Cone-Rod Dystrophy 2

Cone-Rod Dystrophy (CRD2) is an eye disorder resulting in degeneration of the retina at the back of the eye at a young age, causing progressive vision loss.

Key Signs

Severe retinal degeneration, Blindness

Age of Onset

0 to 2 yrs

Juvenile onset


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 CRD2

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 CRD2

crd2 is a progressive eye disorder characterized by degeneration of photoreceptor cells and retinal thinning at a young age impacting bright light vision first followed by dim light vision. The condition progresses rapidly and the loss of vision is usually noticed in puppyhood. Retinal degeneration in crd2 generally leads to severe loss of vision by one year of age and to total blindness in early adulthood. Retinal changes are usually observable by 3 to 6 months of age.

Early on, affected dogs should not be exposed to bright light as it can be irritating or even painful. The diagnosis of crd2 can be confirmed by performing a fundic exam to evaluate the retina. Treatment is supportive.

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 be shown. A carrier dog with one copy of the CRD2 mutation can be safely bred with a clear dog with no copies of the CRD2 mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the CRD2 mutation. A dog with two copies of the CRD2 mutation can be safely bred with a clear dog. The resulting puppies will all be carriers. 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 CRD2 mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene IQCB1
Variant Insertion
Chromosome 33
Coordinate Start 25,078,910
Coordinate End 25,078,911

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Goldstein, O., Mezey, J. G., Schweitzer, P. A., Boyko, A. R., Gao, C., Bustamante, C. D., … Acland, G. M. (2013). IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related terrier dog breeds. Investigative Ophthalmology & Visual Science, 54(10), 7005–7019. View the article