I was very lucky, just as the old Mice Are Nice forum came to a close, to get hold of some gorgeous sealpoint mice: Basil (buck obviously), Velcro and Cheeselet (does).
When I picked them up, I was told that in breeding circles, it is common with sealpoints to inbreed them to preserve the markings. Brother with sister and then offspring with grandad. I'd thought I would pick up a mouse from outside the circle to start a litter with.
Is inbreeding common for these? They don't show any signs of being dimwitted (quite the opposite) or having birth defects.
Ask not what your rodent can do for you...