Twins no longer identical after one brother's year on International Space Station

Brothers Scott, left, and Mark Kelly are the only identical twin astronauts in history. Picture: NASA Twins Study

When do identical twins stop being identical? When one of them blasts into space for a year.

That’s according to the findings from the Nasa Twins Study which found that astronaut Scott Kelly’s genes had altered after he spent just under a year on the International Space Station (ISS).

Scott stayed on the ISS from March 2015 to March 2016 while his identical twin brother Mark, also an astronaut, remained on Earth.

Identical twins share exactly the same genetic make-up as they come from the same fertilised egg, which divides into two embryos.

It is already known that astronauts’ bodies adapt to living in microgravity but that these effects wear off once back on Earth.

However, researchers found that when Scott returned to Earth, 7% of his genes did not return to normal. The remaining 93% of his genetic make-up returned to normal shortly after coming back to Earth.

Nasa said the 7% of genes which did not return to normal “point to possible longer-term changes in genes related to his immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia”.

Researchers conducted a battery of physiological and psychological tests on Scott and compared the results to those of his brother back on Earth. The study found that the genetic caps on the end of Scott’s chromosomes had increased in length.

They usually get smaller as people age.

As a result, Scott may now be biologically older than his twin brother.

When he learned that travelling in space had literally changed his genetics, Scott was more than a little surprised.

“What? My DNA changed by 7%. Who knew?! I no longer have to call Mark my identical twin brother anymore,” he said.

Twins study principal investigator Dr Chris Mason of Weill Cornell Medicine said that space travel causes an increase in methylation, the process of turning genes on and off, and provided additional knowledge in how that process works.

“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,” he said.

Dr Mason said the groundbreaking research would allow researchers to more fully understand the effects of space travel on human biology.

“This study represents one of the most comprehensive views of human biology. It really sets the bedrock for understanding molecular risks for space travel, as well as ways to potentially protect and fix those genetic changes,” he said.

Final results for the Twins Study are expected to be published later in 2018.


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