Double Merle French Bulldogs: Deafness, Eye Defects and Care

How a double merle is created

Merle is caused by an insertion in the PMEL (Silver) gene. It is incompletely dominant: one copy (single merle) usually produces the mottled pattern, and two copies (double merle) produce a much stronger effect.^[1]

When two single merles are bred, about one in four puppies is expected to be a double merle. The risk is easy to miss because some merle carriers look solid. UC Davis calls these "cryptic merle" (also phantom or ghost merle) and warns they "may be misclassified as non-merles."^[1] Only a DNA test of the M locus shows a dog's true merle status.

How to recognize a double merle

UC Davis notes double merles "often can have an all white coat."^[1] Other common signs include pale or blue eyes and eyes that look smaller than normal. Appearance alone is not proof. A mostly white Frenchie may be a piebald rather than a double merle, so a DNA test is the reliable way to know.

Health risks, with numbers

Hearing. A 2009 study tested the hearing of 153 merle dogs with BAER, an electrical test of the hearing pathway. Among double merles, 10% were deaf in one ear and 15% in both ears. Among single merles, the figures were 2.7% and 0.9%.^[2] The Merck Veterinary Manual explains that this type of deafness develops within the first weeks of life and that affected ears are totally deaf.^[3]

Eyes. UC Davis lists ophthalmologic defects among the problems seen in double merles.^[1] These can range from mild changes to eyes that are abnormally small or do not see.

Other systems. UC Davis also mentions abnormalities of the skeletal, cardiac and reproductive systems.^[1]

On top of this, a double merle Frenchie carries all the usual breed risks, including airway disease (BOAS), heat intolerance and spinal problems.

Testing a double merle puppy

• BAER hearing test. Merck calls BAER the most definitive test and notes that deafness in one ear may go undetected without it.^[3] Ask your vet for a referral; many veterinary schools and neurology clinics offer it.
• Eye exam by a veterinary ophthalmologist. This shows the structure of each eye and how much vision is likely.
• Merle DNA test. Confirms the genotype, which matters if anyone ever considers breeding the dog (they should not).

Living with a deaf or low-vision Frenchie

• Use hand signals for sit, come, stay, good and no. Deaf dogs learn them quickly.
• Use a vibration collar (not a shock collar) or a flashing light to get attention.
• Keep the dog on a leash or in a fenced area. A deaf dog cannot hear cars or your call.
• Approach gently and wake the dog with a soft touch or by stamping lightly on the floor, so it is not startled.
• For low vision, keep furniture in the same places, use textured mats to mark stairs and doorways, and talk to the dog as you approach if it can hear.
• Tag the collar with "I am deaf" and your phone number.

Many rescue groups place double merle dogs and can offer practical advice.

Why responsible breeders never pair two merles

UC Davis states plainly that "breeding two merle dogs is discouraged to avoid producing double merle offspring."^[1] A breeder who produces double merles either did not test or chose to take the risk. If you are buying a merle puppy, ask for M-locus DNA results for both parents and walk away from any merle-to-merle pairing.