Best-selling author Terry Pratchett was yesterday commended for his "passion and support" after he announced a donation of £500,000 to help research into the ravages of Alzheimer's disease.

Pratchett was diagnosed with the incurable brain condition three months ago and yesterday condemned the "shameful" lack of funding to help fight it.

With dementia levels in Scotland set to rise by 75% in the next 25 years, the writer behind the Discworld fantasy books spoke out against the patchy provision for sufferers, adding that he wanted to "kick a politician in the teeth".

Pratchett shocked his fans when he announced in December that, at just 59, he had a rare form of early onset Alzheimer's. The author, who has sold more than 55 million books, delivered the news online in typical Pratchett style, calling the incurable disease "an embuggerance".

But yesterday, at an annual conference on Alzheimer's, he admitted that having the disease was like stripping "away your living self a bit at a time".

The condition affects 700,000 people in the UK, but only £11 is spent for each person annually on research, compared with £289 for each cancer patient.

Pratchett said: "There's nearly as many of us as there are cancer sufferers. It's a shock and a shame, then, to find out that money for research is 3% of that which goes to find cancer cures.

"Perhaps that is why I know three people who have successfully survived brain tumours but no-one who has beaten Alzheimer's."

Welcoming the donation, Jim Jackson, chief executive of Alzheimer Scotland, said: "His private experience has been one of fear, dismay and abandonment. There are 58,000 people in Scotland going through the same daily struggle. Pratchett has helped pull back the veil on what is often a hidden, stigmatised illness."

Calling Pratchett "brave", Neil Hunt, chief executive of the Alzheimer's Society, said: "His honesty, candour and courage will do so much to tackle the misunderstanding and stigma that keeps dementia in the shadows. "