There are several recessive genes that could cause hairless or alterations of the coat. A photo might help narrow it done, but after they molt their first time, it should give you a pretty conclusive answer.

Satin coats are very similar to Rex and I believe originated from the Rex gene, sometimes they can go unnoticed until they have Rex-ish babies. Because even though they broke off into their own coat standard, you can still have a rat which by Satin standards is poor, be a rather attractive looking rex.

http://www.ratregistry.org/satin.htm