Researchers Find Cause of Muscle-Stiffness Disease

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.

Two University of Guelph professors have found the cause of the disease that temporarily prevents an animal’s muscles from relaxing after they contract. The research by Andrew Bendall and Brad Hanna is published today in the Journal of Veterinary Internal Medicine .

In humans, so far 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. In animals, scientists have barely begun to scratch the surface of finding the causes of the muscle disease. Bendall and Hanna of the Department of Molecular and Cellular Biology have discovered the mutation associated with Myotonia congenital 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."

That means that even though a blood test has been established to detect Myotonia in the Miniature Schnauzer, it’s unlikely that it 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 which 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."

Bendall and Hanna’s 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 lean something about how the normal protein works," says Bendall.

The fact that Bendall and Hanna have successfully cloned the CLCN1 gene in the Australian Cattle Dog and found the mutation means that 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, since there’s no known treatment for the disease, they often don’t refer clients to Bendall and Hanna for testing.

"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."

Searching for a Calming Effect
Researchers tackle disease that causes muscle spasms in animals

BY ALYSSA CALDER
SPARK PROGRAM

Prof. Andrew Bendall, left, graduate student Dan Finnigan, centre, and Prof. Brad Hanna are studying a muscle cell disease that can cause animals such as their canine companion, Ally, to shake in place uncontrollably. Photo by Vince Filby

A disorder that causes muscular spasms in many animal species is under the microscope of Guelph researchers who want to find the genes behind the disorder and methods to test for them. Knowing its causes, they believe, will help eliminate the disease through selective breeding.

Prof. Brad Hanna and graduate student Dan Finnigan of the Department of Biomedical Studies and Prof. Andrew Bendall, Molecular and Cellular Biology, are looking at domesticated animals such as cats, dogs, horses and Brazilian water buffalo (a food animal in its native country) to shed more light on myotonia congenita, a genetic muscle cell disorder that temporarily prevents muscles from relaxing after they contract. During these episodes, which usually last less than a minute, the animal shakes or shivers in place, unable to move.

Although the condition may be disturbing to a pet owner, it doesn't seem to do any damage to the muscle, says Hanna, so it often goes undiagnosed. But the problem is more serious in large animals. Prolonged muscular rigidity causes the animals to fall over as they try to move, which increases the risk of injury to both the animals and the people working around them. And it's undesirable in animal athletes such as race horses.

“Imagine a race horse that is unable to move out of the starting gate or cattle that stiffen and collapse when they're herded,” says Hanna.

He and Finnigan are focusing on how myotonia congenita works at the cellular level. In healthy animals, passageways in muscle cell membranes called chloride ion channels act as conduits for electrical nerve signals, which enter muscle cells and tell them to contract or relax. But animals afflicted with myotonia congenita have defective channels, causing muscles to contract but not relax right away.

That's where Hanna comes in. He's studying the ion channel function in animal patients suspected of having myotonia congenita. Currently, Finnigan and Bendall are using molecular biology techniques to look for mutations in the chloride ion channel genes. If a mutation is found, the genes responsible for the mutation are incorporated into cell cultures.

From there, Hanna can measure electrical currents in these cells to see whether the chloride ion channels are functioning properly. If they aren't, that means he and his colleagues may have found the mutation that causes myotonia congenita, which is the first step toward stopping the disease.

Hanna and Finnigan hope their research will lead to the development of blood tests for myotonia congenita, so breeders of cats, dogs, horses and livestock can eliminate the disease from their animals through selective breeding. As an added benefit, the researchers can also learn more about the relationship between structure and function of chloride ion channels in normal muscle, which could be of use to other muscle research in the future, Hanna says.

Also involved in this work are Profs. Joane Parent, Roberto Poma and Henry Staempfli and graduate student Ronaldo da Costa, Biomedical Sciences. This research is funded by the Morris Animal Foundation.

The following article appeared in
"At Guelph", Aug 11, 1999:

The following article appeared in
the "Guelph Mercury", Jan 9, 1997: