As I understand, all of our DNA (which, of course, is what 23 and Me is examining) is susceptible to change through random mutation. I've heard it explained that aging is a process in which our older cells are replaced by new cells. But a new cell isn't a perfect copy; it's like a photocopy of the older one, which is in turn a photocopy of the older one, and so on. If you're old enough to have seen many pieces of paper that are a photocopy of repeated photocopying, then you've seen how small deteriorations can add up with repeated copying. Apparently one form of deterioration in living things is mutation of the DNA in our cells.
As "circular" implies, the goal of organisms seems to be to reproduce so the species continues to exist. DNA mutations just happen.
It can help to reassure oneself that it could always be worse: first of all, it's a miracle that YOU (the combination of one particular mother's egg with one particular father's sperm) were born! Then, look around at all those worse off than you: those in vegetative states due to horrible accidents or illnesses; those who are physically or emotionally abused regularly, kids who have seen their parents killed in war zones, and on and on.
I have high blood sugar but am grateful for natural sweeteners such as stevia. I'm 4/4 but very thankful for what Dr. Bredesen has discovered. Dementia was the primary cause of death for my dad, and the secondary cause for my mom; they did not have the info that we do about how to prevent or reverse it.
Life is all how you look at it -- some people are simply more lucky than others. Happy New Year!