No, NASA's astronaut twin hasn't had a DNA rewrite

As we recently detailed, NASA has offered up preliminary findings under its Twins Study, which looks at the impact space travel has on human health. So far, researchers have identified some changes to astronaut Scott Kelly's telomeres, among other things, helping scientists understand the kind of health ramifications space travelers face. It's important to note what NASA didn't find, however.

Science topics aren't easy to digest. In the absence of formal education on the subject matter, understanding complex reports and studies detailing findings is difficult. In light of that, it's no surprise that some misunderstandings about NASA's Twins Study preliminary findings have happened.

Some recent reports claim that Scott Kelly, one of the two subject in NASA's Twins Study, no longer has the same DNA as his twin. That's not true, but rather a misunderstanding of the following statement from NASA:

Another interesting finding concerned what some call the "space gene", which was alluded to in 2017. 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.

Astronaut Scott Kelly and his brother Mark Kelly, who remained on Earth, are still identical twins. Scott's DNA didn't change; what NASA is referring to is gene expression.

As the space agency explained on its website in recent weeks, scientists observed some changes to Kelly's gene expression, most of which returned to normal within hours to weeks of his return home. The remaining 7% are of particular interest because the changes persisted for longer durations of time.

Back in October 2017, the Twins Study Principal Investigator Chris Mason had elaborated on the health investigation, saying:

Some of the most exciting things that we've seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space. With this study, we've seen thousands and thousands of genes change how they are turned on and turned off. This happens as soon as an astronaut gets into space, and some of the activity persists temporarily upon return to Earth.