Well, fairly new I must admit. From what I've read (& was told by one local breeder), Patchworks are Double Rexes. Not true hairless. Hair is just apparently very thin and breaks off (?). And it seems to be a Dominant gene (not recessive at least). The other info I've come across is that they do not seem to have the same health issues that some hairless rats have.
But I am definitely hoping to learn more!