Lately i have been wondering this and googling it, can your dog be mentally handicapped?
Some sites provide info on it, some have done studies that even suggest they sometimes display what humans would consider signs of Autism,
Its really no secret that some dogs are just plain smarter then other ones,
While I wouldn't call them the same things we call them in humans, I think animals DEFINITELY can have mental illnesses/disorders. I mean, OCD is well documented. They can have aggression issues not caused by the way they were raised or fear. Some can have nervous tics or see and react to things that nobody else does. And so on.
And I don't see why some level of mental retardation couldn't also be something that occurs.
I would guess that the pups born with such characteristics would be some of the ones separated from the rest of the litter and not allowed to nurse by mom. Just a guess, would be interested in hearing a breeder's take on that thought.