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

CEA/CH

CEA (Collie Eye Anomaly) is the name given to a group of eye defect afflicting many herding breeds. Currently there are DNA tests for many of herding breeds for CEA, but unfortunately our breed is not one of those breeds*. CEA is a group of eye anomalies, one of which is CH (Choroidal Hypoplasia). Actually the DNA test for CEA is actually a test for the genetic marker indicating CH.

IMPORTANT!

It is important to know that currently there is NO DNA test to identify carrier or affected Pyrenean Shepherds.

* 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 are not accurate in determining whether Pyrenean Shepherds are affected or carriers of CEA/CH or not, therefore…

a clear DNA result does NOT mean that your dog is clear.


Because of this, it is vital and important for breeders and owners to work together to protect our breed. Eradicating this is not simple, since affected dogs may not always be diagnosable after the age of 7 weeks, therefore it is imperative that breeders eye check all of their puppies with an AVCO ophthalmologist before this age.

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 also 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, how can you know then if your dog is affected or not then?

There are only a few ways to know.

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, that the parents are both either carriers or affected, and the littermates are at minimum carriers as well.

Another way to know if your dog is carrier or affected are the results of them being bred. 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 a carrier. Whether intentional or not, it is important to understand the outcome of any breedings done in regards to CH.


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
Affected Dog x Normal Dog: no affected puppies, but all puppies will be carriers

Carrier Dog x Carrier Dog: some affected puppies / some carrier puppies / some normal puppies
Carrier Dog x Normal Dog: no affected puppies / some carrier puppies / some 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!


OPEN SOURCE :: CEA/CH

This project has been started in order for breeders and owners to share publicly their affected and carrier dogs, so that this information can benefit the entire breed.

Please be sure to thank these individuals for their dedication to the breed at large by sharing this information.

Visit this page to view CEA/CH Open Source Dogs. (Coming soon!)


MORE INFO

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.