Two Disease Types

Are there any disease that cause a deterioration of the brain that might cause both physical and mental disability that could lead to insanity or paralysis or both? I'm thinking it could even be a brain tumor maybe? Just want an opinion.

I'm working on a short story and I need the right disease for a character.

One more question: Can aides lead to paralysis?

Anybody knowing the answers to one of both of the questions, I would just love!!!