Yes, the hairless gene is associated with lactation issues (usually its that their nipples are inverted, which is the same problem hairless rats have...the babies are unable to latch onto the nipples)...they also have overgrown nails, can be prone to skin irritation problems, and can have eye problems associated with eyelashes curling inwards and irritating the eye. I recently attained some true hr/hr mice from Simonsen Labs in Cali and so far they haven't really had any skin/eye problems, but they are still young and they have very long nails. I haven't bred them yet, so I have no experience with the lactation issues.