Download Macular corneal dystrophy (MCD)

Macular Corneal Dystrophy in the Labrador
Macular Corneal Dystrophy
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 in their corneas (the equivalent to the windscreen of the eye). This disease
is progressive, and although not painful, can cause marked visual impairment in affected
patients. The only treatment for the disease in people is surgical (fresh corneal transplant
placement), however this has not yet been performed successfully in the dog for the treatment
of canine MCD.
Mutation Identified
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.
DNA Test
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. Please note; we cannot exclude the formal possibility they could develop a
clinically similar but genetically different disorder due to other mutations that are not detected by
this test.
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. Please note; we cannot exclude the formal
possibility they could develop a clinically similar but genetically different disorder due to other
mutations that are not detected by this test.
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GENETICALLY AFFECTED: these dogs have two copies of the MCD mutation and will be
affected with MCD.
Breeding Advice
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 longterm 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.
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