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A DNA test for Multidrug Resistance (MDR1) in Collies.
What is MDR1?
A DNA test for MDR1
Dr. Katrina Mealey and her co-workers at the Department of Veterinary Clinical
Sciences of Washington State University discovered that the cause of Ivermectin
sensitivity in Collies is a deletion mutation in the MDR1 gene. The disorder is
inherited as an autosomal recessive and the mutant allele is called "mdr1-1Δ".
The dominance of MDR1 is incomplete; there are examples of heterozygotes
("carriers") that are susceptible to high dosages of the drugs that cause problems
for the animals that are homozygous for the defective allele ("affecteds").
The mutation mdr1-1Δ causes defects in the coding for P-glycoprotein
resulting in nearly complete loss of its function. At this moment more than
20 therapeutic drugs are known substrates of P-glycoprotein. Several of these
are now known to cause toxic reactions in Collies with at least one
mdr1-1Δ allele.
The MDR1 DNA test yields three possible outcomes:
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Your dog is "clear" (and has two "healthy" alleles: MDR1/MDR1),
it will not develop oversensitivity for the drugs mentioned and, just as
important, it will not pass on the defect (the defective allele) to the next
generation. Your dog would not be expected to experience adverse drug reactions
to normal doses of Ivermectin, loperamide (Imodium ®), some anticancer drugs and
several other drugs.
-
Your dog is a "carrier" (and has one "healthy" allele and one defective
one: MDR1/mdr1-1Δ), it will pass on the defective allele to half
of its offspring. Your dog may experience toxicity after normal doses of
loperamide (Imodium ®), and some anticancer drugs, and after high doses of
Ivermectin (greater than 50 micrograms per kilogram).
-
Your dog is "affected" (and has two defective alleles:
mdr1-1Δ/mdr1-1Δ), it will pass on the defective allele to
all of its offspring in the next generation and it will be expected to
experience toxicity after normal doses of the drugs mentioned above. So it is
one of the animals that will suffer from oversensitivity reactions.
"Dangerous drugs" for oversensitive dogs
Breeds at risk
Breeding policy
Testing for MDR1
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