Eye Committee Report
Collie Eye Anomaly in Border Collies: Year 2000
Border Collies see the world somewhat differently from humans. Not only does the position of their eyes give them much greater peripheral vision, but a higher proportion of rods over cones than in humans makes their vision palette like that of a red/green color-blind person. A reflective area in their retina enables dogs to see in much lower light levels than humans. At a distance their eyes are suited to seeing moving objects much better than stationary ones. Useful traits in herding dogs.
However, things can go wrong. Environmental damage and genetic mutations are always dangers. The major heritable eye disease in Border Collies came from a common ancestor in which the mutation occurred many years ago, first appearing as a problem in the show collie.
This disease, Collie Eye Anomaly (CEA), is caused by a single recessive gene, so that a puppy which receives one copy of the bad gene from its mother and another bad copy from its father will have symptoms of the disease from birth. If it receives one bad copy and one good copy, it will not exhibit symptoms but will be a carrier of the disease. If a carrier is mated to a dog with two good copies, every puppy will have a 50% chance of inheriting one bad copy from the carrier parent, but it can receive only a good copy from the mate. Therefore, no puppy from this breeding will be CEA-affected.
How bad is this disease? It is not fatal, and only a small percentage will have detached retinas and be blind. The rest may have some loss of vision, but can still function quite well. Why, then, are we concerned about this genetic disease? The breed could survive as a working sheep dog at the current frequency of affected births; but, without a cooperative containment effort on the part of breeders and owners, the carrier and affected rate will creep upwards and upwards until there are no more genetically clear dogs at all. What happens then is that the genes which express the severity of the disease come into play. There will be more and more retinal failures resulting in blindness. At some point, the central breeding emphasis will shift from good working ability to good eyes.
Detection is important. The American Border Collie Association, Inc., has offered or subsidized eye examination clinics at sheepdog trials since 1996. It is also the principal donor to a CEA genetic research project of Dr. Gregory Acland at the James A. Baker Institute for Animal Health, Cornell University. Required eye examinations of all dogs entered in the National Finals has also raised awareness of the disease. To register dogs with the ABCA, a member must attest that neither parent nor the dog(s) being registered is known to be affected with CEA.
You can see the weaknesses in this program. While most dogs participating in North American sheep dog trials are examined for CEA and for other eye problems, there are many breeding dogs which are never taken to a Diplomate of the Association of Canine Ophthalmologists (DACVO). It is in everyone's interest to expand the eye examination coverage to all breeding pairs.
Until the DNA test is developed, there will be some inadvertent carrier-to-carrier breeding that produces affected puppies. However, if buyers and breeders learn to include ophthalmic examinations by a DACVO as a part of routine health care, those CEA-affected puppies will be identified and not given a chance to breed. The ones with mild symptoms can still see well enough to participate in all activities and be useful farm, ranch or companion dogs, but progeny are not eligible for registration.
Because some of the breed's most notable herding dogs carried one copy of the CEA gene, the disease began to crop up when these notable dogs appeared in both the dam's and sire's lineage. As a result, some of the best herding dogs are carriers and the ABCA has recommendations for:
owners of known carriers, i.e., those dogs which are the parent of a CEA-affected puppy. ABCA recommends that anyone who inquires about the dog's progeny or as a mate be told that it is a carrier. It also recommends that people who have any of this dog's progeny be informed that all its offspring have a 50% chance of also being a carrier even if the other parent is neither a carrier nor affected.
breeders of a litter in which one parent is a known carrier. The ABCA recommends that all puppies in the litter be given an ophthalmic examination by a DACVO before they are 12 weeks old, if possible. If this cannot be done, it is recommended that the puppy buyers be informed that they must determine from an ophthalmic examination that the dog is not affected with CEA before it is considered for breeding, as the progeny of affected dogs are not eligible for registration.
We are hopeful that Dr. Acland will develop a DNA test in the next few years which can identify dogs that are genetically clear of the disease. That is, the test will identify with 100% accuracy dogs that have no bad copies and so do not have the disease nor do they carry a recessive copy of the CEA gene. A puppy with even one parent that is a genetically clear dog will not have the disease. If the other parent is a carrier, each puppy has a 50/50 chance of being a carrier, but it will not have the disease.
Autosomal recessive diseases like CEA show up because people have line bred to top herding dogs which happen to carry one bad copy of that gene, eventually doubling up on it and causing affected progeny as well as some excellent herding dogs. It is not a disgrace. It is something to be bred away from by using knowledge that the current and future tests provide. Remember, every dog carries mutations which range from very good to very bad. By working cautiously but conscientiously, we can rid the breed of Collie Eye Anomaly without increasing the chances of some other potentially dangerous mutation gaining strength.
Submitted by the ABCA Eye/Hip Committee: Sally Lacy - chair, Denise Wall, Ph.D., Mellissa DeMille Ph.D., Amy Coapman MS