November 1, 2023, 10:12 am | Read time: 4 minutes
Some canine diseases can be effectively treated with medication. However, if your dog has an MDR1 gene defect, administering certain drugs can cause significant harm. PETBOOK explains the role of the MDR1 gene and the consequences of its defect.
Genes are sections of DNA that contain information about the expression of a trait (such as eye color). Each gene has its own specific function. The so-called Multi-Drug Resistance gene (MDR1 gene) is responsible for protecting the brain and nervous system from potentially harmful foreign substances, such as medications. Additionally, MDR1 is involved in the elimination of risky substances in the liver and kidneys and reduces the absorption of these substances in the intestines.
In short, MDR1 ensures that medications and their breakdown products safely exit the body without causing significant harm. But what happens if this gene is disabled?
Overview
What happens with an MDR1 gene defect?
In dogs with an MDR1 defect, substances and active ingredients can pass through the blood-brain barrier unimpeded. Substances like medications can therefore reach the brain directly. Depending on what the dog has ingested or been administered, they can cause devastating damage there.
Symptoms of an MDR1 gene defect include:
- Movement disorders
- Tremors
- Drowsiness
- Vomiting
- Increased salivation
- Other typical signs of poisoning
If the dose of the administered drug is very strong, it can lead to severe poisoning, causing the dog to fall into a coma and, in the worst case, even die.
How is the gene defect inherited?
Compared to an intact gene, the defective MDR1 gene lacks four base pairs. The defect can be inherited in two different ways:
Homozygous: MDR1 (-/-): If both parents pass on the defect, the MDR1 gene is completely absent. Dogs affected by this react particularly strongly to the administration of dangerous substances.
Heterozygous: MDR1 (+/-): In the heterozygous type, only one parent passes on a defective MDR1 gene. The offspring are therefore heterozygous, and the gene’s function is impaired. Animals affected by this may exhibit mild symptoms. They pass on the defective gene with a 50 percent probability to their offspring.
Healthy animals cannot pass on the defect. They belong to the MDR1 +/+ type. Unfortunately, the gene defect is not visible in affected animals. However, certain breeds are more frequently affected.
Which dog breeds are affected?
Some dog breeds that have inherited the gene defect from both parents are significantly more affected by the gene defect than others. The table shows how frequently each specific breed is affected.
[table “119” not found /]How is the gene defect detected in dogs?
It is now quite simple to test a dog for the gene defect. A blood sample is taken from the animal–just one milliliter is sufficient. Every cell in the body, including blood cells, contains DNA. A PCR test can be used to determine if there is a mutation in the MDR1 gene.
If you own one of the listed dog breeds, it is advisable to have your dog tested for the gene defect.
Which medications are dangerous?
In purebred dogs, certain medications from various substance groups trigger particularly strong reactions. There are three different substance groups distinguished.
[table “120” not found /]Please note: This list is not exhaustive and is continually updated by research groups.
Important: Do not administer any medications to your dog without consulting a veterinarian.
When must the dog owner act?
If you have a dog with a diagnosed or even suspected MDR1 gene defect and notice symptoms like signs of poisoning in your dog, do not hesitate and seek a veterinarian or animal clinic as soon as possible. The first minutes and hours are crucial when poisoning is suspected.
Also of interest: New fee schedule for veterinarians! Is insurance now worthwhile?
First Aid for Dogs: What to Do in an Emergency
Recognizing and Treating Heartworms in Dogs
How is the MDR1 gene defect treated?
A targeted treatment or even a cure is not possible, as it is a hereditary disease. If your dog suffers from poisoning due to the MDR1 defect, the therapy depends on the symptoms that occur.
In mild cases, the veterinarian can already help, but in severe cases, inpatient therapy in an animal clinic is often necessary.
Sources
- vetpharm.uzh.ch, “Active and Ingredients: Pharmacogenetics – MDR1 Defect” (accessed on 10/31/2023)
- tierklinik-trillig.de, “MDR-1” (accessed on 10/31/2023)
- mdr1-defekt.transmit.de, “MDR1 Defect in Dogs” (accessed on 10/31/2023)