Gene for altitude illness

Everest: Climbers often have no easy means of descent

Mountaineers struck down by a potentially deadly condition at extreme altitude might have a genetic weakness, scientists believe.

High altitude pulmonary oedema (Hape) is uncommon but it strikes suddenly, and can be highly dangerous.

It happens when a lack of oxygen increases blood pressure in the vessels leading to the lungs, which causes fluid build-up there.

If left uncorrected, the patient literally drowns.

The best solution is to descend as quickly as possible to lower altitude - but sometimes the climber has no easy means of descent.

Between 1968 and 1987, 23 British climbers died above 7,000 metres on peaks.

A study found that four of these were due to either pulmonary oedema or another type of mountain sickness called cerebral oedema.

Researchers from the Shinsu University School of Medicine in Matsumoto looked at a group of climbers who had all suffered from some form of Hape.

Their genetic structure was analysed and the scientists found that many of the Hape group had distinct differences.

Gene variation

In particular, they had two variations of a gene called eNOS.

This gene makes an enzyme which regulates the release of nitric oxide inside blood vessels.

A quarter of the Hape group had one of the gene variations, compared to only 10% of the control group.

Nitric oxide is important at altitude because it is a potent vasodilator - it relaxes the blood vessels, reducing blood pressure, which makes oedema less likely.

Dr Masayuki Hanaoka, who led the research, published in the journal Circulation, said: "It is not a dream to think about transferring the healthy eNOS gene to the human lung to compensate for the insufficient production of nitric oxide."

Testing time

However, the finding could also point the way to a genetic test for susceptability to Hape, which strikes regardless of age or fitness levels.

It may also help researchers find ways of tackling other lung disorders such as primary pulmonary hypertension, emphysema and chronic bronchitis.

Dr Jim Milledge, co-author of "High Altitude Medicine and Physiology", told BBC News Online that it was possible that other genes were involved in Hape.

He said: "There are, in theory, tests which could be done.

"These patients may have high pulmonary artery pressure even at sea level, which could be measured with ultrasound."