We had a dog who was perfectly fine until he reached puberty. Went to puppy training classes and was coming along beautifully.
When his hormones kicked in he turned into a raging ball of aggression. We couldn't sit on the floor. He barked and growled baring his teeth.
I consulted the Vet who advised euthanasia. He offered no hope for behavioural training, or neutering, saying that it would be a waste of money as, in his opinion, the dog had something called rage syndrome. Probably due to inbreeding. I think he was bred for his looks.
We had him euthanized at 18 months old.
We learnt later that the rest of his litter had suffered the same fate.