Hemoglobin concentration of pastoral nomads permanently resident at 4,850-5,450 meters in Tibet

Regulation of haemoglobin concentration at high altitude

Lowlanders sojourning for more than 1 day at high altitude (HA) experience a reduction in plasma volume (PV) that increases haemoglobin concentration and thus restores arterial oxygen content. If the sojourn extends over weeks, an expansion of total red cell volume (RCV) occurs and contributes to the haemoconcentration. While the reduction in PV was classically attributed to an increased diuretic fluid loss, recent studies support fluid redistribution, rather than loss, as the underlying mechanism. The fluid redistribution is presumably driven by a disappearance of proteins from the circulation and the resulting reduction in oncotic pressure exerted by the plasma, although the fate of the disappearing proteins remains unclear. The RCV expansion is the result of an accelerated erythropoietic activity secondary to enhanced renal erythropoietin release, but a contribution of other mechanisms cannot be excluded. After return from HA, intravascular volumes return to normal values and the normalisation of RCV might involve selective destruction of newly formed erythrocytes, although this explanation has been strongly challenged by recent studies. In contrast to acclimatised lowlanders, native highlanders originating from the Tibetan and the Ethiopian plateaus present with a normal or only mildly elevated haemoglobin concentration. Genetic adaptations blunting the erythropoietic response to HA exposure have been proposed as an explanation for the absence of more pronounced haemoconcentration in these populations, but new evidence also supports a contribution of a larger than expected PV. The functional significance of the relatively low haemoglobin concentration in Tibetan and Ethiopian highlanders is incompletely understood and warrants further investigation.

Distinctive biochemistry profiles associated with hyperuricemia between Tibetans and Hans in China

Purpose

We sought to identify distinct risk factors for hyperuricemia in native Tibetan and immigrant Han populations in Tibet, China.

Methods

Three cohorts of male participants aged between 20 and 40 years were enrolled in this study. Biochemical parameters including serum uric acid (UA), fasting plasma glucose, insulin, lactate dehydrogenase (LDH), thyroxin, blood cell count, aminotransferase, and lipid profiles were analyzed. The association of risk factors with UA levels was evaluated using a multivariable line regression model. The effect of UA level on the biochemical parameters between the Hans and Tibetans was evaluated by two-way ANOVA.

Results

The prevalence of hyperuricemia (≥420 μmol/L) was 24.8% (62/250) in the Hans, similar to 23.8% (29/136) in the Tibetans. In the regression analysis, the risk factors that were significantly associated with UA in Hans did not apply to Tibetans. Tibetans had higher fasting insulin (P<0.05) and LDH (P<0.01) levels, in contrast with lower levels of triglycerides (P<0.05), total cholesterol (P<0.01), and low-density lipoprotein-cholesterol (P<0.01) than Hans in normal UA populations. Biochemistry analysis revealed lower albumin levels (P<0.001) and higher levels of all aminotransaminase and especially alkaline phosphatase (P<0.01) in Tibetans than in Hans in both populations. Compared with Hans, Tibetans had lower serum levels of urea, creatinine, and electrolytes in the normal UA population, which were further exacerbated in the high UA population. Tibetans had comparable white blood cell counts as Hans in both normal and high UA populations. In contrast, the red blood cell count and hemoglobin concentration were much lower in Tibetans than in Hans under high UA conditions.

Conclusions

The distinctive biochemistry between Tibetans and Hans may underlie the different etiologies of hyperuricemia in Tibet, China.

The HMOX2 polymorphism contributes to the carotid body chemoreflex in European sea-level residents by regulating hypoxic ventilatory responses

This study investigates whether a functional single nucleotide polymorphism of HMOX2 (heme oxygenase-2) (rs4786504 T>C) is involved in individual chemosensitivity to acute hypoxia, as assessed by ventilatory responses, in European individuals. These responses were obtained at rest and during submaximal exercise, using a standardized and validated protocol for exposure to acute normobaric hypoxia. Carriers of the ancestral T allele (n = 44) have significantly lower resting and exercise hypoxic ventilatory responses than C/C homozygous carriers (n = 40). In the literature, a hypoxic ventilatory response threshold to exercise has been identified as an independent predictor of severe high altitude-illness (SHAI). Our study shows that carriers of the T allele have a higher risk of SHAI than carriers of the mutated C/C genotype. Secondarily, we were also interested in COMT (rs4680 G > A) polymorphism, which may be indirectly involved in the chemoreflex response through modulation of autonomic nervous system activity. Significant differences are present between COMT genotypes for oxygen saturation and ventilatory responses to hypoxia at rest. In conclusion, this study adds information on genetic factors involved in individual vulnerability to acute hypoxia and supports the critical role of the ≪ O2 sensor ≫ - heme oxygenase-2 - in the chemosensitivity of carotid bodies in Humans.

Study of Brain Structure and Function in Chronic Mountain Sickness Based on fMRI

Objective: Headache and memory impairment are the primary clinical symptoms of chronic mountain sickness (CMS). In this study, we used voxel-based morphometry (VBM) and the amplitude of the low-frequency fluctuation method (ALFF) based on blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) to identify changes in the brain structure and function caused by CMS.

Materials and Methods: T1W anatomical images and a resting-state functional MRI (fMRI) of the whole brain were performed in 24 patients diagnosed with CMS and 25 normal controls matched for age, sex, years of education, and living altitude. MRI images were acquired, followed by VBM and ALFF data analyses.

Results: Compared with the control group, the CMS group had increased gray matter volume in the left cerebellum crus II area, left inferior temporal gyrus, right middle temporal gyrus, right insula, right caudate nucleus, and bilateral lentiform nucleus along with decreased gray matter volume in the left middle occipital gyrus and left middle temporal gyrus. White matter was decreased in the bilateral middle temporal gyrus and increased in the right Heschl's gyrus. Resting-state fMRI in patients with CMS showed increased spontaneous brain activity in the left supramarginal gyrus, left parahippocampal gyrus, and left middle temporal gyrus along with decreased spontaneous brain activity in the right cerebellum crus I area and right supplementary motor area.

Conclusion: Patients with CMS had differences in gray and white matter volume and abnormal spontaneous brain activity in multiple brain regions compared to the controls. This suggests that long-term chronic hypoxia may induce changes in brain structure and function, resulting in CMS.

Heterogeneity in Hematological Parameters of High and Low Altitude Tibetan Populations

Introduction

High altitude hypoxia is believed to be experienced at elevations of more than 2500 meters above sea level. Several studies have shed light on the biochemical aspects of high altitude acclimatization, where participants were sojourners to the high altitude from low altitude areas. However, information regarding the difference between the high altitude adapted Tibetans living at high altitude and their counterparts who reside at low altitude are lacking. To understand this, we have measured various hematological parameters in the Tibetan populations, who are residing in both high and low altitudes in India.

Methods

A total of 168 individuals (79 from high altitude (≥4500 meters) and 89 from low altitude (~850 meters) were recruited for this study. Hematological parameters such as red blood cells (RBC) count, hematocrit (HCT), hemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) were measured from the individuals from high and low altitudes. Serum erythropoietin (EPO) was measured by ELISA. Statistical analyses were performed to compare data from both of the altitudes. Gender-wise comparison of data was reported. Correlation analysis was performed within relevant parameters.

Results

Highly significant differences (p <0.0001) between high and low altitude Tibetans were detected in RBC count, HCT, Hb, MCHC in both males and females and in MCV in females. In the case of MCHC, however, age and BMI were potential confounders. Nominally significant differences (p <0.05) were detected in MCV and MCH within males. No significant difference in serum EPO level was found between altitude groups, in any gender. No significant correlation was found between serum EPO with Hb as well as serum EPO with HCT.

Discussion

Our study explores significantly lower RBC count, HCT, Hb, MCH, MCHC and higher MCV in long-term Tibetan residents living at low altitude compared to their high altitude counterparts, which is likely due to the outcome of hematological adaptation to a relatively hyperoxic environment in low altitude areas.

High-Altitude Adaptation: Mechanistic Insights from Integrated Genomics and Physiology

Population genomic analyses of high-altitude humans and other vertebrates have identified numerous candidate genes for hypoxia adaptation, and the physiological pathways implicated by such analyses suggest testable hypotheses about underlying mechanisms. Studies of highland natives that integrate genomic data with experimental measures of physiological performance capacities and subordinate traits are revealing associations between genotypes (e.g., hypoxia-inducible factor gene variants) and hypoxia-responsive phenotypes. The subsequent search for causal mechanisms is complicated by the fact that observed genotypic associations with hypoxia-induced phenotypes may reflect second-order consequences of selection-mediated changes in other (unmeasured) traits that are coupled with the focal trait via feedback regulation. Manipulative experiments to decipher circuits of feedback control and patterns of phenotypic integration can help identify causal relationships that underlie observed genotype–phenotype associations. Such experiments are critical for correct inferences about phenotypic targets of selection and mechanisms of adaptation.

Neural network correlates of high-altitude adaptive genetic variants in Tibetans: A pilot, exploratory study

Although substantial progress has been made in the identification of genetic substrates underlying physiology, neuropsychology, and brain organization, the genotype–phenotype associations remain largely unknown in the context of high‐altitude (HA) adaptation. Here, we related HA adaptive genetic variants in three gene loci (EGLN1, EPAS1, and PPARA) to interindividual variance in a set of physiological characteristics, neuropsychological tests, and topological attributes of large‐scale structural and functional brain networks in 135 indigenous Tibetan highlanders. Analyses of individual HA adaptive single‐nucleotide polymorphisms (SNPs) revealed that specific SNPs selectively modulated physiological characteristics (erythrocyte level, ratio between forced expiratory volume in the first second to forced vital capacity, arterial oxygen saturation, and heart rate) and structural network centrality (the left anterior orbital gyrus) with no effects on neuropsychology or functional brain networks. Further analyses of genetic adaptive scores, which summarized the overall degree of genetic adaptation to HA, revealed significant correlations only with structural brain networks with respect to local interconnectivity of the whole networks, intermodule communication between the right frontal and parietal module and the left occipital module, nodal centrality in several frontal regions, and connectivity strength of a subnetwork predominantly involving in intramodule edges in the right temporal and occipital module. Moreover, the associations were dependent on gene loci, weight types, or topological scales. Together, these findings shed new light on genotype–phenotype interactions under HA hypoxia and have important implications for developing new strategies to optimize organism and tissue responses to chronic hypoxia induced by extreme environments or diseases.

The increase in hemoglobin concentration with altitude varies among human populations

Decreased oxygen availability at high altitude requires physiological adjustments allowing for adequate tissue oxygenation. One such mechanism is a slow increase in the hemoglobin concentration ([Hb]) resulting in elevated [Hb] in high-altitude residents. Diagnosis of anemia at different altitudes requires reference values for [Hb]. Our aim was to establish such values based on published data of residents living at different altitudes by applying meta-analysis and multiple regressions. Results show that [Hb] is increased in all high-altitude residents. However, the magnitude of increase varies among the regions analyzed and among ethnic groups within a region. The highest increase was found in residents of the Andes (1 g/dL/1000 m), but this increment was smaller in all other regions of the world (0.6 g/dL/1000 m). While sufficient data exist for adult males and females showing that sex differences in [Hb] persist with altitude, data for infants, children, and pregnant women are incomplete preventing such analyses. Because WHO reference values were originally based on [Hb] of South American people, we conclude that individual reference values have to be defined for ethnic groups to reliably diagnose anemia and erythrocytosis in high-altitude residents. Future studies need to test their applicability for children of different ages and pregnant women.

Erythropoietin and ferritin response in native highlanders aged 4-19 years from the Leh-Ladakh region of India

The pivotal role of erythropoietin (EPO) in hypoxic adaptation has led to various studies assessing the EPO and ferritin response in native highlanders from Andes and Tibet. We assessed the relationship between EPO, haemoglobin and ferritin in 335 native highlanders (172 boys and 163 girls, aged 4 to 19 years) from Leh-Ladakh, India, who had no history of travel to lowland areas. Complete blood counts, serum EPO and ferritin levels were measured. We stratified study subjects based on age, gender, pubertal status and analysed the EPO and ferritin levels between the stratified groups respectively. The mean EPO level in boys was lower than girls. The mean ferritin level in boys was significantly higher (P = 0·013) than in girls. There was no significant variation in the EPO and ferritin levels amongst the various age groups in our study. Near normal EPO levels since childhood with a negative correlation with haemoglobin is suggestive of a robust adaptive mechanism to high altitude from the early years of life. Low ferritin levels are indicative of decreased iron stores in these native highlanders.

Hematological Parameters in Native Highlanders of Ladakh Aged 4-19 Years

Hematological adaptations to high altitude (HA) are long studied but are focused either on lowlanders visiting HA or native highlanders from Andes and Tibet. The literature on native highlanders from the Indian subcontinent or paediatric highlanders is scarce. We aimed at assessing hematological parameters in native highlanders of Ladakh, India, aged 4-19 years and derive nomograms in an age stratified manner specific to these native highlanders. A total of 335 self-reported healthy native highlanders of Ladakh, without any known comorbidities and not on hematinic nor any drugs in the age group of 4-19 years were included in the study. Complete hemogram including red cell indices was measured. R ver 3.4.0 was used to compare the hematological parameters based on gender/age stratification, pubertal and nutritional status. The hematological reference ranges were created for various parameters in the paediatric population. The mean (SD) haemoglobin (Hb) concentration was 14.74 (2.07) gm/dL. The mean hematocrit (Hct) was 40.43 (5.57%) %, mean corpuscular volume (MCV) was 81.87 (7.22) fL, white blood cell (WBC) count was 7596 (2172) cells/μL and platelets was 378.4 (152.8) × 10³/μL. Hct and MCV increased with age. Hb concentration, Hct, and MCV in girls was significantly lower than boys. Severely underweight subjects (body mass index < 16) showed significantly higher platelet counts compared to their nourished counterparts. The hematological nomograms for the native paediatric highlanders from Ladakh, India have been reported in this study.

Plasma hemoglobin concentration among pregnant and non-pregnant women in Mwanza: are we using correct reference values to diagnose anemia in pregnancy?

Introduction

The definition of anemia has attracted considerable interest because several studies have demonstrated that hematologic profile vary with ethnicity in addition to age, sex and altitude. This has led scholars to recommend the use of population specific hematologic reference values in diagnosing blood disorders. However, there is limited information about Tanzanians population specific hemoglobin (Hb) levels which can be used to set cut-off points to define anemia. This study aimed to determine plasma Hb concentrations among healthy Tanzanian women.

Methods

This cross sectional study was done in Mwanza. Sociodemographic data were collected using questionnaires and plasma Hb concentrations were measured by calorimetric method. Data were analyzed using SPSS.

Results

A total of 215 (162 pregnant, 53 non-pregnant) women with a mean age of 28.2 ± 6.54 years participated in the study. The mean plasma Hb concentrations were 12.0 ± 1.43 mg/dl and 11.9 ± 1.15 mg/dl for pregnant and non-pregnant women respectively. The Hb levels did not significantly vary between pregnant and non-pregnant women. Using WHO reference values, 45.3% non-pregnant and 26.5% pregnant women were found to be anemic while using the population specific reference, only 1.9% of pregnant and none of non-pregnant women would be classified as anemic.

Conclusion

Most Tanzanian women who are diagnosed to have anemia during pregnancy, often had developed lower Hb before pregnancy and operational thresholds for diagnosis of anemia observed in this study are lower than WHO recommended references values. We recommend a large scale study to determine hematological profile of Tanzanian.

Predictive factors and prognostic effect of telomere shortening in pulmonary fibrosis

BACKGROUND AND OBJECTIVE

The abnormal shortening of telomeres is a mechanism linking ageing to idiopathic pulmonary fibrosis (IPF) that could be useful in the clinical setting. The objective of this study was to identify the IPF patients with higher risk for telomere shortening and to investigate the outcome implications.

METHODS

Consecutive Spanish patients were included at diagnosis and followed up for 3 years. DNA blood samples from a Mexican cohort were used to validate the results found in Spanish sporadic IPF. Prior to treatment, telomere length was measured through quantitative polymerase chain reaction (qPCR) and Southern blot. Outcome was assessed according to mortality or need for lung transplantation. A multivariate regression logistic model was used for statistical analysis.

RESULTS

Family aggregation, age of <60 years and the presence of non-specific immunological or haematological abnormalities were associated with a higher probability of telomere shortening. Overall, 66.6% of patients younger than 60 years with telomere shortening died or required lung transplantation, independent of functional impairment at diagnosis. By contrast, in patients older than 60 years with telomere shortening, the negative impact of telomere shortening in outcome was not significant.

CONCLUSION

Our data indicate that young sporadic IPF patients (<60 years) with some non-specific immunological or haematological abnormalities had higher risk of telomere shortening, and furthermore, they presented a poorer prognosis.

Renal association clinical practice guideline on Anaemia of Chronic Kidney Disease

Anaemia is a commonly diagnosed complication among patients suffering with chronic kidney disease. If left untreated, it may affect patient quality of life. There are several causes for anaemia in this patient population. As the kidney function deteriorates, together with medications and dietary restrictions, patients may develop iron deficiency, resulting in reduction of iron supply to the bone marrow (which is the body organ responsible for the production of different blood elements). Chronic kidney disease patients may not be able to utilise their own body's iron stores effectively and hence, many patients, particularly those receiving haemodialysis, may require additional iron treatment, usually provided by infusion.With further weakening of kidney function, patients with chronic kidney disease may need additional treatment with a substance called erythropoietin which drives the bone marrow to produce its own blood. This substance, which is naturally produced by the kidneys, becomes relatively deficient in patients with chronic kidney disease. Any patients will eventually require treatment with erythropoietin or similar products that are given by injection.Over the last few years, several iron and erythropoietin products have been licensed for treating anaemia in chronic kidney disease patients. In addition, several publications discussed the benefits of each treatment and possible risks associated with long term treatment. The current guidelines provide advice to health care professionals on how to screen chronic kidney disease patients for anaemia, which patients to investigate for other causes of anaemia, when and how to treat patients with different medications, how to ensure safe prescribing of treatment and how to diagnose and manage complications associated with anaemia and the drugs used for its treatment.

Protective effects of traditional Tibetan medicine Zuo-Mu-A Decoction () on the blood parameters and myocardium of high altitude polycythemia model rats

OBJECTIVE

To explore the protective effects of Tibetan medicine Zuo-Mu-A Decoction (, ZMAD) on the blood parameters and myocardium of high altitude polycythemia (HAPC) model rats.

METHODS

Forty male Wistar rats were randomly divided into 4 groups by a random number table, including the normal, model, Rhodiola rosea L. (RRL) and ZMAD groups (10 in each group). Every group was raised in Lhasa to create a HAPC model except the normal group. After modeling, rats in the RRL and the ZMAD groups were administered intragastrically with RRL (20 mL/kg) and ZMAD (7.5 mL/kg) once a day for 2 months, respectively; for the normal and the model groups, 5 mL of distilled water was administered intragastrically instead of decoction. Then routine blood and hematologic rheology parameters were taken, levels of erythropoietin and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were tested, and ultrastructural change in the left ventricular myocardium was observed using transmission electron microscopy.

RESULTS

Compared with the model group, ZMAD significantly reduced the red blood cell count, hemoglobin levels, whole blood viscosity at low/middle shear rates, plasma viscosity, erythrocyte electrophoretic time, erythropoietin and 8-OHdG levels, and also increased the erythrocyte deformation index (P<0.05). There was no difference in all results between the RRL and the ZMAD groups. The cardiac muscle fibers were well-protected, mitochondrial matrix swelled mildly and ultrastructure changes were less prominent in the ZMAD group compared with the model group.

CONCLUSION

ZMAD has significant protective effects on the blood parameters against HAPC, and also has the beneficial effect in protecting against myocardial injury.

HMOX2 Functions as a Modifier Gene for High-Altitude Adaptation in Tibetans

Tibetans are well adapted to high-altitude environments. Among the adaptive traits in Tibetans, the relatively low hemoglobin level is considered a blunted erythropoietic response to hypoxic challenge. Previously, EPAS1 and EGLN1, the major upstream regulators in the hypoxic pathway, were reportedly involved in the hemoglobin regulation in Tibetans. In this study, we report a downstream gene (HMOX2) involved in heme catabolism, which harbors potentially adaptive variants in Tibetans. We first resequenced the entire genomic region (45.6 kb) of HMOX2 in Tibetans, which confirmed the previously suspected signal of positive selection on HMOX2 in Tibetans. Subsequent association analyses of hemoglobin levels in two independent Tibetan populations (a total of 1,250 individuals) showed a male-specific association between the HMOX2 variants and hemoglobin levels. Tibetan males with the derived C allele at rs4786504:T>C displayed lower hemoglobin level as compared with the T allele carriers. Furthermore, our in vitro experiments indicated that the C allele of rs4786504 could increase the expression of HMOX2, presumably leading to a more efficient breakdown of heme that may help maintain a relatively low hemoglobin level at high altitude. Collectively, we propose that HMOX2 contributes to high-altitude adaptation in Tibetans by functioning as a modifier in the regulation of hemoglobin metabolism.

CYP17A1 and CYP2E1 variants associated with high altitude polycythemia in Tibetans at the Qinghai-Tibetan Plateau

Tibetans adapt to high altitude environments through low blood hemoglobin concentrations. Previous work has identified that CYP17A1 and CYP2E1 genes exhibit evidence of local positive selection for this Tibetan high-altitude adaptation. Nevertheless, despite this apparent genetic advantage, some Tibetans still develop high altitude polycythemia (HAPC) yet the reasons for this remain unknown. We sought to determine if polymorphisms in CYP17A1 and CYP2E1 genes were associated with susceptibility to HAPC in Tibetans at the Qinghai-Tibetan Plateau in China. We enrolled 63 Tibetan HAPC patients and 131 healthy, age- and gender-matched control Tibetans. All subjects are from the Yushu area of Qinghai where the altitude is over 3500 m. Three SNPs of the CYP17A1 including rs3781287, rs11191548 and rs1004467, and four SNPs of CYP2E1 gene, including rs1536836, rs3813865, rs3813867 and rs743535, were genotyped by the Sequenom MassARRAY SNP assays. We discovered that SNP rs1004467 of the CYP17A1 gene and SNP rs3813865 of the CYP2E1 gene were significantly associated with HAPC risk. Furthermore, we identified a positive correlation between these two SNPs and plasma hemoglobin levels. Thus, taken together, our study is the first to our knowledge to show that polymorphisms in the rs1004467 SNP of CYP17A1 and rs3813865 SNP of CYP2E1 correlate with susceptibility to HAPC.

EPAS1 Gene Polymorphisms Are Associated With High Altitude Polycythemia in Tibetans at the Qinghai-Tibetan Plateau

OBJECTIVE

To test the hypothesis that the polymorphisms in the EPAS1 gene are associated with the susceptibility to high altitude polycythemia (HAPC) in Tibetans at the Qinghai-Tibetan Plateau.

METHODS

We enrolled 63 Tibetan HAPC patients and 131 matched healthy Tibetans as a control group, from the Yushu area in Qinghai where the altitude is greater than 3500 m. Eight single-nucleotide polymorphisms (SNPs) of the EPAS1 gene, including rs12619696, rs13420857, rs2881504, rs4953388, rs13419896, rs4953354, rs10187368, and rs7587138, were genotyped by the Sequenom MassARRAY SNP assay.

RESULTS

The frequencies of the G allele of EPAS1 SNP rs13419896 were significantly higher in the HAPC group than in the control group (P < .05). Moreover, the A alleles of rs12619696 and rs4953354 were prevalent in the HAPC group, and their counterpart homozygotes were prevalent in the normal Tibetan group (P < .05).

CONCLUSIONS

Compared with normal Tibetans, Tibetans with HAPC are maladapted and have a different haplotype in EPAS1 SNPs rs12619696, rs13419896, and rs4953354.

Human high-altitude adaptation: forward genetics meets the HIF pathway

Humans have adapted to the chronic hypoxia of high altitude in several locations, and recent genome-wide studies have indicated a genetic basis. In some populations, genetic signatures have been identified in the hypoxia-inducible factor (HIF) pathway, which orchestrates the transcriptional response to hypoxia. In Tibetans, they have been found in the HIF2A (EPAS1) gene, which encodes for HIF-2α, and the prolyl hydroxylase domain protein 2 (PHD2, also known as EGLN1) gene, which encodes for one of its key regulators, PHD2. High-altitude adaptation may be due to multiple genes that act in concert with one another. Unraveling their mechanism of action can offer new therapeutic approaches toward treating common human diseases characterized by chronic hypoxia.

Adaptations to local environments in modern human populations

After leaving sub-Saharan Africa around 50000-100000 years ago, anatomically modern humans have quickly occupied extremely diverse environments. Human populations were exposed to further environmental changes resulting from cultural innovations, such as the spread of farming, which gave rise to new selective pressures related to pathogen exposures and dietary shifts. In addition to changing the frequency of individual adaptive alleles, natural selection may also shape the overall genetic architecture of adaptive traits. Here, we review recent advances in understanding the genetic architecture of adaptive human phenotypes based on insights from the studies of lactase persistence, skin pigmentation and high-altitude adaptation. These adaptations evolved in parallel in multiple human populations, providing a chance to investigate independent realizations of the evolutionary process. We suggest that the outcome of adaptive evolution is often highly variable even under similar selective pressures. Finally, we highlight a growing need for detecting adaptations that did not follow the classical sweep model and for incorporating new sources of genetic evidence such as information from ancient DNA.

Chronic mountain sickness in Chinese Han males who migrated to the Qinghai-Tibetan plateau: application and evaluation of diagnostic criteria for chronic mountain sickness

BACKGROUND

Chronic mountain sickness (CMS), originally characterized by excess hemoglobin (Hb), is currently diagnosed using score-based diagnostic criteria combined with excessive erythrocytosis and clinical symptoms. However, the current criteria have limited applicability. We applied these criteria to 1,029 Chinese Han males migrated to and have been stayed at the Qinghai-Tibet plateau (3,700-5,000 m) for 2-96 months to investigate the prevalence of CMS and its correlations with Hb concentration, altitude, and the length of residence.

METHODS

Subjects were screened for CMS using the latest approved diagnostic criteria combined with excessive erythrocytosis and clinical symptoms. Hb concentrations were measured, and a cut-off point was determined with k-means clustering. Predisposing factors were evaluated with binary logistic analysis and curve fitting analysis.

RESULTS

(1) The prevalence of CMS at the Qinghai-Tibetan plateau was 17.8% (183/1029 subjects, with CMS score ≥ 6, and Hb ≥ 210 g/L), which is higher than that previously reported. (2) While individuals were identified into two Hb clusters with a cut-off point of 200 g/L, in the low-Hb cluster (Hb < 200 g/L), the oxygen saturation remained stable as the Hb increased; in the high-Hb cluster (Hb ≥ 200 g/L), the oxygen saturation decreased as the Hb increased. (3) Two critical factors associated with CMS development were residence at an altitude of 4,500 m and a 60-month length of residence.

CONCLUSIONS

Our presenting scoring system is more sensitive than previous diagnostic criteria and favors early screening and treatment of patients with CMS. Our finding suggests that an adjusted Hb threshold of 200 g/L (instead of 210 g/L) is more adaptable in Han individuals at all altitudes. The weight of Hb level should score ≥ 6 points using the CMS scoring system because of the pathophysiologic role of excessive erythrocytosis in patients with CMS. In addition, our data suggest the importance of early screening of CMS via regular medical examinations within the first 60 months of residence at high altitudes, especially >4500 m.

The sex difference in haemoglobin levels in adults - mechanisms, causes, and consequences

Men and women have different mean haemoglobin levels in health in venous blood - women have mean levels approximately 12% lower than men. A similar sex-related difference in haemoglobin levels in adult animals is found in many species of mammals, birds and reptiles, indicating that it is an important physiological phenomenon. It is probably a direct effect of sex hormones, both oestrogen and androgens, on erythropoiesis. However, since there is no difference in erythropoietin levels between the sexes, this effect most likely takes place in the kidney, rather than in the bone marrow. Oestrogens dilate and androgens constrict the renal microvasculature: dilation and vasoconstriction in vessels below 300 μm in diameter respectively increase and decrease the haematocrit in blood in arterioles, capillaries and venules, altering the oxygen delivery per unit red cell mass, and providing a mechanism for varying the red cell mass without compensatory changes in erythropoiesis.

Andean and Tibetan patterns of adaptation to high altitude

OBJECTIVES

High-altitude hypoxia, or decreased oxygen levels caused by low barometric pressure, challenges the ability of humans to live and reproduce. Despite these challenges, human populations have lived on the Andean Altiplano and the Tibetan Plateau for millennia and exhibit unique circulatory, respiratory, and hematological adaptations to life at high altitude. We and others have identified natural selection candidate genes and gene regions for these adaptations using dense genome scan data. One gene previously known to be important in cellular oxygen sensing, egl nine homolog 1 (EGLN1), shows evidence of positive selection in both Tibetans and Andeans. Interestingly, the pattern of variation for this gene differs between the two populations. Continued research among Tibetan populations has identified statistical associations between hemoglobin concentration and single nucleotide polymorphism (SNP) genotype at EGLN1 and a second gene, endothelial PAS domain protein 1 (EPAS1).

METHODS

To measure for the effects of EGLN1 and EPAS1 altitude genotypes on hemoglobin concentration among Andean highlanders, we performed a multiple linear regression analysis of 10 candidate SNPs in or near these two genes.

RESULTS

Our analysis did not identify significant associations between EPAS1 or EGLN1 SNP genotypes and hemoglobin concentration in Andeans.

CONCLUSIONS

These results contribute to our understanding of the unique set of adaptations developed in different highland groups to the hypoxia of high altitude. Overall, the results provide key insights into the patterns of genetic adaptation to high altitude in Andean and Tibetan populations.

Genetic adaptation of the hypoxia-inducible factor pathway to oxygen pressure among eurasian human populations

Research into the mechanisms of human adaptation to the hypoxic environment of high altitude is of great interest to the fields of human physiology and clinical medicine. Recently, the gene EGLN1, from the hypoxia-inducible factor (HIF) pathway, was identified as being involved in the hypoxic adaptation of highland Andeans and Tibetans. Both highland Andeans and Tibetans have adapted to an extremely hypoxic habitat and less attention has been paid to populations living in normoxic conditions at sea level and mild-hypoxic environments of moderate altitude, thus, whether a common adaptive mechanism exists in response to quantitative variations of environmental oxygen pressure over a wide range of residing altitudes is unknown. Here, we first performed a genome-wide association study of 35 populations from the Human Genome Diversity-CEPH Panel who dwell at sea level to moderate altitude in Eurasia (N = 691; 0-2,500 m) to identify the genetic adaptation profile of normoxic and mild-hypoxic inhabitants. In addition, we systematically compared the results from the present study to six previously published genome-wide scans of highland Andeans and Tibetans to identify shared adaptive signals in response to quantitative variations of oxygen pressure. For normoxic and mild-hypoxic populations, the strongest adaptive signal came from the mu opioid receptor-encoding gene (OPRM1, 2.54 × 10(-9)), which has been implicated in the stimulation of respiration, while in the systematic survey the EGLN1-DISC1 locus was identified in all studies. A replication study performed with highland Tibetans (N = 733) and sea level Han Chinese (N = 748) confirmed the association between altitude and SNP allele frequencies in OPRM1 (in Tibetans only, P < 0.01) and in EGLN1-DISC1 (in Tibetans and Han Chinese, P < 0.01). Taken together, identification of the OPRM1 gene suggests that cardiopulmonary adaptation mechanisms are important and should be a focus in future studies of hypoxia adaptation. Furthermore, the identification of the EGLN1 gene from the HIF pathway suggests a common adaptive mechanism for Eurasian human populations residing at different altitudes with different oxygen pressures.

Comparison of the pharmacokinetics of sulfamethoxazole in native Han and Tibetan male Chinese volunteers living at high altitude

The aim of this study was to investigate the pharmacokinetics of sulfamethoxazole in native Han and Tibetan healthy Chinese subjects living chronically at high altitude. An open-labeled, controlled, prospective study was conducted in healthy Chinese male volunteers. Sulfamethoxazole 1,200 mg was administered orally to two groups: native Han and Tibetan volunteers living at high altitude (2,500-3,900 m [8,200-12,800 ft]). Blood samples were collected from an indwelling venous catheter into heparinized tubes before (baseline) study drug administration and at 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 12, 24, 36, and 48 h after study drug administration. Sulfamethoxazole in whole blood, plasma, and plasma water, and metabolite N (4)-acetyl-sulfamethoxazole in plasma were determined by HPLC. Tolerability was determined using blood chemistry testing, continuous 12-lead electrocardiogram, and blood pressure monitoring. The protein binding was significantly higher in the native Tibetan group (70.5 %) compared to the native Han group (67.3 %) (p < 0.05). The binding of sulfamethoxazole to red blood cells was 7.4 and 8.3 % in the native Han and native Tibetan groups, respectively. There was no significant difference between the two groups. The AUC(0-∞) was significantly lower in the native Tibetan group compared to the native Han group (p < 0.05), and other pharmacokinetics parameters were found to have no significant difference between the two groups. This study found little changes in the disposition of sulfamethoxazole in these native healthy Tibetan Chinese subjects living at high altitude in comparison to native healthy Han Chinese subjects living at high altitude.

Identifying signatures of natural selection in Tibetan and Andean populations using dense genome scan data

High-altitude hypoxia (reduced inspired oxygen tension due to decreased barometric pressure) exerts severe physiological stress on the human body. Two high-altitude regions where humans have lived for millennia are the Andean Altiplano and the Tibetan Plateau. Populations living in these regions exhibit unique circulatory, respiratory, and hematological adaptations to life at high altitude. Although these responses have been well characterized physiologically, their underlying genetic basis remains unknown. We performed a genome scan to identify genes showing evidence of adaptation to hypoxia. We looked across each chromosome to identify genomic regions with previously unknown function with respect to altitude phenotypes. In addition, groups of genes functioning in oxygen metabolism and sensing were examined to test the hypothesis that particular pathways have been involved in genetic adaptation to altitude. Applying four population genetic statistics commonly used for detecting signatures of natural selection, we identified selection-nominated candidate genes and gene regions in these two populations (Andeans and Tibetans) separately. The Tibetan and Andean patterns of genetic adaptation are largely distinct from one another, with both populations showing evidence of positive natural selection in different genes or gene regions. Interestingly, one gene previously known to be important in cellular oxygen sensing, EGLN1 (also known as PHD2), shows evidence of positive selection in both Tibetans and Andeans. However, the pattern of variation for this gene differs between the two populations. Our results indicate that several key HIF-regulatory and targeted genes are responsible for adaptation to high altitude in Andeans and Tibetans, and several different chromosomal regions are implicated in the putative response to selection. These data suggest a genetic role in high-altitude adaption and provide a basis for future genotype/phenotype association studies necessary to confirm the role of selection-nominated candidate genes and gene regions in adaptation to altitude.

Comprehensive geriatric assessment of elderly highlanders in Qinghai, China II: the association of polycythemia with lifestyle-related diseases among the three ethnicities

AIM

The objective of this study is to disclose the association of polycythemia with lifestyle-related diseases (hypertension, obesity and glucose intolerance) among the three ethnicities in Qinghai, China.

METHODS

The subjects were 393 elderly people (247 Han, 97 Tibetan and 49 Mongolian) aged 60 years and more living in Qinghai (3000 m a.s.l.) in China. The associated factors with polycythemia were analyzed in the subjects. Excessive polycythemia was defined as hemoglobin concentration over 20 mg/dL.

RESULTS

Polycythemia was associated with men, hypoxemia, obesity and high diastolic blood pressure (DBP) in the elderly in Qinghai. Male sex was associated with polycythemia in all ethnicities. Obesity was associated with Han and Tibetan men. Glucose intolerance and activities of daily living were not directly associated with polycythemia after adjustment for sex. There were 7.9% with excessive polycythemia. Independently-associated factors for excessive polycythemia were male sex, body mass index of 25 or more, SpO(2) of less than 85%, DBP of 85 mmHg or more and Han ethnicity (vs Tibetan) by multiple logistic regression.

CONCLUSION

There was a close association of polycythemia with diastolic hypertension and obesity in lifestyle-related diseases in high-altitude elderly people. Han people had a higher hemoglobin concentration after adjustment of lifestyle-related diseases compared with Tibetan people. The difference of hemoglobin concentration may be due to Tibetans undergoing a much longer period of adaptation than Han people. Further study is needed to disclose the association between the difference of hypoxic adaptation, lifestyle-related diseases and chronic mountain sickness for their prevention.

Identifying positive selection candidate loci for high-altitude adaptation in Andean populations

High-altitude environments (>2,500 m) provide scientists with a natural laboratory to study the physiological and genetic effects of low ambient oxygen tension on human populations. One approach to understanding how life at high altitude has affected human metabolism is to survey genome-wide datasets for signatures of natural selection. In this work, we report on a study to identify selection-nominated candidate genes involved in adaptation to hypoxia in one highland group, Andeans from the South American Altiplano. We analysed dense microarray genotype data using four test statistics that detect departures from neutrality. Using a candidate gene, single nucleotide polymorphism-based approach, we identified genes exhibiting preliminary evidence of recent genetic adaptation in this population. These included genes that are part of the hypoxia-inducible transcription factor ( HIF ) pathway, a biochemical pathway involved in oxygen homeostasis, as well as three other genomic regions previously not known to be associated with high-altitude phenotypes. In addition to identifying selection-nominated candidate genes, we also tested whether the HIF pathway shows evidence of natural selection. Our results indicate that the genes of this biochemical pathway as a group show no evidence of having evolved in response to hypoxia in Andeans. Results from particular HIF -targeted genes, however, suggest that genes in this pathway could play a role in Andean adaptation to high altitude, even if the pathway as a whole does not show higher relative rates of evolution. These data suggest a genetic role in high-altitude adaptation and provide a basis for genotype/phenotype association studies that are necessary to confirm the role of putative natural selection candidate genes and gene regions in adaptation to altitude.

Variations within oxygen-regulated gene expression in humans

The effects of hypoxia on gene transcription are mainly mediated by a transcription factor complex termed hypoxia-inducible factor (HIF). Genetic manipulation of animals and studies of humans with rare hereditary disease have shown that modifying the HIF pathway affects systems-level physiological responses to hypoxia. It is, however, an open question whether variations in systems-level responses to hypoxia between individuals could arise from variations within the HIF system. This study sought to determine whether variations in the responsiveness of the HIF system at the cellular level could be detected between normal individuals. Peripheral blood lymphocytes (PBL) were isolated on three separate occasions from each of 10 healthy volunteers. After exposure of PBL to eight different oxygen tensions ranging from 20% to 0.1%, the expression levels of four HIF-regulated transcripts involved in different biological pathways were measured. The profile of expression of all four transcripts in PBL was related to oxygen tension in a curvilinear manner. Double logarithmic transformation of these data resulted in a linear relationship that allowed the response to be parameterized through a gradient and intercept. Analysis of variance (ANOVA) on these parameters showed that the level of between-subject variation in the gradients of the responses that was common across all four HIF-regulated transcripts was significant (P = 0.008). We conclude that statistically significant variation within the cellular response to hypoxia can be detected between normal humans. The common nature of the variability across all four HIF-regulated genes suggests that the source of this variation resides within the HIF system itself.

High Altitude Adaptation in Tibetans

Since the beginning of the Himalayan climbing era, the anecdotal extraordinary physical performance at high altitude of Sherpas and Tibetans has intrigued scientists interested in altitude adaptation. These ethnic groups may have been living at high altitude for longer than any other population, and the hypothesis of a possible evolutionary genetic adaptation to altitude makes sense. Reviewed here is the evidence as to whether Tibetans are indeed better adapted for life and work at high altitude as compared to other populations and, if so, whether this better adaptation might be inborn. Tibetans, compared to lowlanders, maintain higher arterial oxygen saturation at rest and during exercise and show less loss of aerobic performance with increasing altitude. Tibetans have greater hypoxic and hypercapnic ventilatory responsiveness, larger lungs, better lung function, and greater lung diffusing capacity than lowlanders. Blood hemoglobin concentration is lower in Tibetans than in lowlanders or Andeans living at similar altitudes. Tibetans develop only minimal hypoxic pulmonary hypertension and have higher levels of exhaled nitric oxide than lowlanders or Andeans. Tibetans' sleep quality at altitude is better and they desaturate less at night. Several of these findings are also found in Tibetans born at low altitude when exposed for the first time to high altitude once adult. In conclusion, Tibetans indeed seem better adapted to life and work at high altitude, and this superior adaptation may very well be inborn, even though its exact genetic basis remains to be elucidated.

Human behaviour and development under high-altitude conditions

Although we are far from a universally accepted pattern of impaired function at altitude, there is evidence indicating motor, perceptual, memory and behavioural deficits in adults. Even relatively low altitudes (2500 m) may delay reaction time, and impair motor function. Extreme altitude exposure (>5000 m) may result in more pronounced impairment that can persist after returning to the lowlands. Research into the effects of altitude exposure earlier in development is lacking by comparison. Un-acclimatized children can suffer from acute mountain sickness, and, in native populations born at altitude, subtle cognitive and behavioural deficits suggest incomplete adaptation to hypoxia. The study of neurobehavioural functioning at altitude may provide important information about the effects of clinical hypoxia on the human brain and behavioural development.

Hemoglobin levels in Qinghai-Tibet: different effects of gender for Tibetans vs. Han

The Tibetan population, long a resident on the Qinghai-Tibetan Plateau, has lower hemoglobin concentrations than Han Chinese migrants, but it is incompletely known how gender affects the hemoglobin concentrations in the two populations at various altitudes. Measurements of hemoglobin concentration were obtained in 5,887 healthy male and female Tibetan and Han residents aged 5–60 yr, at altitudes of 2,664, 3,813, 4,525, and 5,200 m. Multiple regression equations showed the β-coefficients for altitude and for age were higher ( P < 0.05) in Han men than in Tibetan men and in Han women than in Tibetan women. Analysis indicated a significant three-way interaction between altitude, gender, and ethnicity (χ2 = 3.72, P = 0.05). With increasing altitude, men progressively had more hemoglobin than women in the Han, but not the Tibetan, population. Above 2,664 m, this gender-related difference in hemoglobin concentration increased from childhood to young adulthood more in Han than in Tibetans. We suggest that the Han-Tibetan ethnic difference in the effect of altitude on hemoglobin concentration depends to a large extent on gender.

Hematological differences during growth among Tibetans and Han Chinese born and raised at high altitude in Qinghai, China

This study describes the hemoglobin concentration ([Hb]) and hematocrit (HCT) of over 1,000 Tibetan and Han children, adolescents, and young adults who were born and raised at 3,200 m, 3,800 m, or 4,300 m in Qinghai Province, western China. At 3,200 m, no altitude effect is evident in the hematological characteristics of either group. At 3,800 m and 4,300 m, both groups show [Hb] and HCT values that are above low-altitude norms. At both altitudes, Tibetan and Han children show no differences in the pattern of hematological response up to age 13. Among adolescents and young adults, however, the [Hb] and HCT of Han males and females are elevated compared to Tibetans. This indicates that the adolescent period may involve a divergence in the responses to hypoxia made by some individuals in these two groups. Also, many other adolescents and young adults in both groups show similar hematological characteristics, indicating that many Tibetans and Han share similar hematological responses to hypoxia.

The Qinghai-Tibetan plateau: how high do Tibetans live?

A lower incidence of chronic mountain sickness (CMS) has apparently been observed in Tibetans in comparison to Andeans of South America. In the past, the hypothesis of "geographic differences" has been constructed to explain these population differences. In order to assess the importance of this hypothesis in the development of CMS, this article will first review the geographic factors of the Qinghai-Tibetan plateau where Tibetans live. The plateau is bounded by the Himalayas in the southwest and the Kunlun and Aljin mountains in the northeast. It towers over southwestern China at an average elevation of 4000 m above sea level and is known as "the roof of the world." Covering more than 2.5 million km(2), the Qinghai-Tibetan plateau is the highest and largest plateau in the world. The plateau has a highland continental climate and a very complex topography with great variations. Second, at what altitude do Tibetans live? In 1990 it was estimated that 4,594,188 Tibetans live on the plateau, with 53% living at an altitude over 3500 m. Fairly large numbers (about 600,000) live at an altitude exceeding 4500 m in the Chantong-Qingnan area. People of Tibetan ethnic descent are lifelong high-altitude residents and cannot easily move to higher or lower elevations. Over 90% of the population are engaged in farming and herding. The upper altitude limit of crops is around 4500 m, while the nomads reside above 4800 m and 5500 m. Recently, mining activities in the plateau have sustained a part of the population that lives permanently at altitudes between 3700 and 6000 m. Therefore, the Tibetans living in the Qinghai-Tibetan plateau live at an altitude as high as the Andeans in South America. Thus the apparently low incidence of CMS in Tibetans cannot be ascribed to "geographic differences." We propose that the genetic adaptation to hypoxia that has occurred in Tibetans is of importance in CMS.

Normal hematological values for healthy persons living at 4000 meters in Bolivia

Defining the range of normal hematocrit and hemoglobin levels in residents of high altitude is required to diagnose chronic mountain sickness (CMS) and other conditions defined, in part, by hematocrit or hemoglobin values. We studied 1,934 healthy, young (aged 15 to 29 yr) male and female residents of Potosí, Bolivia (4000 m), to determine the average and normal range of hemoglobin and hematocrit values, defining normal as within 2 standard deviations of the mean or encompassing 95% of the observed variation. Male hematocrit averaged 52.7% and hemoglobin averaged 17.3 m/dL whole blood. The corresponding female values were 48.3% and 15.8 g/dL whole blood, respectively. The range of normal values was 45% to 61% for hematocrit and 13 to 21 g/dL for hemoglobin in the men and 41% to 56% for hematocrit and 12 to 19 g/dL for hemoglobin in the women. These data indicate that hematocrit values above 61% in men or 56% in women and hemoglobin values above 21 g/dL whole blood in men or 19 g/dL whole blood in women are outside the normal range.

The evidence for hereditary factors contributing to high altitude adaptation in Andean natives: a review

Humans have occupied the high plateaus and mountain valleys of the Andes and the Himalayas for thousands of years. Although sea level natives can, and often do, travel in these rarefied reaches, there is little doubt that natives born and raised in the "thin" air are better equipped to deal with the reduced availability of oxygen at altitude. What fraction of the hypoxia defense response of high altitude native populations is due to developmental adaptations acquired during growth and what fraction is due to a genetic component reflecting the effects of selective transmission of beneficial genetic variants through hundreds of generations of antecedents is as yet unresolved. This paper summarizes some of the studies that have been undertaken to address this issue in Andean indigenous populations, primarily with respect to those adaptations thought to be involved in the uptake, distribution and utilization of oxygen in children and adults. Specifically, it focuses on changes in chest morphology, pulmonary function, metabolism and hematology. Space constraints preclude extending this review to the large body of literature concerning prenatal and maternal adaptations although this critical stage in development has likely been subject to significant selective pressures. It is apparent that both nature and nurture influence the acquisition of a high altitude phenotype in humans and while there is some evidence for genetic adaptation in Andean highlanders, it is evident that these characteristics are expressed in concert with substantial environment-dependent developmental adjustments.

Comparative aspects of high-altitude adaptation in human populations

The conditions and duration of high-altitude residence differ among high-altitude populations. The Tibetan Plateau is larger, more geographically remote, and appears to have been occupied for a longer period of time than the Andean Altiplano and, certainly, the Rocky Mountain region as judged by archaeological, linguistic, genetic and historical data. In addition, the Tibetan gene pool is less likely to have been constricted by small numbers of initial migrants and/or severe population decline, and to have been less subject to genetic admixture with lowland groups. Comparing Tibetans to other high-altitude residents demonstrates that Tibetans have less intrauterine growth retardation better neonatal oxygenation higher ventilation and hypoxic ventilatory response lower pulmonary arterial pressure and resistance lower hemoglobin concentrations and less susceptibility to CMS These findings are consistent with the conclusion that "adaptation" to high altitude increases with time, considering time in generations of high-altitude exposure. Future research is needed to compare the extent of IUGR and neonatal oxygenation in South American high-altitude residents of Andean vs. European ancestry, controlling for gestational age and other characteristics. Another fruitful line of inquiry is likely to be determining whether persons with CMS or other altitude-associated problems experienced exaggerated hypoxia during prenatal or neonatal life. Finally, the comparison of high-altitude populations with respect to the frequencies of genes involved in oxygen sensing and physiologic response to hypoxia will be useful, once candidate genes have been identified.

Lung volume, chest size, and hematological variation in low-, medium-, and high-altitude central Asian populations

To evaluate adaptive responses to high-altitude environment, we examined three groups of healthy adult males from Central Asia: 94 high-altitude (HA) Kirghiz subjects (3,200 m above sea level); 114 middle-altitude (MA) Kazakh subjects (2,100 m), and 90 low-altitude (LA) Kirghiz subjects (900 m). Data on chest size (chest perimeter and chest diameter), lung volume (forced expiratory volume (FEV) and forced expiratory volume in 1 sec (FEV1)), and hematological parameters (hemoglobin, erythrocytes, hematocrit, and SaO(2)) are discussed. The results show that 1) chest shape is less flat in the samples living at higher altitude. In the HA sample, chest perimeter is lower but chest excursion is high. 2) In the highlanders, forced vital capacity (FVC) and FEV1 are no higher than in the other samples, even when corrected for stature and body weight. The negative correlation between FVC-FEV1 and age decreases with increasing altitude. 3) The HA and MA samples have higher values of hemoglobin, erythrocytes, and hematocrit. The HA sample has lower SaO(2) and higher arterial oxygen content than the LA sample. No association between hematocrit and age was detected in the four samples. The results indicate that the high-altitude Kirghiz present features of developmental acclimatization to hypobaric hypoxia which are also strongly influenced by other major high-altitude environmental stresses.

Hemoglobin concentration of high-altitude Tibetans and Bolivian Aymara

Elevated hemoglobin concentrations have been reported for high-altitude sojourners and Andean high-altitude natives since early in the 20th century. Thus, reports that have appeared since the 1970s describing relatively low hemoglobin concentration among Tibetan high-altitude natives were unexpected. These suggested a hypothesis of population differences in hematological response to high-altitude hypoxia. A case of quantitatively different responses to one environmental stress would offer an opportunity to study the broad evolutionary question of the origin of adaptations. However, many factors may confound population comparisons. The present study was designed to test the null hypothesis of no difference in mean hemoglobin concentration of Tibetan and Aymara native residents at 3,800-4,065 meters by using healthy samples that were screened for iron deficiency, abnormal hemoglobins, and thalassemias, recruited and assessed using the same techniques. The hypothesis was rejected, because Tibetan males had a significantly lower mean hemoglobin concentration of 15.6 gm/dl compared with 19.2 gm/dl for Aymara males, and Tibetan females had a mean hemoglobin concentration of 14.2 gm/dl compared with 17.8 gm/dl for Aymara females. The Tibetan hemoglobin distribution closely resembled that from a comparable, sea-level sample from the United States, whereas the Aymara distribution was shifted toward 3-4 gm/dl higher values. Genetic factors accounted for a very high proportion of the phenotypic variance in hemoglobin concentration in both samples (0.86 in the Tibetan sample and 0.87 in the Aymara sample). The presence of significant genetic variance means that there is the potential for natural selection and genetic adaptation of hemoglobin concentration in Tibetan and Aymara high-altitude populations.

The effect of maternal nutritional variables on birthweight outcomes of infants born to Sherpa women at low and high altitudes in Nepal

A prospective, longitudinal study was conducted in Nepal to investigate the effects of maternal nutrition on the pregnancy outcome of Sherpa women living at low and high altitudes. It was hypothesized that variation in nutrition and energy expenditure of pregnant women would correlate with variation in infant birthweight. Anthropometric dimensions, energy consumption and expenditure, and demographic and migration information were collected on a large sample of women living in two regions of Nepal: the Khumbu region (3480-3930 m) and Kathmandu (1330 m). This paper reports findings for a subset of the sample; 17 women at low altitude and 21 women at high altitude who became pregnant and were followed during pregnancy. The results showed no significant differences for mean birthweights between the low (X = 3069 ± 341 grams) and high (X = 3099 ± 483 grams) altitude samples. Furthermore, larger birthweights were associated with larger weight gains during pregnancy for the high altitude sample. A stepwise regression analysis found a negative association between high energy expenditures during the second trimester and infant birthweight, but positive associations were found between third trimester calcium and second trimester protein intakes and birthweight. Prepregnancy BMI and stature were associated positively with infant birthweight, suggesting that good nutritional status prior to pregnancy may play an important role in pregnancy outcome for this population. Am. J. Hum. Biol. 9:751-763, 1997. © 1997 Wiley-Liss, Inc.

Reference limits for routine haematological measurements in 7-14-year-old children living at an intermediate altitude (1869 m, Erzurum, Turkey)

In order to obtain reference limits, complete blood counts were performed using an automated haematology analyser (Cell-Dyn 1500) on venous blood samples from 718 healthy children living at 1869 m altitude. At first, to obtain appropriate populations for obtaining reference values, the factors of per capita income, parental educational status and antecedent infection(s) were assessed with respect to their effects on each parameter. Of the subgroups classified according to these factors, those which were affected in terms of haematological values were excluded. The effects of age and sex on the parameters were evaluated, and reference values were arranged according to age groups to facilitate clinical use. Among the reference values which we suggest for children living at about 2000 m altitude, those of haemoglobin, haematocrit, red blood cell count and mean cell volume are significantly higher than sea-level values. In addition, our results indicate that intermediate altitude has no effect on other routine haematological values.