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DNA Test For Type A Miniature Schnauzer PRA

Report of the Eye Committee

Margaret Pratt, Chairman

 

True to his word that the Baker Institute would continue working on Miniature Schnauzer PRA, Dr. Aguirre surprised us with an email on September 8, 2000, advising that

 

1.     they have found a gene mutation that causes one form of PRA in Miniature Schnauzers that they are calling “Type A Miniature Schnauzer PRA”, and

2.     they have developed a DNA test for Type A PRA.

 

John Hoffman and I then had conference calls on September 29, 2000, with Dr. Aguirre and with Dr. Jeannette Felix, in order to obtain further details.  Dr. Felix heads OptiGen, a genetics testing laboratory that offers testing licensed from Cornell.  OptiGen will do the testing.

 

Type A Miniature Schnauzer PRA

 

Dr. Aguirre believes that the disease previously called Photoreceptor Dysplasia (“pd”) probably represents at least 2 different gene defects that are currently under study.  Because of this uncertainty, the Baker Institute is no longer using the term pd for the form of PRA that it has identified at the molecular level.

The Type A gene is responsible for only 1 of the 2 – or possibly more – forms of PRA that occur in Miniature Schnauzers.  Type A is not one of the genes the researchers examined during the AMSC/AKC-funded research.  (They have still not succeeded in cloning the “novel” gene found during the research we funded.)

The researchers are now finalizing their work for publication, and Cornell University is submitting a patent application for the Type A gene and test on behalf of the Foundation Fighting Blindness, the entity that has been funding Dr. Zhang’s work since the end of 1998.  The Baker Institute is not releasing detailed information regarding the Type A gene and mutation until those tasks have been completed.

 

Clinical Expression of Type A PRA


While a big step forward, the identification of the Type A gene mutation leaves many questions unanswered.  We do know the following:

 

1.     Some affected Schnauzers do not test positive for Type A PRA.

2.     The researchers do not yet know of any differences in clinical expression between Type A PRA and the other type(s).  Thus, animals who are affected may have either Type A or some other type.  The only way to tell is by testing.

3.     The Type A mutation has a partially dominant expression.  That is, some “carrier” animals show retinal degeneration when examined clinically and/or by ERG.  This is a likely explanation for the clinically symptomatic animals that were produced in the cross-breedings to Poodles and Elkhounds.  The symptomatic animals were likely partially expressed Type A PRA rather than a product of some interaction between Miniature Schnauzer PRA and the forms found in Elkhounds and Poodles.

4.     The researchers do not yet know whether Type A is the most common form of PRA in Miniature Schnauzers or whether it is a less frequent form than others.  This makes establishment of a registry – discussed below – of particular importance.

 

Testing


OptiGen advises that the test for Type A Miniature Schnauzer is now available to breeders.  Click here for details on submitting samples for testing.

 

We urged Dr. Aguirre and OptiGen to keep the cost of testing as low as possible in order to maximize testing, pointing out that there has been some resistance to testing for Myotonia Congenita at $75.  The pricing is considerably better than the $400 Cornell initially charged for the Irish Setter PRA tests, but not as low as the University of Pennsylvania charges for the tests it performs:

 

1.               Regular Price:  $160 US per test.

2.               Reduced Price for two or more puppies in a litter tested at the same time while still puppies:  $128 US per test.

3.               Reduced Price for samples drawn at Specialty Shows and sent in as a group:  $128 US per test

4.               Special Limited Time Offer for tests of animals whose blood samples are accompanied by (a) a certificate of an ACVO certifying that the animal has PRA, and (b) a pedigree:  $80.  To get this price, the owner must consent to the blood sample being used for further research if the sample tests negative (i.e., clear) for Type A PRA.

 

There is also a 5% discount for owners who fill out the Submission Form on-line, and print out a copy to accompany the samples, since doing so saves OptiGen the expense of typing the information manually from the hard copy Submission Form.

 

OptiGen will try to accomplish a 2-week turnaround time on submitted samples, but cautions that the turnaround time could slip depending on sample volumes.


Samples Submitted During the Research Phase

Cornell will provide, without charge, the results of testing the samples that were sent by Miniature Schnauzer owners to the Baker Institute for use in the research, either through the AMSC's organized effort or independently, if the samples were tested as part of the research.  (Not all of the samples were tested.)

 

Cornell has provided the AMSC with a form by which the results of testing the research phase samples may be requested.  The form is available only through the AMSC.  Cornell will not furnish the form directly.  Click here to download the form in Acrobat (pdf) format.  If for some reason, you cannot download the form, you can request a copy from me (MWPratt@aol.com) or Vera Potiker (Vera Potiker).  The Baker Institute asks that breeders NOT call the Institute asking for information.  It does not have the personnel to field the calls.  OptiGen does not have information regarding the research phase samples.  The Eye Committee is doing its utmost to communicate the pertinent information promptly to all who were kind enough to submit samples, including AMSC members and non-members alike.

 

Although there is no requirement that they do so, the Eye Committee asks owners of the dogs whose samples were furnished for the research to share the results with the Eye Committee.  The Eye Committee will not release any information about specific animals, but the information may help us to tie down which of the lines in which PRA is known to exist seem to be more likely to carry Type A and which are more likely to carry some other type.

Registry


For reasons of client/doctor confidentiality, the Baker Institute cannot provide the AMSC with the test results of these or other dogs directly, without specific permission from each individual owner.  The Baker Institute has told us that it is critical that owners register their test results with the AMSC as that will be the only way that we will be able to ascertain in which lines Type A PRA is prevalent and in which it is not.

 

The AMSC Board  has authorized the Eye Committee to set up a registry of animals tested clear of Type A PRA, as has been done with Congenital Cataracts and as the Board has approved for Myotonia Congenita.  It is anticipated that the registry will contain the following information:

 

  1. Name of Dog
  2. Registration Number
  3. Sex
  4. Date of birth
  5. Name of Owner
  6. Type A PRA DNA Test Certificate Number
  7. CERF Number

 

Dr. Aguirre advises us that it is necessary to require that the animals listed in the registry have current CERF numbers because otherwise the AMSC could find itself having listed animals who test clear for Type A PRA but who are clinically affected with some other type of PRA.

Because PRA is complex and involves more than one disease, the Eye Committee also asks owners who receive test results indicating that the dog in question is an affected or “carrier” to provide those results to the Committee in the hope that such information may allow the Committee to help the researchers learn in which lines Type A PRA may be concentrated.  However, no results indicating affected or “carrier” status will be included in the registry or otherwise publicly disclosed.  The information will be gathered strictly to help the Committee assist the researchers.

 

The information requested is a little more extensive than has been requested in connection with Congenital Cataracts and Myotonia Congenita.  That is a result of the greater complexity inherent in Type A PRA, and specifically that it is only one type of PRA among two or more types that cannot yet be distinguished by clinical symptoms.

 

Breeding Recommendations:

Optigen and the Baker Institute have made the following breeding recommendations.  These breeding recommendations are more complex and stringent than for other disorders because (1) PRA in Miniature Schnauzers consists of at least 2 different genetic defects, and (2) Miniature Schnauzer Type A PRA mutation can cause disease in some “carriers.”

 

  1. OptiGen recommends breeding only animals that have tested clear for Type A PRA.  Neither affecteds nor “carriers” should be used in breeding programs.  All dogs testing affected are or will be affected.  Some dogs testing as “carriers” could be or become affected, although some “carriers” will not have disease symptoms.  Depending on whether a tested dog is a “carrier” or affected, it will transmit the mutant gene to some or all of its progeny.
  2. If a dog (Dog A) tests clear for Type A PRA, yet has a parent or grandparent (Dog B) that has had a clinical diagnosis of PRA (type unknown), OptiGen strongly recommends that the affected ancestor (Dog B) be tested for Type A PRA.  If Dog B tests clear for Type A PRA or is not available for testing, one should proceed as if Dog A has some type of PRA and Dog A should not be bred.

 

Updated:  November 24, 2000

 

Update, November 6, 2001: 

Through 9/30/01 OptiGen had tested 28 Miniature Schnauzers for Type A PRA and all were normal.