Preliminary results from a NASA study on a pair of identical twins suggests that space travel could have long-lasting effects on the human body.
While astronaut Scott Kelly's DNA did not change during his year on the International Space Station (ISS), much of his gene expression – how genetic information is turned into functional molecules in the cell – did change compared with his pre-flight status and that of his twin Mark on Earth.
Scott's gene expression mostly returned to pre-flight levels following his return to Earth. However, 7 percent of his genes, however, were still being expressed differently six months later. These genes, which NASA is collectively referring to as the 'space genes', are related to his immune system, DNA repair and bone formation networks.
Changes to gene expression happen all the time. 'If you put someone into a stressful and different environment, they're going to have gene expression changes,' Dr Dan Arking at the Johns Hopkins University School of Medicine in Baltimore Maryland, who did not work on the study, told The Verge.
NASA said the changes in Scott Kelly's gene expression are in the expected range for humans undertaking stressful activities on Earth, such as mountain climbing or scuba diving.
Scott and Mark are the only identical twin astronauts in history, offering a unique opportunity for an extensive nature versus nurture study. While Scott lived on the ISS, Mark acted as an Earth-bound control subject. Researchers took biological samples from each twin before, during and after Scott's mission so that they could evaluate the potential risks to the human body in space. The team, which comprises of lead scientists from a variety of universities and government laboratories, is investigating how space travel affects human telomeres, biochemistry, cognition and gut microbiome among other parameters.
NASA scientists already have a good understanding of what happens to a human body during standard six-month missions aboard the ISS, but the twins study will give insights of a longer duration. NASA hopes this research will help plan manned missions to Mars - which will take approximately three years, and beyond.
Some media reports of the preliminary findings on the Kelly twins have been imprecise, suggesting that there is now a 7 percent difference in the fundamental DNA of Scott and Mark – rather than just their gene expression. But the twins have taken this opportunity to jokingly disown each other. As Mark tweeted: ′I used to have an identical twin brother. Then this happened...′