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Italian Greyhound PRA-1      IG-PRA1 Test    Code 210

For breeds: Italian Greyhound

As a result of years of genomic research conducted by Drs. Goldstein, Acland, Aguirre, and their team at Cornell University's Baker Institute College of Veterinary Medicine, OptiGen is pleased to offer a diagnostic DNA test for Progressive Retinal Atrophy (PRA) in the Italian Greyhound. OptiGen's IG-PRA1 test is highly predictive of development of PRA in the breed and its use will help Italian Greyhound breeders avoid producing pups that will grow up to develop this form of PRA.

PRA in the Italian Greyhound   

IG-PRA1 is considered a "late-onset" PRA, meaning that the first symptoms of retinal degeneration are not observed until the dog has reached maturity. Typically, IG-PRA1 affected dogs are first diagnosed by a veterinary ophthalmologist during a routine eye exam when dogs are between 3-5 years of age. The symptoms of IG-PRA1 are very similar to other (unrelated) forms of late onset PRA such as prcd and crd3. Loss of retinal cells leads to increased reflectivity from the mirrored tapetal cells in the back of the eye and retinal vessels are pruned as the number of retinal cells needing to be nourished diminishes. The disease itself is painless but affected dogs should be regularly monitored by an ophthalmologist to treat possible secondary effects of PRA (the most widespread form of PRA across dog breeds) IG-PRA1 first presents as a loss of vision in dim light conditions due to degeneration of rod cells in the retina. This stage is followed by decreased vision in bright light conditions due to the death of cone cells in the retina. Complete blindness is the end result.

Inheritance of IG-PRA1 and other form(s) of PRA in the breed

IG-PRA1 has been presumed to be inherited as an Autosomal Recessive (AR) trait, meaning that two copies of the mutation must be present in order for disease to occur. Data gathered during the Cornell study indicate that the IG-PRA1 risk allele identified by Goldstein et al., is completely concordant with the disease when two copies of the allele are present. All Italian Greyhounds that were homozygous for the IG-PRA1 risk allele were diagnosed with PRA and two copies of the risk allele were never observed in any Italian Greyhounds with normal eye exams (at the risk age or older).

It must be noted however that a subset of PRA-affected Italian Greyhounds in the study carried only one copy of the IG-PRA1 risk allele, suggesting that the disease may represent a mode of inheritance called "Autosomal Dominant with Incomplete Penetrance" (ADIP). The majority of dogs in the research that carried only one copy of the risk allele did not develop PRA.

One of the PRA-affected dogs in the study did not carry any copy of the IG-PRA1 risk allele - indicating that at least one other form of PRA is present in the breed. This could explain why some dogs that carry only one copy of the IG-PRA1 risk allele are diagnosed with PRA-they may be carrying two forms of the disease. The Italian greyhound is a relatively rare breed with a high degree of relatedness within the population so it would not be terribly surprising to find some individuals carrying more than one form of PRA.

Risk of Developing PRA based on OptiGen IG-PRA1 test results:

IG-PRA1 Risk Allele Test Result

Risk of Developing PRA

 

 
Normal/Clear/Low Risk


 

NORMAL dogs are at VERY LOW RISK of being affected with PRA associated with IG-PRA1 risk allele. At least one other form of PRA that is not associated with the IG-PRA1 risk allele is present in the Italian Greyhound. OptiGen stresses that DNA tests are a valuable tool but do not replace the importance of regular eye exams by a board certified veterinary ophthalmologist.

 

 


Carrier/Moderate Risk

CARRIERS may be at increased risk of developing PRA associated with IG-PRA1 risk allele. It is not known at this time whether the PRA observed in a minority of Carriers of the IG-PRA1 risk allele is due to another, as yet uncharacterized, form of PRA or whether IG-PRA1 is inherited as a dominant trait with incomplete penetrance. It is especially important for Carriers to receive regular eye exams by a board certified ophthalmologist. Sharing eye exam results with OptiGen will help support ongoing research on PRA in the Italian Greyhound.

 

 


Affected/High Risk

AFFECTED dogs carry two copies of the IG-PRA1 risk allele and thus have the genetic make-up that indicates they are at HIGH RISK to develop PRA due to the IG-PRA1 risk allele. These dogs are very likely to develop PRA associated with the IG-PRA1 risk allele by the time they reach 5-7 years of age. It is especially important for dogs that carry two copies of the IG-PRA1 risk allele receive regular eye exams by a board certified ophthalmologist. Sharing eye exam results with OptiGen will help support ongoing research on PRA in the Italian Greyhound.

Use of the DNA test for IG-PRA1 and Breeding Recommendations

Advice on how to make best use of the DNA test for IG-PRA1 needs to account for the possibility that the disease may be inherited in an ADIP manner and that the presence of a single copy of the risk allele may cause PRA in some Italian Greyhounds. One recommendation is clear, regardless of the mode of inheritance: Two dogs carrying at least one copy of the IG-PRA1 risk allele should not be bred together.

Another clear recommendation is that Italian Greyhounds that have been diagnosed clinically with PRA should not be bred, regardless of how many copies (0,1 or 2) of the IG-PRA1 risk allele they carry because it is possible that their PRA is due to another, as yet uncharacterized, form of PRA.

Whether to breed Carriers of the IG-PRA1 risk allele is a difficult question to answer. Dramatic, complete and immediate removal of carriers from a closed/highly related population such as Italian Greyhound's would definitely not be recommended if we were certain of an Autosomal Recessive mode of inheritance. Indeed, the ability to breed Carriers of an AR-inherited disease (to a genetically normal mate) is one of the great advantages of DNA testing. If IG-PRA1 is inherited in the ADIP manner then producing Carriers of the IG-PRA1 risk allele would not be advised. As more Italian Greyhounds from the general population are tested for the IG-PRA1 risk allele, we will be able to obtain a better assessment of the relative risk of Carriers of the IG-PRA1 risk allele developing PRA and better clarify the mode of inheritance of IG-PRA1.

Continuing Research

In an effort to further our understanding of PRA in the Italian Greyhound, OptiGen encourages owners who submit samples for IG-PRA1 testing to include any eye exam information with their order forms. OptiGen provides Free DNA testing to pedigreed dogs that have been diagnosed with PRA by a board certified veterinary ophthalmologist. Contact genetest@optigen.com for further details.

Prevalence of IG-PRA1 in the breed

The American College of Veterinary Ophthalmology's reference, "Ocular Disorders Presumed to be Inherited in Purebred Dogs", Sixth edition 2013 indicates that ~3% of the Italian Greyhounds examined between 2010-2012 were diagnosed with PRA by board certified veterinary ophthalmologists. Based on the sample set collected for research by Goldstein et al., it is expected that the majority of these cases would be homozygous for the IG-PRA1 risk allele. If so, it would be estimated that >20% of the Italian Greyhound population is likely to carry the risk allele. OptiGen is able to provide updates on the actual frequency of the risk allele in the population as more widespread testing of the breed occurs.

References: Manuscript by Goldstein et al. in preparation.

 

 


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