Dr. Bell

Dr. Bell's statement to the Scottish Terrier owners and breeders:

I have been studying cerebellar abiotrophy (ataxia) in the Scottish Terrier, supported by the STCA HTF, for
over five years. This is a slowly progressive degenerative condition that affects muscular coordination and movement. It does not affect the senses. Ataxia refers to the clinical symptom of incoordination, while abiotrophy refers to the premature death of Purkinje cells in the cerebellum region of the brain that causes
the incoordination.

The signs of incoordination in CA affected Scottish Terriers have been recognized by owners or breeders as early as 10 weeks of age, and as late as 4 years of age. Recognition of clinical signs has more to do with
the severity of the disorder than the actual onset of cerebellar degeneration. Many affected dogs remain
with mild incoordination their entire lives, and live out a normal life span. Other affected dogs progress to
the point where they can not walk without assistance (as older dogs) due to the disorder.

Since 1978, I have been working with Dr. Alexander de Lahunta of Cornell University on cerebellar degeneration in Gordon Setters, Old English Sheepdogs, and Scottish Terriers. Dr. de Lahunta is world recognized as the leading authority on veterinary neuroanatomical diagnosis, and cerebellar disorders.
All three breeds present with similar clinical signs and onset, and in all three we have proven an autosomal recessive mode of inheritance. Over the years, we have developed a diagnostic protocol to make a clinical diagnosis of cerebellar abiotrophy in these breeds. As the defect in these breeds is in a single (Purkinje)
cell type in the cerebellum, the clinical signs of the disorder on neurological examination are very specific.
Our diagnostic protocol can be performed with a review of the clinical history of the dog, and a diagnostic videotape that shows us the specific normal and abnormal movements necessary to make the clinical diagnosis.

With the history and clinical signs, we have high confidence that this diagnostic protocol rules out other neurological and musculoskeletal disease, including Scottie Cramp, infectious and inflammatory disease, disease due to toxins or injuries, and birth defects or injuries during birth. Through this protocol, we have been able to comfort most breeders and owners that their dog does not have CA, as well as being able to confirm a clinical diagnosis of CA. Several owners and breeders have gone through the clinical diagnosis protocol, where there are definitely clinical signs of cerebellar disease, but the video or history does not rule out all other causes, and we are not able to make a diagnosis. The diagnostic protocol is designed to be conservative; so that we know we are excluding dogs from this diagnosis that probably have CA. In these cases, we recommend further diagnostic testing, examination, or additional videotape of specific movements. For owners and breeders that question a clinical diagnosis, we also encourage and will assist with further diagnostic testing and confirmation.

Of the 43 Scottish Terriers on which a clinical diagnosis of cerebellar abiotrophy has been made, 11 have
gone on to further diagnostic testing of necropsy, or MRI diagnosis. All 11 have been confirmed with CA.
Six of the Scottish Terriers with necropsy or MRI findings of CA were originally clinically diagnosed by Dr.
de Lahunta and me. Of 24 Old English Sheepdogs that were clinically diagnosed with CA, 13 of 13 were eventually confirmed by pathology. Of 52 Gordon Setters that were clinically diagnosed with CCA, 25 of 25 were eventually confirmed by pathology.

Since I began working with Dr. de Lahunta, no dogs of which we agreed upon a clinical diagnosis of cerebellar abiotrophy have ever been documented by further testing to have a disorder other than CA. This is not to say that it is impossible for us to misdiagnose the disorder, or that a misdiagnosis will not occur. However disorders or conditions in the Scottish Terrier that could mimic the clinical course and presentation of CA, and fulfill the diagnostic protocol would be extremely rare.

As Dr. Olby's molecular genetic research project into CA is now underway, I am concentrating my efforts on getting blood samples submitted from all dogs and their families who have been diagnosed with CA. As you

Therefore, I have proposed an open CA database of affected Scottish Terriers. Dogs who have confirmation of CA (based on my and Dr. de Lahunta's determination) can be released by their owner or breeder and listed in the database. With such a database, we can institute a relative risk pedigree analysis program to assist breeders in making informed breeding decisions, and diminish the risk of producing more CA affected Scottish Terriers. This service has been available to the Gordon Setter and Old English Sheepdog breeds for many years, and they have been able to considerably diminish the frequency of affected dogs, even without a test for carriers.

Some people object to placing Scottish Terriers with clinical diagnoses of CA into an open CA database, and recommend only listing dogs with necropsy diagnoses. This would be unfair to breeders and the Scottish Terrier breed. Most clinically diagnosed CA affected dogs are family pets, and will live long lives. Proposing early euthanasia just to gain a pathological diagnosis is unthinkable. As Dr. Olby stated, the differentiation between pathologically confirmed cases and those with clinical diagnoses are required for her molecular genetic research. However, Dr. Olby, Dr. de Lahunta and I are very confident in the cases that have been clinically diagnosed. Keeping the breeders in limbo based on the extremely rare possibility of a misdiagnosis, versus providing a useful tool for them to manage the disorder does a disservice to the breed.

Openness on health issues does not mean that breeding programs will be ruined. The release of pedigrees would be as a complete set, so that the broad pedigree spread of the defective gene will be obvious, and no single breeder or dog would be singled out. An open health database and pedigree analysis service will allow breeders to knowledgeably continue their breeding programs, while diminishing the risk of producing CA affected dogs. There are objective ways to accomplish this with open health information. No breeding programs need to be abandoned in this process.

In instituting the relative risk pedigree analysis program, I will present all of the information that is necessary for any breeder to determine the risk of dogs being carriers of the defective gene causing CA, and the risk of proposed matings producing carrier or affected offspring. While I will provide this pedigree analysis service to owners for a fee, it is likely that many will be able to accurately determine CA risk themselves, by studying the released pedigrees from the open health database and the pedigrees of their dogs.

When comparing the CA risk between prospective matings, all breeders must keep in mind that the purpose of their breeding is to produce quality Scottish Terriers. Breeding decisions cannot be made on CA analysis alone. CA risk, along with other factors that involve the temperament, conformation, and health of the dogs all need to factor into your breeding decisions. Contrary to what has been posted on some e-mail lists, I will not be making breeding decisions for you based on CA analyses. You alone are responsible for your breeding decisions.

The gene causing cerebellar abiotrophy is old, apparently low frequency, and widespread in the Scottish Terrier gene pool. Nothing that we can do at this time will prevent all new CA affected dogs from being produced. However, an objective open CA database will allow breeders to breed more knowledgeably, and choose matings that diminish the risk of producing CA affected dogs. It is not fair to allow breeders to continue to breed blindly and continue to unwittingly produce more CA affected dogs when the knowledge is there to prevent them.

I continue to be available to the STCA, its members, and all Scottish Terrier owners and breeders while working on this project.

Sincerely,

Jerold S Bell, DVM
Clinical Associate Professor of Genetics
Department of Clinical Sciences
Tufts Cummings School of Veterinary Medicine