My mother has Alzheimer's, and I have the ApoE4 gene. Knowing is better.

The only other options are (a) knowing after it's too late to do anything, or (b) knowing at the exact moment science makes a discovery. Since we can't know (b) ahead of time, we're left with either knowing ahead of time, or too late.

Knowing sucks, but it sucks less than any other option.