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Startle Disease (Discovered in Irish Wolfhounds)

Startle Disease, also known as hyperekplexia, is a rare muscle cramping disorder. Signs of the disease can be seen in very young puppies, and include muscle stiffness and tremors when handled.

Key Signs

Muscle stiffness, Tremor, Difficulty or inability to stand, Rigid posture, Cyanosis

Age of Onset

At birth

Present at birth


Autosomal Recessive

For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their puppies if bred.

Likelihood of the Condition

High likelihood

At risk dogs are highly likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a dog with Startle Disease

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about Startle Disease

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.

For Breeders

Planning to breed a dog with this genetic variant?

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.

Technical Details

Gene SLC6A5
Variant G>T
Chromosome 21
Coordinate Start 42,583,698
Coordinate End 42,587,925

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Gill, J. L., Capper, D., Vanbellinghen, J. F., Chung, S. K., Higgins, R. J., Rees, M. I., … Harvey, R. J. (2011). Startle disease in Irish wolfhounds associated with a microdeletion in the glycine transporter GlyT2 gene. Neurobiology of Disease, 43(1), 184–189. View the article