Macular Corneal Dystrophy in the Labrador Retriever
Macular corneal dystrophy (MCD) is a hereditary disease that can affect middle-aged Labrador Retrievers. Affected dogs will develop cloudy eyes, due to an abnormal accumulation of glycosaminoglycans (carbohydrates) in their corneas (the equivalent to the windscreen of the eye). The disease is progressive, and although not painful, can cause marked visual impairment in affected dogs. The only treatment for the disease in people is surgical (corneal transplant), however this has not yet been performed successfully in the dog for the treatment of canine MCD.
Right eye of a five-year-old Labrador Retriever affected with Canine Macular Corneal Dystrophy
In 2013 veterinary ophthalmologists at the Animal Health Trust were the first to report this disease in the dog. Since then, multiple Labrador Retrievers have been diagnosed with this condition, from several European countries. Veterinary ophthalmologists and scientists from the Kennel Club Genetics Centre at the Animal Health Trust have identified the mutation for MCD in the Labrador and made a DNA test available. The mutation is recessive, meaning only dogs that inherit two copies of the mutation are affected by MCD; dogs with one copy (carriers) or no copies (clears) cannot develop MCD, although carriers will pass the mutation onto about half of their puppies if they reproduce.
Labrador Retriever owners who use the MCD DNA test will be sent results identifying their dog as belonging to one of three categories. In all cases the terms ‘normal’ and ‘mutation’ refer to the position in the DNA where the MCD mutation is located; it is not possible to learn anything about any other region of DNA from the MCD DNA test.
CLEAR: these dogs have two normal copies of DNA and will not develop MCD as a result of the MCD mutation.
CARRIER: these dogs have one copy of the mutation and one normal copy of DNA. These dogs will not develop MCD themselves as a result of the MCD mutation but they will pass the mutation on to approximately 50% of their offspring.
GENETICALLY AFFECTED: these dogs have two copies of the MCD mutation and will be affected with MCD.
Please note we cannot exclude the possibility that clear or carrier dogs could develop a clinically similar, but genetically different, disorder due to other mutations that are not detected by this test.
The MCD mutation is recessive so both clear and carrier dogs can be safely bred with, provided at least one of the mating pair is clear of the mutation. Carriers should always be included in the first one to two generations that follow the launch of a DNA test for a recessive mutation, regardless of the frequency of the mutation, to give breeders the opportunity to capture desirable traits, such as breed type and temperament, before they start to select for dogs that are clear of the mutation.
Elimination of the MCD mutation from the breed should be the long-term goal now that a DNA test for that mutation is available. But, providing all breeding dogs are tested for the mutation prior to mating, Labrador breeders should take their time and ensure that desirable traits are not eliminated along with the disease mutation and that the genetic diversity of the breed is not reduced.
A 10% discount is available when at least 20 samples are submitted within a month. Interested parties should contact firstname.lastname@example.org with a start date to request a discount code.