The story about English Cocker Spaniels and the ERG ...
Thanks to OptiGene for kind permission to re-print this letter.
"The stated age for diagnosis of PRA in the ECS keeps changing. Why?"
RESPONSE - Even though this disease is caused by a mutation in the same gene
that causes PRA in Labradors, Portuguese water dogs and Chesapeake Bay
retrievers, the disease in ECS appears to be unique in its slow progression.
In the other breeds, the disease has a very specific window for the age of
diagnosis, both by clinical exam and by ERG. That is NOT the case in ECS.
Early in the research on the breed, it was felt that the disease could be
diagnosed clinically between 4-6 years, and by ERG by eighteen months.
Unfortunately, THAT was wrong!! The ages were revised to 4-8 yrs by clinical
examination, and by 2.5-3 years of age by ERG. THAT was wrong once again. To
summarize many years of clinical experience, research and FRUSTRATION, this
is the hardest breed in which to clear a dog by clinical examination.
Dr. Aguirre says, "Over the past several years I have seen too many dogs who
I have examined yearly, and found them normal until 10-11 years of age when
I thought the ophthalmoscopic changes appeared suspicious for PRA. On
subsequent examinations, the disease progressed to develop PRA at 11-12
years. In parallel, I have done VERY detailed ERG studies on ECS and have
cleared them at 4-5 years of age. This type of ERG is extremely time
consuming and detailed, and not done except for research purposes. Again, I
have found that a few of the dogs I cleared by ERG at ages greater than 4
did develop the prcd form of PRA. As you can imagine, this age is far beyond
the age when we normally would clear other breeds by ERG in our lab. When
you consider that the ERG procedures done in many different areas are never
so detailed and, in fact, are not of diagnostic quality in many cases, it is
not surprising that I am concerned about clearing a dog of PRA after a given
To summarize, there are ECSs with the prcd form of PRA whose disease was
diagnosed as early as 3 years of age in some cases, and 11-12 years in
others. These dogs had the Pattern C genotype with the OptiGen test. The
recommendations from OptiGen (see below) are accurate to the best of current
knowledge and experience. Obviously, in science we keep an open mind to
facts, and change recommendations based on these findings.
OptiGen recommendations regarding ECS:
In English Cocker Spaniels, the prcd form of PRA can occur very late in life
in some dogs. Similarly, ERG testing in this breed has several limitations,
and early diagnosis (before 4-5 years of age) is difficult. A normal ERG
cannot be used to rule out the disease in English Cocker Spaniels younger
than 8 years of age. In some cases, an affected dog could have an ERG that
appears normal later than 8 years of age.
CONCLUSION - The current test for the prcd form of PRA in ECS does have some
limitations, as have been described from the start. Perhaps this test isn't
useful to all owners and breeders of ECS. To use the test results, one must
study and take into consideration the above information and the information
on the prcd-PRA page under "Tests" or the information provided in the
OptiGen brochure on PRA testing. If you need a copy, please email or call