Thanks so much for all the replies to date.

I'm hoping that diet won't be an issue if he is diagnosed with diabetes. We also have a Havana who has a very delicate little tummy, so both of them are fed an organic wet food which contains 75% meat. They do get dried food too (Royal Canin), but Bod doesn't eat so much of this. We've worked very hard to find a diet to suit them both, so I'm hoping this can at least stay the same.

I'm not sure of any genetic issues - if some weird things do come up after our next visit to the vet, I think I might get in touch with the breeder to check up on that.

I'm just hoping it's not kidney failure, as the vet did say that whilst it could be managed in the short term, the long term outlook wasn't good.