Several stories this week have proclaimed that the DNA of former NASA astronaut Scott Kelly changed during his year living on the International Space Station. The stories say that 7 percent of his genes did not return back to normal when he came back to Earth. It makes it seem as if the space environment permanently altered his genetic code. The problem? That's not true. From a report: The mistake stems from an inaccurate interpretation of NASA's ongoing Twins Study. When Scott went to space in 2015, his identical twin Mark -- also a former NASA astronaut -- stayed on the ground. The idea was that Mark would serve as a control subject -- a nearly identical genetic copy that NASA could use to figure out how the space environment changed Scott's body. Some fascinating results have come out of the experiment. For one thing, Scott's gut bacteria changed significantly while he was in space. And yes, he did experience genetic changes. The protective caps on the ends of his DNA strands -- known as telomeres -- increased while in space. But space didn't permenantly alter 7 percent of his DNA. [...] NASA also confirmed this in a statement to The Verge: "Scott's DNA did not fundamentally change," a NASA spokesperson said. "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."