NASA Uses Twin Brother Astronauts to Determine How Spaceflight Alters Body's Genetics

Mark Kelly stayed Earthbound while Scott Kelly went into orbit for almost a year aboard the International Space Station. Samples taken before, during and after show that the twins had changes on a genetic level.EXPAND
Mark Kelly stayed Earthbound while Scott Kelly went into orbit for almost a year aboard the International Space Station. Samples taken before, during and after show that the twins had changes on a genetic level.
Photo from NASA

When astronaut Scott Kelly was selected to spend a "year in space" aboard the International Space Station, the fact that his twin brother, Mark, is also an astronaut gave NASA the chance to do a bonus project.

NASA scientists collected data and samples on how Mark's body was faring on Earth while Scott  took samples of his own body and tracked how he was doing in orbit. Since NASA hopes to send astronauts to Mars by the 2030s, a trip that is expected to take at least a year, the contrast between the twin astronauts was a huge opportunity to find out what else happens to a body when it's in space. Now NASA scientists have shared their initial findings from the study.

We already knew that if you spend a lot of time in space, the body slowly begins to break down from the effects of too little gravity and too much radiation. Some of the effects are pretty obvious — bones thin, muscles atrophy and the heart even shrinks because in a micro-gravity setting, it no longer has to work as hard to pump blood to the legs.

But the twin study found that the changes run deeper than that. Astronauts must feel different once they've seen the stars up close, but it turns out they also actually are changed, on a genetic level, once they've gone to outer space and then come back.

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Initially, when Kelly first came back from his stint aboard the ISS, he was an inch taller, but that was the only obvious, immediate difference reported. Kelly quickly shrank back down to his original height as his body readjusted to gravity, but there were changes on a deeper level that NASA has revealed in preliminary results reported in a meeting of scientists working on NASA's Human Research Program held in Galveston last week.

The scientists have done a detailed probe of the genetic differences between Scott, who spent almost a year in space, and Mark, who was here on Earth. The genetic sampling done before, during and after Scott's trip shows that Scott's gene expression, DNA methylation and other biological markers are different from those of his identical twin brother, which is a strong indicator that these changes happened while Scott was in orbit.

From the lengths of the twins’ chromosomes to the microbiomes in their guts, “almost everyone is reporting that we see differences,” Christopher Mason, a geneticist at Weill Cornell Medicine, says, according to Nature.

These findings aren't final by any means. In fact, the data the scientists are analyzing is so "fresh" that some of it is still coming out of the sequencing machines, Mason tells Nature.

On top of that, because this study involves only two people, the Kelly brothers, some of the findings may be due to the rigors of prolonged spaceflight, but some may just be caused by natural differences between the two. Since the experiment only involves the two brothers, it's tricky to apply the findings in a general way.

Still, the initial data has shown some key alterations between Scott and Mark during their year apart. Studies of the pair's telomeres, the caps on the ends of their chromosomes, showed that during spaceflight Scott's telomeres grew longer than his brother's. This was not what scientists had expected would happen, says Susan Bailey, a radiation biologist at Colorado State University, in a NASA release. A second lab looked at the samples and confirmed the finding.

More puzzling still, once Scott came home, his telomeres shrank back down to his pre-flight levels. Scientists are now conducting a separate study looking at the telomere length of ten astronauts, which will be completed in 2018.

And in another fascinating turn, DNA methylation, the reversible addition of a chemical marker to DNA that can affect gene expression, decreased in Scott while he was in orbit and increased for Mark during that same stretch of time. Once Scott came home, the DNA methylation for both men went back to close to pre-flight levels. The scientists studying these results don't know what that means yet.

There were also changes in gene expression between the twins. This can happen based on differences in sleeping habits, and eating different foods, but Scott's gene expression changes were more pronounced, though considering he spent nearly a year eating freeze-dried food and trying to sleep while floating in space, maybe this one pretty much explains itself.

So that's what NASA scientists have learned so far. Getting actual studies published will take a while, because of both the sheer amount of data and the need to go over it carefully to ensure that anything the Kelly brothers want to keep personal stays out of any reports.

But either way, these first tidbits from the study alone have opened up some fascinating questions about what happens to the body when it slips the bonds of Earth.


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