Identical twins in space

What happens to identical twins when one of them goes to space?
16 April 2019

Interview with 

Lindsay Rizzardi, Johns Hopkins University


A picture of the Earth from the ISS space station


The results of an ambitious study to explore how the human body is affected by flight has just been announced. Twelve teams from various universities across America have been looking at cells, genetics and general physiology. Lindsay Rizzardi, from Johns Hopkins University, spoke to Izzie Clarke about these out-of-this-world results...

Izzie - Fancy a trip to space? The years of physical and mental training, the waiting, will you be chosen for a mission? Then you get strapped into a rocket, blasted off into space and live on the International Space Station for months. Most of the time, astronauts are up on the ISS for up to 6 months, but in March 2015 an American astronaut called Scott Kelly was one of two people selected for a year-long mission to space, and there was something special about Scott that grabbed scientists’ attention...

Lindsay - The idea for the study came from Scott Kelly himself. He knew he was scheduled to go on the one-year mission and approached NASA and was like hey, you know I've got a twin brother that's going to be here and we’ve both been astronauts, would it be cool to study us, since we’re twins and we have the same genetic sequence? And NASA said yes, that would be fantastic.

Izzie - That's Lindsay Rizzardi. She was a part of a team at the Johns Hopkins University that looked into the genetic information of Scott and his twin Mark. The key factor being that, as an identical twin, their DNA is the same, and this was the beginning of a mammoth study to explore the impacts on the human body of life in space compared to that back on Earth. Lindsay and her supervisor, Andrew Feinberg, were interested in something called methylation, which is a process that goes on in your DNA.

Lindsay - What DNA methylation actually is is it’s a chemical tag that gets deposited on your DNA. And it doesn't change your DNA as far as changing the sequence or anything like that, but what it does do is it can regulate gene expression and how they are turned ‘on’ and ‘off’.

Izzie - Now, say your genetic code is a cookbook. If you take one single instruction -  that's a gene and that's akin to a single recipe. Now these methylation markers are like putting a mark on that recipe to say "reduce your portion size". So if there are a lot of these methylation markers on a recipe i.e. your gene, it essentially reduces the amount it's making and ultimately stops a gene from doing its job, otherwise known as being 'turned off'.

Lindsay - So, for instance, if you have a lot of these modifications near the beginning of a gene it typically results in that gene being turned off. If there's not much methylation around genes tend to be turned on or expressed. And so what we hypothesised was that we would see big changes in Scott during his time in space that we wouldn't see in Mark.

Izzie - But that's not exactly what they found. In fact, Lindsay and the team found no long-lasting major differences between Scott and Mark's genetic code.

Lindsay - Mark actually had more variation globally in his DNA methylation levels than Scott did. Now we were surprised by this at first, but then we started thinking harder about it and it's like well, of course, Scott is in an isolated environment on the space station for a whole year, his diet is limited, his environment’s not changing much; whereas Mark on Earth could travel, he could eat whatever he wanted. Given that, it's not as surprising that we didn't see as much variation in Scott. Now what is interesting is that we saw genes that were involved in inflammation and in stress response having altered methylation, and we didn't see changes of those same genes in Mark.

Izzie - But how can you compare two people needing fresh blood samples when one of them is orbiting 400 km above you?

Lindsay - It was actually logistical nightmare. What we had to do was coordinate sample collections with scheduled visits to the space station by the Soyuz. So whenever they would get a resupply, Scott or one of his crewmates would have to draw his blood and put it right on the rocket to come back to Kazakhstan, and then in Kazakhstan there’d be a plane waiting to take it Houston, and then in Houston it would get on a truck to the lab. And somebody would have to be at the lab, whether that be noon or 3 o'clock in the morning waiting on the sample so they could separate those cell populations that we needed, freeze them down and ship them out to the labs. So is quite a feat, and I think one of the great accomplishments of this study is actually getting all of that logistics worked out so that this is how we can do things in future.

Izzie - Especially in a future that may involve human space flights to Mars...

Lindsay - Definitely. I mean, I think if you're going to plan space missions to Mars then you need to be prepared. Any information that we gather on the potential risks of this longer duration spaceflight is going to be beneficial. And you're going to have to take it into account when you plan longer longer duration missions because it’s interesting too, this was the first time an astronaut had been in space for over a year, at least for us. We actually saw a lot of our changes happening in that last six months of flight, and so it really is the longer duration that we're starting to see effects.


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