Terry Pratchett, one of the best-known English writers of this century, and author of the Discworld series, has been diagnosed with a very early stage of Alzheimer :

http://www.paulkidby.com/news/index.html

The author himself insists that [he] aten't dead, and that the disease is still in its very early stage, but I still find such a fate a very cruel thing for such a witty author (who so far I had not the luck to meet in person).