It is a very sad disease. My mom has it. It sounds like they caught Mr. Pratchett's early, which is good (certainly not good that he has it, though!). If some of the meds out there work for him it can be slowed down. I think, too, that it might be a plus because he writes. He's using his brain cells more than some. So, as he says, there'll be more books coming from him.