Shadows in flight by Orson Scott Card

Bean stole away from the wars of Earth with three of his children - the three who share his genetic mutation that gives brilliance and a short life.  A ship to the stars will give them a chance - a chance for the scientists of Earth to find a treatment, if not for him, then for his children.  As the long decades on Earth flash by in a moment on their near-lightspeed ship, they flee into the future.
         The three, called Ender, Carlotta, and Sergeant, work to learn enough to help in the effort.  But Earth holds no minds more brilliant than those of bean and his children, and there is no cure.  As the generations pass, there comes a time when no one on Earth remembers them, save as a voice on the ansible, a distant whisper from the stars.
         And then their ship's life support begins to fail, and Bean's children must save themselves.