I have compiled a list of diseases, alphabetically speaking, and I'm quite happy with some of the ones I've come up with (try googling Morgellons, if you are in the market for odd...) but there are certain letters which have a dearth of catchily-named and/or truly weird diseases associated with them. I haven't decided whether to cling to my list (all of which is real stuff) or to simply invent a disease and its symptoms for the purposes of my story. It has to be annoying, exotic, or odd - but if it's to be real it also has to be something that people have actually HEARD of, and that makes my ground rather shaky on certain letters. It also cannot be a wholly scientific name - for instance, I can't cop out and go with Opthalmic Anything, because I don't want to have to spell hard words and this IS a YA book.
So. THese are the criteria.
The disease has to have a reasonably catchy and/or descriptive name
The disease has to have a set of symptoms which are obvious, annoying, embarrassing or otherwise noteworthy
Your letters are A, G, H, K, N, Q, R, T, X.
I already have an entry for some of the above, but if anyone comes up with anything better, I'll take it!
Have at it. Do something rash...