NASA's twin study throws up an early genetic curveball
Scientists have begun poring over some of the preliminary data from NASA's landmark twin-study, which looks at the genetic differences between astronaut Scott Kelly who lived aboard the International Space Station (ISS) for a year, and his identical twin Mark (also an astronaut), who didn't. It is still very early days, but the results are already throwing up some surprises including large changes in gene expression and longer-than-expected telomeres.
The motive for NASA's unprecedented twin study is to investigate the impacts of space travel on the human body. ISS veteran Scott Kelly, who already had 180 days aboard the orbiting laboratory under his belt, spent another 340 days there across 2015 and 2016. This brought his lifetime total to 520 days in space before he returned on March 1, with a SpaceX Dragon capsule delivering critical research samples a couple of months later.
Scott's brother Mark is also an astronaut, having spent a total of 54 days in space between 2001 and 2011. The pair share almost identical genomes and life experiences, so the thinking is that by taking measurements before, during and after Scott's most recent stay on the ISS, scientists can unravel some of the mysteries around the physical effects of spending time in space.
"Almost everyone is reporting that we see differences", says Christopher Mason, a geneticist at Weill Cornell Medicine in New York City and one of the project scientists working on the study. "The data are so fresh that some of them are still coming off the sequencing machines."
One of the differences was found in the twin's telomeres. If you picture a chromosome as an X-shaped unit of DNA, telomeres are the caps on the end of each leg of the X. These act as a buffer so that no important DNA is spilled from the chromosomes as cells divide, though this causes the telomeres to shorten over time. This process is linked to aging and much of the recent research around telemores has focused on regulating their length as a way of slowing or reversing our biological clocks, and even preventing cancer.
Studies into each of the brothers' telomeres revealed that Scott's grew to be longer while he was in space, but returned to their normal length pretty quickly once he returned to Earth. This is the opposite of what the scientists expected to happen. They are now conducting separate research into telomere length in ten other astronauts and hope that the results may help them better understand this mysterious effect.
Also of interest to the scientists are the observed changes in gene-expression, the process through which the genetic code is used to direct production of structures of the cell. For us folks here on Earth, changes in gene expression can occur through lifestyle changes, such as diet, sleep and even taking up meditation. But Scott's changes were larger than normal, which the scientists suspect may be a result of eating freeze-dried food for a year and sleeping while floating in space.
Another early finding from the study relates to DNA methylation. This is a mechanism whereby chemical structures derived from methane are added to the DNA molecule as a way of controlling gene expression. This process is thought to play a role in regular development, X-chromosome activation, gene suppression and cancer. The researchers found that it was lowered in Scott during his stay in space, while it increased in Mark during the same time, though both returned to normal after Scott returned to Earth.
The researchers are still trying to work out what all these differences mean. Part of that includes trying to determine if they are truly a result of spaceflight or are just natural variations. There is also the matter of the small sample size – the twins amount to only two people and the results might not be generalizable.
Final, publishable results of the study are still a long way off, while it is also possible that the full data may never be released given the sensitive and personal nature of it. But already the research is giving a space community gearing up for an assault on Mars plenty of food for thought.