The gene contains a single 'word', repeated over and over again: CAG, CAG, CAG, CAG ... The repetition continues sometimes just six times, sometimes thirty, sometimes more than a hundred times. Your destiny, your sanity and your life hang by the thread of this repetition. If the 'word' is repeated thirty-five times or fewer, you will be fine.
Most of us have about ten to fifteen repeats. If the 'word' is repeated thirty-nine times or more, you will in mid-life slowly start to lose your balance, grow steadily more incapable of looking after yourself and die prematurely.

Auteur: Matt Ridley