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Health > Multi Drug Resistance MDR1

The problem is due to a mutation in the multi-drug resistance gene (MDR1). This gene encodes a protein, P-glycoprotein, that is responsible for pumping many drugs and other toxins out of the brain. Dogs with the mutant gene can not pump some drugs out of the brain as a normal dog would, which may result in abnormal neurologic signs. The result may be an illness requiring an extended hospital stay--or even death.

It is well known that Collies and related breeds can have adverse reactions to drugs such as ivermectin, loperamide (Imodium®), and others. It was previously unknown why some individual dogs were sensitive and others were not. Advances in molecular biology at the Veterinary Clinical Pharmacology Laboratory at WashingtonStateUniversity's College of Veterinary Medicine have led to the discovery of the cause of multi-drug sensitivity in affected dogs.  

A test has recently been developed at WashingtonStateUniversityto screen for the presence of the mutant gene*. Instead of avoiding drugs such as ivermectin in known susceptible breeds, veterinarians can now determine if a dog is normal, in which case the drug can be administered or abnormal, in which case an alternative treatment can be given.

Affected Breeds:
Australian Shepherds
Shetland Sheepdogs (Shelties)
Old English Sheepdogs
German Shepherds
Long-haired Whippets
Silken Windhounds
mixed breed

Breeder's Note:
The only way to know if an individual dog has the mutant MDR1 gene is to have the dog tested but the good news is that if the parents of a puppy have been tested and found NOT to be carriers of the MDR1 mutation than all the puppies in that litter will also be clear of the mutation. OFA will clear by parentage for first generation puppies.

Multi-Drug Resistance (MDR1) Testing Requirements and Costs

Rev. 15 January 18

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