My grandmother had Parkinson's and it was awful. How long until I can go to the doctor, get some blood drawn, and see if I'll develop it one day?
What would you do if you found out you would? (I ask as someone whose great-grandfather, great-uncle, and grandfather all had Parkinson’s.) I’ve avoided any testing because, as far as I know, there’s nothing preventative to be done. I’d love to hear otherwise. I’ve broached the subject with my last two primary care physicians and both advised that there was no point in knowing.
E.g decide to have children or not, plan a will. Live life to the max. Potentially get a head start on treatment if one were ultimately available, even if super experimental and maybe even not working in the end.
Honestly, there are many reasons to know beforehand and not a lot of reasons to not know.