Australian Cattle Dogs
Specializing in AKC Registered Austrailian Cattle Dogs since 1989!
Dr Acland's Interview on PRA and Notes from the TN Eye Clinic
Many people have a vague understanding of PRA. Most know it is a heritable
eye disease that causes progressive degeneration of the retina and usually
results in eventual blindness. Following a recent eye clinic, I asked Dr
Acland if he would mind answering some common questions regarding PRA as it
affects Australian Cattle Dogs. He was glad to oblige. Here are his responses
in his own words.
Pam: Why are we now differentiating prcd from the disease that was formerly
called PRA in ACDs? Please give us a brief description of prcd and its
effects on ACDs.
Dr Acland: PRA is a general term for a group of diseases that are clinically
similar. There are many different genetic causes for PRA, one of which is the
gene we term prcd. Much of what people want to know is on the web at 2 sites.
You are free to copy material from these sites, as I wrote it and
hold the copyright. Although the information is a bit old, it is correct
We have shown recently, at least in some ACDs, that their PRA is caused by
the prcd gene. We have shown this in 2 ways: 1) by using the prcd marker test
in several pedigrees, and 2) by crossbreeding 2 different PRA affected ACDs
to prcd affected dogs, and getting prcd affected pups.
The prcd form of PRA in ACDs is much the same as in other breeds. Dogs become
clinically affected usually between 3 and 5 years old, though occassionally
at a younger age (2.5 years in at least 1 dog that I have seen) and in a
large minority of dogs at much later ages. We do not know the latest age at
which an ACD can first show signs of prcd, and this is true in other breeds
as well. I currently do not accept that an ACD is unaffected unless it passes
a CERF exam at at least 8 years, although most dogs that are 6 or over and
have a normal fundus will remain nonaffected.
It has become very clear however that not all ACDs diagnosed as affected or
suspicious with PRA are affected with prcd, and many of these are not
affected with PRA.
Pam: What age is typical to see onset of prcd? Without a blood test, in
order to be considered "clear" (could still be a carrier) how old does a dog
have to be? In other words, at what age could we stop doing slit lamp tests
and be sure that the dog would not later develop prcd? Can an ERG detect PRA
earlier? Will a clear ERG test mean a dog will stay clear all its life?
Dr Acland: ERGs work well in some forms of PRA, if done carefully. In the
prcd form of PRA an ERG can detect retinal dysfunction in some dogs prior to
the development of clinical disease. This is generally true, for example, in
the fast form of prcd seen in poodles. It is less true of the slow form of
prcd seen in some other breeds (e.g. English Cocker Spaniels) and has not
been determined at all in ACDs. In the ACD I would regard an ERG as a very
valuable research tool, but as a totally unproven clinical diagnostic tool
and would not advise owners or breeders to waste their money on it.
Pam: Can dogs that develop prcd at an old age, say 9 or 10 years, only
produce children that get the disease late too? Or can these dogs produce
offspring that have an earlier onset, say 3 or 4?
Dr Acland: I don't know. This is an important question, and one of the main
reasons I am interested in ACD PRA as an academically interesting problem.
Pam: How common is prcd in cattle dogs? What percentage of the breed are
carriers? Affected? Do you have an idea of how many clear, non-carriers that
the breed may have?
Dr Acland: I don't have hard numbers. I would guess that about half the ACDs
diagnosed as affected or suspicious are affected with prcd, and that there
are probably twice as many unrecognized cases as there are known cases. This
suggests that there are a few % (1-4% ?) of affected dogs. This in turn means
that the carrier rate is probably in the 25% range.
Pam: Do we have an accurate blood test to determine if a dog is affected, a
carrier, or clear non-carrier? How accurate is it? Will it be available
through local vet offices or just through veterinary ophthalmologists and
universities once it is on the market? Do you know what the cost will be? How
early will we be able to test dogs to know their status and will we be able
to stop doing slit lamp exams?
Dr Acland: Our research laboratory has developed a marker test for prcd. This
was patented by Cornell University and licensed to Optigen, LLC. When we are
convinced that an accurate version of this test can be used in ACDs, I expect
that Optigen will make it available. The current test which is available for
Portuguese water dogs and other breeds is not yet effective in ACDs. When
Optigen releases a test for prcd in ACDs it will be available through their
When the test is available, it can be done as young as the dog can spare a
small blood sample.
Because PRA is not the only eye disease in ACDs, and prcd may not be the only
form of true PRA in ACDs, one should still have eye exams on potential or
actual breeding stock at regular intervals.
Pam: Some dogs have been diagnosed (by slit lamp) with PRA (prcd) then
examined by some one else and found not to have it. How does this happen and
what are some of the other non-heritable and hereditary conditions that can
affect ACDs that may be incorrectly diagnosed as PRA? How can breeders guard
against inaccurate diagnosis?
Dr Acland: A significant percentage of ACDs diagnosed as PRA-affected, and
paricularly when diagnosed as PRA suspicious, do not have PRA. Most of these
dogs have an acquired form of retinal disease that I term Focal or Multifocal
Acquired Retinopathy. This disease affects several breeds including most
herding dogs, coursing borzois, and racing sled dogs. It has been described
on the web at http://www.sheepdog.com/genetics/eyes.html.
This disease is sometimes described as "Distemper scars", or "Worm Scars" or
"Inflammatory Retinopathy" on eye exam forms, but is regularly misdiagnosed
as PRA. It characteristically affects one eye (usually the
left) worse than the other, and is much more common in male dogs than females.
Never accept a single diagnosis from any one, especially as a basis for
making a critical decision re showing, breeding, or neutering a dog. Always
get a second opinion.
Pam: Do cattle dogs just have prcd or is there another type of PRA in the
breed? Is there another condition that mimics PRA, but isn't? How can we tell
the difference and does this disease have a name and what do we know about it?
Dr Acland: This is the critical question that I am currently trying to figure
out. What we have to do is 1) get a prcd test that works really well for ACDs
that are truly affected with prcd, and doesn't give false positives; 2) then
work out which of the dogs that appear to be affected clinically are not
affected by the test; and 3) see if all of these are just acquired disease,
or do some clearly have another genetic form of PRA.
Pam: Often when speaking in terms of non-carrier, carrier, and affected,
researchers label them A, B, and C, respectively. Once we have the blood test
and enough dogs have been tested to give breeders an indication of how many
fall in which categories, how do we know which dogs to breed? This said, we
know we must keep other breed attributes intact in the pursuit of clear eyes.
Is there a point where it would be necessary to breed C's to A's? What about
B to B? Are there a percentage of dogs in the breed
population in each category that tell us when we need to resort to breeding
affecteds? How do we go about this to keep the other breed characteristics
and keep the gene pool diverse enough, yet still try to eradicate prcd?
Dr Acland: The current marker test for prcd classifies dogs into 3 groups:
pattern A, pattern B, and pattern C. You can read a lot about how this works
at the Optigen website
In brief, Pattern A dogs are
proven non carriers for prcd; Pattern B dogs cannot be affected with prcd but
can be carriers; and Pattern C dogs are at risk of being affected, although
some of these are only carriers, and a few may actually be normal
Pattern A dogs can be bred to any other dog and will not produce affecteds.
This means that even Pattern B and C dogs can be bred to Pattern A dogs, and
do not have to be discarded from the breeding population.
You are going to find that a great number of the best dogs in the population
will test Pattern B or Pattern C. It is vital that breeders do not
indiscriminately eliminate these dogs from breeding. Doing so would
have drastic effects on the diversity in the gene pool, and will create many
more problems than would be solved.
Thank you for your time!
Pam Gipson Beaty
A brief background on Dr Greg Acland…
Greg Acland, a veterinarian in his native Australia, came to the United
States in 1976 to take up residency at the University of Pennsylvania and
complete the requirements to become a veterinary ophthamologist. There he met
Dr Reuben and also Gus Aguirre whose research specialty was PRA. In 1978, Dr
Acland completed his residency, but opted to stay on and continue researching
PRA with Dr Aguirre. In 1992, the primary laboratory was moved to Cornell
although a lab is still operated at Penn.
SOME NOTES FROM THE EYE CLINIC HELD IN TENNESSEE FEB 2001:
At our clinic some dogs who had previously been misdiagnosed as being
suspicious for or having PRA were actually clear. Some of these dogs had the
focal lesions that Dr Acland pointed out in his interview. One had very
heavy pigment which made parts of the retina appear duller as they would in a
PRA affected dog.
It is important to have dogs examined yearly or as often as possible. For
instance, if a dog does show up with acquired focal lesions, it is good to
know at what age they occurred. If these lesions become too numerous, they
can eventually lead to the retina dying off and the condition becomes
indistinguishable from PRA if the lesions are in both eyes. There is no other
species of animal that is affected by these lesions. In clinical studies, and
Dr Acland concurs, these lesions do not appear to be heritable.
Another reason for yearly exams is if a dog does develop PRA, it is helpful
to know at what age it was affected. It is not as helpful to examine a dog at
2 and then not again until it is 6 or 7 only to find it has PRA. Worse is to
check the dog only until it is a few years old and stop! Since this breed
often does not become affected until 5 or 6, eye exams after that age are
imperative. As mentioned, even if we do get an accurate prcd test shortly, it
will not rule out other eye problems, so periodic exams are still a good
idea. Often dogs with PRA are only checked once they begin showing clinical
signs such as bumping into things in low light. It can take a long time for
PRA to progress and a clinical exam might have pointed out the problem much
earlier. In breeding stock, it is of utmost importance to know what condition
exists and when it developed so breeders can decide how to handle that
knowledge in their breeding programs.
True PRA must affect both eyes! It should affect both eyes at a similar rate.
A dog that is suspicious in one eye but not in the other, may well not have
PRA. If a dog truly has PRA a steady progression should be noted when the dog
is rechecked in 6-12 months. A dog that continues to be labeled suspicious
over a period of years probably does not have PRA. It can be DNA blood tested
for the prcd gene to find out.
Dr Acland has personally diagnosed cattle dogs as young as 2 ˝ years and as
old at 10, although in the older dog, he felt the PRA had progressed
extensively and it was likely that the dog had been affected around age 8. So
it is important to keep checking the old dogs, even if they have other eye
anomalies. You can still rule out PRA. Cataracts may or may not be present
with PRA and PRA may or may not be present in dogs with cataracts! The 2 can
be mutually exclusive. Some dogs with PRA never go completely blind
especially if they don't have cataracts to complicate matters.
Given the above situations, it is VERY important to know the abilities of
your ophthamologist. If he/she does not know ACD eyes well, your dog could
get misdiagnosed. Unfortunately some of the dogs at the clinic had already
been altered because of their "PRA" diagnosis. Always get a second opinion!
More importantly, have someone examine your dog's eyes who knows the breed. I
would even go as far as to encourage breeders to use the same ophthamologist
every year for every dog so one person can track their dogs year by year and
note any changes and watch their development. I would also strongly urge
breeders to get together and plan yearly eye clinics, hopefully with Dr
Acland, if his schedule permits.
Pam Gipson Beaty