The Altitude Gene, A Denisovan Gift

Jan. 23, 2015

By Medical Discovery News

Altitude Gene, A Denisovan Gift

Those traveling to the Himalayas have a tough time adjusting to the harsh altitude. But for those native to Tibet, called the Roof of the World due its location 14,700 feet up, it’s not a problem. That’s because Tibetans have adapted to this harsh environment partly due to a gene they inherited from an extinct species of prehumans called the Denisovans.

Anyone traveling to high altitudes like those in Tibet can get altitude sickness and there is no way to predict who will get it. The severity of it varies according to genetics and the rate of ascent, but it is not influenced by age, gender, physical fitness, or previous altitude experience. Symptoms can include headaches, nausea, dizziness, fatigue, shortness of breath, loss of appetite, and disturbed sleep. Severe symptoms could indicate high altitude cerebral edema, which impairs brain function, progresses rapidly, and can become life-threatening in a matter of hours.

However, Tibetans live at these extreme altitudes without developing these problems. So how did they adapt to such a challenging environment?

Studies have linked the Tibetan’s adaptation to high altitude with several genes, including a unique form of the EXPAS1 gene. This gene responds to low oxygen levels to increase hemoglobin production. However, Tibetans with this gene do not have elevated levels of hemoglobin. This seems counterintuitive, since increasing hemoglobin could increase the amount of oxygen being transported in the blood. This would be advantageous at altitudes where the availability of oxygen is reduced, which then limits the uptake of oxygen in the lungs. On the other hand, increasing red blood cells would also thicken the blood, making it less efficient in distributing oxygen and increasing the risk of stroke. The Tibetan variant of EXPAS1 gene might then be protective, but we don’t know how exactly it works.

We know that the ancestors of Nepal’s Sherpa people carried the Tibetan EXPAS1 gene variant about 30,000 years ago. Today, only Tibetans carry this version of the gene, no other modern humans have it. New data suggests it may have come from an extinct population of prehuman called the Denisovans. So far they have only been found in a cave in the Altai Mountains in southern Siberia in East Central Asia. More proof is needed to eliminate another extinct species, the Neanderthals, who also have a version of EXPAS1 similar to the Tibetan one. This is another example of genes acquired by interbreeding between Homo sapiens and other ancient species. About 5 percent of the genetic information of Australasians is shared with Denisovans, while 2.5 percent of human DNA originates from Neanderthals. Modern humans have bits of DNA from these ancient species that have made important contributions to the success of our genome.

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