Dear everyone who has shared this: the truly freakish thing is not that the DNA is different, but that relativistic effects mean that one twin is now YOUNGER.

Not sure how to calculate the total, but a GPS satellite needs constant readjustment or the accuracy drifts. Ballpark guess, the one in space experienced a few minutes less than the one at home, over a full year. But I could easily be wrong by orders of magnitude. NASA Twins Study Verifies Long-Term Health Effects of Space Travel