Research Question

Hello to anybody reading this, I'm doing some research for a novel I'm writing, and am searching for an illness which fits certain specific criteria. i.) The illness has to have the potential to be fatal, with or without treatment. ii.) The illness has to have either no or very few visible symptoms. iii.) A patient diagnosed with the illness has to be able to live for two or more years before the illness becomes fatal.

I know it's a pretty morbid question, but I would be very grateful for any help in the matter.