>Although having the good version of APOE doesn't mean you'll never get it, and having the bad version doesn't mean you're guaranteed to get it.
Well, having the bad version of the genes certainly doesn't guarantee anything if you don't live long enough too. Only 5% of all people who have the disease have developed symptoms before the age of 65 after all, while average life expectancy of men in the US is at 76. It's very well likely to be predisposed to diseases like these and not develop symptoms because something else killed you before it could show up.
Well, having the bad version of the genes certainly doesn't guarantee anything if you don't live long enough too. Only 5% of all people who have the disease have developed symptoms before the age of 65 after all, while average life expectancy of men in the US is at 76. It's very well likely to be predisposed to diseases like these and not develop symptoms because something else killed you before it could show up.