Thrifty phenotype versus cold adaptation: trade-offs in upper limb proportions of Himalayan populations of Nepal.

The multi-stress environment of high altitude has been associated with growth deficits in humans, particularly in zeugopod elements (forearm and lower leg). This is consistent with the thrifty phenotype hypothesis, which has been observed in Andeans, but has yet to be tested in other high-altitude populations. In Himalayan populations, other factors, such as cold stress, may shape limb proportions. The current study investigated whether relative upper limb proportions of Himalayan adults (n = 254) differ between highland and lowland populations, and whether cold adaptation or a thrifty phenotype mechanism may be acting here. Height, weight, humerus length, ulna length, hand length and hand width were measured using standard methods. Relative to height, total upper limb and ulna lengths were significantly shorter in highlanders compared with lowlanders in both sexes, while hand and humerus length were not. Hand width did not significantly differ between populations. These results support the thrifty phenotype hypothesis, as hand and humerus proportions are conserved at the expense of the ulna. The reduction in relative ulna length could be attributed to cold adaptation, but the lack of difference between populations in both hand length and width indicates that cold adaptation is not shaping hand proportions in this case.

Xtreme Everest 2: unlocking the secrets of the Sherpa phenotype?

Xtreme Everest 2 (XE2) was part of an ongoing programme of field, laboratory and clinical research focused on human responses to hypoxaemia that was conducted by the Caudwell Xtreme Everest Hypoxia Research Consortium. The aim of XE2 was to characterise acclimatisation to environmental hypoxia during a standardised ascent to high altitude in order to identify biomarkers of adaptation and maladaptation. Ultimately, this may lead to novel diagnostic and treatment strategies for the pathophysiological hypoxaemia and cellular hypoxia observed in critically ill patients. XE2 was unique in comparing participants drawn from two distinct populations: native ancestral high-altitude dwellers (Sherpas) and native lowlanders. Experiments to study the microcirculation, mitochondrial function and the effect that nitric oxide metabolism may exert upon them were focal to the scientific profile. In addition, the genetic and epigenetic (methylation and histone modification) basis of observed differences in phenotype was explored. The biological samples and phenotypic metadata already collected during XE2 will be analysed as an independent study. Data generated will also contribute to (and be compared with) the bioresource obtained from our previous observational high-altitude study, Caudwell Xtreme Everest (2007).