Marquis Cattle Dogs

 The Opti-Gen "prcd" PRA Test

The OptiGen prcd-PRA Test

The OptiGen prcd-PRA test is a DNA-based test that helps you avoid one form of Progressive Retinal Atrophy (PRA). PRA refers to a group of diseases that cause the retina of the eye to degenerate slowly over time. The result is declining vision and eventual blindness. “prcd” stands for “progressive rod-cone degeneration” which is the type of PRA known in several breeds.

Both in ASTCDs and ACDs, the predominant form of PRA is prcd-PRA. However, there are known cases either of acquired (non-inherited) retinal degeneration or a non-prcd type of PRA. (Acquired retinal disease appears to be frequent in working dogs and could lead to mis-diagnosis of prcd-PRA on a clinical basis.) These conditions are not detectable with OptiGen’s test for prcd-PRA. In such cases, a PRA-affected dog could get a test result of Normal/Clear or Carrier. Such a dog would not have prcd-PRA disease, but would have some other type of retinal disease. Owners must understand and accept this limitation in order to use the OptiGen test wisely.

What is the usual age at diagnosis?
ACDs have been diagnosed with prcd-PRA over a very wide age range – as young as 3 years and through 8 years or older. Although the typical age of diagnosis is 4 to 6 years, a dog cannot be considered free of prcd-PRA until at least 8 years of age with a clear eye exam. As more dogs are examined, it’s likely that even younger and older dogs will be discovered showing first signs of prcd-PRA.
 

How frequent is PRA in ACDs?
There isn’t a good estimate of frequency of PRA in ACDs yet, but the carrier frequency is expected to be quite high, possibly approaching 50%. More about this will be learned as testing goes on. Since there could be a high carrier rate, owners should choose to test key dogs in their lines first.

 

Are there any proven cases of false negative in this test?
Two dogs out of 250 research dogs did not show as “affected” using the prcd-PRA mutation test for ACDs, even though they appeared to have PRA upon exam by Dr. Acland. Upon further pedigree research, it is believed that these dogs do not have prcd-PRA. If this is accurate, they are not false negative for prcd. Rather, they are “positive” for another disorder and do not have prcd-PRA. They may have another, rare form of PRA or an acquired retinal degenerative disorder. OptiGen will follow-up on any ACDs that do not test as genetically affected but subsequently are diagnosed with PRA.

 

Are there any proven cases of false positives in this test similar to other breeds?
So far there is no known case of a false positive in ACDs. There is no experience so far that a Carrier dog might actually be Normal/Clear, nor that an Affected dog might actually be a Carrier or even Normal/Clear. This situation is very different than for the initial prcd-PRA test in other breeds where the rate of false positives was substantial.