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News Release

May 14, 2007

Researchers Find Cause of Muscle-Stiffness Disease

Watch video of dog with disorder

Imagine a dog running after a ball only to stiffen up and fall over because of a genetic muscle cell disorder. It may sound almost comical, but this disorder, called myotonia congenita, affects dogs, cats, horses, water buffalo and even people.

Four University of Guelph researchers have found the cause of the disease that temporarily prevents an animal’s muscles from relaxing after they contract. The research by Profs. Andrew Bendall, Department of Molecular and Cellular Biology; Brad Hanna and Dan Finnigan, Department of Biomedical Sciences; and Roberto Poma, Department of Clinical Studies, is published today in the Journal of Veterinary Internal Medicine.

In humans, more than 80 mutations of the skeletal muscle chloride channel gene (called CLCN1),which temporarily prevents muscles from relaxing after they contract, have been found so far. In animals, scientists have barely begun to scratch the surface of finding the causes of the muscle disease. Bendall and Hanna have discovered the mutation associated with myotonia congenita in Australian cattle dogs and in a Maltese-cross dog.

“There are probably eight breeds of dogs known to have myotonia, but up until our study, the miniature schnauzer was the only breed for which a specific genetic mutation had been found,” says Bendall.

Adds Hanna: “I think there’s a misunderstanding among some veterinary practitioners that once you find a mutation that causes the disease, that’s it. The human example shows us clearly that, no, in different families there may be different mutations.”

This means that even though a blood test has been established to detect myotonia in the miniature schnauzer, it’s unlikely the test will detect the disease in any other breed of dog. Because Bendall and Hanna found the mutation in the Australian cattle dog, they were able to develop a blood test to detect the disease in that breed. The test is now offered at the provincial diagnostic Animal Health Lab at U of G.

“We found that in the Australian cattle dog, it’s a truncation mutation, so there’s actually a portion of the skeletal muscle chloride channel that’s missing,” says Hanna. “Eighty-eight amino acids are missing at one end of the channel.”

This research will not only benefit the owners of Australian cattle dogs, but “by identifying the kinds of mutations that affect the function of the protein, you can also learn something about how the normal protein works,” says Bendall.

The fact that he and Hanna have successfully cloned the CLCN1 gene in the Australian cattle dog and found the mutation means they are now able to find mutations in other breeds more quickly.

Since their success in Australian cattle dogs, they’ve also discovered the mutation in a Maltese-cross with a severe case of myotonia. “We have found a missense mutation, which results in the substitution of one amino acid for another in the protein,” says Hanna. “That amino acid has not been found to be mutated in this way in humans, so we’re in the process of doing the functional work to determine the significance of this change.”

When veterinarians diagnose myotonia in animals, they often don’t refer clients to Bendall and Hanna for testing because there’s no known treatment for the disease.

“We would be interested in hearing from veterinarians who have identified animals of any breed or any species with a similar disorder,” says Hanna. “It’s possible, especially with purebred animals, for this type of disease to become widely disseminated, so by developing blood tests, we can help breeders eliminate these disorders.”