CEA,  CEA/CH,  CH,  Choroidal Hypoplasia,  Health

CEA/CH

Collie eye anomaly: a congenital syndrome of ocular anomalies characterized by bilateral and often symmetrical defects including any combination of choroidal hypoplasia, coloboma and retinal detachment(s). (From the OFA Eye Disease Glossary)

Choroidal hypoplasia: a congenital, inherited, non-progressive defect primarily affecting the choroid resulting in some or all of the following: decreased or lack of pigment in the retinal pigment epithelium or choroid, tapetal thinning and reduced or abnormal choroidal blood vessels. (From the OFA Eye Disease Glossary)

Coloboma: a congenital abnormality in ocular development usually characterized by focal absence of tissue, commonly (though not exclusively) located at the 6 o’clock position associated with failure of closure of the optic fissure. (From the OFA Eye Disease Glossary)

Retinal detachment: a separation of the neurosensory retinal from the retinal pigment epithelium.
Retinal dysplasia: abnormal development of the retina present at birth. This condition is non-progressive and recognized in 3 forms: folds, geographic, detached. (From the OFA Eye Disease Glossary)

CEA (Collie Eye Anomaly) is the name given to a group of eye defect afflicting many herding and other breeds. The clinical effects of CH vary greatly among affected dogs within a breed, including between parent and offspring and even within a litter.

Most often the disease presents itself in Pyrenean Shepherds as a non-vision affecting mild form. Even though it is caused by a different gene in Pyr Sheps, than in most other breeds, it does appear to be an autosomal recessive in Pyrenean Shepherds like it is in other breeds.

Currently there are DNA tests for a number of breeds for CEA, but unfortunately our breed is NOT one of those breeds. (The DNA test for CEA is actually a test for Choroidal Hypoplasia, one of the components of CEA.) During the research phase, it was determined that the gene causing CH in the other breeds was not the same gene causing CH in Pyrenean Shepherds. *

Because of this…
No currently available DNA test for CEA/CH will identify carrier or affected Pyrenean Shepherds, therefore if your dog has DNA tested clear for CEA/CH, it does NOT mean that your dog IS clear.


Because we have no DNA test to work with, it is vital and important for breeders and owners to work together to protect our breed. (Here is an article that discusses how another breed did this before they had DNA testing.)

The good news is that for most Pyrenean Shepherds it expresses itself in a mild form, and is not usually vision affecting. Even so, it is important not to let it become pervasive in the genetic population, as it has in some breeds.

PLEASE NOTE: WE ARE NOT ADVOCATING THAT DOGS WHO ARE AFFECTED OR CARRIERS BE SUDDENLY OR COMPLETELY REMOVED FROM THE GENE POOL!

The Pyrenean Shepherd is a breed with small numbers and the population is too small for such drastic measures, so removing all affected dogs from the breeding population is not advisable. We are suggesting that, with knowledge and understanding of the gene pool with respect to CH, and with careful testing of puppies, this condition can slowly be bred away from over time.  (Please see Rhonda Hovan’s excellent article about this: Uncommon Breeding Strategies [Rhonda Hovan – OFA Board of Directors]).


So, if the DNA tests results are not valid, how can you know whether your dog is affected or not?

There are only a few ways…

The most reliable way to know if your dogs are affected or not is for all puppies to have their eyes examined by a boarded ACVO Ophthalmologist between 5-7 weeks of age. The age for this is very important! Affected dogs may “go normal” and it may not show up in tests done at a later age. They will however, still be affected.

Some affected dogs will still be evident as being affected when they are older, but many are not. That means that if a dog has NOT been eye checked until after 5-7 weeks, even if that have a clear eye exam, they still may be affected.

It is also important to know that if there are ANY affected dogs in a litter, because that would indicate that the parents are both either carriers or affected, and the littermates are at minimum carriers as well.

Another way to know more information about whether your dog may be a carrier or affected are the results of their puppies eye exam. Some people may even choose to do a test breeding on important individuals, especially if they are concerned that the dog may potentially be affected or be a carrier. Whether intentional or not, it is important to understand the outcome of any breedings done in regards to CH.

Spending time evaluating the risk factors of any potential breedings is important. Study your pedigrees before doing the breedings. Using Open Source | CEA/CH information can help you identify affected dogs and carriers, as well as close relatives of these dogs that may pose a risk as well.

All in all, educating ourselves about this health issue and working together is how we will limit the impact of this health defect on our breed.


Various Breeding Scenarios

Affected Dog x Affected Dog: all puppies will be affected
Affected Dog x Carrier Dog: all puppies will be affected or carriers (about 50% affected and 50% carriers)
Affected Dog x Normal Dog: no affected puppies, but all puppies will be carriers

Carrier Dog x Carrier Dog: about 25% affected puppies / about 50% carrier puppies / about 25% normal puppies
Carrier Dog x Normal Dog: no affected puppies / about 50% carrier puppies / about 50% normal puppies
Normal Dog x Normal Dog: all puppies normal – no affected puppies / no carrier puppies


The Future

While we can all hope that some day we will have a DNA test to screen dogs with, many breeds in the past have nearly eradicated recessive traits through careful breeding. That is one of the benefits of working with a recessive gene, which CH seems to be.

The downside of working with recessive genes is that they can be passed on and on for generations without showing up, giving a false sense of security, when all the time the gene is becoming more and more pervasive in the population. There are some breeds where it is almost impossible to find an unaffected dog because a gene has been spread throughout almost the entire breed.

The important thing in eradicating this defect from our population is for open discussion to occur, and for everyone to educate themselves about it. This is not just a problem in a few lines… it impacts all of us, so please eye check all your puppies before 7 weeks whether they are going to be bred or not!


DNA TESTS

There are currently NO DNA tests approved for Pyrenean Shepherds. If you look at the various companies offering DNA test for CEA/CH they do not list Pyrenean Shepherds as one of the breeds for this test, and that is because they do not identify the gene for it in Pyr Sheps. (Please see first article below.)

* Affected Pyrenean Shepherds (both with just CH and with the full spectrum of CEA) participated in the original research done by Cornell University / Optigen that the current tests are based on, and it was determined at that time that CH in Pyrenean Shepherds was NOT caused by the same genes identified as causing CH in the other breeds participating in this research, therefore the current tests licensed to various companies in the United States are not accurate in determining whether Pyrenean Shepherds are affected or carriers of CEA/CH. (There could however be cases that test positive if they have had the gene introduced from another breed, but the gene typically causing CH in Pyrenean Shepherds is not the same gene causing it in other breeds.)


RESEARCH & ARTICLES

Breed relationships facilitate fine-mapping studies: A 7.8-kb deletion cosegregates with Collie eye anomaly across multiple dog breeds (Multiple Authors)

Quote from the Abstract and article – “We…use(d) the multibreed approach to fine-map Collie eye anomaly (cea), a complex disorder of ocular development that was initially mapped to a 3.9-cM region on canine chromosome 37. … Sequence analysis revealed that all affected dogs share a homozygous deletion of 7.8 kb in the NHEJ1 gene. Two dogs from the Berger des Pyrenees breed that were clinically diagnosed as affected with colobomas were tested but did not have the 7799-bp deletion.

CEA/CH Genetic Testing & Information (IPDF DogWellNet)

CEA/CH causes abnormal development of the choroid – an important layer of tissue under the retina of the eye. Since the choroid layer does not develop normally from the start, the primary abnormality can be diagnosed at a very young age by an opthamologist. 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. 

Collie eye anomaly in Canis lupus familiaris (University of Sydney)

Collie eye anomaly (CEA) is a complex developmental defect of the posterior segment of the eye characterized by choroid hypoplasia, with blindness occurring in severe cases.

Collie Eye Anomaly In Australian Shepherds (CA Sharpe – ASGHI)

Even though the Australian Shepherd has a different gene for CEA/CH (and a DNA test), this article is important to read, as the strategies used in the breed before DNA testing can be used as successfully in the Pyrenean Shepherd to manage CEA/CH.