Twin study finds space flight causes changes at the genetic level

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Scott Kelly spent 340 days in space in 2015–16, giving him a lifetime total of 520 days. Mark Kelly, also an astronaut, had previously flown in space for a total of 54 days over four space-shuttle missions between 2001 and 2011.
Space case

Because the two men have almost identical genomes and similar life experiences, NASA arranged to have blood and other biological samples taken from them to try and observe biological changes brought about by long-duration spaceflight.

Studies of the twins' telomeres, the caps on the ends of their chromosomes, showed that during spaceflight Scott's telomeres grew to be longer than his brother's. “That is exactly the opposite of what we thought,” says Susan Bailey, a radiation biologist at Colorado State University in Fort Collins. A second lab has studied the same samples and confirmed this puzzling increase in telomere length, she says.

Once Scott returned to the ground, the length of his telomeres returned to his pre-flight levels relatively quickly. The scientists are working to figure out what this means, and are running a separate study of telomere length in ten unrelated astronauts that, when completed in 2018, may shed more light on how spaceflight affects telomeres.

DNA methylation — the reversible addition of a chemical marker to DNA that can affect gene expression — decreased in Scott during flight and increased in Mark over the same period, Feinberg says. Levels for both men returned close to preflight levels after Scott came back to Earth. What this means isn’t yet clear, Feinberg says.

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