What are you feeding? A low quality food can cause hair loss and thinning. Do you put clothes on him? A detergeant or a certain material could cause this. Also allergies whether it be something he is laying in or something he is eating could be causing it? Think back to see if there has been any changes in his diet or the things he does daily?
I would take him to the vet and have a scraping done just in case it is a parasite as it could be so many different things? If he has the blue gene in him he could also have Alopecia but I am not sure if this would have popped up sooner than this?
We have a Coatimundi that gets small bald spots from where she lays in her cage in certain spots, my vet had my by liquid vitamin E and put that on the spots and it cleared it up
Take him to the vet and get him checked out and keep us posted