Everything You Need to Know About MDR1 in Dogs

There are many benefits of DNA testing for dogs. With one swab of the cheek, you can determine your dog’s breed mix, trace her ancestry back to her great grandparents, or even find out how she got her short legs or cute, floppy ears.

And you can discover if your pup has a genetic condition that could impact her health (or the way you and your veterinarian provide care). One of the most important gene mutations to test for is in the MDR1, or Multidrug Resistance Mutation 1, gene (also known as ABCB1).

What is MDR1?

The MDR1 gene produces the protein p-glycoprotein in dogs (as well as other animals, including humans). This protein is a drug transport pump that plays an important role in limiting drug absorption and distributionparticularly to the brain—and enhancing the excretion and elimination of many drugs that are used in dogs. 

Put more plainly, the MDR1 gene helps make sure drugs don’t linger in the brain longer than is safe or necessary. But what does that mean for your dog?

MDR1 in Shelties

Let’s say you get a new puppy and you want her to be spayed. Your veterinarian will need to put her under anesthesia for this procedure, which requires various drugs.

If your pup has two functioning copies of the MDR1 gene, she should process the medications appropriately. That means she will be properly sedated during the procedure, her cells will pump out the medications normally afterward, and she’ll recover as expected.

However, if she has the MDR1 mutation—also known as multi-drug sensitivity—her cells will fail to clear the medications from the brain like a normal dog would. As a result, higher levels of the drug will stay in her brain and increase the neurologic effects of the medication. In other words, she’ll be more sensitive to the drugs.

Depending on the medications used, this can produce side effects such as lethargy, weakness or disorientation. In more severe cases when a dog carries two copies of the MDR1 mutation, this drug sensitivity can be life-threatening.

So, whether your pup has the MDR1 gene mutation is something you and your veterinarian would want to know before she undergoes surgery.

MDR1 Drug List: Medications Affected by Multidrug Resistance Mutation 1

Not all drugs are affected by the MDR1 mutation. Common medications that can be impacted by MDR1 are:

  • Ivermectin, selamectin, milbemycin and moxidectin (antiparasitic agents) 
  • Loperamide (over-the-counter antidiarrheal agent)
  • Doxorubicin, vincristine and vinblastine (chemotherapy agents)
  • Acepromazine (tranquilizer and pre-anesthetic agent)
  • Butorphanol (pain control and pre-anesthetic agent)
  • Apomorphine (used to induce vomiting)

It’s important to note, however, that having the MDR1 mutation doesn’t necessarily mean a dog should never receive these or other affected medications. For example, the doses of ivermectin, selamectin, milbemycin and moxidectin in FDA-approved heartworm preventives are low enough to be used safely even in dogs that have two copies of the MDR1 mutation. It’s only when these drugs are administered at higher doses that dogs with the mutation will develop signs of toxicity.

By taking into account your dog’s MDR1 status, your veterinarian will be able to select appropriate drugs and doses for your dog. In many instances, alternate medications can be used in place of those impacted by MDR1. Or your veterinarian may be able to prescribe your pup a lower, safer dose of an affected drug.

MDR1 in Dogs

Dog Breeds That Are At-Risk for MDR1 Gene Mutations

Herding breeds are most at-risk for MDR1 drug sensitivity. These include (but are not limited to):

Purebred dogs are not the only ones at risk for the MDR1 mutation. Mixed-breed dogs may also carry the mutation as the result of a recent or distant ancestor. A WISDOM PANEL DNA test can identify your dog’s breed make-up and reveal whether she is positive for MDR1.

How Do Dogs Inherit the MDR1 Gene?

Dogs receive one copy of the MDR1 gene from their father and one from their mother. If both parents pass on a mutated gene, the puppy will have two copies of the MDR1 mutation.

This means two things:

  1. The dogs will display a sensitivity to affected drugs
  2. They will pass a copy of the gene mutation to their puppies

When dogs inherit a copy of the gene mutation from only one parent, they may still react to affected drugs. And they will have a 50% chance of passing the mutation on to their puppies.

How to care for dogs with MDR1

What to Do if Your Dog Has MDR1

If your dog has one or two copies of the MDR1 mutation, make sure you share that information with your veterinarian. It’s also a good idea to tell anyone who cares for your dog, such as pet sitters, doggie daycare attendants or groomers. That way, if there’s an emergency and you or your regular veterinarian are not available, everyone will have the information they need to provide the safest treatment to your pup.

The MDR1 mutation will not typically prevent your dog from receiving routine preventive care such as heartworm protection or dental cleanings. But it’s important for your veterinary team to know about your dog’s MDR1 status so they can proactively plan the appropriate care for your furry friend.

Test Your Dog’s DNA for MDR1

As a pet parent, the sooner you test your dog for MDR1, the better. All of our current U.S. WISDOM PANEL DNA products screen for this condition and will determine if your dog carries any copies of the gene mutation.

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The mission of WISDOM HEALTH™ veterinary science and research is to facilitate responsible pet care by enhancing the well-being and relationship between pets, pet owners, breeders, shelters and veterinarians through valuable insights into pets as individuals. Through the genetic testing of dogs and cats we aim to make advances in science towards a better world for all pets so their owners can love them longer.

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