The disorder is late onset and clinical signs are usually observed from 6 years of age. The clinical signs include ataxia, behavioral changes, and seizures. Cognitive changes associated with this form of the disease include impaired ability to recognize and respond to previously learned commands, increased sensitivity to loud or unexpected sounds and sleep disturbances. Some dogs may exhibit signs of aggression. Affected dogs may also show persistent vocalization and suffer from vision impairment. The condition is progressive and the lifespan of affected dogs after diagnosis is rarely over two years due to severity of the clinical signs.

Treatment is supportive care, however, due to the progressive nature of the condition, clinical signs typically lead to euthanasia for welfare reasons.

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 NCL12 mutation can be safely bred with a clear dog with no copies of the NCL12 mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the NCL12 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 NCL12 mutation could develop due to a different genetic or clinical cause.