Health and Welfare
Eye conditions in the American Cocker Spaniel:
future prospects for diagnosis and prevention
Dr Sally Ricketts, Kennel Club Genetics Centre, Animal Health Trust
The American Cocker Spaniel (ACS) breed suffers from several eye conditions that range in severity and are well documented within the breed. Conditions that are currently certified under the British Veterinary Association KC/ISDS eye scheme include hereditary cataract (HC), glaucoma, retinal dysplasia and generalised progressive retinal atrophy. Clinically, the ACS also frequently presents with distichiasis, corneal lipidosis and dry eye. These conditions are seen during a BVA eye examination but they are not certified under the scheme.
HC in the ACS has a very variable age of onset and clinical presentation, with cataracts occurring in different parts of the lens, and there is often dissimilarity between the two eyes. For this reason, and because the possible genetic mechanism causing HC in the ACS is currently unknown, any type of cataract in the ACS has to be considered hereditary. HC in the ACS, although variable, can be blinding, so it is very important for dogs to undergo regular yearly eye examinations throughout their lives to allow early diagnosis and appropriate management.
DNA research overview
At the Kennel Club Genetics Centre at the Animal Health Trust (AHT), research is being conducted to attempt to identify causal genetic factors that contribute to the development of HC in the ACS. The main aim of this work is to develop a DNA test that can be offered to breeders to help them make sensible breeding decisions to reduce the risk of producing clinically affected dogs. For these studies DNA samples are collected from both HC-affected and unaffected dogs in the form of buccal (cheek) swabs, and DNA from the affected dogs (known as ‘cases’) is compared to the DNA of the unaffected dogs (known as ‘controls’). This process is called a ‘genome-wide association study’ and scans thousands of unique points in the DNA to identify regions of the genome that are consistently shared between dogs affected with HC, but that are not shared with unaffected dogs. When a region of DNA that is associated with HC has been identified, additional analysis is carried out to refine the region of interest and identify the causal mutation that is contributing to the risk of developing HC in the ACS. Once the causal mutation has been identified a DNA test can be developed.
To date scientists at the Kennel Club Genetics Centre have assessed the DNA of around 30 HC-affected ACSs (‘cases’) and 20 unaffected ACSs (‘controls’) at around 22,000 unique points in the DNA. These initial investigations failed to find any region of DNA associated with HC, suggesting that this condition in the ACS is complex and may be caused by several different mutations, and is not a simple ‘Mendelian’ condition caused by a single gene mutation. This situation is not unique to the ACS—the picture is looking very similar for HC in five other breeds being studied at the AHT.
The good news is that there is now a better scanning array available to scientists that will assess the DNA at around 174,000 unique points, thus providing a more in-depth screen than for previous studies, and there have been several technological advances in the field of genetics and genomics that allow pinpointing a mutation to be much easier once an associated region is identified. However, for research to progress and be successful the sample collection is critical and your help is needed!
Sample collection for the HC project in the ACS is ongoing at the Kennel Club Genetics Centre at the AHT. If you would like to contribute to the research, scientists are very keen to collect samples from dogs affected with any bilateral cataract (both eyes) and from dogs with current clear eye examinations and over the age of six years. The AHT will provide DNA collection swab kits, free of charge, to individual owners or clinicians—contact Bryan McLaughlin at firstname.lastname@example.org.
For HC-affected dogs, or ‘cases’, at least 25 samples from each different form of cataract (i.e. posterior cortical/anterior cortical, etc) found in the ACS are required. This is because it is possible that each form might be caused by a different mutation, and so each set will need to be investigated separately. For this reason it is crucial that a sample sent in for research has accompanying clinical information and details of eye examinations. This allows researchers to group dogs with similar types of cataracts.
Due to the variation in age of onset of HC in the ACS, the unaffected dogs, or ‘controls’, need to be as old as possible, but at least 6 years of age. This helps to prevent possible misclassification, as very young dogs may still go on to develop cataracts. For these ‘control’ dogs, up-to-date eye examinations stating that the dog has clear eyes are required when the sample is submitted for research. The number of ‘control’ dogs required is usually equivalent to the number of ‘cases’, and the same control set can be compared against the different case sets described above. For both ‘cases’ and ‘controls’ it is really important to update the scientists with any changes in health that might have occurred since a sample was submitted, as this could have implications for the research.
The importance of regular eye examinations through to older age
Whilst a DNA test may hopefully become available in the future, the lack of current knowledge underlying the mode of inheritance for HC and its genetic causation has several implications for ACS breeders. The code of ethics suggested by the ACS Club of Great Britain (found at http://www.acscgb.com/) is to avoid breeding before two years old, and to breed only with individuals that have clear current eye certificates and whose parents also have current clear eye certificates. Whilst this is a sensible approach, the varying age of onset for HC in the ACS and its possible genetic complexity highlights the importance of regular eye examinations throughout life, rather than just prior to breeding, and for the results of these to be made available to the community. Moreover for conditions such as generalised progressive retinal atrophy, clinical diagnosis is only usually possible from three years onwards. However, breeding with older individuals that have current clear eye certificates and whose parents also still have healthy eyes allows the creation of older generation pedigrees and might help to reduce some of the risk of producing clinically affected dogs.
So what does the future hold regarding diagnosis and prevention of HC in the ACS? Hopefully at least one or more genetic mutations underlying HC in the breed will be known and tools will become available to breeders to help inform them of the risk of breeding two particular individuals.
The author thanks all owners who have submitted samples and information from their dogs or who have made financial contributions to this project to date. The author also thanks Dr Cathryn Mellersh and Christine Heinrich (DVOphthal DipECVO MRCVS) for their valuable contributions to this article.
Eye Matters -- By Yvonne Knapper
With the notorious TV program on pedigree dogs, the show/breeding dog world has had a most severe knock.
We all know that sensationalism gets peoples attention . That is a fact. It was sad that the pedigree dog wasn't better presented, neither was the exhibiting side .
Having said that, I do feel that some of the basic facts that were put forward in the programme were breeders own fault. Harsh words, but true.
People will always be people, that will never change. Some breeders say that they do their best to breed happy-healthy dogs, but they will stop at nothing to win in the ring. Fact.
If that means they will bend the rules to suit themselves, they will.
How often have I heard as an excuse as to why we shouldn't breed from a dog/bitch “ who has an afflicted parent. So long as we do it with care it is alright, is the answer”
There is NO excuse, however good that specific dog/bitch is.
We have NEVER done it and we had to disregard some top imported stock at huge expense and heartache.
In today's climate we still have breeders who do not eye test, or they eye test at the time of breeding, but once they have had the litter they do not continue testing the parents, until they are at least 8 yrs of age. The parent[s] are put in a pet home, so that is the excuse as to why they are not being tested again. By which time , the progeny , being still young, are being bred from again. Of course they are still young, but clear at the time and so it goes on.
We found that pet people are the most understanding and we have not come across anyone saying no to future testing. We point out to them, it is no good testing with what we breed, continuation is the key here after all. We tell them, pet people want a healthy dog , not one who has to go to the vet and empties their bank balance in the process, as well as breaking their hearts.
Cataracts can appear up to 8 yrs and are considered hereditary by Prof Yakely [ USA], who has carried out an extensive research programme. It is his opinion, and guidance on minimalizing the problem, is that we disregard any dog/bitch with an opacity, HOWEVER SMALL AND INSIGNIFICANT under the age of 8. We should not breed from their progeny, IF we really want to have a chance of eradicating the problem. He said that the problem has reached such proportions [we have over 25 types of cataract in our breed] . . that we must take drastic action.
Our breed also suffers from PRA [Optigen offer a one off test from America for that] and Glaucoma.
Many still do not test for Glaucoma. There is a one off test for that too, [in UK] so there is no excuse. Yes it is not cheap but surely it is worth it to make sure you wont get it later on and then breed puppies who have a higher chance of getting this very painful condition ?
The only solution for the patient is to remove the eye.* We tried medication, but it did not work in the long run. The dog seems fine, but once the eye has been removed, it is remarkable how the dog comes to life again. It plays again and doesn't mind being touched on the head once more. Before, it had the most chronic migraine. Glaucoma, if it is inherited, will affect both eyes.
* see the Animal Health trust new laser option
Sadly, there are many other problems in our breed too, which breed hasn't got some.
But it is up to us to try and breed happy healthy dogs, first and foremost if we do not want to be investigated by the press and then we could be dictated to as to what we can or cannot do.
The show world is changing fast, it is up to us to ensure that we don’t lose what we have always enjoyed.
As to other inherited problems, such as hips etc, lack of positive information has led some breeders to ignore or downplay the importance of these defects. Some are allegedly waiting for the specific mode of inheritance to be determined before they select seriously against these defects.
Unfortunately, we may never be able to determine the precise genetic base, although this does not mean that we shouldn't try.
On the positive side , we do know 2 important things about these traits, namely they are INHERITED and that their incidence CAN be reduced by selective breeding.
The American Cocker is a most loveable, biddable little chap, please do not ruin the breed or let the dictators do it for us.
As your Breed Health Co-ordinator i am hoping to conduct a breed health survey later in the year and would welcome any information of health concerns you would like investigating. I hope i will have the support of all three clubs and any of you who are Assured Breeders will be included as the Kennel Club have said that as members of this scheme you are obliged to take part
I would like to conduct a breed health survey later in the year and also get a supply of cheek swabs to help the AHT with the research into eye problems in the breedDouble click to insert body text here ...