Telomeres, are the “caps” that protect the ends of DNA strands.

On Earth, these telomeres get depleted over the course of a person’s lifetime as each round of DNA replication wears away at them.

However, in space, the findings were contradictory to what the scientists were expecting. They assumed that due to the immense stress on the body, these telomeres would shorten. But, on the contrary, they had increased in length considerably.

But, a critically large amount of telomeres were lost during the body's return back to normal on earth, which is a cause for concern.

Under stressful situations, normally, there is a change in genetic expression.

Accordingly there were changes, but, the unexpected finding was that, these changes in gene expressions, seemed to have accelerated(6 times more) during the latter 6 months of the mission.

This is concerning, because for extended space missions, this could imply that genetic expression could alter exponentially leading to severe consequences. 

Upon returning, about 90% of these altered genetic expressions returned back to preflight states.

A decline in cognitive efficiency was reported.

NASA had prepared a set of questions to assess various mental state and cognition.

Upon return, even though Scott’s in-flight measures were stable, his “cognitive efficiency,” or his speed and accuracy in completing the test battery, dropped once he got back to Earth.

The decrease lingered over the six months after his return, till it reverted back.

This is a complication due to the obvious complexity of a space mission, which would require a pretty good cognitive state.

His gut microbiome showed altered bacterial proportions, although the overall bacterial diversity was intact.

Several proteins also changed during the spaceflight.

• Elevated levels of collagen, a structural protein was seen in his urine. Looking at this measure along with physiological changes—like those observed in Scott’s eyeballs and vascular system—could be a sign that the body was restructuring.
• Researchers also observed heightened levels of aquaporin 2, a protein that tends to be a marker of dehydration.

This study was in no way conclusive or predictive, because of the very small sample size(just one pair of twins), a short study period, just to name a couple of reasons.

However, it has given an idea of potential changes to be expected and a foundation for upcoming research in the field of prolonged deep space exploration.