The Dirty Dozen Plus a Few: Frequency of Hereditary Diseases in Australian Shepherds
Originally published in the 2000 Australian Shepherd Annual

by C.A. Sharp

Although Australian Shepherd is a generally healthy breed, it is no stranger to genetic disease. The incidence of these diseases has been increasing over the past 20 years. Dr. George Padgett's recent book, Control of Canine Genetic Diseases, lists over 40 different diseases for Aussies gleaned from the veterinary literature. This isn't as bad as it sounds on the face of it as several of the items noted are very rare. However, those forty-odd listings should serve as a caution. It takes only one popular sire to turn today's rarity into tomorrow's genetic nightmare.

In order to make informed breeding decisions, breeders must know which conditions have the greatest impact on health and which disease genes have the highest frequency in the population. Clinically affected dogs are only the tip of the genetic disease iceberg. Some diseases, like cataracts and epilepsy, can be late-onset; a dog's status may not be known until it is several years old. Others, like autoimmune disease, are genetically pre-disposed so not all who have the genes will become sick. Depending on the mode of inheritance there will be some percentage of carriers, normal dogs who will never exhibit disease but who can produce affected offspring.

Exact percentages of carrier/affected individuals for any given disease or defect can be difficult if not impossible to determine due to any or a combination of the following:
1. Complex or unknown modes of inheritance.
2. No carrier-screening tests.
3. No official reporting agency or disease registry.
4. Skewed statistics due to insufficient data or non-reporting of affected individuals.
5. Owners who don’t tell breeders and breeders who cover-up or deny.

Conditions have been classified below as frequent, common, occasional, or rare. "Frequent" in this instance does not mean most Aussies are going to have one of these diseases, but that they are the diseases most likely to be encountered. Cataracts, for example, are easily the most common hereditary problem in the breed, but only about 4% of the Aussies in the Canine Eye Research Foundation's (CERF) data for 1998 and 1999 were affected.

Classifications used here are the author's best educated guess, based on nearly two decades of collecting information on hereditary disease in Aussies. Specific diseases have been ranked and classified based on her knowledge and experience, as well as data gathered in the recent breed health surveys conducted by Dr. Leos Kral of West Georgia State University and by the Australian Shepherd Club of America. In addition, data from CERF, the Veterinary Medical Data Base and the breed longevity study conducted by Dr. John Armstrong of the University of Ottawa were reviewed and considered in estimating relative frequency of occurrence.

Frequent Problems
Hip dysplasia and eye diseases have long been recognized as frequently encountered problems in Australian Shepherds. HD and our two most common eye defects (cataract and iris coloboma) deserve that classification, as do a few other diseases and defects.

(1) Cataracts are easily the most common of the breed's several eye diseases. Not all cataracts are hereditary, so it is important to have the dog examined by a qualified veterinary ophthalmologist to determine the cause. Any cataracts which form on he posterior cortical or sub-cortical area of the lens should be regarded as highly suspicious. If a dog has bilateral (both eyes) cataracts in this area and they advance over time, even slowly, they should be considered hereditary. Some other types may also be hereditary, but they are not as frequently seen. Most affected Aussies first show signs around 2-3 years of age, however inherited cataracts can start as early as one year or as late as 7 or 8. It is important to get annual screening exams from a qualified veterinary ophthalmologist so cataracts can be detected as early as possible. Results should be registered with CERF.

(2) Dental Faults, including bad bites and missing teeth, are second only to cataracts in frequency. Fortunately, their health impact on most individuals is insignificant, but they do represent serious conformation and structural faults and should not be disregarded. Once rare, missing teeth are now very frequent some lines, largely because they have often been dismissed as "unimportant." Bad bites - overshot, undershot or anterior cross-bite (wry) - are encountered by most long-term breeders at some point. The inheritance of all these faults is probably polygenic, rendering them difficult to breed out and likely to become worse if attitudes remain indifferent. As they require no special screening to detect, breeders should take close note of every dog’s dental status and that of its relatives before using it for breeding.

(3) Autoimmune Diseases This class of diseases has come out of nowhere for Aussies over the past decade. They ares considered as a class because individuals suffering from one may develop others and it is not unusual to have different autoimmune diseases occur in a single family. The ones most frequently encountered in Aussies are thyroiditis, lupus (discoid and erythmatosus) and generalized demodetic mange. There is a genetic pre-disposition toward these diseases, but actual illness is precipitated by an environmental trigger.

(4) Hip Dysplasia was first recognized in Aussies in the early 1970's. In spite of the fact that many breeders have been screening for generations, it remains a regularly encountered problem due to its complex inheritance (polygenic with environmental influence). The most serious cases are crippling and painful. Since both screening and disease registries are available, all Aussies intended for breeding should be screened and the results should be submitted to a registry whether they pass or fail. In lines where it occurs often, screening of non-breeding animals will give the breeder a better picture of which breeding animals carry a heavier load of HD genes.

(5) Epilepsy is perhaps the most frightening disease that an Aussie breeder or owner may encounter. Once rare, reports of affected dogs are becoming more and more frequent. At present there is no screening test for this disease, which usually manifests around 1.5 to 3 years of age but can occur earlier or later. The youngest confirmed case of primary (hereditary or idiopathic) epilepsy to come to the author's attention was 8 months old. Since seizures can occur for a variety of reasons, it is vital that any seizing dog be thoroughly examined and tested by a veterinarian. Primary epilepsy will cause multiple seizures which will continue for the course of the dog's life. Untreated, they may become more frequent and/or severe. Some affected dogs can maintained on medication, at least for a while. Others will die. The increasing frequency of this disease is exacerbated by people who refuse to accept that it is inherited or who are deceitful about its presence.

(6) Iris Coloboma is the second most frequently encountered eye defect. Affected dogs are born missing a portion of the iris. The condition may be unilateral and almost always occurs in merles. It was once fairly rare but has become common due to the use of affected individuals for breeding and an attitude among some breeders that it is unimportant. In most cases, impact on vision is insignificant though large colobomas can cause discomfort in bright light. Iris coloboma should be detected on the dog's first eye exam but may be missed in dilated eyes if the coloboma is small.

(7) Allergies A significant number of Aussie owners complain of their dogs having allergies. To some degree, this may be attributable to the considerable attention allergies receive in the popular media, encouraging owner-diagnosis (and sometimes treatment) of problems which may not be allergies. However, there are sufficient numbers of dogs diagnosed with allergies in the Veterinary Medical Data Base that it is apparent breeders need to pay more attention to this particular health problem. Allergies are probably genetically pre-disposed, but environmental factors play a major role in their development.

(8) Cancer, though not always hereditary in origin, was the most frequently identified non-accidental cause of death noted in Armstrong’s breed longevity study. The data on dogs from decades past indicated that most cancer deaths occurred in elderly dogs. However, the historical trend has been toward cancer death at younger age. The author is not aware of any specific type being more prominent than others. A breed cancer survey would be well-advised.

Common Problems
Though not encountered as often as the "frequent" problems, the following still occur with uncomfortable regularity.

(9) Persistent Pupiliary Membrane will sometimes be noted when young puppies are examined. At this point it may not be significant; many PPMs are reabsorbed. For the purposes of this article, the author disregarded CERF statistics for PPM in dogs under 6 months of age. If PPM persists into adulthood it should be considered a hereditary defect. PPMs are often benign, however they can obscure vision or cause blinding opacities of the lens or cornea.

(10) Distichaisis, the presence of abnormal eyelashes growing toward the eye, is yet another disease that is increasing in frequency due to breeder disregard. Given that it can cause constant discomfort or pain to the affected dog and left untreated may result in severe corneal scarring, it does have a significant impact on health. Mode of inheritance is unknown.

(11) Retained Testicles The author was surprised to discover in the recent ASCA breed health survey, that a significant number of people indicated they were owners or breeders of males with retained testicles (chryptorchid/monorchid). Retained testicles cannot produce viable sperm and have a significantly increased risk of developing testicular cancer. This condition is polygenic and while it is sex-limited, the genes may be carried by males or females.

(12) Collie Eye Anomaly has become less frequent in occurrence over the past decade, probably due to the effort of breeders with affected lines to eliminate it once it's simple recessive mode of inheritance was known. CEA can be detected in a puppy’s first eye exam but may be missed if the dog is 8 weeks old or more, due to the "go normal" phenomenon. It should be noted that so-called "go normals" are not unaffected, but can no longer be diagnosed by visual exam. CERF statistics indicate that about 1% of Aussies are affected with CEA. This implies that as many as 18% may be carriers.

The above frequently and commonly encountered problems comprise the Australian Shepherd's "Dirty Dozen", but there are a variety of less often encountered problems of which breeders should be aware. The diseases listed as occasional or rare problems, while not frequent but should still be treated seriously. Effort should be made to prevent their increase.

Occasional Problems

Patent Ductus Arteriosus is a potentially lethal heart defect. The first sign noted is usually a heart murmur, however not all murmurs are PDA. As the most frequently reported of the less common problems, PDA deserves careful attention from breeders. If a puppy exhibits a murmur that persists beyond four months of age, more thorough exam should be done to determine the cause. Some dogs with PDA will be cured by surgery and a few live relatively normal lives with no treatment at all. The condition is probably polygenic.

Osteochondritis Desicans occurs when a bit of cartilage within a joint tears or breaks loose, causing pain. In dogs it most frequently occurs in the shoulder or elbow joints. When in the elbow, it is considered a form of elbow dysplasia. Fast growth, heavy bone or large size may be pre-disposing factors. Rottweilers and Bernese Mountain Dogs, for instance, frequently suffer from OCD. Affected Aussies are usually on the larger, heavier-boned end of the breed spectrum. However the author is aware of Aussies with OCD which were neither large nor heavy-boned. Mode of inheritance is unknown.

Corneal Dystrophy A review of the 1998-1999 CERF statistics showed, to the author's surprise, that this condition was reported in roughly one dog out of 200. It has the potential to seriously impact vision. Mode of inheritance is not known. It can be independently inherited or occur secondary to thyroid disease disease, which is not rare in the breed. The author speculates that at least some of the cases in Aussies may actually be due to thyroiditis and would recommend that affected dogs be tested for thyroid function.

Patellar Luxation is often thought to be a disease of toy dogs, but larger breeds, including the Aussie, are also affected. It may affect one or both rear legs. The mode of inheritance is not known.

Rare Problems
While infrequent in occurrence, the following are here because there have been multiple reported cases of each of them.

Porto-Systemic Shunt is a liver defect causing severe-to-fatal health problems. Mode of inheritance is unknown.

Pelger-Huet Anomaly is a killer of unborn and newborn puppies. An incomplete dominant, any puppy inheriting two copies of the gene will not survive. Dogs with just one copy are almost always healthy. Carriers can be screened with a blood smear and should not be bred to each other. Offspring of carriers should be screened to determine their status. Where a non-carrier of the same cross is of similar quality, it should receive breeding preference over its carrier sibling.

von Willebrand's Disease is a bleeding disorder similar to hemophilia. Mode of inheritance in Aussies is not known. VWD can be secondary to thryroid disease. Any dog which tests positive for vWD should also be tested for thyroid function.

Elbow Dysplasia has been receiving more attention from Aussie breeders over the past few years. If a dog exhibits continuing or intermittent front-end lameness with no obvious cause, it should be screened for elbow dysplasia. Any dog closely related to a dog with elbow dysplasia should also be screened. Mode of inheritance is polygenic.

Rage Sundrome is a neurological disorder. The affected dog will suddenly attack anyone or anything in its vicinity, without warning or any behavioral cue. The episodes are felt to be a form of seizure. Due to the extreme danger such dogs pose, and lack of any effective treatment, euthanasia is only sensible option. Mode of inheritance is unknown.

Hemophilia types A and B occasionally show up in Aussies. Both types are X-linked, so the gene is almost always inherited from the dam. Affected males can pass it on if they are bred. Unaffected males do not carry the gene.

Muscular Dystrophy is another X-linked disorder that has been noted in Aussies and will be passed in the same manner as hemophilia.

Strategies
Every breeder who remains active for an extended period of time will encounter hereditary disease. When this happens, the worst thing one can do is ignore it or cover it up. Simple honesty would go a long way to reducing frequency of most hereditary diseases, but being open often exposes the forthright individual to attack and intimidation from those who feel their breeding programs will be damaged by the information. The dark side of human nature is far more difficult to cure than any hereditary disease. An ethical breeder must bear the slings and arrows, taking whatever steps are necessary to limit further genetic damage to his kennel and the breed as a whole.

When a hereditary disease is diagnosed, the affected dog should be removed from the breeding pool. Aussies are a very populous breed. Many unaffected animals are available, so there is no need to breed a dog known to have an inherited disease.

If a disease is life-threatening or has serious life-long health impact, and is also rare, stringent steps should be taken to eliminate all possible carriers to prevent its spread. A "scorched earth" policy with diseases which occur more often can have a deleterious effect by removing too many dogs from the population at once. For the more frequent conditions, first-step relatives of an affected (parents, offspring and siblings) should be removed from breeding and extreme care used when making mate selections for other relatives.

If impact on health is moderate or minor and it is possible to identify carriers, known carriers should never be bred together. Preference should be given to non-carriers. If there is no way to determine carrier status for certain, individuals which have produced multiple affected offspring - especially with multiple and/or unrelated mates - should be assumed to be carriers and removed from further breeding.

Conclusion
Hereditary disease is a growing problem for the Australian Shepherd, but it does not need to remain so. If breeders make conscientious efforts to reduce disease incidence through using available screening tests and disease registries, removing affected animals from the breeding population and, most importantly, being open and honest with each other, there is no reason why our breed cannot continue in good health for decades to come.