NASA issued a clarification on reports indicating that astronaut Scott Kelly's DNA has changed after spending over a year in space.

NASA says what really changed is Kelly's gene expression and that the change is very minimal.

Headlines in the past weeks captured NASA's preliminary findings on the Twins Study and interpreted it as a change in Kelly's DNA. The U.S. space agency wants to correct the information and maintained that Scott is still identical to his twin brother, Mark.

No Change In DNA

Deoxyribonucleic acid or DNA is the hereditary material in humans and all organisms. It is considered as a person's genetic code. Nearly every cell in a person's body has the same DNA and Scott's DNA did not change.

"Mark and Scott Kelly are still identical twins; Scott's DNA did not fundamentally change. What researchers did observe are changes in gene expression, which is how your body reacts to your environment. This likely is within the range for humans under stress, such as mountain climbing or SCUBA diving," reads an official update from NASA.

"Great summary of our work but we have been talking about gene expression differences and not DNA difference between the twins," Daniela Bezdan, research director of the Mason Laboratory of Integrative Genomics at Weill Cornell Medicine, tweeted in reaction to reports on Scott's DNA change.

Susan Bailey, one of the lead researchers involved in NASA's Twins Study from the Colorado State University, said that she is concerned about how the stories on the NASA's preliminary findings are being sensationalized.

'Space Genes' And Gene Expression

NASA said 93 percent of Kelly's genes returned to normal after landing. The 7 percent, which it initially referred to as "space genes," are the only changes in Kelly's gene expression during spaceflight and had not returned to preflight after six months on Earth.

"Seven percent of the genes that changed their expression during spaceflight were still altered after six months back on Earth," says Christopher Mason, from Weill Cornell Medicine.

NASA says its scientists are still understanding how long-term spaceflight affects the human body on a molecular level and more comprehensive results will confirm what really happened to Kelly's body while in space.

Bezdan said official papers and data regarding the Twins Study update are being prepared.

How Scott Has Changed?

Kelly, a former U.S. navy captain, a military pilot, an engineer, and a retired NASA astronaut, was in space for a total of 520 days.

He spent 340 consecutive days in low Earth orbit at the International Space Station.

Kelly revealed that his time in space has changed his perspective.

"I think it makes you a more empathetic person. More in touch with humanity and who we are, and what we should do to not only to take care of the planet but also to solve our common problems, which clearly are many," Kelly said.

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