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PRA Pedigrees

PRA and the Glen

Progressive Retinal Atrophy

CONE ROD DYSTROPHY (crd3) MUTATION TEST IN THE GLEN OF IMAAL TERRIER

EYE TESTING SESSIONS IN 2010

BOCHUM PRA RESEARCH PROJECT

FUND RAISING FOR THE BOCHUM PROJECT

FURTHER TO THE ANNOUNCEMENT BY OPTIGEN THAT A DNA TEST IS AVAILABLE TO BREEDERS
TO DETERMINE WHETHER GLENS ARE NORMAL, CARRIER OR AFFECTED FOR CRD3 (CONE ROD DYSTROPHY)
PLEASE REFER TO THE LINK ABOVE FOR "Expected results for breeding strategies using the OptiGen crd3 test"

NB Some breeds of dog have more than one type of inherited eye disease
and so it is important that we continue to have our Glens eye tested regularly throughout their lives



PRA (Progressive Retinal Atrophy) is the topic of much heated discussion and debate within the Glen community. The views expressed on this page do not necessarily reflect the views, or practice, of all Glen of Imaal Terrier breeders.

The page is divided into two sections. Please click on the links below:


INTRODUCTION


This section states some of the known facts about PRA and the Glen. It goes on to discuss breeding considerations.


TABLE


This is a "reference" section to check out basic breeding outcomes for PRA.


To return to the other PRA pages, please click on the Progressive Retinal Atrophy or the PRA and the Glen links.

Written: February 2004
Revised: April 2004
Updated: June 2010
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INTRODUCTION


What do we know about PRA and the Glen?

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PRA in Glens is believed to be late onset i.e. it is unlikely to be diagnosed in puppies.

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PRA in Glens is believed to have an autosomal recessive mode of inheritance i.e. the PRA gene has to be inherited from both parents for the dog to be affected.

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To date, we are aware of Glens testing "affected" as young as 2yrs & 2mths and as old as 7yrs & 10mths. The older Glen had previous "clear" eye test results.

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Eye-testing can identify affected Glens. However, a "clear" test result cannot differentiate the normal Glen from the carrier Glen or even the Glen who goes on to test affected at a later date.

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If a Glen tests affected, then both its parents must be carriers (at least).

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If a Glen produces an affected, it must, therefore, be a carrier (at least).


Why should we eye-test our Glens?

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The principle reason for eye testing should be to provide information for breeders, so that they can make "informed and considered" breeding selections. It is important that all Glens, whether they are pet, show or working Glens, are tested, not just breeding stock.


What is "informed and considered" breeding selection?

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I feel that an "informed and considered" breeding selection is one where there is no, or minimal, risk of producing an affected Glen, given the information available (at time of breeding) regarding the PRA status of siblings (brothers and sisters) and parents, as well as grandparents and great grandparents, and all their siblings and progeny (offspring).

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Breeders are certainly using the eye test results to identify affected Glens and exclude them from any future breeding programme, but are we doing anything to actively impact on the number of affected Glens being produced?

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CARRIER x CARRIER and CARRIER x AFFECTED both have the potential to produce AFFECTED Glens - see TABLES.

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"Dr. Gustavo Aguirre, the head of PRA research at the Baker Institute of Cornell University Veterinary School, and other genetic experts advise against using any affected dog, any known carrier, or any dog with a 25% or greater probability of being a carrier in any breeding program. This is done in order to limit the spread of the defective gene, and to reduce the chance of inadvertently breeding a carrier to another carrier. Offspring of an affected parent are always carriers or affected depending on the other parent. Offspring of a known carrier have a 50% probability of being carriers if the other parent is genetically normal. Grandchildren of a known carrier have a 25% probability of being carriers. (These probabilities apply only over large numbers, and will not necessarily apply to a specific litter.)"

 

Ref: www.bmd.org/health/pra.html#gene (1998)

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Some would argue that breeding selection, applying the criteria described by Aguirre (see above), will lead to the demise of the breed, given our relatively small gene pool and breed population. On the other hand, if the only method of breeding selection that we employ is the avoidance of affected animals, the inadvertant use of "not-yet-known" affected animals and carriers within the breed population, all of whom will test "clear", will almost certainly ensure that we continue to produce many more Glens who will eventually go blind.


Untested Glens

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Eye testing has been in place for long enough now, that we should be able to use Glens that have tested parents and grandparents (at least) in their pedigree.

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It is simply not acceptable for Glens with untested parents to be used in a breeding programme.


At what age should a Glen first be bred from?

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We all agree that the Glen is a "late-maturing" breed, so why not wait until three to four years before first breeding?

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If it is a breeder's policy to breed at age two, then the breeding Glen's parents could be just four years old and the grandparents only six years old. Knowing that it is possible for a Glen to test "clear" before testing affected at nearly eight years old, this means that we could have three, possibly even four, generations of Glens with unknown PRA status. We know from bitter experience that Glens we had assumed to be normal (at time of breeding) turn out to be carriers, and Glens that we had assumed had carrier status (at time of breeding) turn out to be affected. Should we be breeding Glens as young as two years of age?

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On the other hand, if it is a breeder's policy to wait until age four for first breeding, then the breeding Glen's parents could be as old as eight years of age. If the parents test "clear" over the age of eight, then we can probably safely assume that there is no risk of them (the parents) being affected.

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In the absence of a DNA test, we need to be making breeding decisions that will be beneficial, not detrimental, to the future of the Glen of Imaal Terrier.

Since it would appear that the Glen community cannot come to any international agreement on guidelines for breeding selection, it rests on each and every breeder to ensure that they are fully aware of all the information available regarding the PRA status of dogs in any proposed pedigree, and that they can, with a clear conscience, say that their breeding selections are being made with the best interests of the breed at heart.

The International PRA Database co-ordinators (see PRA and the Glen page) will provide the following information to anyone wishing to research the PRA status of Glens:

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List of tested Glens

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List of known carrier status Glens

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List of affected Glens

The Glen of Eden database - www.glenofeden.nl/index.php?id=16 - is an extensive pedigree database providing the Glen researcher with multi-generation pedigrees, PRA and heartcheck results, and an advanced search facility. Access is for registered users only. Please click here to register online.

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TABLE

Parents

 

Progeny (Offspring)

 

Each puppy has a ...

PP x PP

Normal x Normal

x

=

 

100% chance of being normal

PP x Pp

Normal x Carrier

x

=

 

50% chance of being normal
50% chance of being a carrier

PP x pp

Normal x Affected

x

=

 

100% chance of being a carrier

Pp x Pp

Carrier x Carrier

x

=

 

25% chance of being normal
50% chance of being a carrier
25% chance of being affected

Pp x pp

Carrier x Affected

x

=

 

50% chance of being a carrier
50% chance of being affected

pp x pp

Affected x Affected

x

=

 

100% chance of being affected

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