Human Exploration Research Opportunities - Differential Effects on Homozygous Twin Astronauts Associated with Differences in Exposure to Spaceflight Factors (Twins Study) - 07.11.18

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Identical twins are genetically almost the same, so studying them provides scientists a unique opportunity to examine how environment, diet and other outside factors affect human health and performance. Human Exploration Research Opportunities - Differential Effects on Homozygous Twin Astronauts Associated with Differences in Exposure to Spaceflight Factors (Twins Study) is an integrated compilation of ten studies at multiple research centers that take advantage of a unique opportunity: Studying the effects of space travel on identical twins. One astronaut remains in space for a year while his twin stays on Earth, and researchers study changes in measures related to the fields of genetics, psychology, physiology, microbiology and immunology.
Science Results for Everyone
Information Pending

The following content was provided by Craig E. Kundrot, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: Twins Study

Principal Investigator(s)
Susan Bailey, Ph.D., Colorado State University, Fort Collins, CO, United States
Mathias Basner, Ph.D., M.D., M.Sc., University of Pennsylvania, Philadelphia, PA, United States
Andrew Feinberg, MD, MPH, Johns Hopkins University School of Medicine, Baltimore, MD, United States
Stuart M. C. Lee, Ph.D., KBRwyle, Houston, TX, United States
Christopher Mason, Ph.D., Weill Cornell Medical College, New York, NY, United States
Emmanuel J. Mignot, M.D, Ph.D., Stanford University, Palo Alto, CA, United States
Brinda Rana, Ph.D., University of California, San Diego, La Jolla, CA, United States
Scott M. Smith, Ph.D., NASA Johnson Space Center, Houston, TX, United States
Michael Snyder, Ph.D., Stanford University, Stanford, CA, United States
Fred W. Turek, Ph.D., Northwestern University, Evanston, IL, United States

Information Pending

NASA Johnson Space Center, Human Research Program, Houston, TX, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Earth Benefits, Scientific Discovery, Space Exploration

ISS Expedition Duration
March 2015 - March 2016

Expeditions Assigned

Previous Missions

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Experiment Description

Research Overview

  • Multiple studies collect biological samples from the crew members (urine, blood, feces, cheek cells, and saliva). Biological samples provide a means for investigating the physiological responses to spaceflight.
  • The biological samples are processed and analyzed to yield results in the fields of genetics, microbiology, and immunology.
  • A psychological study looks at a phenomenon called “space fog” – a lack of alertness sometimes reported by astronauts in orbit.
  • An immunological study examines the immune response to flu vaccines given at specified points in time to each of the study subjects.
  • One study looks at telomeres, which are little “caps” on the ends of DNA. On earth telomeres have been linked to aging and stress, so in looking at this, scientists hope to get an idea of whether space radiation is prematurely aging space travelers.
  • Another study examines space-related cardiovascular disease risk. It looks at oxidative stress and inflammation during and after space flight, and relates these to long-term changes in vascular structure and function, which might predict future development of atherosclerosis in astronauts.
  • Three-fourths of American astronauts have experienced vision problems while on-orbit. Studies previously conducted on the ISS have indicated these problems are due to structural changes of the eye and possibly elevated intracranial pressure. The Twins Study conducts additional testing to identify structural changes of the eye and their causes, thereby assisting in the development of countermeasures.


NASA’s Human Research Program (HRP) and the National Space Biomedical Research Institute have instituted a program to compare the effects of spaceflight accumulated over one year and observe changes in the genetic makeup between twin brothers. This project initiates a pilot demonstration focusing on the use of integrated human analyses to better understand the biomolecular responses to the physical, physiological, and environmental stressors associated with spaceflight. The project emphasis is on the collection of biological specimens and psychological testing from one twin in orbit on the ISS and the collection of corresponding samples and data from his twin on the ground. Sample collection and data analysis occurs before, during and after the one-year mission.
The samples and data collected are:
  • Saliva as an indicator of genetic changes.
  • Buccal cells as an indicator of genetic changes.
  • Feces to study changes in the GI microbiota.
  • Urine to look for markers of bone and calcium metabolism, markers of oxidative damage in the vascular system and, with deuterium/ sodium bromide tracer, to look at intracellular and extracellular water transport.
  • Blood undergoes various analyses to look at genetic changes, oxidative markers, stress indicators, intracellular and extracellular water transport, bone and calcium metabolism, nutrition and general health status.
  • A battery of tests, Individualized Real-Time Neurocognitive Assessment Toolkit for Space Flight Fatigue (Cognition), to measure how spaceflight-related physical changes, such as microgravity and lack of sleep, can affect cognitive performance. Cognition includes ten brief computerized tests that cover a wide range of cognitive functions, and provides immediate feedback on current and past test results. The software allows for real-time measurement of cognitive performance while in space.
  • An immunological study examines the blood for an immune response to flu vaccines given at yearly intervals to each of the study subjects.
  • Diet logs (for 3 days prior to fecal sample collections) to correlate changes in GI microbiota with diet.
  • Ultrasounds to assess venous and arterial structure and function.
  • MRI sessions in the pre/post phase only to examine vascular dynamics (head/neck blood flow, cerebrospinal fluid pulsatility).
  • Blood Pressure measurements.
  • Imaging measures indicative of body fluid movement such as Cerebral and Cochlear Fluid Pressure (CCFP), Distortion Product Otoacoustic Emissions (DPOAE), Optical Coherence Tomography (OCT), Intraocular Pressure (IOP).
The one-year ISS mission offers a special opportunity to conduct a longitudinal study of twins. The integration of the investigations allows for a more complete and accurate assessment of how genes may change due to environmental factors over time during the year of spaceflight in a continuous effort to reduce the health and performance impacts of human space exploration.

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Space Applications
Comparing orbiting crewmembers with people on Earth provides insight into how and why spaceflight changes the human body, but this is difficult because every person is genetically different. Studying physical changes between two identical twins is a unique opportunity to learn about spaceflight’s effects without the confounding factor of dramatically different genetics. Scientists compare the twins’ cognitive function, metabolic profiles, gastrointestinal flora, immune system and genetics to gain insight into how spaceflight changes the human body. Results can improve the understanding of how humans adapt to spaceflight, and can be used to develop countermeasures that maintain crew health.

Earth Applications
Identical twins have almost exactly the same genes, yet their health can be very different. For example, studies have shown that one twin may develop cancer while the other is not susceptible. This investigation improves understanding of how spaceflight stressors alter a human’s cognitive function, metabolism, gastrointestinal flora, immune system, and genetics. Results could be used to develop new treatments and preventative measures for stress-related health risks on Earth.

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Operational Requirements and Protocols

A total of two subjects are required for this investigation. In-flight sessions requiring biological samples are planned for flight days 7, 15, 30, 45, 60 (occurs no earlier than [NET] FD75), 90, 120, 150, 180, 191, 233, 240 (blood/urine NET FD263), 270, 300, 360, R-45, R-14, and R-1. Those samples are any combination of frozen blood, ambient blood, buccal swabs, saliva, urine collections and/or fecal swabs. Urine collections are tied to blood collections such that blood must be drawn within 24 hours of urine collection start. No exercise should occur within 8 hours prior to a frozen blood draw except FD 191 where the constraint is no exercise within 4 hours prior to the draw. Ambient blood samples must be delivered to the Johnson Space Center (JSC) for processing within 72 hours of collection and should be scheduled as close to the Soyuz undock as possible. Frozen samples must remain frozen through landing and delivery to PI (-20°C is max allowable temp at delivery to PI; -80°C preferred). Buccal and saliva samples are collected in conjunction with Microbiome and/or Salivary Markers saliva collections; when possible, buccal/saliva samples should be collected on the same day as blood is collected. Buccal and saliva samples are collected immediately upon waking and before eating, drinking, or brushing teeth. Fecal collection is from the first bowel movement of the day (performed in conjunction with Microbiome fecal collections). Diet logs (obtained via data sharing) are completed in association with fecal swab collections. A flu vaccine inoculation occurs, on or within, 7 days after the FD 180 blood collection; the vaccination must occur at least two weeks prior to the next Salivary Markers session and at least 30 days prior to the FD 233 Twins Study blood collection. A post-vaccination blood draw (subset of the normal frozen blood collection) is performed 11 days (±3) after the inoculation. The flu vaccine must be refrigerated on ascent through the FD 180 injection. Cognition testing occurs at about FD 15, 45, NET 75, 120, 150, 180, 206, 233, NET 263, 300, R-14. Remote Guidance and real time video downlink are required for ultrasounds occurring on FDs 15, 45, 60 (NET FD75), 150, 180, 240 (NET FD263), 300, R-45, and R-14. Real time video downlink is required for Optical Coherence Tomography (OCT) and tonometer readings on FDs 45, 150 and R-45. As a general rule, data sharing between the investigators occurs as much as possible. All biological samples are returned to Earth for analysis, ideally within a year of the sampling date.

The Twins Study collects biological samples (urine, blood, fecal, buccal and saliva samples) and returns them to the ground. Additionally, cognition tests, diet logs and imaging measures such as ultrasound are collected and the data is returned to the ground. All of these data are distributed to the PI’s for integrated analysis. The completed analysis gives an integrated picture of genetic changes due to environmental factors, in an effort to reduce the health and performance impacts of human space exploration.

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Decadal Survey Recommendations

Animal and Human Biology AH16
Behavioral and Mental Health B3

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Results/More Information

Information Pending

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Related Websites

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image NASA Image: JSC2015E004209 - NASA astronaut Scott Kelly along with his brother, former Astronaut Mark Kelly at the Johnson Space Center.
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image NASA Image: 201503260005 - NASA Astronaut Scott Kelly, left, and his identical twin brother Mark Kelly.
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image NASA Image: ISS045E028258 - NASA astronaut Scott Kelly gives himself a flu shot for an ongoing study on the human immune system. The vaccination is part of NASA’s Twins Study, a compilation of multiple investigations that take advantage of a unique opportunity to study identical twin astronauts Scott and Mark Kelly, while Scott spends a year aboard the International Space Station and Mark remains on Earth.
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image NASA Image: JSC2015E089532 - View of former astronaut Mark Kelly during his flu shot in support of the Twin Studies with his brother Scott Kelly.
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