The first clinical signs of congenital myasthenic syndrome in Golden Retrievers can be observed in 6-8 weeks old puppies. Affected puppies show severe exercise-induced muscle weakness. Affected puppies have abnormal gait that becomes shorter and stiffer with continued walking to the point that the puppy will lie down. Muscle weakness is caused by a deficiency of acetylcholinesterase which is essential for proper muscle contraction.

Upon initial observation of clinical signs, affected dogs should be closely monitored to assess welfare and devise a supportive care treatment plan. Due to the progressive nature of the disease, affected dogs are often euthanized for welfare reasons by 1 year of age.

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to occur. A carrier dog with one copy of the CMS mutation can be safely bred with a clear dog with no copies of the CMS mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the CMS mutation. Puppies in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected puppies. Please note: It is possible that disease signs similar to the ones caused by the CMS mutation could develop due to a different genetic or clinical cause.