What is a progressive neurological disease that affects adults (in 30's or 40's) where the patient approximately 10-20 years after onset of symptoms?

Please clarify. There is a word or phrase or something missing from your question. "What is a progressive neurological disease that affects adults (in 30's or 40's)" is okay, but the rest makes no sense. You can see that, right? Please repost your question with clearer wording.