Scott Kelly did not mutate into a genetic freak during his life aboard the International Space Station.
Perhaps you had this impression last week when several news agencies falsely reported that 7 percent of the astronaut's genes had changed after his year on the International Space Station. Kelly added to the confusion with cheeky tweeting:
This, as many have pointed out, was utter nonsense. Kelly's genetic code – the thousands of base pairs that make up his DNA – did not change. Instead, in its long-term study with Kelly, NASA shared some (confusingly phrased) preliminary evidence of changes in the way its genes were used during its time in space and on its return.
The episode was a complete communication misfire, which originated from a misinterpreted press release from NASA. But it turns out that there is a lot of confusion about this story, about why NASA was primarily interested in Kelly's genes, how DNA gene expression works. Let's clear things up.
Scott Kelly spent a year in space. NASA is curious what that means for the human body.
Scott Kelly and the Russian cosmonaut Mikhail Kornienko spent 201
But Kelly and Kornienko did not just try to put their names in the book. The duration of the mission was an important test for future long-term missions to Mars and beyond. A trip to Mars would take several months to a year, and NASA is curious to see how much of that amount of time in space is spent on the human body.
NASA and its international partners usually hold astronauts for six-month missions aboard the space station. But even half a year in space takes a toll.
Astronauts usually report diminished vision, which does not return to normal after their return. Bones can become brittle under weightlessness. Muscles atrophy. It's harder to sleep in space. And scientists are worried that extended missions could have far-reaching effects on human biology, from changing the amount of beneficial bacteria in the gut to reducing the strength of the immune system.
NASA will compare the changes in Kelly's body with those of astronauts who have spent shorter times in space. The basic question is: Does extra time in the room lead to even more interference?
As a subject, Scott Kelly is special. Maybe you've heard of his identical twin brother Mark Kelly. Mark was also an astronaut, and he now advocates gun control alongside his wife, former Rep. Gabrielle Giffords.
The Kellys went to NASA and pointed out that Mark Kelly, having the same DNA, could provide an interesting control for the tests. NASA liked the idea and asked an outside researcher to come up with proposals to investigate the differences in the Kelly twins.
In total, there are 10 research projects that NASA calls a "twin study," ranging from studying the cognitive abilities of Kelly twins, to assessing changes in gene expression, to showing signs of altering their metabolism.
It's not a perfect control (more on that below), but because the researchers have data from multiple times for each twin, they can compare. If Scott's level in any of these tests is very different from Mark's, then perhaps those changes may be due to the time Scott has spent in space.
How the NASA Press Release Was Misunderstood
Here's been going on and off. In a January 31 news release, NASA reported:
Researchers now know that 93 percent of Scott's genes returned to normal after landing. However, the remaining 7 percent point to potential longer-term changes in genes related to their immune system, DNA repair, bone formation networks, hypoxia and hypercapnia.
When the news release was released in January, it drew modest attention. NASA did not report the results of the final study (expected later this year). It was rather a reminder: Hey, we're still working on it.
In mid-March, some outlets have picked up the press release, "for reasons that are still unclear," as the Atlantic Ocean explains.
Newsweek for example: "Scott Kelly: NASA Twins Study confirms that Astronaut's DNA has actually changed in space." Live Science performed a similar article admirably admitted later: "Scott Kelly was completely out of place with Genesis Story."
This was wildly misguided, in part because NASA did not explain what "gene mutations" meant. Scott Kelly's DNA did not change. If 7 percent of your DNA changes, you're not human anymore. Humans and chimpanzees share 98.8 percent of their genetic code. If 7 percent of your genes have changed, who knows what you would be. (NASA also surprisingly referred to the genetic changes that occurred in a "space gene," which is not a thing, meaning that NASA meant only genes that could be impacted during space travel.)
Scott Kelly is still human , And he is still Mark Kelly's twin with identical DNA. So, what has changed?
Gene Expression, Briefly Explained
Humans have about 20,000 genes that are contained in 23 chromosomes of DNA. You have each of these genes in every single cell of your body. Yet our cells are different – a neuron does not look like the cells that line your stomach. And they have very different functions. It transmits electrical and chemical signals throughout the nervous system; the other oozes acid to digest food.
The differences are not due to differences in DNA, but to how they are expressed. Complex chemical reaction pathways and feedback loops cause certain genes to be activated and certain genes to be turned off. Each gene encodes a protein (a building block of the body), and depending on which genes are activated, different structures are built and different things happen.
Subtle changes in gene expression will not turn your neurons into blood cells, but they can change their way of functioning. Changes in gene expression can cause cells to become cancerous or trigger a chain of events that increase a person's chance of developing heart disease.
There are several ways to identify changes in gene expression. One is, by looking at RNA levels, the messenger molecule that helps to execute and create the protein encoded by a gene. Another is the search for methylation, where a DNA molecule is essentially labeled with a chemical. This chemical can prevent this portion of the gene from activating, as explained by Nature .
NASA reported changes in the expression of genes related to [Scott Kelly’s] immune system, DNA repair, bone formation networks, hypoxia and hypercapnia [überschüssiges Kohlendioxid im Blutkreislauf]. That's not much, so we'll do it. I have to wait for the final paper to better evaluate those claims. In an update to their press release, NASA said the change in expression of Kelly's genes by 7 percent was "very minimal" and likely "within the range for people under stress, such as mountaineering or diving."
Another arm of the twin study examines changes in Kelly's telomeres, which are regions of DNA that act like caps on strands of chromosomes. Changes in telomere length are a measure of cellular health (they tend to get shorter with age). Oddly enough, NASA reported that Kelly's telomeres were growing while in space. This is another claim that we need to evaluate more carefully when the final paper comes out.
It is too early to say how one year in space could affect Kelly's long-term health
Overall, it is difficult to draw concrete conclusions about which aspects of spaceflight these changes brought (assuming they're real)] That's why genes turn on and off all the time, and these cycles are influenced by "basically everything," says Ran Blekhman, a genetics researcher at the University of Minnesota. Stress, nutrition, exposure to pathogens, physical activity, and even loneliness could affect the way genes are turned on and off. Many genes also run in a circadian rhythm, ie they switch on and off regularly in the 24-hour cycle. Damn, there was even a study that found meditation-altered gene expression.
All this noise makes the work of identifying significant changes in gene expression (such as those that make the difference between a cancer cell and a healthy cell) and what causes these changes very tedious work.
And if there are changes, it will be difficult to assign them to any aspect of space travel. They could be caused by living in weightlessness, lack of exercise or disturbed sleep, or by dieting with freeze-dried foods. They could just be coincidence.
What can we learn from this twin study?
Andy Feinberg is a molecular biologist at Johns Hopkins University, who is involved in the Kelly twin study and is investigating the methylation of Kellys genes. (The press release did not refer to his findings but to the results of another lab.)
The plan, he says, is for all researchers involved in the twin study to write a scientific paper and submit it to a peer Review and then, hopefully, be included in an academic journal.
Feinberg warns that the genetic tests in the twin studies should not provide any definitive conclusions about the effects of spaceflight on our genetics. You could never do that with just one subject and one control. "You could make a hypothesis out of that, but you could not prove anything," he says.
Overall, researchers are not just looking at genetics. They consider measures of cognitive function, immune function, metabolism and vital signs. In all of these studies, the data could suggest a comprehensive history of how space affects health, a hypothesis that should be tested in future missions.
What is underestimated but perhaps more important, this twin study is a way for scientists to refine their methods of performing biological tests on astronauts. For example, he says he and his colleagues spent some time in the "vomit comet" – the NASA plane that mimics the effects of weightlessness – so that they could develop rigorous blood collection procedures for the astronauts to collect samples.
"Just figuring out how to do these things is a big deal," he says. Even if the results are just one hypothesis to be tested in the future, that's fine. The work of preparing people for interplanetary travel is "intergenerational," he says. This study is only a small step.
So scientists can not learn much about how space affects the way our genes work by Scott and Mark Kelly. But they will have a better idea of how to answer that question in the future.