This test is a linkage test that is not 100% accurate as compared to a direct test. Both Dr. Agruirre at Cornell and Dr. George Brewer at Michigan State are conducting research to identify the gene or gene mutation responsible for prcd (progressive rod cone degeneration) itself. We will look forward to a direct test that identifies the prcd gene.
To better understand the differences between linkage tests and direct tests you can refer to OptiGen and VetGen web sites.
In the meantime, I am submitting a series of four articles that I wrote beginning in 1991 which should be of interest to the newer Lab breeders that may not know much of the background of what transpired regarding the subject of PRA in our breed. I hope you find it interesting and informative leading to the present day progress in that field.
The first of the four articles is reprinted from an article that appeared in The Labrador Review December/January issue 1991 and the others follow in sequence.
Ironically, though, this current concern is not new to our breed. Back in the early 1970’s there was a group of dedicated Lab breeders on the East Coast that were actively pursuing the problem and they worked diligently to surface the problems then. There were many articles written in publications at that time which are available for the asking.
What our greatest concern now is Generalized Progressive Retinal Atrophy. It is inherited in a recessive fashion such as the yellow coat color in Labs is recessive to black. The whole of the area of the retina at the back of the eye is affected and the condition gradually becomes more severe, usually starting at three to five years of age and eventually causing blindness. Detailed descriptions of the yea disease (and Hereditary Cataracts, Central Progressive Retinal Atrophy and Retinal Dysplasia) are available in current publications...”seek and you shall find.”
What many breeders are concerned with is how the mode of inheritance will affect offspring of a Lab that has produced GPRA. For example, if a stud dog has produced GPRA as a recessive but still carries the dominant normal gene. He will only produce the syndrome when bred to a female carrying the recessive trait or a female that is affected that carries two recessive genes for the lesion.
The main concern is how to eliminate GPRA when it has normally been established that the signs of same are relatively late and a Lab could have produced it before it was detected by the breeder. GPRA can be detected by an ophthalmologist examination at approximately two to five years or age and older for testing. Our long-range hope is genetic fingerprinting (DNA) which can be used to detect animals carrying the PRA gene, but funds of extensive research are sorely needed for same. This is a problem that needs to be addressed by the Lab community ... sources for funds.
In the meantime, it would behoove all of us who are dedicated to the breed to study any/and all information available on the subject of hereditary eye diseases and have regular and widespread eye testing on an annual basis with all of our stock at all ages. If an eye exam by a board certified ophthalmologist detects any suspicious lesion an ERG test would be in order.
There is a small group in the Washington state area that has been working on a computer program that will be recording pedigrees of all documented GPRA affected Labs. This gathering of information is only being compiled with permission of owners who have consulted with the owners of the sire and dam. Please do not confuse this with a witch hunt ... far from it. This information will be released only so that we can be aware of what lines have produced affected Labs. It is also being made available to inform the Lab community that this problem has surfaced in all of our breeding lines so we can no longer point a finger at a single line, or Lab, and hide our heads in the sand.
Having just returned from an extended visit in England, you will be interested o know that this is a current concern world-wide. While in the UK I was fortunate enough to be able to spend quality time with Lab breeders from Sweden, Finland, Norway and Germany in round-table discussions all of the above information came to the surface. Once again, this is not a new problem to our breed ... the Scandinavian countries publish all inherited problems in Labs and have these lists available upon request. Many US Lab breeders have been in possession of this information for many years via Sweden.
My only regret on the subject o GPRA is that we did not take notice back in the early 1970’s when this same problem loomed and worked together to combat it then, instead of 20 years later. Incidentally, there were articles at that time, reprinted by courtesy of the LRC, Inc., “The Field” and “The Retriever Field Trial News.” The LRC of Southern California even had a program on the subject because of the increase of number of Labs showing this anomaly in the 1970’s.
Another interesting fact that may be of interest to some Lab breeders is that dogs that were examined under the BVA/KC scheme and were certified free of PRA in England were published in the Kennel Gazette at that time. Unfortunately, though, the examinations were concluded at four years of age. The belief today is that eye examinations should be done annually until the end of the Lab’s life.
We, like the UK (and other countries) are not going to ignore the current concern. There are seminars being planned by noted ophthalmologists throughout both countries. There are many articles available currently and various Lab clubs are pursuing this subject here in the US and the UK. Currently, the LRC of Central Connecticut will present Dr. Gustavo Aguirre, Professor of Ophthalmology, University of Pennsylvania. The seminar will be on March 28th at the Holiday Inn, Cherry Hill, New Jersey. Make reservation check payable ($30.00)) to LRCCC PRA Research Fund and mail to Mrs. Enid P. Bloome, 5 Wake Robin Road, Norwalk, CT 06851. It is my personal hope that this seminar will be videotaped and same will be offered for sale to all Lab area clubs throughout the US. Contact Enid at 1-203-846-0455 for information.
Also in the planning stage are more than several Lab breeders that have intentions of doing test breedings. This subject is a little more complex than meets the eye, thus another article will be written on this subject in the near future. There is not total agreement even among the board ophthalmologist on this subject at the present time, but you will be pleased to know that some Lab breeders that have GPRA affected Labs are more than willing to work in all different avenues to facilitate test breedings. In fact, I have found that most breeders with affected Labs (and known carriers) are truly open, willing to work in any way with other breeders and are deeply concerned with what solutions may arise as a result of the test breedings.
These same people, world-wide, are taking a stand to help the breed in any way possible .. an unselfish approach that will separate “the men from the boys” in our breed facing this current scare.
This same article mentioned test breeding pending and the purpose of same is to identify carriers when bred to know affected. It has been my observation that this is not an easy task. It appears as though any test breeding should stay within specific type of PRA characteristics for the breed. It is thought that two groups fall within the board classification of PRA - (1) Rod-Cone Dysplasia (abnormal development of the retina and (2) Progressive Rod-Cone Degeneration (rods and cones developed normally and the degenerated). It is currently presumed that Labs fall into the latter category.
Given the assumption that PRA is a simple recessive until proven otherwise, then test mating within our own breed characteristic, let’s assume that a Lab suspect to be a carrier is bred to a known affected PRA Lab mate ... a minimum of six puppies gives a 97 percent chance of confidence that normal puppies mean that said mate is not a PRA carrier. As the number of pups in the litter increases in size, so does the percentage ... nine to ten puppies would be considered ideal.
These puppies could be tested between two to six years (depending on the ophthalmologist) with an ophlhalmoscope or at one and one half years with an electroretinograph (ERG) properly controlled. Histology can be done at approximately eight to ten months of age with special laboratory conditions and special laboratory personnel (both at a premium). There is need for a research laboratory set up just for this alone ... that need is overwhelming. Histology is an irreversible option, of course.
In test breeding a suspect PRA carrier to a known carrier, a litter of eleven to twelve puppies are needed with the above criteria used for testing. All of the above is only feasible if the Lab you are using have the same PRA characteristic, that you are testing for the same disease and that is what you will be looking for in the progeny.
Many breeders are having difficulty with the recessive gene inheritance pattern and I feel it is best shown in the chart included in the article that was part of the literature handed out at the March 28th seminar presented by Dr. Agruirre. Remember, the percentages change with the number of puppies in the litter.
It would be lovely if we had a system such as the Swedish Kennel Club - PRA affected Labs and producers have registrations withdrawn and within two generations they have a handle on PRA. But this ideology does not exist in our country, thus we have to depend on the above mentioned methods until biochemical screening methods are available to identify carriers of PRA; and, subsequently, we can remove them from our breeding programs. We must have patience as there are absolutely no guarantees and we cannot hurry for the right answer to the problem of PRA. We must strive for corrective methods and we must give thought to how we will give financial support to help research laboratories across the country. Remember, this research on the molecular biology of the canine gnome (total genetic information present in a call) will create a linkage map; and, hopefully, markers can be established for gene responsibility for all genetic hereditary disorders byway of a blood sample.
We must also remember, although PRA appears to be paramount in the breed today, we have other genetic problems that cannot be forgotten or overshadowed. We must strive to accomplish all this without losing breed type or temperament. WHAT A TASK!
This meeting will take place in Germany on June 15, 1991 following the World Dog Show in Dortmund. This meeting is a “private initiative, not supported by professional organizers or breed club so far.” The main purposes of the meting shall be (1) To exchange information and views on the subject of PRA and OCD in the Labrador Retriever (2) To feed back that information tot he breed clubs of the participating countries for their further consideration (in the case of the US - 26 area clubs and our parent club) (#) The meeting must not become a witch hunt. Of course we will speak about facts concerning stud dogs, brood bitches and their progeny - but nothing else except facts! There might possibly be two knowledgeable speakers at the meeting.
I am one of the lucky ones that was invited to attend this meeting and will be attending at m own expense. I have been working gathering pertinent materials on PRA and OCD to take to the meeting with me. When all of our contributions (from throughout the world) are composed, they will be mailed back to the participating counties following a meeting and will be shared by all.
During the month of May I will be spending a day days at CERF and will, hopefully, be able to enrich this meeting with whatever materials CERF believes would be of interest to the countries in other part of the world. I also hope to have information from the University of Michigan on current research on OCD. OFA has been asked to help me fill out a questionnaire which is required of each person attending this meeting (written in English with copies for each person in attendance). Needless to say, this same questionnaire will be completed by CERF.
Also included in the materials I will be taking with me will be full information on the Wind-Morgan Program Diagnosis of Heritable Join Disease in the Labrador Retriever, articles on many other genetic problems that exist in our breed today, articles dating from the 1960’s-1991 in regard to eye diseases, a transcript of Dr. Aguirre’s recent seminar and much more. Many people have been very helpful in sending me so much of this material and it is quite an uplift to be getting support from other breeders that care about the problems in Labs from the past until the present time.
It is my hope that this magazine will be n your hands well before the date of June 15th so that if you have any suggestions for anything that might add to the strength of this meeting, I would be more than happy to hear from you and will work with you on anything that might be penitent.
The idea of sharing any and all problems that we might have in the breed could be the ultimate goal for further meetings such as this. The feedback from all the breed clubs of the participating countries will be of the utmost important to us all and will be shared by all.
Prior to this final official summary, I would like to share with you my personal thoughts, observations and reactions to the conference as a whole.
Rest assured that pertinent information photocopied from the US and material available for review at the conference location was ample. Our VMDB/CERF printouts were of interest mostly to the speakers who were more familiar with the data. Many articles regarding eye diseases and osteochondritis dissecans were available for review for anyone interested (including transcript of Dr. Arguirre’s most recent seminar on PRA and a five year OCD printout on Labs from VMDB).
In regard to the US questionnaire submitted, CERF filled out all information regarding eyes and OFA did the same for OCD. Only other required comments were filled in by myself. Copies of the questionnaires from participating countries will be sent to all 26 area clubs and parent club. Anyone interested in individual copies, please contact me directly.
There is a notation to be made in regard to the Swedish Kennel Club control scheme for hereditary eye diseases that I would like to clarify at this time. “Parent must have eyes examined if offspring is to be registered and offspring to dogs with PRA, and offspring to dogs that have produced PRA will not be registered.” Also, “dogs born in 1989 and later must have ID tattooed if eye certificates are to be registered.”
The agenda identifying the speakers is available on request. There will be substitutes noted - one for illness and other an itinerary conflict with the Federation Cynologique International meeting that was taking place in Dortmund, Germany at the same time as this conference.
The meeting that took place leads this report into a very optimistic one, in that one of the many aspects of this meeting may result in an international grading scheme for OCD. As soon as any news resulting from the FCI meeting in this regard is made available, I will see that it will be circulated to all area clubs and the parent club.
In that we all have access to any data from VMDB/CERF, we can all be aware of the US statistics (this is assuming you are all privy to my correspondence and that from CERF earlier in June). If not, please contact me for same.
The questionnaires show us how the US percentages of incidences of PRA and OCD compare to other countries represented at this conference. We have also been exposed to advice from leading authorities in both fields (especially here in the US) and must follow the breeding practices they advise. We also need to address the problem of raising funds to be channeled for research in DNA fingerprinting so that we can identify carriers to make the process quicker.
Now the fun part of this initial report - the meeting was held in a simply wonderful country inn with exquisite facilities. Dr. Kraft did a great job with all preparations. All the participants were warm, congenial and well informed. If any dissension existed, they certainly did not surface. There was little talk about affected or known carriers of PRA at the meeting. Of course, reference was made to percentiles that would be affected by same during presentations by the speakers. The effect of the meeting was soothing and I hope the official summation will reflect the same mood that I perceived.
For continued sharing of information on genetic problems (also including hip dysplasia, epilepsy, and other eye diseases - retinal dysplasia, enrtropion and hereditary cataracts) and other issues in the breed, I must have area and parent club (and certainly individual) reactions to this concept if we are to continue sharing thoughts and information international for the betterment of the breed.
It is important to find out what interest US Lab breeders have in working together toward a common goal; that is, pulling together to try to combat genetic problems in our breed without losing our type, temperament and trainability that make Labs one of the most popular breeds internationally. I feel we have a commitment to make to our breed and I am only hoping for your enthusiastic support of same.
Even though some of our top producers have produced some genetic faults, we must become more vigilant on how to combat these problems through knowledge and sharing of information so as not to lose outstanding quality and characteristics that they have added to many of our breeding program.
"Click on the Yellow Lab to return home"
