Terry Pratchett announces he has Alzheimer’s disease

Discworld artist Paul Kidby’s web site has a letter from Terry Pratchett announcing that he has early onset Alzheimer’s disease. The letter, posted on on this page, is reprinted below:
Folks,
I would have liked to keep this one quiet for a little while, but because of upcoming conventions and of course the need to keep my publishers informed, it seems to me unfair to withhold the news. I have been diagnosed with a very rare form of early onset Alzheimer’s, which lay behind this year’s phantom “stroke”.
We are taking it fairly philosophically down here and possibly with a mild optimism. For now work is continuing on the completion of Nation and the basic notes are already being laid down for Unseen Academicals. All other things being equal, I expect to meet most current and, as far as possible, future commitments but will discuss things with the various organisers. Frankly, I would prefer it if people kept things cheerful, because I think there’s time for at least a few more books yet :o)
/s/ Terry Pratchett
PS I would just like to draw attention to everyone reading the above that this should be interpreted as “I am not dead.” I will, of course, be dead at some future point, as will everybody else. For me, this maybe further off than you think—it’s too soon to tell. I know it’s a very human thing to say “Is there anything I can do,” but in this case I would only entertain offers from very high-end experts in brain chemistry.