Space travel causes an increase in the process of turning genes on and off, leading to massive changes in their expression, preliminary results from NASA's twin study have shown."Some of the most exciting things that we've seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space," principal investigator Chris Mason of Weill Cornell Medicine, Cornell University, New York."With this study, we've seen thousands and thousands of genes change how they are turned on and turned off. This happens as soon as an astronaut gets into space, and some of the activity persists temporarily upon return to Earth," Mason said in a statement released by NASA.When retired twin astronaut Scott Kelly returned to Earth in March 2016, the "Twins Study" research intensified with investigators collecting samples from him and his twin brother, retired astronaut Mark Kelly. The researchers began combining the data and reviewing the enormous amount of information looking for correlations."This study represents one of the most comprehensive views of human biology," Mason said."It really sets the bedrock for understanding molecular risks for space travel as well as ways to potentially protect and fix those genetic changes," Mason added.Final results for the study are expected to be published in 2018, NASA said.