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

Unravelling the Lesser Known Facets of Angiotensin II Type 1 Receptor

PURPOSE OF REVIEW

Hypertension is an important risk factor in various pathologies. Despite enormous advancements in health sciences, the number of hypertensive individuals is increasing worldwide. The complex interplay between genetic and epigenetic factors seems to be a promising pathway to exploring the pathophysiology of hypertension.

RECENT FINDINGS

Various single gene and genome wide association studies have generated huge but non-reproducible data that highlights the role of some additional but as yet unidentified factor(s) in disease outcome. Dietary pattern and epigenetic mechanism (mainly DNA methylation) have shown a profound effect on blood pressure regulation. Angiotensin II and its receptors are known to play an important role in maintaining blood pressure; hence, a larger section of antihypertensive drugs targets the renin-angiotensin system (RAS). Angiotensin II type 1 receptor (AT1R), besides maintaining blood pressure, also has a role in cancer progression. Besides other pathways, RAS still remains the main player in blood pressure regulation. Additionally, AT1R has recently emerged as a molecule with diverse roles ranging from physiologic to cancer progression.

Angiotensin II receptor 1 gene variants are associated with high-altitude pulmonary edema risk

Previous studies demonstrated that Angiotensin II Receptor 1 (AGTR1) may play an important role in the development of high-altitude pulmonary edema. We envisaged a role for AGTR1 gene variants in the pathogenesis of HAPE and investigated their potential associations with HAPE in a Han Chinese population. We genotyped seven AGTR1 polymorphisms in 267 patients with diagnosed HAPE and 304 controls and evaluated their association with risk of HAPE. Statistically significant associations were found for the single nucleotide polymorphisms (SNPs) rs275651 (p = 0.017; odds ratio [OR] = 0.65) and rs275652 (p = 0.016; OR = 0.64). Another SNP rs10941679 showed a marginally significant association after adjusting for age and sex in the additive genetic model (adjusted OR = 1.44, 95% CI = 1.01-2.04, p = 0.040). Haplotype analysis confirmed that the haplotype "AG" was associated with a 35% reduction in the risk of developing HAPE, while the haplotype "AA" increased the risk of developing HAPE by 44%. These results provide the first evidence linking genetic variations in AGTR1 with HAPE risk in Han Chinese individuals.

Associations of high altitude polycythemia with polymorphisms in EPHA2 and AGT in Chinese Han and Tibetan populations

High altitude polycythemia (HAPC) refers to the long-term living in the plateau of the hypoxia environment is not accustomed to cause red blood cell hyperplasia. The pathological changes are mainly the various organs and tissue congestion, blood stasis and hypoxia damage. Although chronic hypoxia is the main cause of HAPC, the related molecular mechanisms remain largely unclear. This study aims to explore the genetic basis of HAPC in the Chinese Han and Tibetan populations. We enrolled 100 patients (70 Han, 30 Tibetan) with HAPC and 100 healthy control subjects (30 Han, 70 Tibetan). To explore the hereditary basis of HAPC and investigate the association between EPHA2 with AGT and HAPC in Chinese Han and Tibetan populations. Using the Chi-squared test and analyses of genetic models, rs2291804, rs2291805, rs3768294, rs3754334, rs6603856, rs6669624, rs11260742, rs13375644 and rs10907223 in EPHA2, and rs699, rs4762 and rs5051 in AGT showed associations with reduced HAPC susceptibility in Han populations. Additionally, in Tibetan populations, rs2478523 in AGT showed an increased the risk of HAPC. Our study suggest that polymorphisms in the EPHA2 and AGT correlate with susceptibility to HAPC in Chinese Han and Tibetan populations.

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.

High altitude pilgrimage medicine

Religious pilgrims have been going to high altitude pilgrimages long before trekkers and climbers sojourned in high altitude regions, but the medical literature about high altitude pilgrimage is sparse. Gosainkunda Lake (4300 m) near Kathmandu, Nepal, and Shri Amarnath Yatra (3800 m) in Sri Nagar, Kashmir, India, are the two sites in the Himalayas from where the majority of published reports of high altitude pilgrimage have originated. Almost all travels to high altitude pilgrimages are characterized by very rapid ascents by large congregations, leading to high rates of acute mountain sickness (AMS). In addition, epidemiological studies of pilgrims from Gosainkunda Lake show that some of the important risk factors for AMS in pilgrims are female sex and older age group. Studies based on the Shri Amarnath Yatra pilgrims show that coronary artery disease, complications of diabetes, and peptic ulcer disease are some of the common, important reasons for admission to hospital during the trip. In this review, the studies that have reported these and other relevant findings will be discussed and appropriate suggestions made to improve pilgrims' safety at high altitude.

Association between genetic polymorphisms of ACE & eNOS and diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, with multiple genetic and environmental factors involving in its etiology. ACE and eNOS gene were considered to have important roles in the development and progression of DN. In this study, a case-control study was carried out to investigate the effects of 7 SNPs in ACE gene and 2 SNPs in eNOS gene in the development of DN in Northern China.7 SNPs including A240T, A2350G, A5466C, A2215G, T3892C, C1237T and C3409T of ACE gene and 2 SNPs (G894T and T786C) of eNOS gene were genotyped by polymerase chain reaction restriction fragment length polymorphism method. 431 type 2 diabetic patients with nephropathy (cases) were compared to 420 type 2 diabetic patients without nephropathy (controls) in the study. Data were analyzed by SPSS 17.0 and HaploView software. The frequency distribution of A2350G, 4 haplotyps in ACE gene and G894T in eNOS gene were demonstrated to be different between case and control groups significantly. Whereas other SNPs and haplotypes had no differences in two cohorts. The results revealed that variations of ACE and eNOS gene had association with DN, which indicated ACE and eNOS gene may play an important role in pathogenesis of DN in Northern Chinese Han population.

Association of polymorphisms in angiotensin and aldosterone synthase genes of the renin–angiotensin–aldosterone system with high-altitude pulmonary edema

Studies on different populations have suggested variability in individual susceptibility to altitude sickness depending on genetic makeup. The renin–angiotensin–aldosterone system (RAAS) pathway plays a key role in regulation of vascular tone and circulatory homeostasis. The present study was undertaken to investigate the possible association of the RAAS in the development of high-altitude pulmonary edema (HAPE) in lowlanders exposed to high altitude. Three categories of subjects were selected: individuals who developed HAPE on acute induction to high altitude ( HAPE); individuals tolerant to high-altitude exposure who showed no symptoms of HAPE (resistant controls; rCON); and natives of high altitude ( HAN). Genetic variants in the genes of the RAAS such as renin ( REN), angiotensin ( AGT), angiotensin-converting enzyme ( ACE), aldosterone synthase ( CYP11B2) and angiotensin II receptor type 1 ( AGTR1) have been investigated. The T174M polymorphism in AGT showed a significant difference in HAPE and HAN and also HAN and controls. Also, genotyping in the CYP11B2 T-344C promoter region resulted in a significant difference between HAPE and HAN both at genotypic and allelic levels. The genotypic difference was statistically insignificant for the AGTR1 A1166C 3’ UTR. The present investigation demonstrates a possible association between the polymorphisms existing in the RAAS pathway T174M and CYP11B2 C-344T and sensitivity of an individual to develop HAPE. The results also indicate the existence of ethnic variation between the HAN and the other two groups comprising lowlanders.

The ACE gene and human performance: 12 years on

Some 12 years ago, a polymorphism of the angiotensin I-converting enzyme (ACE) gene became the first genetic element shown to impact substantially on human physical performance. The renin-angiotensin system (RAS) exists not just as an endocrine regulator, but also within local tissue and cells, where it serves a variety of functions. Functional genetic polymorphic variants have been identified for most components of RAS, of which the best known and studied is a polymorphism of the ACE gene. The ACE insertion/deletion (I/D) polymorphism has been associated with improvements in performance and exercise duration in a variety of populations. The I allele has been consistently demonstrated to be associated with endurance-orientated events, notably, in triathlons. Meanwhile, the D allele is associated with strength- and power-orientated performance, and has been found in significant excess among elite swimmers. Exceptions to these associations do exist, and are discussed. In theory, associations with ACE genotype may be due to functional variants in nearby loci, and/or related genetic polymorphism such as the angiotensin receptor, growth hormone and bradykinin genes. Studies of growth hormone gene variants have not shown significant associations with performance in studies involving both triathletes and military recruits. The angiotensin type-1 receptor has two functional polymorphisms that have not been shown to be associated with performance, although studies of hypoxic ascent have yielded conflicting results. ACE genotype influences bradykinin levels, and a common gene variant in the bradykinin 2 receptor exists. The high kinin activity haplotye has been associated with increased endurance performance at an Olympic level, and similar results of metabolic efficiency have been demonstrated in triathletes. Whilst the ACE genotype is associated with overall performance ability, at a single organ level, the ACE genotype and related polymorphism have significant associations. In cardiac muscle, ACE genotype has associations with left ventricular mass changes in response to stimulus, in both the health and diseased states. The D allele is associated with an exaggerated response to training, and the I allele with the lowest cardiac growth response. In light of the I-allele association with endurance performance, it seems likely that other regulatory mechanisms exist. Similarly in skeletal muscle, the D allele is associated with greater strength gains in response to training, in both healthy individuals and chronic disease states. As in overall performance, those genetic polymorphisms related to the ACE genotype, such as the bradykinin 2 gene, also influence skeletal muscle strength. Finally, the ACE genotype may influence metabolic efficiency, and elite mountaineers have demonstrated an excess of I alleles and I/I genotype frequency in comparison to controls. Interestingly, this was not seen in amateur climbers. Corroboratory evidence exists among high-altitude settlements in both South America and India, where the I allele exists in greater frequency in those who migrated from the lowlands. Unfortunately, if the ACE genotype does influence metabolic efficiency, associations with peak maximal oxygen consumption have yet to be rigorously demonstrated. The ACE genotype is an important but single factor in the determinant of sporting phenotype. Much of the mechanisms underlying this remain unexplored despite 12 years of research.

The genetics of altitude tolerance: the evidence for inherited susceptibility to acute mountain sickness

OBJECTIVE

Acute mountain sickness (AMS) has become a significant environmental health issue as improvements in transportation, "environmental tourism," and resource development lure more people to the highlands. Whether there is a genetic contribution to AMS susceptibility is a central question in high-altitude medicine. This article provides a systematic review of the evidence supporting such an innate predisposition.

METHODS

Scientific literature databases were screened using the terms "acute mountain sickness/AMS" and "altitude illness" combined with the terms "DNA," "gene," "genetic," or "polymorphism."

RESULTS

Sixteen genes from a variety of pathways have been tested for association with AMS and variants in eight showed positive associations suggesting that AMS is an environmentally mediated polygenic disorder.

CONCLUSIONS

The data suggest that genotype contributes to capacity to rapidly and efficiently acclimatize to altitude; nevertheless, the mechanisms by which this occurs have yet to be elucidated.

Incidence and Symptoms of High Altitude Illness in South Pole Workers: Antarctic Study of Altitude Physiology (ASAP)

Introduction:

Each year, the US Antarctic Program rapidly transports scientists and support personnel from sea level (SL) to the South Pole (SP, 2835 m) providing a unique natural laboratory to quantify the incidence of acute mountain sickness (AMS), patterns of altitude related symptoms and the field effectiveness of acetazolamide in a highly controlled setting. We hypothesized that the combination of rapid ascent (3 hr), accentuated hypobarism (relative to altitude), cold, and immediate exertion would increase altitude illness risk.

Methods:

Medically screened adults (N = 246, age = 37 ± 11 yr, 30% female, BMI = 26 ± 4 kg/m²) were recruited. All underwent SL and SP physiological evaluation, completed Lake Louise symptom questionnaires (LLSQ, to define AMS), and answered additional symptom related questions (eg, exertional dyspnea, mental status, cough, edema and general health), during the 1st week at altitude. Acetazolamide, while not mandatory, was used by 40% of participants.

Results:

At SP, the barometric pressure resulted in physiological altitudes that approached 3400 m, while T °C averaged −42, humidity 0.03%. Arterial oxygen saturation averaged 89% ± 3%. Overall, 52% developed LLSQ defined AMS. The most common symptoms reported were exertional dyspnea-(87%), sleeping difficulty-(74%), headache-(66%), fatigue-(65%), and dizziness/lightheadedness-(46%). Symptom severity peaked on days 1–2, yet in >20% exertional dyspnea, fatigue and sleep problems persisted through day 7. AMS incidence was similar between those using acetazolamide and those abstaining (51 vs. 52%, P = 0.87). Those who used acetazolamide tended to be older, have less altitude experience, worse symptoms on previous exposures, and less SP experience.

Conclusion:

The incidence of AMS at SP tended to be higher than previously reports in other geographic locations at similar altitudes. Thus, the SP constitutes a more intense altitude exposure than might be expected considering physical altitude alone. Many symptoms persist, possibly due to extremely cold, arid conditions and the benefits of acetazolamide appeared negligible, though it may have prevented more severe symptoms in higher risk subjects.

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.

Polymorphisms of renin-angiotensin system genes as a risk factor for high-altitude pulmonary oedema

The genes of the renin—angiotensin system (RAS) play an important role in the regulation of pulmonary vascular tone. Although studies on individual genes polymorphisms have reported association with high-altitude pulmonary oedema (HAPE), studies on multiple genes or epistasis are lacking. We therefore investigated the association of the RAS polymorphisms with HAPE. In a case-control design, we screened 163 HAPE-resistant/controls (HAPE-r) and 160 HAPEpatients (HAPE-p) of Indian origin for eight polymorphisms of four RAS genes, ACE, AGT, AGTR1 and AGTR2. Significant difference in genotype and allele frequencies of the ACE I/D and AGT M235T polymorphisms was observed between HAPE-p and HAPE-r ( p < 0.05). In three-locus haplotype analysis of AGT the haplotype GTM was significantly higher in HAPE-p (29%) and haplotype GTT in HAPE-r (27%) after Bonferroni correction ( p < 0.006). The differences were insignificant for polymorphisms from AGTR1 and AGTR2. The MDR (multifactor dimensional reduction) approach for gene—gene interaction depicted individual polymorphism M235T as the best disease predicting model (cross validation consistency, CVC = 10/10). We found a significant association of D allele of ACE and M allele of AGT with HAPE. The findings are supported at the haplotypic level as well as through nested genetic interaction between the RAS gene polymorphisms using the MDR approach.

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.

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.

Keeping pace with ACE: are ACE inhibitors and angiotensin II type 1 receptor antagonists potential doping agents?

In the decade since the angiotensin-converting enzyme (ACE) gene was first proposed to be a 'human gene for physical performance', there have been numerous studies examining the effects of ACE genotype on physical performance phenotypes such as aerobic capacity, muscle function, trainability, and athletic status. While the results are variable and sometimes inconsistent, and corroborating phenotypic data limited, carriers of the ACE 'insertion' allele (the presence of an alu repeat element in intron 16 of the gene) have been reported to have higher maximum oxygen uptake (VO2max), greater response to training, and increased muscle efficiency when compared with individuals carrying the 'deletion' allele (absence of the alu repeat). Furthermore, the insertion allele has been reported to be over-represented in elite athletes from a variety of populations representing a number of endurance sports. The mechanism by which the ACE insertion genotype could potentiate physical performance is unknown. The presence of the ACE insertion allele has been associated with lower ACE activity (ACEplasma) in number of studies, suggesting that individuals with an innate tendency to have lower ACE levels respond better to training and are at an advantage in endurance sporting events. This could be due to lower levels of angiotensin II (the vasoconstrictor converted to active form by ACE), higher levels of bradykinin (a vasodilator degraded by ACE) or some combination of the two phenotypes. Observations that individuals carrying the ACE insertion allele (and presumably lower ACEplasma) have an enhanced response to training or are over-represented amongst elite athletes raises the intriguing question: would individuals with artificially lowered ACEplasma have similar training or performance potential? As there are a number of drugs (i.e. ACE inhibitors and angiotensin II type 1 receptor antagonists [angiotensin receptor blockers--ARBs]) that have the ability to either reduce ACEplasma activity or block the action of angiotensin II, the question is relevant to the study of ergogenic agents and to the efforts to rid sports of 'doping'. This article discusses the possibility that ACE inhibitors and ARBs, by virtue of their effects on ACE or angiotensin II function, respectively, have performance-enhancing capabilities; it also reviews the data on the effects of these medications on VO2max, muscle composition and endurance capacity in patient and non-patient populations. We conclude that, while the direct evidence supporting the hypothesis that ACE-related medications are potential doping agents is not compelling, there are insufficient data on young, athletic populations to exclude the possibility, and there is ample, albeit indirect, support from genetic studies to suggest that they should be. Unfortunately, given the history of drug experimentation in athletes and the rapid appropriation of therapeutic agents into the doping arsenal, this indirect evidence, coupled with the availability of ACE-inhibiting and ACE-receptor blocking medications may be sufficiently tempting to unscrupulous competitors looking for a shortcut to the finish line.

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.