He's actually my husband's and I've only known him since he was 2 - he's 6 now, but hubby says he has been like this almost his whole life. He's Japanese if that matters somehow.
The poor thing throws up all the time and yet he is still overweight. He has to have very specific foods - Kitten Chow for dry food and Friskies canned food, but the Friskies has to be the chunky ones with pieces of food and sauce - or the throwing up gets worse. Being an adult cat on kitten food is probably the main reason for his extra weight - he's about 14 1/2 # on the frame of a cat that should be 10 or 11. It also means that the rest of our cats eat the Kitten Chow too because we can't risk him eating something else, and only one of them is young enough to need kitten food. We have asked vets about it and they just tell us they don't know what is causing it, but that according to their tests there is nothing wrong with him. He's also very lazy. I don't know if it is just his nature or if the same thing that makes him throw up takes all his energy from him. He was neutered as a kitten, but now seems to have some issue with girl cats - he had no experience with them until he was 4 1/2, and now we have 3 girls that he hates as well as one other boy that he does get along with - I have no idea if that is somehow related or not.