(CNM) CENTRONUCLEAR MYOPATHY
CNM is a muscle disorder that is inherited in Labrador retrievers. It has been recognized
in the retriever community for decades and known as "muscular myopathy". It is
inherited as an autosomal recessive trait, meaning that the disease allele must be
inherited from both parents in order to produce an affected puppy. Carriers of CNM
appear normal, but they will pass the mutant disease allele on to half of their puppies.
Whenever two carriers are bred, there is a likelihood that affected puppies will be born.
At birth, affected puppies are indistinguishable from their normal littermates, but muscle
weakness and muscle atrophy become evident at an early age. Some affected pups
show disabling signs at 6 to 8 weeks of age, while in others severe signs do not become
evident until 3 to 5 months of age. Affected puppies exhibit muscular weakness, an
awkward gait and decreased exercise tolerance. Severely affected pups may have a
low head carriage, and a gait characterized by short, stilted strides. The hind legs are
often advanced simultaneously in a synchronous, bunny hopping fashion. Most affected
puppies are euthanized due to poor quality of life.
Prior to 2003, the diagnosis of CNM required muscle biopsy of affected puppies. In
2003, Drs. Stephanie Blot and Laurent Tiret at the Alfort School of Veterinary Medicine
in France identified the genetic mutation causing CNM and made a test available to
Labrador Retriever owners worldwide.
DNA testing can confirm that an affected puppy with symptoms has CNM.
More importantly, testing can be used to determine whether healthy individual dogs are
carriers of CNM (possessing one disease allele and one normal allele) or whether they
are clear of the mutation. This is important information to have about a dog prior to
breeding so that a breeder can avoid producing puppies affected by CNM.
If a carrier is bred to a non-carrier, none of their pups will be affected, but 50% will be carriers.
If a carrier is bred to a carrier, approximately 25% of the puppies will be clear of the mutation,
50% will be carriers and 25% will be affected and likely die of CNM.
Testing for CNM involves the collection and submission to the laboratory in France of an
oral swab for DNA. This should be done by a veterinarian. The veterinarian will also
verify the identity of the dog being tested (microchip or tattoo) for the laboratory. Dogs
that are clear of the CNM mutation will be published on the CNM website list of clear
dogs (no charge), and all results are eligible for posting on the Orthopedic foundation for
animals (OFA) for a nominal charge.
Owners who would like to have their dog tested for CNM at the WCVM should do
the following:
(1) Make an appointment with the Small Animal Medicine service for DNA testing.
(2) Go to the CNM website www.labradorcnm.com at least 4 days before your
appointment.
Follow the prompts (Testing Your Labrador) and answer the questions and pay the fee
( $55 USD with a credit card).
(3) The laboratory will send you an email within 48h with a submission number and
some paper forms. Print these forms and bring them with you to your appointment.
(4) The laboratory will also send you a package in the mail with some paper forms,
mailing envelope and DNA brushes. This will probably not arrive before your
appointment - we will use some that we have here. We do ask, however, that you send
the brushes to us when you get them to replace our supply.
Send to: Veterinary Teaching Hospital Pharmacy, 52 Campus Drive, University of
Saskatchewan, Saskatoon, SK S7N5B4
(5) Do not give your dog anything to eat or drink (except water) for 4 hours before your
appointment.
(6) During the appointment:
- A veterinarian will collect a history and examine your dog. If your dog is due for routine
procedures such as annual examination or vaccination these can be completed during
the same visit.
- Your dog's permanent identity will be verified (microchip or tattoo) if possible. If your
dog has a tattoo please bring a copy of their CKC or AKC registration papers stating the
tattoo number for your dog in case one of the letters/numbers is difficult to read.
-We will perform the DNA swabs, fill out the required forms and seal the samples in
envelopes according to directions from the laboratory
(7) We will give you the samples in a sealed, pre-addressed envelope to mail to the
laboratory. We recommend mailing the CNM test via First Class Mail (Canada Post) to
the French laboratory.
(8) The VTH fee will be the fee for an office call plus a $35.00 DNA collection and
processing fee (includes the swabs). If more than one DNA test is done during one visit,
(CNM plus EIC for example) there will not be an additional charge.