Retired NASA astronaut Scott Kelly became known as the American who spent the most time in space. Did his DNA really change after a year in space?

From 2015 to 2016, Scott Kelly spent 340 consecutive days at the International Space Station in low-orbit Earth.

During his 20-year career as a NASA astronaut, he spent a total of 522 days in space and it's the longest ever for any U.S. citizen. He retired in April 2016 and released a memoir Endurance: A Year in Space, a Lifetime of Discovery.

Twins Study

The Twins Study, launched by NASA last year, is the stepping stone toward long-duration space flight such as a journey to Mars.

Scott and Mark, the only identical twin astronauts in NASA, were the subjects of the study, with one in space and the other on Earth.

The study looked more closely at the individual health of each brother. It also used technologies in genetic sequencing to determine individual responses to the spaceflight environment. The research also looked at the molecular level to whole body and brain functions.

In an update, NASA announced that the Twins Study confirms the preliminary findings of the research that studied Scott and his brother Mark, also a former NASA astronaut. It focused on finding out how stressful can a trip to Mars be on the human body.

Scott's well-documented stay in space became the basis for NASA's Human Research Program investigators workshop in 2017, wherein scientists and researchers analyzed the impact of a long-term stay in space on the human body.

The preliminary findings were corroborated, with some additions. The biological changes Scott underwent when he returned and started readapting to life on Earth were also studied, as well as comparisons and differences between Scott and Mark.

The final integrated results of the Twins Study will be released this year.

Genome Sequencing

While in space, a study found out that Scott's telomeres or his chromosomes appeared to have lengthened, but also shortened within 2 hours after his return to Earth.

The initial findings also stated the following: Scott's folate went up during inflight, likely due to better food choices from the space food system; the flu vaccines given in space and on Earth yield the similar immune responses, and his cognition was not affected during the 12-month mission but he registered decrease in speed and accuracy after the mission.

Also, Scott's stress hormone Cortisol was at low normal while in space, but IGF-1 hormone levels increased over the course of the year. This hormone is implicated in bone and muscle health and was likely impacted by heavy exercise countermeasures during flight.

A completed genome sequencing on the DNA and RNA of Scott and Mark's white blood cells showed that each twin has hundreds of unique mutations in their genome. The scientists will look closer to see if a space gene could have been activated while Scott was in space. A previous result showed that Scott grew two inches taller in space.

Probing The Space Gene?

"Researchers now know that 93% of Scott's genes returned to normal after landing. However, the remaining 7% point to possible longer term changes in genes related to his immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia," says Monica Edwards of NASA Human Research Strategic Communications.

"I did read in the newspaper the other day... that 7 percent of my DNA had changed permanently," says Kelly in reaction to NASA's announcement. "And I'm reading that, I'm like, 'Huh, well that's weird."

Additional research analysis on the preliminary finding is in process.

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