The clinical signs can be seen in puppies only a few weeks old. An affected dog suffers from muscle hypertrophy and has stiff movements. It can have difficulties rising after rest and in rapid changes of posture. The disorder is characterized by a bunny-hopping gait. An affected dog may also suffer from superior prognathism (protrusion of one or both jaws), ptyalism (excessive salivation), dental abnormalities, and increased respiratory sounds during exercise. The tongue of affected dogs is enlarged and stiffens when touched.

Affected dogs may need assistance after rest or during muscle cramping to allow them to get to their feet and move normally. Some assistance may also be needed for everyday tasks such as stair climbing.

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 Myotonia Congenita (Discovered in Australian Cattle Dog) mutation can be safely bred with a clear dog with no copies of the Myotonia Congenita (Discovered in Australian Cattle Dog) mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the Myotonia Congenita 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 Myotonia Congenita mutation could develop due to a different genetic or clinical cause.