Is it possible for a dog to have a personality disorder?

If you had a 10 month old Lab jumping up and biting you, you would be seriously injured. Are you sure this large boisterois puppy is not just playing uncontrollably?

In any case you will need to have the dog examined by a ver and assessed by a professional behaviourist. If the dog is "biting" seriously then euthanasia is the best option, but I suspect this is just lack of training. Have you spoken to the (responsible?) breeder who sold you the dog?

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I would start with taking your pup tot he vet and have a battery of tests run. If it appears to be nothing medical than try having your pup assessed by a professional trainer.

It's called lack of training & exercise....

Interesting how every one now has an excuse as to why people do not train & exercise their dogs properly...the dogs must have Multiple Personality Disorder....OMFG! ;)

Taking what you wrote at face value then yes he does have a personality disorder.
Presumably you have told him this is unacceptable behaviour by correction and redirection onto something else and this has simply failed to make a difference.
Does he use Calming Signals at all? See the article in the link, and you can send these signals back to him as well. If he's not using them then I'd hazard a guess he was either not socialised properly as a very young puppy before you got him, or he really is a dog with a mental problem.
http://www.canis.no/rugaas/onearticle.php?artid=1
If he is using those signals then there is an excellent chance that traditional training techniques will work.
What I think you need to do now is get him asessed by a qualified trainer with a broad understanding of traditional and modern techniques. If they say he's dangerously unreliable then next take him to the vet to see if there is anything physically wrong with him. If there is nothing curable there then sadly he's one of those unlucky dogs that didn't get to make it into adulthood as a family pet. If you do need to have him put to sleep don't blame yourself because you will have given him every chance.
It's so important to see puppies with their parents and to get them from breeders who ensure that the puppy is both normal and correctly socialised.
Good luck. I hope he makes it.

Have you had him since 8-9 weeks? Have you trained him yourself? Have you sent him to obedience classes?

If all yes then it sounds serious. If not then you should get a professional trainer to come in and help. Your dog must have had some misunderstanding somewhere that he is the owner!

If it was your first dog then it sounds right too. My first was a 10-lb Peke and he thought I was his slave, No. 1 though.

Your puppy surely loves you or else he will not lick you and go cuddling up to you. But he doesn't know what he is allowed and what he is not. Unfortunately he is already 10 months old and he is big so it is safer you get professional help on this.

Even with my Cocker Spaniel, only 30lb or so fully grown, I started with NO NO whenever he touched my skin with his teeth during play. I would tap his chin from under with a finger and say no in a stern voice. At the same time I looked straight into his eyes. He knew I was in command all the time and I was very upset when his teeth touched me. Sometimes I press his teeth with my finger just to scare him and he sure get scard. And this is the way it is supposed to be.

Another tip though, always disturb your puppy when he eats. Do it playfully, start with petting him on the back gently and say good boy...., and get to shifting his bowl a little while he digs in. He will grow up not guarding food and belonging. You surely don't want him to start biting when someone picks up something from the floor or touches one of his toy.

I gather this belonging guarding could well be the reason he suddenly starts to bite.

Of course exercise him a lot will help too.

Not really, but what is possible is an inherited temperament fault, or perhaps even something medical going on like a brain tumour (sad to say). I don't like this 'change in facial expression' and would be quite concerned about this. I'm not sure about putting him on medication, much as there might be something to calm him.

Have you spoken to his breeder about what's going on? If he's responsible, he should be ready to take a look at your puppy and help you, especially if he knows his breed, and his bloodlines.

Apart from his breeder, I think you need to discuss what's happening with your vet, if only to see if it does have a medical cause.