Skip to main content

MDR1 defect

A representation of MDR1 defect

The MDR1 defect is a genetic disorder that occurs in some dog breeds. It affects the function of a protein that is responsible for the transport of drugs and other substances across the blood-brain barrier. This can lead to severe side effects or even death if the dog receives certain medications. In this article you will learn more about the MDR1 defect, how it is diagnosed and treated and how you can protect your dog.

What is the MDR1 defect?

MDR1 stands for Multi-Drug Resistance 1 and is the name of a gene that contains the instructions for a protein called P-glycoprotein. This protein is present in the cell membranes of many organs and tissues, including the brain, liver, kidneys and intestines. It has the task of pumping various substances out of the cells or preventing them from entering the cells. In this way, it protects the cells from harmful or toxic substances.

In dogs with the MDR1 defect, the gene is defective or completely absent. This means that the P-glycoprotein does not function properly or is not produced at all. As a result, the blood-brain barrier, which protects the brain from harmful substances in the blood, becomes more permeable. If the dog is now given drugs that are normally kept out of the brain by the P-glycoprotein, they can enter the brain in high concentrations and trigger severe neurological symptoms. These can manifest themselves as

  • tremors
  • convulsions
  • Ataxia (loss of balance)
  • blindness
  • coma
  • Death

Not all drugs are dangerous for dogs with the MDR1 defect. The best known are:

  • Ivermectin (an anti-parasitic agent found in many dewormers)
  • Loperamide (an anti-diarrheal agent found in many human medications)
  • Doxorubicin (a chemotherapeutic agent against cancer)
  • Cyclosporine (an immunosuppressant used to treat autoimmune diseases)
  • Acepromazine (a tranquilizer)
  • Butorphanol (a painkiller)

However, there are many other medications that can be potentially dangerous. Therefore, you should always inform your vet if your dog has or may have the MDR1 defect before giving them any medication.

Which dog breeds are affected?

The MDR1 defect is mainly found in herding dogs and their crossbreeds. The most common breeds affected are

  • Collie
  • Shetland Sheepdog (Sheltie)
  • Australian Shepherd
  • Border Collie
  • Long-haired Whippet
  • McNab Shepherd
  • English Shepherd
  • Old English Sheepdog

However, other breeds can also have the MDR1 defect if they are related to one of the above-mentioned breeds or have been crossed. The MDR1 defect is inherited in an autosomal recessive manner. This means that a dog is only affected if it has inherited the defective gene from both parents. If it has only inherited the defective gene from one parent, it is a healthy carrier and can pass the defect on to its offspring.

How is the MDR1 defect diagnosed?

The MDR1 defect can be diagnosed using a simple genetic test. A sample of blood or saliva is taken from the dog and sent to a laboratory. There, the gene is analyzed and it is determined whether the dog is normal (+/+), a carrier (+/-) or affected (-/-). Depending on the provider, the test costs between 40 and 80 euros and can be ordered from any vet or online.

How is the MDR1 defect treated?

The MDR1 defect cannot be cured, but dogs can be protected from the dangerous consequences by not giving them any medication that affects the P-glycoprotein. This includes not giving any medication to other dogs in the household that the affected dog could ingest. You should also make sure that the dog does not have access to waste, feces or carcasses that could be contaminated with parasites or toxins.

If the dog has accidentally been given a dangerous drug or is showing symptoms, you should see the vet immediately. There are some antidotes that can weaken or cancel out the effect of the medication if administered in time. Depending on the severity of the symptoms, the dog may also require intensive medical treatment.

How can I protect my dog?

If you have a dog that has or may have the MDR1 defect, you should take the following measures:

  • Have your dog tested to know his genetic status.
  • Tell your vet about your dog's MDR1 defect and get a list of safe and unsafe medications.
  • Do not give your dog any medication without consulting your vet.
  • Keep all medications out of your dog's reach.
  • Avoid sharing your dog with other dogs that have been given medication.
  • Keep your dog away from possible sources of infection.
  • Have your dog regularly checked and treated for parasites, but only with safe medication.
  • Do not breed with a dog that has the MDR1 defect or is a carrier.

MDR1 deficiency is a serious disease that can endanger your dog's life. But with a little care and attention, you can protect your dog from the risks and give him a happy and healthy life.

The authors assume that a veterinarian should be consulted if an animal is ill and that medication should only be taken after consultation with a doctor or pharmacist. Only an individual examination can lead to a diagnosis and treatment decision.

We help you find the nearest vet → This way