Prion diseases are very rare. There are on average only about 300 reported cases in the U.S. every year. Because of its rarity it can be difficult to diagnose. Dr. Greg Eckel is very aware of the topic because his wife has been inflicted with a prion disease. It's been a very scary struggle for him and his family as she struggles with this incurable disease. What are prion diseases specifically? What causes them? What symptoms exist?