The findings may also help researchers find causes of other lung disorders. These include chronic mountain sickness, primary pulmonary hypertension, emphysema and chronic bronchitis.
High-altitude pulmonary edema (HAPE) occurs in seemingly healthy people after rapid exposure to altitudes higher than 2,500 meters (8,175 feet), particularly when the people exert themselves.
HAPE causes fluid in the lungs, difficulty breathing, severe weakness and dangerously rapid heartbeats. Death occurs in 44 percent of people who are not treated with oxygen or drugs, or moved to a lower altitude. About 1 percent of the Japanese population is susceptible to the condition.
Researchers first recognized HAPE as a specific disorder in 1960. Before that, people who experienced its symptoms were diagnosed as having pneumonia or heart failure. "It is a hazard to mountaineers, trekkers, skiers and people moving to high altitudes," says study co-author Masayuki Hanaoka, M.D., Ph.D., a specialist in high-altitude medicine at Shinshu University School of Medicine in Matsumoto, Japan.
Japanese researchers found that two variations, or polymorphisms, in the endothelial nitric oxide synthase (eNOS) gene occurred significantly more often in people who suffered HAPE than in a group of mountain climbers who had never experienced the condition. eNOS is a key enzyme involved in the release of nitric oxide in the blood vessels. Nitric oxide regulates the tone of blood vessels by causing them to relax, or dilate, to increase blood flow. Drugs called vasodilators that elicit this response in blood vessels can prevent HAPE as well as treat it.