The first clinical signs of Startle Disease, or hyperekplexia, can be observed in one week old puppies. The affected puppies respond to handling with rigid limbs and tremors. Relaxation or sleeping eases the clinical signs. Affected puppies have difficulties standing and they develop a stiff posture with all four limbs extended. Cyanosis or bluish discoloration of mucous membranes is also characteristic of hyperekplexia. Cyanosis can be observed especially when an affected puppy is nursing. The condition is severe and progressive. Affected puppies are usually euthanized before three months of age.

The wellbeing of affected puppies should be closely monitored. Because of the severity of the clinical signs, affected puppies are usually euthanized on welfare grounds before three months 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 Startle Disease (Discovered in Irish Wolfhounds) mutation can be safely bred with a clear dog with no copies of the Startle Disease mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the Startle Disease 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 Startle Disease mutation could develop due to a different genetic or clinical cause.