THE best-selling fantasy author Terry Pratchett has been diagnosed with a rare form of early-onset Alzheimer's disease.
In a brief note to fans, Pratchett, 59, said he was taking the news "fairly philosophically".
"I am not dead," Pratchett insisted. "I will, of course, be dead at some future point, as will everybody else."
Writing on the website of Paul Kidby, who has illustrated many of his books, he continued: "I would have liked to keep this one quiet for a little while, but because of upcoming conventions and the need to keep my publishers informed, it seems unfair to withhold the news."
Pratchett, is best known for his Discworld series, which explores the residents of a very flat, very weird and almost invariably hilarious planet dominated by the sprawling, chaotic city of Ankh-Morpork. To date, he has sold more than 55 million books and seen his series translated into 27 languages.
In October, doctors told the author he had suffered a mini-stroke two or three years ago. He had medical tests after having problems with his dexterity and hand-eye co-ordination.
After a series of scans, he was diagnosed with a very rare form of early-onset Alzheimer's as a result of the stroke.
Alzheimer's disease is the most common form of dementia, and people in the early stages may experience lapses of memory and have problems finding the right words. As the disease progresses, they become confused and forget names, appointments and recent events.
He said: "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."
He said he was continuing to work on the completion of his next book, Nation.