What is wrong with this dog?

One of my friends dog, Kenny, is having a health issue. For some reason, he is always urinating in the house. He is potty-trained and he usually let's you know when he has to go outside, but Kenny will just pee in the house without telling you. Also, he's getting very thin that you can see his ribs, but trust me, he eats A LOT! That dog loves to eat. I am there all the time and I see that they feed him regularly. What do you think could be wrong with Kenny? They are going to take him to the vet very soon, but I just wanted to do some research and find out if anyone knows what the problem could be. Thanks so much and God bless. : )