Type A-PRA Test -- Updated Dec. 31, 2012
For: Miniature Schnauzer
In 2000 the mutation that causes Type A PRA in the Miniature Schnauzer was identified through research conducted at the Baker Institute, Cornell University (unpublished data). Although the mutation was shown to be fully penetrant and completely predictive of disease, its frequency in the Miniature Schnauzer population was not known. In the intervening years that OptiGen has provided DNA testing for Type A PRA, we have determined that this mutation is rare in the Miniature Schnauzer and is not currently the major cause of PRA in the breed. Only a few hundred Miniature Schnauzers have been tested for the Type A mutation over the years but, as of 2013, no Carriers or Affected dogs with this mutation have been identified in the general population of Miniature Schnauzers. The original lines of Miniature Schnauzers that carried Type A PRA may have successfully eradicated the mutation or it may still be present at a low frequency in the breed. All recent cases of PRA in Miniature Schnauzer that OptiGen has received through OptiGen’s PRA Research program have been tested for Type A PRA and found to be Normal/Clear of that mutation.
Phosducin is NOT the gene responsible for Type A PRA
A misconception that the Phosducin (PDC) gene is associated with Type A PRA has caused at least one laboratory to incorrectly identify a benign DNA sequence change (termed a “polymorphism”) in the Phosducin gene as the Type A PRA mutation. Although this polymorphism was originally suspected as a cause of Photoreceptor Dysplasia (PD) in the Miniature, further research revealed that the polymorphism appears to be benign and has no association with retinal disease--including PD and PRA (unpublished data). It is important to keep in mind that in their 1998 publication (Zhang, Q., Acland, G., Parshall, C.J., Haskell, J., Ray, K. and Aguirre, G. Characterization of canine photoreceptor phosducin cDNA and identification of a sequence variant in dogs with photoreceptor dysplasia. Gene 215:231-239, 1998) the Baker Institute scientists were very cautious in their interpretation of the findings. They indicated that "since some affected dogs are heterozygous for the mutant allele, and some are homozygous for the wild-type allele, this putative PDC missense mutation, if it is indeed a disease causing mutation, it does not account entirely for the genetics of inherited retinal degeneration in the miniature schnauzer breed." That caution was subsequently validated by additional research that completely excluded the Phosducin gene and led to identification of gene and mutation causing Type A PRA. As the test for Type A PRA using the Phosducin polymorphism is NOT appropriate, OptiGen, LLC encourages breeders of Miniature Schnauzers to not use the results in breeding decisions.
OptiGen’s Research PRA in the Miniature Schnauzer Research:
OptiGen is actively supporting a genetic research project aimed at identifying the other mutation(s) that cause PRA in the Miniature Schnauzer. Owners of any/all Miniature Schnauzers that have been diagnosed with PRA by a veterinary ophthalmologist are encouraged to contact OptiGen to learn more about this project and how to submit samples for the study. The samples will be tested for Type A PRA and also, possibly, for other
PRA-causing mutations that are compatible with the clinical signs. The
results of these tests will be reported to the owner. Pedigrees and clinical history of the dogs are required for this research. OptiGen maintains a strict confidentiality policy and no information on samples that have been submitted is released without written permission of the owner. For more information on the research, or to inquire about submitting samples for this study, please contact firstname.lastname@example.org.