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IVERMECTIN SENSITIVITY IN COLLIES SOLVED!:

When heartworm prevention medication was introduced in 1983, it was considered a major advancement in veterinary medicine. Widespread use of the medication and popular belief that even large doses can be safely given to dogs, led to a new problem especially prevalent in one breed - Collies. When given a high dosage of the heartworm medication, many Collies developed severe neurological signs that often resulted in death due to respiratory arrest. The symptoms would appear within 8 to 24 hours characterized by dilated pupils and blindness and progressing into lack of coordination and inability to stand. In severe cases, the problem would develop into coma followed by death. Early studies established a clear link between affected dogs and a high level of an ivermectin, an antiparasite medication.

Even though a controlled low dosage of the heartworm medication allowed for noticeable reduction of side effects, unexplained cases of toxic reactions to certain drugs in certain breeds would still be recorded and remained a mystery. Statistical data on drug sensitivity included, in addition to Collies, such breeds as Australian Shepherds, Bearded Collies, Border Collies, Shetland Sheepdogs, etc. and drugs ranging from an over-the-counter antidiarrheal medication, Loperamide, and pain controller, Butorphanol, to some chemotherapy drugs.

The mystery has finally been solved. A recent study by Dr. Katrina Mealey at the College of Veterinary Medicine of Washington State University has identified that the problem of drug sensitivity relates to a genetic mutation in the multidrug-resistanc e gene (MDR1). One of the responsibilities of the gene MDR1 is the production of a protein called P-glycoprotein (P-gp). This protein allows many toxins and drugs to be removed from the brain. An affected dog lacks functional P-glycoprotein that leads to toxins not being pumped out of the brain and, as a consequence, to an abnormal neurological reaction. The mutation has an autosomal recessive way of inheritance which means that, in order to be affected (super sensitive to drugs), a dog has to have both genes mutated. However, even the presence of a single mutation increases drug sensitivity in a dog.

A new DNA test for the presence of the mutation in MDR1 gene allows for the detection of affected dogs as well as dogs carrying a single mutation. Knowing the dog's status will help veterinarians to properly administer treatment and will help breeders to eliminate this disease in their bloodlines.

To learn more about ordering the test, please visit HealthGene.

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