MDR1 Information

Many herding dog breeds are afflicted with a mutation of the multi-drug resistance (MDR1) gene. This gene encodes a protein (P-glycoprotein) that is responsible for removing certain drugs and toxins from the brain. Dogs that carry the MDR1 genetic defect cannot rid their brains of the problem drugs. The result is a neurotoxic buildup that can cause abnormal neurological symptoms and/or death.  

Breeds known to carry the MDR1 mutation include Australian Shepherds of all sizes, Collies, English Shepherds, Longhaired Whippets, McNabs, Old English Sheepdogs, Shetland Sheepdogs, and Silken Windhounds.  Research has shown that every three of every four Collies and two of every four Australian Shepherds (of any size) have at least one copy of the mutated gene.  This also means that if your mixed breed dog has, or you think s/he might have, any of these breeds in its pedigree, you should test your dog and avoid the drugs on the list until you have test results.

A simple check swab test or a blood test is available to screen for the presence of the mutated MDR1 gene. Test results indicate if the dog carries two, one or no copies of the mutated gene. For further information on the MDR 1 genetic mutation and the test, visit the website of the Veterinary Clinical Pharmacology Laboratory at Washington State University's College of Veterinary Medicine at

Download and print the MDR1 Problem Drug Info Sheet

Give a copy to your vet for your dog's medical records, and carry a copy in your car.

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