I say this without any attempt at humor, "kill yourself peacefully before you're unable to and the people around you refuse to"

If I knew I had a prion disease, I'd be making plans to die peacefully unaware, or suddenly, the moment a symptom shows up.

My only real firsthand experience with prion diseases is Fatal Familial Insomnia, and the person was strapped into hospital bed restraints after a suicide attempt, and the only thing they would do when they chose to speak was beg for us to let them die because they can't keep going like this anymore.

Edit: honestly I do not know if there is any way to treat other prions, but to my knowledge there isn't. It's just "ease their suffering as they slowly die in front of you"