Altitude sickness is two illnesses, according to Edinburgh scientists.
The condition, triggered by falling oxygen levels, causes mild sickness, headaches and life-threatening problems affecting the heart, lungs and brain.
Researchers at Edinburgh University said they had shown it is actually "at least two separate syndromes".
The scientists said climbers and skiers who suffer from the potentially deadly condition could be treated more effectively following the new insight.
Altitude sickness occurs at heights above 2,500 metres.
Using a computer analysis method for grouping genes together, researchers studied patterns of symptoms among people in high altitude areas in Bolivia and Kilimanjaro in Tanzania.
One group experienced disrupted sleep but minimal headache, while another group only reported headaches and little disruption to sleep.
Others meanwhile experienced a mixture of symptoms.
For more than 20 years, the condition has been diagnosed using a symptom score called the Lake Louise consensus.
A score for each symptom, including headache, fatigue and sleep disturbance, is added up and a diagnosed reached.
The findings, which have been published in the PLOS ONE journal, will also be presented at an international altitude sickness meeting later this year.
Dr Ken Baillie, of The Roslin Institute at Edinburgh University, said: "For more than two decades we have thought of altitude sickness as a single disease.
"We have now shown that it is at least two separate syndromes that happen to occur in the same people at a similar time.
"Studying these syndromes in isolation will make it easier to understand the cause of each one, and to test new treatments."