Clinical signs of the disease typically emerge around 6 months of age but the age of onset can vary from as young as 6 weeks to 1.5 years of age. Clinical signs begin with myoclonic jerks/twitches or the trunk, forelimbs, and nodding of the head. The appearance can resemble severe startling or even an electric shock. Twitches of varying intensity are most commonly seen in relaxed dogs that are beginning to sleep. The frequency of these twitches can be very high, even 150 twitches per day. The ability to sleep and rest is thus impaired. Affected dogs can also be sensitive to light with visual stimulus triggering epileptic activity. Approximately 38% of affected dogs progress to having generalized tonic-clonic seizures. Biological factors, such as vaccination or heat might affect the frequency and/or initiation of clinical signs.

Antiepileptic drugs are used to reduce epileptic activity. Levitiracetam and potassium bromide seem to achieve a good response. Affected dogs should be kept in a safe environment and in a way that they do not harm themselves during epileptic activity. Seizure control can sometimes be impossible to achieve and euthanasia may be elected on welfare grounds.

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 develop. A carrier dog with one copy of the Juvenile Myoclonic Epilepsy mutation can be safely bred with a clear dog with no copies of the Juvenile Myoclonic Epilepsy mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the Juvenile Myoclonic Epilepsy 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 Juvenile Myoclonic Epilepsy mutation could develop due to a different genetic or clinical cause.