Epilepsy was recognized in ancient times and
was undoubtedly one of the "difficult" diseases
Hippocrates referred to. Epilepsy consistently ranks in the top 10 diseases of dogs. It is a visually
ugly disease that impairs the functioning of the dog and its relationship to its human family. There are
many researchers trying to open the door to progress by finding the first epilepsy gene.
Any animal may have a seizure if the "seizure threshold" is passed by too much excitation in the
brain. In addition to the external metabolic influences, there are internal factors in a neuron that
regulate how excitable that cell is. The makeup of all the internal machinery of the neuron and its
interactions with its neighbors is determined by the genetics of the animal. A mutation in certain genes
can cause these cells to be more excitable and thus more likely to slip over the threshold into
seizures. It is presumed that this is the basis of hereditary epilepsy, but until the genes are found that
are responsible, we won't know for sure. Even dogs with hereditary epilepsy only seizure
intermittently. Other influences that we don't understand regulate when that lower seizure threshold
will be crossed and an actual seizure occur.
There are different types of seizures and included
in what is called idiopathic epilepsy. Seizures
are broadly divided into two types; generalized and focal (or partial) seizures.
In a generalized seizure, the electrical storm appears to arise everywhere at once. This generalized type of seizure is also broken down to Grand Mal and Petit Mal Seizures the former being more severe.
In a partial seizure, the abnormal electrical activity arises
in a small area of the brain.
Simple focal seizures (also sometimes called minor motor or focal motor seizures) and Complex focal
seizures originate in the areas of the brain that control emotions and behavior (the temporal lobes)
and are sometimes called psychomotor seizures.
What else looks like seizures?
There are other conditions which can cause
episodes which might be confused with seizures.
Dogs with severe ear infections may develop inflammation of the inner ear (vestibular system) and
dizzy spells. Dogs with heart disease my have fainting spells. There is a sleep disorders which cause
episodes of collapse or excess movements during dreaming. A thorough history and physical
examination by your veterinarian should allow them to distinguish between these conditions and
There is also a disease which is more properly
classified as movement disorders which can look
very similar to epilepsy. The movement disorder in humans that fits into this gray zone is called
paroxysmal dyskinesia. Paroxysmal means that there are brief attacks of the symptoms with the dog
appearing perfectly normal between the episodes, the same way there are discrete attacks of seizures
in epilepsy. Dyskinesia refers to an abnormal, involuntary movement or posture (dys= bad and
kinesis = movement). Still others may be simply muscle spasms or fainting spell, but since the dog
cannot tell us what they feel, all we can do is look at the episode and the results of our tests, and try
to classify it as best we can.
Right now, we don't know exactly how epilepsy
is inherited in dogs. It may well be that there are
different modes of inheritance and different genes involved in various breeds and families. Preliminary
results from the Canine Epilepsy Project suggest that there are two or more genes involved in some
of these families. There are several genes associated with epilepsy in humans and mice, and these
genes are being investigated as possible candidates for the culprit in canine epilepsy.
What determines when my pet will have seizures?
No one knows what it is that determines when
an epileptic will have seizures. The only thing we
can predict about epilepsy is that it's unpredictable. Some pets appear to have seizures very
regularly, while in others, the seizures appear to be precipitated by specific events such as stress, or
changes in the weather. However, when we try to use what's happened in the past to predict when
the next seizure may occur, we usually aren't very successful. For many epileptics, there is no pattern
to their seizures.
Here are some of the scientists that are actively researching the
disease and attempting to
find genetic markers to isolate the genes responsible for epilepsy.
From the University of California Davis, Anita Oberbauer Ph D professor of animal science.
From the University of Minnesota, Ned Patterson, DVM research fellow
in the Department of Small
Animal Clinic Sciences and James R Mickelson Ph D associate professor of veterinary pathobiology.
There is also a website, Canine Epilepsy Network at http://www.canine-epilepsy.net
represents 67 breeds in its DNA collection. This site offers basic information about canine epilepsy.
Its information is gathered from Studies done at the University of Missouri-Columbia.
Of these researchers the following information has resulted:
· There were suggestions that a single gene had a significant effect on the incidence of seizures although several genes are involved in producing the disease.
· One very promising set of markers were found on one chromosome
and another at a different marker that showed a tendency toward being associated
with causing seizures.
· Once research continues there is high hopes that a definite gene will be isolated in a very specific region in the dogs genes. This work in the long run, will identify a gene that is intimately involved in seizures and such a gene will regulate brain activity in all dog breeds and give a starting point to look for changes in other breeds affiliated with seizure disorders.
· Epilepsy appears to be a recessive trait but not enough information
has been collected to determine whether more than one gene is involved.
· There is strong evidence that the incidence of the disease occurs more frequently in males but has yet to be conclusive and may give clues down the road.
Although the incidence of seizures in our Rat Terrier breed is ranking as the #1 disease we can all have high hopes that research is on the way and we will in the future be able to take precautions to lessen the occurrences in the future. Unfortunately it is not here yet and we can only be aware of what we as breeders have produced in the past and be prudent about taking the affected dogs out of our breeding programs.
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