Overview
*Optigen Officially Licensed*
Part of the official UK Kennel Club testing scheme in Australian Shepherd, Bearded Collie, Border Collie, Collie (Rough), Collie (Smooth), Lancashire Heeler, Retriever (Nova Scotia Duck Tolling) and Shetland Sheepdog
Collie Eye Anomaly/Choroidal Hypoplasia (CEA/CH) is a developmental defect of the eye. Specifically, the abnormal development of the choroid – an important layer of tissue under the retina of the eye – in which there is a decrease in the development of the blood vessels. Puppies can be diagnosed by an ophthalmologist as early as 6-8 weeks of age. As the puppies get older the tapetum (the reflective layer at the back of the eye) develops and this can hide the signs of CEA. This phenomenon is called “go normal”, but it does not mean that CEA goes away or gets better. Affected dogs can also have optic disc coloboma and retinal detachment.
The clinical effects vary greatly among affected dogs within one breed, between parent and offspring and even within a litter. Most often the disease presents as a mild form in affected dogs and the presence of the disease can only be detected upon ophthalmologic examination; the dog retains normal vision throughout life. However, dogs with mild disease can produce severely affected offspring.
The A 7.8-kb deletion in the gene called NHEJ1 that causes Collie Eye Anomaly in collie breeds is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Collie Eye Anomaly during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Collie Eye Anomaly as a result of the NHEJ1 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Collie Eye Anomaly should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the NHEJ1 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Collie Eye Anomaly, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.
