained from leukocytes, and a 346-bp fragment of the HIF1A gene containing the C1772T polymorphism was amplified using polymerase chain reaction. Fragments were sequenced to reveal individual genotypes, and the associations between HIF1A genotype and EPO, Sao2, AMS responses to hypoxia and HVR were examined.

RESULTS

The magnitude of the hypoxic responses was highly variable between individuals. The increase in participants' EPO responses ranged from 89% to 388% of baseline values following hypoxia, while Sao2 values during the exposure ranged from 71% to 89%. The HVR ranged from -0.04 to +2.18 L x min(-1) x Sao2 %(-1) among participants. No significant differences in EPO, Sao2, AMS, or HVR results were observed between the HIF1A CC genotype and the combined CT/TT genotype group.

CONCLUSION

In this study, the HIF1A C1772T polymorphism does not appear to influence EPO, Sao2, or AMS responses during acute hypoxic exposure, or the magnitude of the HVR.

A role for succinate dehydrogenase genes in low chemoresponsiveness to hypoxia?

The detection of hypoxia by the carotid bodies elicits a ventilatory response of utmost importance for tolerance to high altitude. Germline mutations in three genes encoding subunit B, C and D of succinate dehydrogenase (SDHB, SDHC and SDHD) have been associated with paragangliomas of the carotid body. We hypothesized that SDH dysfunction within the carotid body could result in low chemoresponsiveness and intolerance to high altitude. The frequency of polymorphisms of SDHs, hypoxia-inducible factor type 1 (HIF1alpha) and angiotensin converting enzyme (ACE) genes was compared between 40 subjects with intolerance to high altitude and a low hypoxic ventilatory response at exercise (HVRe < or = 0.5 ml min(-1) kg(-1); HVR- group) and 41 subjects without intolerance to high altitude and a high HVRe (> or = 0.80 ml min(-1) kg(-1); HVR+). We found no significant association between low or high HVRe and (1) the allele frequencies for nine single nucleotide polymorphisms (SNPs) in the SDHD and SDHB genes, (2) the ACE insertion/deletion polymorphism and (3) four SNPs in the HIF1alpha gene. However, a marginal significant association was found between the synonymous polymorphism c.18A>C of the SDHB gene and chemoresponsiveness: 8/40 (20%) in the HVR- group and 3/41 (7%) in the HVR+ group (p = 0.12). A principal component analysis showed that no subject carrying the 18C allele had both high ventilatory and cardiac response to hypoxia. In conclusion, no clear association was found between gene variants involved in oxygen sensing and chemoresponsiveness, although some mutations in the SDHB and SDHD genes deserve further investigations in a larger population.

Genotype at the missense G894T polymorphism (Glu298Asp) in the NOS3 gene is associated with susceptibility to acute mountain sickness

Acute mountain sickness (AMS) is a potentially serious affliction that frequently occurs in travelers to altitudes above 2500 m. The probability of developing AMS depends on environmental factors such as rate of ascent and altitude attained; however, familial clustering and recurrence rates suggest that there may be a genetic contribution to the etiology of the condition. The underlying pathophysiology of AMS is unknown, but it may involve vasogenic edema secondary to hypoxia-induced sympathetic response and endothelial dysfunction. Nitric oxide is a potent vasomodulator, and variants in the gene that encodes endothelial nitric oxide synthase (NOS3) have been shown to affect blood pressure. We tested the hypothesis that haplotypes, as determined by tagSNPs, in NOS3 would be differentially represented in individuals with and without AMS sampled at the Janai Purnima Festival at Lake Gosain Kunda, Nepal, at 4380 m. Seven SNPs were tested, and a highly significant association (p = 0.004) was found for genotypes of the commonly studied missense polymorphism Glu298Asp (rs 1799983; G/T transversion at base 894). The T allele, which previously has been associated with hypertension, was overrepresented in individuals with AMS (0.30 vs. 0.10), but not significantly when the data were corrected for multiple testing (p = 0.024). These data suggest that a variant in a gene involved in nitric oxide synthesis is a risk factor for developing AMS.

The cerebral effects of ascent to high altitudes

Cellular hypoxia is the common final pathway of brain injury that occurs not just after asphyxia, but also when cerebral perfusion is impaired directly (eg, embolic stroke) or indirectly (eg, raised intracranial pressure after head injury). We Review recent advances in the understanding of neurological clinical syndromes that occur on exposure to high altitudes, including high altitude headache (HAH), acute mountain sickness (AMS), and high altitude cerebral oedema (HACE), and the genetics, molecular mechanisms, and physiology that underpin them. We also present the vasogenic and cytotoxic bases for HACE and explore venous hypertension as a possible contributory factor. Although the factors that control susceptibility to HACE are poorly understood, the effects of exposure to altitude (and thus hypobaric hypoxia) might provide a reproducible model for the study of cerebral cellular hypoxia in healthy individuals. The effects of hypobaric hypoxia might also provide new insights into the understanding of hypoxia in the clinical setting.

Angiotensin-converting enzyme genotype and arterial oxygen saturation at high altitude in Peruvian Quechua

The I-allele of the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism has been associated with performance benefits at high altitude (HA). In n = 142 young males and females of largely Quechua origins in Peru, we evaluated 3 specific hypotheses with regard to the HA benefits of the I-allele: (1) the I-allele is associated with higher arterial oxygen saturation (Sa(O(2))) at HA, (2) the I-allele effect depends on the acclimatization state of the subjects, and (3) the putative I-allele effect on Sa(O(2)) is mediated by the isocapnic hypoxic ventilatory response (HVR, l/min(1)/% Sa(O(2))(1)). The subject participants comprised two different study groups including BLA subjects (born at low altitude) who were lifelong sea-level residents transiently exposed to hypobaric hypoxia (<24 h) and BHA subjects (born at HA) who were lifelong residents of HA. To control for the possibility of population stratification, Native American ancestry proportion (NAAP) was estimated as a covariate for each individual using a panel of 70 ancestry-informative molecular markers (AIMS). At HA, resting and exercise Sa(O(2)) was strongly associated with the ACE genotype, p = 0.008 with approximately 4% of the total variance in Sa(O(2)) attributed to ACE genotype. Moreover, I/I individuals maintained approximately 2.3 percentage point higher Sa(O(2)) compared to I/D and D/D. This I-allele effect was evident in both BLA and BHA groups, suggesting that acclimatization state has little influence on the phenotypic expression of the ACE gene. Finally, ACE genotype was not associated with the isocapnic HVR, although HVR had a strong independent effect on Sa(O(2)) (p = 0.001). This suggests that the I-allele effect on Sa(O(2)) is not mediated by the peripheral control of breathing, but rather by some other central cardiopulmonary effect of the ACE gene on the renin-angiotensin-aldosterone system (RAAS).

Erythropoiesis-stimulating agents and other methods to enhance oxygen transport

Oxygen is essential for life, and the body has developed an exquisite method to collect oxygen in the lungs and transport it to the tissues. Hb contained within red blood cells (RBCs), is the key oxygen-carrying component in blood, and levels of RBCs are tightly controlled according to demand for oxygen. The availability of oxygen plays a critical role in athletic performance, and agents that enhance oxygen delivery to tissues increase aerobic power. Early methods to increase oxygen delivery included training at altitude, and later, transfusion of packed RBCs. A breakthrough in understanding how RBC formation is controlled included the discovery of erythropoietin (Epo) and cloning of the EPO gene. Cloning of the EPO gene was followed by commercial development of recombinant human Epo (rHuEpo). Legitimate use of this and other agents that affect oxygen delivery is important in the treatment of anaemia (low Hb levels) in patients with chronic kidney disease or in cancer patients with chemotherapy-induced anaemia. However, competitive sports was affected by illicit use of rHuEpo to enhance performance. Testing methods for these agents resulted in a cat-and-mouse game, with testing labs attempting to detect the use of a drug or blood product to improve athletic performance (doping) and certain athletes developing methods to use the agents without being detected. This article examines the current methods to enhance aerobic performance and the methods to detect illicit use.

Treatment of high altitude pulmonary edema at 4240 m in Nepal

High altitude pulmonary edema (HAPE) is the leading cause of death from altitude illness and rapid descent is often considered a life-saving foundation of therapy. Nevertheless, in the remote settings where HAPE often occurs, immediate descent sometimes places the victim and rescuers at risk. We treated 11 patients (7 Nepalese, 4 foreigners) for HAPE at the Himalayan Rescue Association clinic in Pheriche, Nepal (4240 m), from March 3 to May 14, 2006. Ten were admitted and primarily treated there. Seven of these (6 Nepalese, 1 foreigner) had serious to severe HAPE (Hultgren grades 3 or 4). Bed rest, oxygen, nifedipine, and acetazolamide were used for all patients. Sildenafil and salmeterol were used in most, but not all patients. The duration of stay was 31 +/- 16 h (range 12 to 48 h). Oxygen saturation was improved at discharge (84% +/- 1.7%) compared with admission (59% +/- 11%), as was ultrasound comet-tail score (11 +/- 4 at discharge vs. 33 +/- 8.6 at admission), a measure of pulmonary edema for which admission and discharge values were obtained in 7 patients. We conclude it is possible to treat even serious HAPE at 4240 m and discuss the significance of the predominance of Nepali patients seen in this series.

Cerebrovascular responses to altitude

The regulation of cerebral blood flow (CBF) is a complex process that is altered significantly with altitude exposure. Acute exposure produces a marked increase in CBF, in proportion to the severity of the hypoxia and mitigated by hyperventilation-induced hypocapnia when CO(2) is uncontrolled. A number of mediators contribute to the hypoxia-induced cerebral vasodilation, including adenosine, potassium channels, substance P, prostaglandins, and NO. Upon acclimatization to altitude, CBF returns towards normal sea-level values in subsequent days and weeks, mediated by a progressive increase in PO2, first through hyperventilation followed by erythropoiesis. With long-term altitude exposure, a number of mechanisms play a role in regulating CBF, including acid-base balance, hematological modifications, and angiogenesis. Finally, several cerebrovascular disorders are associated with altitude exposure. Existing gaps in our knowledge of CBF and altitude, and areas of future investigation include effects of longer exposures, intermittent hypoxia, and gender differences in the CBF responses to altitude.

Common Haplotypes in the β-2 Adrenergic Receptor Gene Are Not Associated with Acute Mountain Sickness Susceptibility in Nepalese

Acute Mountain Sickness (AMS), the most common and least serious of the altitude-related illnesses, is frequently experienced by sojourners traveling above 2500 m. Although altitude and rate of ascent are likely the most critical factors in determining whether the condition will develop in a person, interindividual variation and patterns of susceptibility suggest that there may be genetic risk factors as well. We hypothesized that variants in the gene that encodes the beta-2 adrenergic receptor (the principal catecholamine receptor in the lungs) are involved in the etiology of AMS and tested this hypothesis in cohorts of Nepalese individuals who developed or did not develop AMS when attending the Purnima Festival at Lake Gosain Kunda at 4380. Polymorphisms that could serve as markers for the common haplotypes encompassing the gene were chosen using the HapMap database. We found no association between any alleles at the seven highly informative polymorphic loci (tagSNPs) that we assayed and AMS status, suggesting that variants in, or near, the beta-2 adrenergic receptor gene do not contribute to AMS susceptibility in this population. This study is the first application of the HapMap database and associated haplotype mapping tools to the understanding of altitude-related pathologies.

Clinical perspective of hypoxia-mediated pulmonary hypertension

Pulmonary hypertension is a condition associated with a variety of pulmonary disorders whose common denominator is alveolar hypoxia. Such disorders include chronic obstructive pulmonary disease, pulmonary fibrosis, sleep-disordered breathing, and exposure to high altitude. Acute hypoxia is characterized by vasoconstriction of small pulmonary arteries, a phenomenon called hypoxic pulmonary vasoconstriction. With prolonged hypoxia, thickening of the smooth vascular layer of the small pulmonary arteries occurs, a phenomenon described as pulmonary vascular remodeling. Although the core mechanisms of both vasoconstriction and remodeling are thought to reside in the smooth muscle cell layer, the endothelium modulates these two processes. The purpose of this review is briefly to (a) discuss the mechanisms of hypoxic pulmonary hypertension as it pertains to certain disease states, and (b) examine the pathways that have potential therapeutic applications for this condition.

No Association Between Variants in the ACE and Angiotensin II Receptor 1 Genes and Acute Mountain Sickness in Nepalese Pilgrims to the Janai Purnima Festival at 4380 m

Koehle, Michael S., Pei Wang, Jordan A. Guenette, and Jim L. Rupert. No association between variants in the ACE and angiotensin II receptor 1 genes and acute mountain sickness in Nepalese pilgrims to the Janai Purnima Festival at 4380 m. High Alt. Med. Biol. 7:281-289, 2006.--Acute mountain sickness (AMS) causes significant morbidity among visitors to altitude. The primary contributors to developing AMS are altitude and rate of ascent; however, the substantial variation in susceptibility between individuals has led a number of investigators to propose that there may be genetic predilection to the disease. The ACE I/D polymorphism has been shown to predict performance among elite mountaineers. This study compares genotype and allele frequencies at the ACE I/D locus, two other loci in the ACE gene, and one locus in the angiotensin-2 receptor gene between individuals who did, or did not, express signs of AMS while attending a high altitude religious festival in Nepal (4380 m). Subjects (80 males, 23 females) were recruited and genotyped. All subjects were Nepalese. Forty-four of the subjects had been diagnosed with AMS by physicians at a high altitude health camp; the rest were free from altitude illness. All subjects were genotyped at polymorphic loci in the genes encoding angiotensin converting enzyme (ACE) and angiotensin II receptor type 1 gene (AGTR1). The polymorphisms examined were two single nucleotide polymorphisms (SNPs) in ACE (ACE(A-240T), dbSNP rs4291; and ACE(A2350G), dbSNP rs4343), the intronic Alu insertion in ACE (ACE I/D), and the SNP ATR(A1166C), (dbSNP rs17231380) in AGTR1d. All polymorphisms in ACE were found to be in linkage disequilibrium. No significant associations were found between AMS incidence and any of the alleles, suggesting that variants at these loci do not contribute to susceptibility to AMS in this population.