Not sure if this is the correct place to post this, but please note the post is serious and in good faith. I understand Terry has a disease and I am sure all that is best and can be done is being done for him, I also used to live down the road in Gerrards X. I am a professional herbalist and work with a number of polysaccharide extracts, one of which could be worth looking at; please note I'm not selling anything!
"Hericium Erinaceus" or "Lions Mane Mushroon" / "Monkey Head Mushroom" has been found not to cure, but to be of clinical benefit to people suffering from a number of Alzheimers related issues thanks to NGF (Nerve Growth Factor) which the mushroom stimulates the body in to producing. A 30% polysaccharide extract taken as a fairly pleasant tea 3 times daily could do nothing, could help a few symptoms or more - I claim nothing, but if anyone is in direct contact with Mr Pratchett, please do pass on the information - and avoid the wiki page at all costs, there are some good white papers out there but I don't have links to hand.
I hope nobody takes this post in bad taste, it is serious and not a bunch of hippie hokum!