New tests could spare soldiers from debilitating sickness at high altitudes--and mitigate cattle deaths in the Rockies

Chris 73, Wikimedia Commons

On his 27th birthday, David Hillebrandt and his wife Sally began to climb Mount Kenya, the second-highest mountain in Africa after Kilimanjaro. Instead of gearing up and heading straight for the mountain's tallest peakwhich reaches 5,199 metersthe couple started their journey more leisurely, trekking through scenic ridges and valleys around the mountain at an altitude of about 3,000 meters.

David, who today serves as a medical advisor to the British Mountaineering Council, already had considerable climbing experience at the time: he had scaled a 5,790-meter peak in Pakistan and 3,960-meter peaks in the European Alps. Sally, in contrast, had never done any serious climbing and did not consider herself a mountaineer.

But Sally wasn't the one who needed to stop and turn around.

"I am meant to be this tough, rugged mountaineer," David says, "and I celebrated my birthday by throwing up all over the place." Plagued by a throbbing headache and relentless nausea, David retreated to lower ground. He knew from previous climbs that he was prone to altitude sickness, but he thought circling the mountain at 3,000 meters would be a good way to acclimatize. This time it didn't do the trick. Even though she was a far less experienced climber, Sally adjusted to the altitude much faster.

It wasn't experience that made the differenceit was genetics. Scientists have known for a while that some people are inherently more susceptible to altitude sickness than othersand that this susceptibility is heritablebut only now are they on the trail of the culprit genes. Preliminary studies suggest that a group of six genes predicts who will get altitude sickness with greater than 90 percent accuracy. Such a precise genetic test would greatly benefit the military, which currently has no way of predicting which soldiers will fall ill when flown to high altitudes and would rather not waste money on expensive acclimatization drugs. In a parallel research effort, scientists have been searching for the genes that determine which cows develop altitude sickness, also known as brisket disease, when they graze in the Rocky Mountains. Because tens of thousands of cows die in the western U.S. from brisket disease annually, ranchers would like nothing more than to strip the responsible genes from the breeding population.

Written in blood The pursuit of a genetic test for altitude sickness began in earnest a few years ago in Robert Roach's laboratory at the University of Colorado. In 2010, 28 people in Roach's lab ascended to an altitude of 4,875 meters without ever leaving the ground. Roach placed his volunteers in a large metal box called a hypobaric chamber and gradually sucked out air with a vacuum pump, reducing atmospheric pressure to mimic a high altitude, low-oxygen environment. Roach purposefully recruited a mixture of people who were susceptible to altitude sickness and people who had never had problems in high climes. As expected, about half of the 28 volunteers felt sick in the chamber, whereas the others felt fine.

Roach took samples of his volunteers' blood, isolated their DNA and programmed a computer to search for genetic differences between the people who got sick and those who didn't mind hanging out in thin air. The program identified six genes that are expressed at unusually high or low levels in people who felt sick; some of the genes are linked to oxygen transport. Looking at the expression levels of those six genes alone was enough to distinguish people who became ill from those who did not with about 95 percent accuracy.

The following year, Roach collaborated with Benjamin Levine of the University of Texas Southwestern Medical Center to try the rudimentary genetic test on a larger group of volunteers. This time, instead of bringing the mountain to his lab, Roach decided to move his lab to the mountain.

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Mountain Maladies: Genetic Screening Susses Out Susceptibility to Altitude Sickness