What do you mean by "crippling disease?" The last dog that I came across like this puppy later was dx with HD :-(
Temperament issues are every bit as crippling as structural abnormalities. A dog that is very fearful can become a liability if he becomes fear-reactive. And you may always have to manage his environment carefully.
They can be great pets though.
On the other hand, you have had him for three weeks, and he is not repsonding and bonding with anyone, it is not a good sign. He is a little older, but it should take days to adjust not weeks. Not for a four month old puppy.
I don't mean he will have trouble getting around. But he very may well have trouble getting around anything he thinks is scary, and anything new.
He's young. I don't like that he will not eat or take treats when anyone is around. I think you should read up on how to manage a shy dog. there's a book, Help for the Shy Dog
, I think by Deborah Wood which is pretty good.
Then again, maybe your best bet is to invest in a good behaviorist/trainer.
With a pup this fearful, you will have to do all the socialization and you are already beyond the socialization period. This does not mean that he can't be socialized, it just means it will be a bit more difficult and take longer. With this pup who is afriad of typical and repeated household noises, it's going to be a challenge.
He is crippled in this sense. The question is, can you help him to find his legs.