Summary: MDR1 may be one of the most widely-known disorders in collie-type dogs, causing medication sensitivity in dogs who are affected. MDR1 is an incomplete dominant gene, meaning that dogs with even one copy are at-risk for reactions and dogs with two copies only have a more exaggerated effect from the disorder-meaning a dog with any number of copies of the mutation should be treated as affected. The sensitivities to medications include various anti-parasitic agents, some sedatives, certain opioids, and more. Your veterinarian should be informed prior to any treatments if your dog has been tested as affected by a reliable genetic testing company.

Screening: Genetic testing is readily available through many lab companies and often may be combined in a panel of other breed-relevant disorders for cost-effective genetic screening.

Inheritance: Incomplete dominant. Clear dogs will not be affected, however dogs with one or two copies will experience effects proportional to the number of mutant copies they are affected with.