When both parents are dapple (merle), on average a quarter of the puppies inherit two copies of the gene. These "double dapple" or "double merle" dogs typically carry large areas of white, especially over the head.
The same gene that removes pigment from the coat also disrupts pigment cells in the inner ear and the developing eye. Double dapples have markedly elevated rates of deafness in one or both ears, and eye defects ranging from small or missing eyes (microphthalmia) to malformed pupils and blindness.
It is entirely avoidable
The fix is simple: never breed dapple to dapple. A dapple bred to a non-dapple, non-piebald partner cannot produce a double dapple. Every reputable breed club — the German, British and American — explicitly warns against the mating, and many registries will not register the resulting litters.
This is also why a dapple's cryptic-dapple status matters. A dog that carries merle but shows almost no pattern can be bred to a visible dapple by accident. DNA testing for the merle allele removes the guesswork.
If you are offered one
Double dapple dogs can make wonderful pets and many live full lives with adjustments for reduced sight or hearing. Rescuing one is a kindness. Paying a breeder a premium for a "rare white dachshund", though, funds exactly the practice the clubs are trying to end.
Ask any dapple breeder directly what the other parent is. A straight answer of "also dapple" should end the conversation.
