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mdr gene

June 4th, 2008, 07:30 AM
I'm starting to hear about an mdr gene that is being found in herding dogs. It supposedly makes those that have it sensitive to certain medications like heartworm medication. I'm wondering if that's why my Sheltie and a friend's Sheltie started having seizures gradually leading to death. My 5 year old dog had seizures over a 6 month period, then became blind, gradually lost strength, started to fall over then died just as we were about to have her put to sleep because she had started to exhibit signs of something painful in her stomach or intestines. Does anyone know more about this.

Dr Lee
June 4th, 2008, 07:41 PM
For others reading this, mdr gene stands for Multi Drug Resistance gene and is found primarily on certain breeds but it is thought that dogs outside of the breed can also have this gene. It was discovered in Washington State University. Here is their description...

"Advances in molecular biology at the Veterinary Clinical Pharmacology Laboratory at Washington State University's College of Veterinary Medicine have led to the discovery of the cause of multi-drug sensitivity in affected dogs. The problem is due to a mutation in the multi-drug resistance gene (MDR1). This gene encodes a protein, P-glycoprotein, that is responsible for pumping many drugs and other toxins out of the brain. Dogs with the mutant gene can not pump some drugs out of the brain as a normal dog would, which may result in abnormal neurologic signs. The result may be an illness requiring an extended hospital stay--or even death."

I actually just had one of my patients recently tested for this gene because we were going to treat his dog for demodex which used much higher doses of ivermectin than it found in heartworm prevention. The test is, of course, done through Washington State University. Here is a site that includes information and test order kits.

As far as heartworm prevention medication causing the signs and tragic loss of your pet, unless you were using a strange brand or going off label in high doses, then this is not the cause. This is an excerpt directly off of the Washington State site regarding ivermectin...

"the dose of ivermectin used to prevent heartworm infection is SAFE in dogs with the mutation (6 micrograms per kilogram)"

I am very sorry to hear about you and your friends dogs. :pawprint: