Adapting to Altitude - A Study on Tibetans

Tibetans have adapted to life at high altitudes in less than 3,000 years, according to a new study that could, in the light of this information, focus on pre-birth oxygen deprivation diseases.

"This is the fastest genetic change ever observed in humans," said Rasmus Nielsen, a University of California Berkeley biology professor who led the statistical analysis and genome-wide comparison between the Tibetans and the Han Chinese.

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According to the study, published in the July 2 issue of Science magazine, the Tibetans and the Han Chinese split into two separate populations some 2,750 years ago, with the larger group moving to the Tibetan plateau where it dwindled while the low-elevation Han expanded dramatically.

The Tibetans, however, quickly evolved a unique ability to live above 4,000 meters (13,000 feet), where oxygen levels are 40 percent lower than those at sea level.

"For such a very strong change, a lot of people would have had to die simply due to the fact that they had the wrong version of a gene," said Nielsen.

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Comparing the genes of both ethnic groups, researchers found more than 30 genes with DNA mutations that have become more prevalent in Tibetans than Han Chinese, nearly half of which are related to how the body uses oxygen.

One mutation in particular spread from fewer than 10 percent of the Han Chinese to nearly 90 percent of all Tibetans. It is near a gene called EPAS1, a so-called "super athlete gene" identified several years ago that is associated with improved athletic performance, Nielsen said.

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The gene codes for a protein involved in sensing oxygen levels and perhaps balancing aerobic and anaerobic metabolism.

The new findings could steer scientists to still unknown genes that play a role in how the body deals with decreased oxygen, and perhaps explain some diseases, including schizophrenia and epilepsy, associated with oxygen deprivation in the womb, Nielsen said.

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"The new finding is really the first time evolutionary information alone has helped us pinpoint an important function of a gene in humans," he added.

Adaptation to low oxygen levels has allowed many peoples, from Andeans to Tibetans, to live at high altitude.

When people from lower elevations move above 4,000 meters they typically tire easily, develop headaches, produce babies with lower birth weights and have a higher infant mortality rate.

Tibetans have none of these problems, despite lower oxygen saturation in the blood and lower levels of hemoglobin levels, which gives blood its red color, and binds and transports oxygen to the body's tissues.

The study used genome data and a large team of researchers from the Beijing Genomics Institute in Shenzhen, China's flagship genome center.

The research was funded by various Chinese, American and Danish organizations.

Source-AFP