Multidrug Resistance 1 is a genetic mutation in a protein that transports drugs out of the brain. This mutation causes sensitivity to certain drugs, including ivermectin and loperamide. Because of this lack of drug clearance from the brain, affected dogs experience neurological symptoms such as ataxia or even death. MDR1 can be tested for in any breed, but is most commonly found in the breeds listed below.

Transmission

Autosomal codominant 

Breed

McNab, Rough Collie, Waller, Whippet, Australian Shepherd, Border Collie, German Shepherd , Old English Sheepdog, Shetland Sheepdog, Silken windhound, White Swiss Shepherd, Miniature American Shepherd