THE MDR1 MUTATION
(Also called the ABCB1-1delta mutation)

Collie (Photcredit: Morguefile.com)

Australian Shepherd (Photcredit: Morguefile.com)

Border Collie (Photcredit: Morguefile.com)

Old English Sheepdog (Photcredit: Morguefile.com)

In normal patients, the P-glycoprotein is involved in keeping drugs out of certain tissues including the patient's nervous system. A healthy P-glycoprotein system is what allows many drugs to be safe for mammals even in very high doses. Unfortunately, Collie-related breeds (and some other breeds) commonly have a mutation in the genes that make P-glycoprotein. (This has been called the "MDR1- mutation but has recently been renamed the "ABCB1-1Δ" mutation.) This mutation can create dangerous drug sensitivity. Lists of relevant drugs and how to modify doses properly have been published.

Because of the prevalence of the P-glycoprotein gene mutation, genetic testing is recommended for dogs of the following breeds: Collie, Shetland sheepdog, Australian Shepherd, Old English Sheepdog, Long-Haired Whippet, and possibly other herding breeds. Test kits, which employ a simple cheek swab, can be ordered directly from the Washington State University Veterinary School via the link below and many of the commercially available canine DNA heritage tests include this mutation in their panel:

https://prime.vetmed.wsu.edu/2022/08/29/mdr1-testing/

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