I is for Itaiitai.
Itaiitai is also often spelled itai itai, or itai-itai.
Here's a tidbit from The Superior Person's Book of Words, by Peter Bowler:
ITAIITAI n. A bone disease caused by cadmium. Said to be derived from the Japanese equivalent for "Ouch, ouch!" The interest of this to the lexicographer lies in the possibility of forming similar neologisms in English to provide more directly meaningful names for other diseases and conditions. Thus, "Eek, eek!" for arachnophobia; "Er, er" for aphasia; "Unh, unh!" for constipation; "Ha, ha!" for alopecia; "Oh, no!" for impotence; and so on.
Now I'm having fun coming up with my own names. How about "Eww, eww!" for halitosis?
Wanna play? Got any meaningful names for a disease or condition?