The story of twin astronauts: one who has lived a year in the most space

Spending a year in space causes alterations in the DNA of astronauts that persist after their return to Earth, which could lead to long-term health risks. This is the main conclusion of an international survey conducted by NASA that badyzed with unprecedented depth the impact of a stay in the International Space Station (ISS) on the body of an astronaut by comparing it to his twin brother, left on Earth.

Despite this, the authors note that the work, published today in Science, shows that the human body can maintain a good state of health during long-term space missions.

Scott and Mark Kelly are the only two astronauts in the world to share the same DNA because they are identical twins. Both are veterans of the US Navy and NASA and have traveled in space many times.

In March 2015, Scott Kelly embarked on a one – year mission on the ISS while his brother Mark continued working for the US Space Agency. It is Scott himself who had the idea to take this unique opportunity to compare the evolution of the body of two genetically identical people, one on earth and the other. other in the space. Thus, in order to verify the effects of a long-term space mission, a research project involving more than ten teams from around the world has emerged.

During the 342 days that Scott Kelly spent on the ISS, orbiting 400 km from the Earth's surface, he diligently submitted to a battery of medical tests to badyze every aspect of his life. health. Where possible, their samples came immediately to Earth aboard supply capsules. Otherwise, Kelly would freeze them at 80 degrees below zero until they can get to the lab. "There were incredible challenges," said Andrew Feinberg, director of the Center for Epigenetics at Johns Hopkins University in Baltimore, USA, and co-author of the work, at a press conference. For logistical and security reasons, "we had the right to take less Scott's blood than the one allowed for a child admitted to the hospital," he recalls. Meanwhile, on Earth, his brother Mark has undergone the same tests, even though he continued to lead a normal life to refer to.

It was already known that the space environment had an impact on the body: astronauts lose density in the bones, their microbiota and the activity of their genes change and their cognitive abilities are affected. At present, the results of the study on twins confirm what we already suspected and provide new information.

Scott Kelly's cognitive abilities were slightly reduced after his trip, probably due to the increase in blood pressure in the head due to microgravity. Six months after his return, he was almost back to normal, although the researchers detected mild persistent deficiencies longer than expected.

Kelly's genes have also adapted to life in space, especially those related to the immune system. But it was by returning to Earth that a very brutal change took place: after landing, the activity of genes involved in inflammation, the body's reaction to a sudden change in the environment corresponding to the experience of astronauts, has increased significantly. They cite this moment as the most difficult of their missions. "The molecular data clearly indicate that, if space is restricted, landing is much harder for the body, at least the first few days," said Christopher Mason, geneticist at Weill Cornell Medical Center in New York. York (United States). .) And co-author of the study.

90% of Scott Kelly's genes regained their initial level of activity when they returned to their habitat, but some remained altered six months later. For the moment, we do not know what consequences this may have in the long term.

What worries most researchers, however, are the anomalies appeared in the chromosomes of the American astronaut. The void of space is bathed in cosmic rays, a high-energy radiation that can damage DNA. On the surface of the Earth, the magnetic field of our planet protects us from it, but on the low Earth orbit, where the ISS is, this shield is a little weaker.

During his stay at the station, Scott Kelly received a total radiation dose of 150 microsieverts (mSv), fifty times more than everyone on Earth, but eight times less than the dose of which would expose astronauts traveling on Mars. Cosmic rays caused breaks in their DNA, which caused the exchange of fragments of their chromosomes or the reverse of their order. These changes persisted in the long term, even after returning to Earth.

On the other hand, Kelly's telomeres grew while they were on the ISS. Telomeres are structures at the ends of chromosomes that protect them during cell division. They play a fundamental role in aging and cancer. Although physical exercise and a balanced diet – what all ISS astronauts are forced to do – help maintain telomere length, one does not know what could be the cause of their growth.