This study is is the first step of a full study named CHEMOGENE because it explores the genetic determinant of an alteration of the chemoreflex. This reflex determines hyperventilation when the pressure of oxygen falls in the blood. This happens when subjects travel to high-altitude where oxygen levels diminish in the atmosphere. Subjects with such an altered chemoreflex are intolerant to altitude and develop pulmonary or cerebral edema associated with a severe headache. In this study we compare subjects tolerant to high altitude (8000 meters)to subjects intolerant to altitude. The chemoreflex is measured i.e. the hyperventilation associated with hypoxia and all subjects are scanned for the genes implicated in the mitochondrial respiratory chain. The idea is that subjects with an impaired oxygen sensing will exhibit an altered chemoreflex and will be intolerant to high-altitude.

Subjects are selected at an outpatient clinic specialised in the diagnosis of tolerance to altitude, where the chemoreflex is analyzed during a bicycle exercise performed with a oxygen deprived air simulating a 8000 meters altitude.

All subjects will go later to high altitude for trekking usually. The patients are those subjects with an altered chemoreflex who exhibited cerebral edema or pulmonary edema during the trekking.

The controls are the subjects with a normal chemoreflex who did not exhibit any trouble during their journey.

Fourty subjects of each group are included. A blood sample is withdrawn and studied for succinate dehydrogenase genes in a blind fashion.

After completing the inclusion the allelic mutations will be compared in the two groups.

Inclusion Criteria:

• Chemoreflex sensitivity measured (normal or pathologic)
• Journey to high-altitude (well tolerated or with a severe disease such as pulmonary edema or cerebral edema)

Exclusion Criteria:

• Asthma,
• Arterial hypertension,
• Drug treatment