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Description
The MDR1 gene, or multi-drug resistance gene, codes for a protein
that is responsible for protecting the brain by transporting potentially
harmful chemicals away from the brain. In certain breeds, a mutation
occurs in the MDR1 gene that causes sensitivity to Ivermectin, Loperamide,
and a number of other drugs. Dogs with this mutation have a defect
in the P-glycoprotein that is normally responsible for transporting
certain drugs out of the brain. The defective protein inhibits the
dog's ability to remove certain drugs from the brain, leading to
a buildup of these toxins. As a result of accumulation of toxins,
the dog can show neurological symptoms, such as seizures, ataxia,
or even death.
Dogs that are homozygous for the MDR1 gene, meaning
that they have two copies of the mutation, will display a sensitivity
to Ivermectin, and other similiar drugs. These dogs will also always
pass one copy of the mutation to all potential offspring. Dogs that
are heterozygous, meaning they have only one copy of the mutation,
can still react to these drugs at higher doses. Also, there is a
50% chance a dog with one copy of the mutation will pass it on to
any offspring.
MDR1 has been found in a variety of breeds. It
is prevalent in most herding breeds, such as Shepherds and Collies.
Some studies have suggested that the frequency of this gene is over
50% in Collies and Long-Haired Whippets.
MDR1 Testing
Animal Genetics offers DNA testing and detection of a
linkage gene mutation in the MDR1 gene in:
Australian Shepherds
Collies (Rough and Smooth)
English Shepherds
German Shepherds
Long-haired Whippets
McNabbs
Miniature Australian Shepherds
Old English Sheepdogs
Shetland Sheepdogs
Silken Windhounds
Mix-breeds with any of the above in their background
Drug Sensitivity
There are many different types of drugs that have been
reported to cause problems. The following is a list of some of the
drugs.
Ivermectin (found in heartworm medications)
Loperamide (Imodium over the counter antidiarrheal agent)
Doxorubicin, Vincristine, Vinblastine (anticancer agents)
Cyclosporin (immunosuppressive agent)
Digoxin (heart drug)
Acepromazine (tranquilizer)
Butorphanol ("Bute" pain control)
The following drugs may also cause problems: Ondansetron, Domperidone,
Paclitaxel, Mitoxantrone, Etoposide, Rifampicin, Quinidine, Morphine
Cost
$45.00 US per sample.
Sample Collection
Collect sample using buccal swabs provided by Animal
Genetics. Ensure that the dog has not eaten within a few hours of
sample collection. Any food particles can inhibit the test. Rub
each of the swabs along the inside of the dog's mouth for 10-15
seconds, and allow the swabs to dry thoroughly. Label the provided
envelope with the dog's name, and place the swab inside it. Download
and complete a submission form for each sample and send along with
payment to Animal Genetics for testing.
Results
Results
are given using the following symbolic notation:
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M1/M1
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The
dog carries two copies of the mutant gene and is homozygous
for the MDR1 mutation.
The dog will react to Ivermectin, or other listed drugs,
and will always pass on a copy of the mutated gene to its offspring. |
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n/M1
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Both
the normal and mutant copies of the gene detected. Some sensitivity
to listed drugs can occur. Dog is a carrier for the
MDR1 mutation, and can pass on
a copy of the defective gene to its offspring 50% 0f the time. |
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n/n
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Dog
tested negative for the MDR1
gene mutation, and will not pass on the defective gene to its
offspring. |
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