Since the first spaceflight in 1961, the United States National Aeronautics and Space Administration (NASA) has sought to increase mankind’s knowledge of space exploration. Critical to these efforts has been the study of how the harsh conditions of space and reentry into Earth’s atmosphere affect the human body. This knowledge has grown tremendously since the early days of spaceflight, but a study of genetically identical individuals has never been conducted.
In collaboration with the National Space Biomedical Research Institute (NSBRI), NASA’s Human Research Program launched the Twins Study in March 2015. This 1.5 million USD initiative aims to understand the effects of long duration space travel on the human body to improve countermeasures for advanced missions and to personalize astronaut safety. The Twins Study is run by ten principal investigators and compares the genetic and molecular profiles of identical twin astronauts Mark and Scott Kelly by integrating various “omics” – microbiome, immunome, genome and epigenome – with information on their telomeres, cognitive performance, and biochemical profiles. Upon Mark’s retirement in October 2011, he had accrued roughly 54 space days over 4 missions. On March 28, 2015, Scott Kelly began a one year long mission to the International Space Station with Russian cosmonaut Mikhail Kornienko, while Mark remained on Earth. The Kellys gave blood, saliva, urine, and fecal samples prior to Scott’s departure, during the mission, and for a period following Scott’s return. Including previous spaceflights, Scott had experienced roughly ten times the total space days as his twin by the end of his one year mission. Investigators will continue to study Scott’s telomeres for 720 days post-landing.
The Twins Study is also the first to investigate the effects of long duration space radiation and microgravity (weightlessness) in genetically identical human subjects. Radiation – the emission of energy waves that travel through a medium until they are absorbed by matter – is classified as non-ionizing or ionizing. In daily life, we are exposed to low level radiation from environmental sources, as well as many electronic devices. Outside Earth’s protective atmosphere and magnetic field, high frequency ionizing radiation from the Sun and beyond poses considerable health risks to astronauts due to potential DNA damage. NASA’s probes reveal that even the shortest round trip to Mars could increase an astronaut’s risk of developing fatal cancers by 3.6% due to radiation exposure. Previous studies have also demonstrated that the effects of long term microgravity can reduce muscle mass and induce bone demineralization at a rate of 1-1.5% per month, which increases the likelihood of kidney stone formation. While some of these effects are reversible upon return to Earth, astronauts must undergo extensive exercise countermeasures during spaceflight to mitigate these outcomes.
Could NASA use these results to direct astronaut recruitment towards individuals who are genetically predisposed to better withstand spaceflight conditions?”
In January 2017, NASA released their preliminary findings on the Twins Study at the Human Research Program Investigator’s Workshop. Since telomeres shorten with age, radiation biologists had expected telomere shortening during the one year mission. Surprisingly, they found that Scott’s telomeres had lengthened compared to those of his twin on Earth, but returned to pre-mission length shortly after his return. During the final months of the mission, Scott also showed reduced bone formation and increased levels of IGF-1 (insulin-like growth factor), a regulator of bone growth and density; investigators speculate the increased IGF-1 could be due to the exercise countermeasures.
Prior to the study, the Kellys received genetic counseling to help them understand the implications of whole genome sequencing. Despite the current legislation that allows them to withhold details of their genetic information beyond the Twins Study, the issue of genetic privacy remains a concern. Could NASA use these results to direct astronaut recruitment towards individuals who are genetically predisposed to better withstand spaceflight conditions? The organization plans to release a summary publication later in 2017, followed by detailed scientific reports. In the meantime, investigators will continue to unravel the implications of these findings for the future of space exploration.