Scott Kelly, one of the most multimedia astronauts in history, as we could see with his famous YouTube videos, returned to Earth in March 2016.
After passing the negligible 340-day figure up there, his DNA changed.
DNA in space
What he did Scott Kelly while at the International Space Station (ISS), he participated in an experiment in which he evaluated the way in which genes are affected by long periods of microgravity.
As a control element, Scott Kelly's twin brother was used in the experiment, Mark, who is also an astronaut but who remained on Earth.
What the preliminary results reveal is that Scott experienced changes in gene expression and a shortening of the telometers (the ends of the chromosomes). Apparently, being in space cuts the telomeres, but we don't know what the consequences of all this will be until the conclusions of the study are not made public.