MDR1 GENE MUTATION:
I recommend all breeding dogs AND family companions to be tested for Multi-Drug Resistance. It will aid you and your veterinarian in choosing safe medication and doses. If you do not know your dog's MDR1 status, please treat your dog as "affected" by the mutation until proven otherwise by testing. Even if your dog is clear, it is wise to avoid problem drugs when there are other options available.
To summarize this mutation, Multidrug Sensitivity in Dogs is a gene mutation where P-glycoprotein is affected. P-glycoprotein is a drug transport pump that is important in limiting the amount of drug that is absorbed and distributed into the brain. P-glycoprotein also aids in the excretion of drugs used in dogs.
This gene mutation is actually common in herding breeds such as the Standard, Miniature, and Toy Australian Shepherds, Collies, Border Collies, German Shepherds, Whippets (sighthound breed), and other Sheepdogs. In breeds such as Australian Shepherds and Mini American Shepherds, we cannot completely eradicate the gene as it would impact our gene pool in a very negative way because it is so common. As a breeder, we should be careful of how we pair our breeding dogs and avoid producing Mutant/Mutant dogs when possible. While this mutation can sound scary, it is easily manageable if you are knowledgeable about it unlike other diseases that you cannot control its development.
So what can this mutation do? MDR1 gene mutation can cause a dog to have a decreased ability to limit absorption and distribution of certain drugs. Delayed excretion of the drugs can cause drug toxicity in come drugs and at higher doses. If you are not knowledgeable about the medications to be cautious with, you may see symptoms of toxicity which vary depending on the drug that was given but may include twitching or seizures. Washington State University (WSU) was the first lab to discover this a create a genetic test for MDR1. My information here is in reference to their recommendations, but there are many other sources of information out there that may or may not be reliable.
Here is Washington State University's link. It is a GREAT idea to print this out and take to your veterinarian and ask to have a note or alert put on your dog's account about his/her MDR1 status. It is unfortunate how many veterinarians do not know much about MDR1 and the specific drugs to take into account.
This gene mutation is actually common in herding breeds such as the Standard, Miniature, and Toy Australian Shepherds, Collies, Border Collies, German Shepherds, Whippets (sighthound breed), and other Sheepdogs. In breeds such as Australian Shepherds and Mini American Shepherds, we cannot completely eradicate the gene as it would impact our gene pool in a very negative way because it is so common. As a breeder, we should be careful of how we pair our breeding dogs and avoid producing Mutant/Mutant dogs when possible. While this mutation can sound scary, it is easily manageable if you are knowledgeable about it unlike other diseases that you cannot control its development.
So what can this mutation do? MDR1 gene mutation can cause a dog to have a decreased ability to limit absorption and distribution of certain drugs. Delayed excretion of the drugs can cause drug toxicity in come drugs and at higher doses. If you are not knowledgeable about the medications to be cautious with, you may see symptoms of toxicity which vary depending on the drug that was given but may include twitching or seizures. Washington State University (WSU) was the first lab to discover this a create a genetic test for MDR1. My information here is in reference to their recommendations, but there are many other sources of information out there that may or may not be reliable.
Here is Washington State University's link. It is a GREAT idea to print this out and take to your veterinarian and ask to have a note or alert put on your dog's account about his/her MDR1 status. It is unfortunate how many veterinarians do not know much about MDR1 and the specific drugs to take into account.
LINK: vcpl.vetmed.wsu.edu/problem-drugs
Drugs to remember:
This mutation is passed on as a single allele would be. The sire and dam are either Normal/Normal, Normal/Mutant, or Mutant/Mutant. While a Normal/Mutant (carrier) dog can be affected, Mutant/Mutant dogs are much more at risk. We try to avoid this situation best we can. To put things in perspective, my first Mini American Shepherd, Sapphire, is MDR1 Normal/Mutant (carrier). Her breeder did not test any of his dogs for any genetic diseases and so I had no idea about her MDR1 status. Actually, I didn't even KNOW about MDR1 when I bought Sapphire 8 years ago. Working as a vet tech, I gave her monthly Heartgard and didn't decrease butorphanol doses when preforming dental cleanings. She had never shown any adverse reactions to these medications. Since testing her, I have taken better care to avoid or reduce these medications.
To test for this gene mutation, a cheek swab or blood sample must be submitted to one of the many companies that test for it through DNA samples. Washington State University offers a patent protected diagnostic test and is the most reliable source since they first discovered the mutation and established the testing. Other sources of testing are PawPrint Genetics, Gensol, and VetGen.
To learn more about this topic, please visit: https://vcpl.vetmed.wsu.edu/
Drugs to remember:
- Ivermectin is the most problematic of all the drugs that we know of. It is a common antiparasitic in Heartgard and for livestock. Please DO NOT USE Heartgard even if your dog is clear for the mutation. There are better options available.
- Milbemycin and Selamectin are also antiparastics known to be filtered by the MDR1 protein, but they do not pose as much risk as ivermectin. For this reason, I recommend Interceptor Plus OR Sentinel Spectrum for routine heart worm prevention.
- Loperamide, also known as Immodium, is an antidiarreal medication that WSU determined WILL cause toxicity at the doses used to treat diarrhea. I do not see this medication recommended often at all in general practice, but very good to be aware.
- Butorphanol is very commonly used as a preanesthetic drug to aide in short term pain control and sedation. It is often given with dexmedotomidine prior to routine surgery such as spays and neuters. It is recommended to reduce the dose given to mutants and carriers or just change to a different drug per your veterinarians protocols.
- Acepromazine is a sedative sometimes given before anesthesia or for scary events such as fireworks. However, Acepromazine is becoming less and less used. It is recommended to reduce the dose by WSU. HOWEVER, my experience leads me to suggest NOT using Acepromazine at all because there are better options, one option being TRAZODONE (light sedation and anti-anxiety) for stressful situations or prior to anesthesia.
- Apomorphine is a medication used to induce vomiting soon after a dog ingests something they shouldn't have, particularly something toxic. Dose reductions are recommended by WSU.
- Chemotherapy Agents (Vincristine, Vinblastine, Doxorubicin, Paclitaxel) are recommended to have doses reduced in order to avoid SEVERE toxicity.
- Other medications to take note of are listed on WSU's website: https://vcpl.vetmed.wsu.edu/problem-drugs
This mutation is passed on as a single allele would be. The sire and dam are either Normal/Normal, Normal/Mutant, or Mutant/Mutant. While a Normal/Mutant (carrier) dog can be affected, Mutant/Mutant dogs are much more at risk. We try to avoid this situation best we can. To put things in perspective, my first Mini American Shepherd, Sapphire, is MDR1 Normal/Mutant (carrier). Her breeder did not test any of his dogs for any genetic diseases and so I had no idea about her MDR1 status. Actually, I didn't even KNOW about MDR1 when I bought Sapphire 8 years ago. Working as a vet tech, I gave her monthly Heartgard and didn't decrease butorphanol doses when preforming dental cleanings. She had never shown any adverse reactions to these medications. Since testing her, I have taken better care to avoid or reduce these medications.
To test for this gene mutation, a cheek swab or blood sample must be submitted to one of the many companies that test for it through DNA samples. Washington State University offers a patent protected diagnostic test and is the most reliable source since they first discovered the mutation and established the testing. Other sources of testing are PawPrint Genetics, Gensol, and VetGen.
To learn more about this topic, please visit: https://vcpl.vetmed.wsu.edu/
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For my full report on MDR1 while in college, click here.
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