Astronaut's DNA no longer matches twin’s after a year in space

Astronomer Scott Kelly spent a year in space and returned a changed man.

Kelly, who lived on the International Space Station while his identical twin Mark Kelly stayed on Earth, returned after 340 days with 7% of his genes altered, according to NASA.

The shocking transformation means Scott is no longer genetically identical to his twin.

Scott, who shared his own surprise over the latest NASA twin study results, tweeted, “What? My DNA changed by 7%! Who knew? I just learned about it in this article.”

“This could be good news! I no longer have to call @ShuttleCDRKelly my identical twin brother anymore,” he added.

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Astronaut Scott Kelly returns to Earth
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Astronaut Scott Kelly returns to Earth
Members of NASA support team help International Space Station (ISS) crew member Scott Kelly of the U.S. to get off a helicopter on arrival from the landing site at the airport of the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)
Expedition 46 Commander Scott Kelly of NASA rests in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
International Space Station (ISS) crew member Scott Kelly of the U.S. shows a victory sign after landing near the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)
Russian cosmonauts Mikhail Kornienko, left, Sergey Volkov of Roscosmos, center, and Expedition 46 Commander Scott Kelly of NASA, rest in chairs outside of the Soyuz TMA-18M spacecraft just minutes after they landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
Russian cosmonaut Mikhail Kornienko of Roscosmos is carried into a medical tent after he and Expedition 46 Commander Scott Kelly of NASA and Russian cosmonaut Sergey Volkov landed in their Soyuz TMA-18M spacecraft in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
Expedition 46 Commander Scott Kelly of NASA rests in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
Russian cosmonaut Sergey Volkov of Roscosmos is carried into a medical tent after he and Expedition 46 Commander Scott Kelly of NASA and cosmonaut Mikhail Kornienko landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
International Space Station (ISS) crew member Scott Kelly of the U.S. reacts after landing near the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)
Russian cosmonaut Mikhail Kornienko of Roscosmos rests in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Expedition 46 Commander Scott Kelly of NASA and Russian cosmonaut Sergey Volkov landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
A search and rescue team works at the site of landing of the Soyuz TMA-18M space capsule near the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)
Russias Soyuz TMA-18M space capsule carrying the International Space Station (ISS) crew of US astronaut Scott Kelly and Russian cosmonauts Mikhail Kornienko and Sergei Volkov lands in a remote area outside the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)
The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA
NASA astronaut Scott Kelly with his crewmates on the International Space Station on March 1, 2016. Photo credit: NASA
NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA
NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA
NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA
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Some changes — like the lengthening of Scott’s telomeres, or the endcaps of chromosomes that shorten over time — reversed once he was subject to Earth’s gravity again.

But other changes persisted after six months. Researchers found a deficient amount of tissue oxygenation in Scott’s cells, along with stress to mitochondria, which transform nutrients into energy, and increased inflammation.

Scott, who became the first American astronaut to spend a year in space, returned to Earth in March 2016.

The Twin Study, seen as the ultimate test of nurture versus nature, “may prove useful in the development of new treatments and preventive measures for related health issues on Earth,” according to NASA.

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Scott Kelly space walks
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Scott Kelly space walks

Scott Kelly ‏(@StationCDRKelly): "Day 212 Getting my game face on for #spacewalk Thanks for sticking w me #GoodNight from @space_station! #YearInSpace"

Scott Kelly ‏(@StationCDRKelly): On the grid! Back from #spacewalk & tweet ability down. Real-life lesson in importance of connectivity. #YearInSpace

Scott Kelly ‏(@StationCDRKelly): "#SpaceWalkSelfie Back on the grid! Great first spacewalk yesterday. Now on to the next one next week. #YearInSpace"

Scott Kelly (‏@StationCDRKelly): "Teamwork! @astro_kjell and I working outside @Space_Station with @Astro_Kimiya inside getting us safely out the door"

Scott Kelly ‏(@StationCDRKelly): "Coming back in yesterday. Still trying to wrap my head around why we call it #spacewalk, not spacework. #YearInSpace"

Scott Kelly (‏@StationCDRKelly): "#FlashBackFriday Last Friday #spacewalk. Seems like I've held this position all week but on the inside. #YearInSpace"

Scott Kelly ‏(@StationCDRKelly): "#ThrowbackThursday I admit, last week I took a #selfie at work. #YearInSpace" 

Expedition 45 commander Scott Kelly and flight engineer Kjell Lindgren prepare their extravehicular mobility unit spacesuits and tools in the Quest airlock. Kelly and Lindgren will use the spacesuits for two upcoming spacewalks outside the International Space Station on Oct. 28 and Nov. 6, 2015. (Photo via NASA)
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