QUESTIONS AND ANSWERS ABOUT COLLIE EYE ANOMALY IN THE NOVA SCOTIA DUCK TOLLING RETRIEVER
Please scroll down the page to read the answers to questions about CEA or click on any of the links to go to specific questions.
Part 1: Information about the CEA test
- When will the CEA test be available for Tollers?
- Can the OptiGen CEA collie test work for the Toller?
- Does OptiGen have any idea or estimate of the accuracy rate of the CEA test for the samples it has done?
- What will the cost be for the CEA test?
- Do researchers recommend all breeding stock be tested with the CEA mutation test?
- Will a registry of test results be established similar to the prcd-PRA registry?
Part 2: Information about CEA
- What is Collie Eye Anomaly?
- What breeds are affected by Collie Eye Anomaly?
- How was CEA determined to be a problem for the Toller?
- Can a Toller’s eyes with CEA become worse? Might he later go blind?
- How is CEA inherited?
- What is the estimated carrier and affected rate for CEA in the Toller?
- What does “go normal” mean in CEA?
- Is there any way to estimate the percentage affected by CH, coloboma or more severe forms of CEA in Tollers?
- With regard to CH, will the light areas darken as the dog ages and “go normal” or will they remain light? How many genotype “affected” in the test samples received clear CERF examinations?
- What is the percentage of genotype affected presenting themselves as “go normals” as opposed to the more severe forms of the genotype and why the differentiation?
- Can a dog diagnosed with CH be issued a CERF certificate?
- What can a breeder do regarding CEA?
- How will the information of normal, carrier and affected dogs be shared?
- At what age do you recommend an eye examination in puppies if for some reason their parents could not be tested?
- What if I have more questions?
The CEA test became available to Tollers on April 17, 2006. OptiGen provided discounted rates during the initial testing.
Please refer to the OptiGen website to register online or download appropriate forms for requesting the test.
The current CEA test available at OptiGen works for Tollers. The same mutation in the same gene causes CEA in the collie breeds and Tollers. The test for Tollers at OptiGen will be the same and called the CEA or Collie Eye Anomaly Test.
Does OptiGen have any idea or estimate of the accuracy rate of the CEA test for the samples it has done?
Accuracy of the test is very high (approaching 100%) since it is detecting a specific gene mutation.
Go to the Optigen website for current pricing structures depending on what you order.
Optigen has reserved DNA for Tollers previously tested for prcd-PRA. A new sample is not required. Follow ordering instructions on OptiGen’s Website.
If you are ordering both the prcd and the CEA test for the first time you only need to send one sample. One tube of blood can be used for both OptiGen tests.
YES. A breeder will not know if their breeding stock carries the CEA gene without doing the blood test. The HGC also recommends that breeding stock be cleared for this disorder to prevent the increase in carrier and affected rates in Tollers.
Based on experience with Border collies and other CEA-affected sheepdogs, breeding advice would be the same for all genetically tested affected dogs, regardless of the clinical symptoms. It is known that mildly affected dogs can produce offspring that are severely affected.
Discontinued. The HGC of the NSDTRC (USA) will be establishing a registry for dogs in the US. This will include all Tollers that are determined to be normal and will include information from dogs that are carriers or affected with owner permission. OptiGen will forward normal results to the club registry directly, however they will not release carrier or affected results to us. It would be up to each owner to submit their results with permission for us to post them to our registry. This information will be available from the NSDTRC (USA) website from a link on the Health & Genetics page. The results will not be available until the end of the second quarter after June 30, 2006. Meanwhile, speak directly to the breeder to find out about the CEA status of a particular dog or puppies.
In October 2007, the Club approved establishing an Open Registry for PRCD-PRA and CEA/CH thus permission to list as carrier or affected is no longer required.
Effective January 1, 2009, the database for CEA and PRCD-PRA was turned over to the Orthopedic Foundation for Animals (OFA).
Collie Eye Anomaly, also known as CEA, is an inherited disease causing defects in the formation of the eye. CEA has now been determined to be a genetic disorder in the Nova Scotia Duck Tolling Retriever. Several forms of the disease are recognized, but the most common is a lesion on the back of the eye called choroidal hypoplasia (CH). All dogs affected by CEA have choroidal hypoplasia, by definition. CEA is not a progressive disease like prcd-PRA and most affected dogs may only have mildly impaired vision. More severely affected dogs may have pits (colobomas) affecting the retina and nearby tissues and in the most severely affected eyes, retinal hemorrhaging and detachments can occur, resulting in blindness.
Varying degrees of CEA and definitions are listed below:
Choroidal Hypoplasia, Chorioretinal Change, Choroidal Dysplasia: These refer to abnormalities in the coloring or pigmentation of the choroid or central layer of the eye's lining. This is the most common abnormality found in CEA and all dogs with CEA have CH. However it is the least harmful and mildest form of CEA. Most dogs with this form function normally with no ill-effects or loss of vision.
Coloboma, Ectasia, Staphyloma: While not completely synonymous, these terms all refer to a cupping or bulging in the eyeball usually in the area of the optic nerve. Colobomas are the most common more serious complication of CEA. Colobomas can be described as a pit in the eye or a blister at the back of the eye that you can see with an ophthalmoscope. Colobomas vary and can be small or large and occur in approximately 25% of dogs with CEA.
Interestingly, you cannot have CEA without CH and won’t have coloboma without CH.
A third set of complications which occur exclusively in dogs with coloboma include retinal detachment or hemorrhaging in the eye. About 5-10% of dogs with CEA have these severe complications, which can lead to blindness. These percentages are based on experience with the Collie Breeds. It remains to be seen if these figures hold true for Tollers.
Vascular Disease, Tortuous Blood Vessels: These terms describe defects in the vessels of the eye, which are responsible for its blood supply or "nourishment." These may be malformed, undersized, or even lacking.
Retinal Detachment: Loosening or separation of the innermost, or retina, layer from the wall of the eye. This may involve a tiny area or the entire retina. It can be either one or both eyes. The complete detachment of the retina results in blindness in that eye.
There is usually no significant visual deficit with CH or coloboma, but may lead to a blind spot in the eye. These conditions usually do not affect the working ability of a dog.
The traditional herding breeds are affected including Rough and Smooth Collies, Shetland Sheepdogs, Australian Shepherds, Border Collies, Lancashire Heelers and now Nova Scotia Duck Tolling Retrievers. The carrier rate varies among breeds with the highest occurrence in collies. CERF data of affected breeds are listed in the table below (from Optigen’s website)
|Frequencies Based on CERF Eye Exams in the U.S. from 1991 to 1999|
|Collie - Rough & Smooth||66.7%||8.75%||1.88%|
To date, there is very little scientific data regarding the percentage of Tollers affected with Choroidal Hypoplasia, coloboma or retinal detachment. This is a relatively new development in the breed with an overall predicted carrier rate of only 5%. However, certain lines tracing to a common ancestry have a greater carrier risk.
Early this year a Toller owner took their young dog to a CERF clinic where it was diagnosed with Collie Eye Anomaly or CEA. After seeking a second opinion since this disorder is not commonly known in Tollers, the second eye vet agreed with the first -- that the Toller indeed had Coloboma and Choroidal Hypoplasia (CH) -- both eye conditions seen with CEA. In a short time, two other related Tollers were also diagnosed with either CH or Coloboma as a result of breeders and owners communicating with each other. Next, prominent researcher Dr. Greg Acland and his research team and OptiGen scientists began several studies to see if indeed a new genetic eye problem existed in Tollers. Until now CEA has only been found in traditional herding/collie breeds such as the Australian Shepherd, Border Collie, Rough and Smooth Collie and Shetland Sheepdog. A CEA mutation test was made available to these breeds in 2005 by OptiGen.
The collie OptiGen CEA genetic test was done on these few suspect Tollers and researchers confirmed they indeed were affected with CEA and carried two copies of the CEA disease gene. Further testing of the parents confirmed they were carriers of the CEA disease gene, but did not show signs of CEA. Fortunately the researchers had access to DNA reserved from its earlier blood sample already available from dogs who had been previously tested for prcd-PRA and with further genetic testing, pedigree analyses and genetic sleuth work, they determined the problem was not just confined to this handful of Tollers.
Pedigree analysis identified common ancestry that is likely the source of the disease gene, and further identified several dogs that were predicted to be carriers if the suspected lines of descent were correct. Some of these dogs already had previously submitted prcd DNA samples at OptiGen, and with further tests, in each case researchers confirmed these dogs were carriers and transmitting the CEA disease gene.
Optigen then took a "random" sample of 22 unrelated Toller DNAs and tested these for the CEA mutation. They selected samples from unrelated Tollers with none sharing parents, owner, or kennel name and coming from the US, Canada and Europe. This revealed one more carrier from 22 dogs tested, and the pedigree of this dog also fitted the pattern revealed from the first cases. OptiGen further conducted tests that identified several dogs now known to be progeny of CEA-carrying Tollers, and found that as expected, about 50% of these are carriers and 50% are genetically clear.
According to Dr. Acland some meaningful conclusions can be made from these studies. First, the CEA disease is indeed present in Tollers and has been segregating in the breed for multiple generations. They examined pedigrees 6 generations back, but feel the CEA gene tracks back to the beginning of the breed. Thus it is not a new mutation, or a recent accidental introduction of collie blood to the breed. The CEA mutation was probably introduced during the foundation years of the breed, before the books were closed, and presumably from the historical contribution of "farm collies" as noted in Alison Strang's book and other sources.
Second, the incidence of carriers across the breed as a whole seems to be fairly low -about 1 in 22 or about a 5% carrier rate. The predicted affected rate would translate to only 0.5% of Tollers across the breed. However, in lines that have line bred to particular ancestors, the carrier rate can be much higher. In such pedigrees, the carrier rate can rapidly increase to as much as 25-50% within a few generations, and that is when CEA affected dogs start to turn up.
Third, the OptiGen CEA Collie test can be used for the Toller. Much like the prcd-PRA test, breeding stock can be tested and breeding strategies used to prevent this disease. As long as a normal dog is used in each breeding, CEA will not be produced.
Not usually as CEA usually presents in the mild form of Choroidal Hypoplasia. The majority of dogs mildly affected will have perfectly adequate eye vision throughout their life. However, a dog born with a coloboma, may later suffer loss of sight if a detachment or a severe hemorrhage occurs. More severe cases of CEA can have colobomas. Colobomas are depressions or excavations in the back of the eye and may involve the optic disk and/or surrounding area. Colobomas may involve one or both eyes and may be very small and shallow or extremely large and deep. Large optic disc colobomas can cause retinal detachment because the large "hole" in the back of the eye can cause the accumulation of fluid behind the retina. Bleeding in the back of the eye can also occur in CEA and is thought to be secondary to colobomas and retinal detachments and blindness.
Choroidal hypoplasia, the primary lesion in CEA, is an autosomal recessive disorder. Autosomal means it is passed on and expressed equally in males or females. Recessive means a dog may carry the mutant CEA gene and pass it on to its offspring without having the disease itself. A dog is defined as clear or normal if it has no CEA genes. A dog is defined as a carrier if it has one CEA gene and one clear or normal gene. Both the carrier and the clear dogs will be unaffected and will test negative for CEA in an eye exam. A dog is defined as affected if they carry two copies of the CEA gene. The outcomes of the different crosses of these dogs are as follows:
Clear X Clear = 100% CEA Clear puppies
Clear X Carrier = on average, 50% CEA Clear, 50% CEA Carriers
Clear X Affected = 100% CEA Carriers
Carrier X Carrier = on average, 25% CEA Clear, 50% CEA Carriers, 25% CEA Affected
Carrier X Affected = on average, 50% CEA Affected, 50% CEA Carriers
Affected X Affected = 100% CEA Affected
The first three crosses or breeding strategies will not produce disease and can be implemented without producing an affected dog. The latter three crosses do produce disease, and as with prcd-PRA, are not recommended.
Evidence exists that some other parts of the syndrome are inherited differently, which may explain why some littermates will have a milder form of the problem than their littermates or close relatives. Variable expression of the disease is found in all affected breeds.
CEA is a complex disease with more than one gene involved which makes it different from prcd-PRA. The classic affected dog has the CH and this can be seen as young as you can see into the dog’s eyes and up to 11-12 weeks of age. The CEA gene mutation test will predict if a dog has this disorder with nearly 100% accuracy.
Researchers ESTIMATED the carrier rate to be approximately 5% in a very small sample of unrelated Tollers. This was done by testing 22 NSDTR’s selected at random from the blood samples held at OptiGen, but none sharing parents, owner, or kennel name and coming from the US, Canada and Europe. This is somewhat a rough estimate, but adequate to get a sense of carrier frequency, that is, lower than prcd-PRA but high enough to indicate a genetic problem of significance. Within a particular pedigree known to pass CEA, carrier rate can reach 25 to 50% in some breedings.
There really is no such thing as a reliable estimate of breed wide incidence because pedigrees occur in clusters. The frequency of carrier rate will vary: it can be zero or can be as high as 50% within a line of carriers. So although the carrier rate is estimated to be low overall across the breed, it can segregate into certain lines.
As far as affected rate, the rule of thumb is that the affected rate is 1/10th the carrier rate. So across the Toller breed at this time it is estimated to be 0.5%. However in particular pedigrees that carry the CEA gene this could rise to 25-50%. If two carriers were mated, the expected carrier rate would be 50% with 25% normal and 25% affected puppies. That means 1 in 4 pups could be affected if two carriers are bred.
The term “go normal” was created to describe collie pups that were observed to have choroidal hypoplasia when young (say, 6-12 weeks old) but definitely had no recognizable sign of it with an eye exam at a later age (say, over 1 year of age). This is presumably due to later pigmentation development in the eye that masks the choroidal hypoplasia abnormality. However, the only lesion that can "go normal" is the pale area of choroidal hypoplasia. The coloboma is a permanent lesion. In any case, the genotype is not changed in these dogs. These dogs are affected with a form of CEA, but usually a milder form that appears to be normal but in reality is hidden by further color development in the eye.
The fact that CERF examinations have not detected CH in Tollers may be due to the common breeder practice of CERFing dogs near age 2 years rather than between 6-12 weeks of age. Perhaps some Tollers who might be affected by CEA are mildly affected with CH, “go normal” and therefore CERF clear.
Dogs that “go normal” still are genetically affected by CEA. Although these dogs rarely exhibit visual problems, they are affected by the disease and if bred to another affected or carrier dog, can produce more severe forms of CEA. According to Dr. Acland, most breeds affected with CEA don’t go normal, but we cannot be sure of this for the Toller,
Since there are few reports of CH by eye vets, the Toller may experience the “go normal” phenomenon more often than other breeds. But this is speculation at this time.
Is there any way to estimate the percentage affected by CH, coloboma or more severe forms of CEA in Tollers?
At this time there is not enough evidence to predict the percentage of Tollers affected by CH, coloboma or more severe forms of CEA in Tollers. We have heard of cases of coloboma in the US and are now aware of several cases from overseas, but coloboma are relatively uncommon affecting only a few Tollers each year. However if breeding stock is not checked, the carrier rate for CEA could climb and we would likely see more cases of coloboma and perhaps retinal detachments, hemorrhaging and even blindness.
With regard to CH, will the light areas darken as the dog ages and “go normal” or will they remain light? How many genotype “affected” in the test samples received clear CERF examinations?
At this time we just DO NOT KNOW. Eye vets have not examined Tollers young enough and therefore the data is incomplete. We cannot assume that the findings in the other herding breeds affected with CEA will hold true for the Toller. But after testing and further investigation these questions may be able to be answered in the future.
What is the percentage of genotype affected presenting themselves as “go normals” as opposed to the more severe forms of the genotype and why the differentiation?
Again, at this time we do not know the answer to these questions. Young dogs have not been routinely examined.
Because of its hereditary nature, the policy of CERF is to recommend that any dog with CEA (of any severity) not be bred and affected dogs will not receive a CERF number unless the breed club has not determined CH to be a problem for that particular breed.
However, since this is a genetic problem in Tollers and a gene test exists, a dog with CEA can be bred with the assurance disease will not be produced if a normal dog is used in each breeding. Researchers and the HGC are working with CERF and the American College of Veterinary Ophthalmologists to educate them about this new finding in Tollers.
Fortunately, the OptiGen CEA mutation test can be used for Tollers as of April 17, 2006.
If you would like to determine if your breeding stock is clear, a carrier of or affected by CEA follow these simple steps:
If your dog has been previously tested for prcd-PRA by OptiGen, then your dog has DNA reserved from its earlier blood sample already available for testing at the lab. There will not be a need to see your vet or draw new blood. Simply complete the OptiGen order form with payment and send it to Optigen. Make sure you check the box on the form that indicates you have all ready tested your Toller for prcd-PRA – That is, check the statement “Blood sample is already at OptiGen” whether or not you paid for long-term storage.
If your dog has not been previously tested for prcd-PRA by OptiGen you can have both or just one test done. Just go to the website at http://www.optigen.com/ and follow the instructions on their website. You will need to have a vet or vet tech draw blood according to the instructions outlined by OptiGen.
If the gene test has not been used on your breeding stock yet, meanwhile:
For owners of known Carriers (unaffected dogs that have produced a CEA affected puppy) – the NSDTRC (USA) HGC recommends that anyone who inquires about the dog's progeny or as a mate, be told that it is a carrier. It also recommends that people who have any of this dog's progeny be informed that all its offspring have at least a 50% chance of also being a carrier even if the other parent is neither a carrier or affected.
For breeders of a litter in which one parent is a known Carrier - The NSDTRC (USA) HGC recommends that all puppies in the litter be tested for CEA using the OptiGen CEA test OR have them examined by an eye vet between 8-11 weeks of age.
Do not breed two known carriers together, as this will likely result in affected puppies.
- In October 2007, the Club approved establishing an Open Registry for PRCD-PRA and CEA/CH thus permission to list as carrier or affected is no longer required.
- Effective January 1, 2009, the database for CEA and PRCD-PRA was turned over to the Orthopedic Foundation for Animals (OFA).
DISCONTINUED. The HGC of the NSDTRC (USA) will be establishing a registry for dogs in the US. This will include all Tollers that are determined to be normal and will include information from dogs that are carriers or affected with owner permission. OptiGen will forward normal results to the club registry directly, however they will not release carrier or affected results to us. It would be up to each owner to submit their results with permission for us to post them to our registry. This information will be available from the NSDTRC (USA)website from a link on the Health & Genetics page. The results will not be available until the end of the second quarter after June 30, 2006. Meanwhile, speak directly to the breeder to find out about the CEA status of a particular dog or puppies.
At what age do you recommend an eye examination in puppies if for some reason their parents could not be tested?
If you are not sure of the CEA status of the parents, puppies can be examined by an eye vet between the ages of 8-11 weeks and CH and coloboma can be recognized easily at that age. However, the eye examination will not be able to tell you if a particular puppy is a carrier for the CEA gene.
Please contact either Jane Folkman or Sue Van Sloun of the Health and Genetics Committee. Their contact information is listed below:
|Jane Folkman, Chair
|Sue Van Sloun, CoChair
CLICK HERE to go to the CEA Discovered information page.