High altitude DNA clue18th May 2010
Tibetans, whose ancestors first inhabited the world's highest, most isolated regions thousands of years ago, are the only population in the world whose genes help them cope with high altitude, according to a recent joint study between US and Chinese researchers.
The researchers found that, over thousands of years, Tibetans went through unique physiological changes, and today survive at high altitudes because their genes cause them to produce less haemoglobin.
Josef Prchal, a geneticist at the University of Utah and one of the senior authors of the study, said that researchers may be able to use their new found understanding of of Tibetans in treating people with certain cancers, such as chronic myelogenous leukaemia.
Co-author Lynn Jorde, also a geneticist at the University of Utah, said that, for the first time, scientists had windows by which to peer into subtle interactions between gene, organism, and environment.
Tibetans have lived in their region of Asia for as long as 21,000 years.
Many villages in Tibet lie at altitudes of between 11,000 and 17,000 feet, where oxygen levels are reduced by one third, compared to sea level.
Though humans respond in a variety of ways to reduced oxygen levels, usually it is by producing extra haemoglobin.
In turn, the bloodstream is flooded with red blood cells, and oxygen enters the body's muscles and brain.
Prchal said that people usually thought of haemoglobin as being good for them, because it helped moves oxygen around the body.
He said that, however, that too much haemoglobin made the blood too thick.
At extremely high elevations, people often encounter altitude sickness, also known as acute mountain sickness (AMS).
AMS happens to people at altitudes above 8,000 feet.
The sickness can resemble the flu, carbon monoxide poisoning, or a hangover.
Over many millennia, Tibetans have evolved so that their blood haemoglobin levels remain lower than average, which makes researchers wonder whether or not their bodies are more susceptible to physical strain.
Prchal enlisted the help of Rili Ge, a researcher at the Center for High Altitude Medicine in China's western province of Qinghai.
Together, the two researchers identified a Tibetan village where there had been no recorded intermarriage with ethnic Chinese.
Although the Center for High Altitude Medicine would not agree to send any Tibetan DNA samples abroad, they allowed the US researchers to gather data on 31 unrelated Tibetans from the isolated Qinghai village, Madou.
Tatum Simonson, also a geneticist from the University of Utah, travelled to Madou to supervise the DNA extractions, though she was not allowed to bring DNA samples out of the country.
Prchal said that haemoglobin was one of many factors that helped Tibetans respond to high altitudes.
He said that Tibetans did not have just one gene that helped them survive at high altitudes, but perhaps more than 10, all associated with blood circulation and metabolism, which ultimately made their hearts more efficient than average people.
Simonson said that his research supported the idea that evolution was a tinkerer, improvising its work without a plan in mind.
Hugh Montgomery, a geneticist at University College London, said that the study would help people understand how patients with heart failure and lung disease coped with low blood oxygen.
He said that it might also eventually give researchers clues to new drug therapies.
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