Researchers have identified two genes that appear to explain why Tibetans are able to live comfortably in rarefied air at very high altitudes.

Dubbed the roof of the world, Tibet is the highest region on earth, with an average elevation of 4,900 metres (16,000 ft).

To find out if Tibetans may have special genetic features that allow them to breathe easy in high places, scientists analysed the genes of 31 Tibetans who were unrelated to each other, and compared them to the DNA of 90 Chinese and Japanese individuals living in low-lying areas.

In a paper published in the journal Science on Friday, the scientists from China and the United States said they hunted for genetic variations in locations that previous studies associated with adaptation to high altitudes.

Two genes - EGLN1 and PPARA on human chromosomes 1 and 22 respectively - turned up consistently, said co-author Jinchuan Xing from the Eccles Institute of Human Genetics at the University of Utah School of Medicine in the United States.

“Their exact roles in high-altitude adaptation is unclear. Both EGLN1 and PPARA ... may cause a decrease of the haemoglobin concentration,” Xing wrote in reply to questions from Reuters.

Tibetans have unusually low blood haemoglobin levels, which allows them to thrive at high altitudes. But it is only now that experts have managed to trace this feature back to genes.

When people who normally live in lowlands visit Tibet, the lack of oxygen in their bodies may cause altitude sickness, which can develop into fatal heart or brain inflammation.

“Presumably Tibetans have developed a regulation mechanism to control the haemoglobin concentration to prevent these negative effects,” Xing wrote.

SOURCE:  Science, online May 13, 2010.