Dear lord, I hope the diagnosis is mistaken. Alzheimer's is one of the worst diseases you can have... I didn't know there was such a thing as "early onset". I had a great uncle who had the regular variety (related by marriage I think... I hope...). It was just awful, not only for him but everyone around him.

Glad he can put a light face on it though. I guess if all else fails he can adopt the Douglas Adams method and say that if any of his works beyond such and such a date don't contradict at least one other work, they aren't official Pratchett.