Recent Article on DM in Australian Shepherds:

Degenerative Myelopathy is a debilitating disease that causes gradual paralysis in many dog breeds. It is caused by a degeneration of the spinal cord that onsets typically between 8 and 14 years of age. It presents first with the loss of coordination of the hind legs. It will typically worsen over six months to a year, resulting in paralysis of the hind legs. If signs progress for a longer period of time, loss of urinary and fecal continence may occur and eventually weakness will develop in the front limbs. An important feature of DM is that it is not a painful disease.

This has been a long since argued subject that started once genetic testing became a common practice for breeders. If you are on genetics pages you will see the debates between breeders and owners each either swearing DM is very prevalent in Aussies or that Aussies are not susceptible to the disease the way other breeds clearly are.

It looks like we now have an answer... Which side were you on?

BREED TESTING:
Although any dog can be tested for DM, it is possible that the genetic background that predominates in some breeds prevents the development of symptoms even in dogs testing affected (at risk). At this time we are reluctant to recommend testing for members of breeds where the University of Missouri has not yet proven susceptibility to DM through microscopic examination of spinal cords from deceased dogs that exhibited symptoms of the disease. The required evidence of association between the genetic mutation and actual spinal cord evaluations has only been proven in the breeds listed:

American Eskimo Dogs
Bernese Mountain Dog
Borzoi
Boxers
Cardigan Welsh Corgi
Chesapeake Bay Retrievers
German Shepherd Dog
Golden Retriever
Great Pyrenees
Kerry Blue Terriers
Pembroke Welsh Corgis
Poodle
Pug
Rhodesian Ridgeback
Shetland Sheepdog
Soft Coated Wheaten Terriers
Wire Fox Terrier

I just want to make a note that the Australian Shepherd is NOT on the list of breeds that have been proven to be susceptible to DM.

Read the full article here: https://www.ofa.org/diseases/dna-tested-diseases/dm

MDR1 FAQs

Australian Shepherds, along with several other mostly collie-type breeds, can carry a genetic mutation that makes them sensitive to certain drugs. Use of those drugs can cause serious neurological illness or death.

Fortunately, there is an extremely accurate DNA test that will let you know whether your dog has this mutation. All you have to do is provide a cheek swab. It isn't even necessary to go to the vet. However, we have tested all of our adult dogs and can tell you if there is any need to test your puppy depending on its parents. 

What is MDR1?
MDR1 is the abbreviated name of a gene called Multi-Drug Resistance 1. A mutation of this gene causes sensitivity to Ivermectin and a number of other drugs. Dogs with the mutation will react to those drugs. Having two copies of the mutation will lead to drug reactions, but having a single copy can also confer some sensitivity with some drugs. Dogs with this mutation have a transport defect - the drug goes in to their brains, fails to be transported out, and builds up to toxic levels. This causes serious neurological problems including seizures and sometimes death.

Which drugs cause reactions?
Ivermectin was the first drug recognized to cause a reaction, but it is far from the only one. Ivermectin at low dosage, as found in heartworm medications, will not cause a reaction. The larger doses needed for worming will. Other commonly administered drugs on the list include acepromazine and Imodium. Fortunately, there are alternative medications available if your dog requires treatment.

The drugs involved can be found on the website below.
http://vcpl.vetmed.wsu.edu/problem-drugs

Which breeds are affected?

Australian Shepherds
Collies (Rough and Smooth)
English Shepherds
McNabbs
Miniature Australian Shepherds
Old English Sheepdogs
German Shepherd Dogs
Long-haired Whippets
Shetland Sheepdogs
Silken Windhounds
Mix-breeds with any of the above in their background

How common is the MDR1 mutation in Aussies?
32% of the Aussies and 49% of Mini-Aussies have at least one copy of the gene.

How do I know if my dog has the MDR1 mutation?
If your dog has already reacted to one of these drugs, it has the mutation. However, reactions can be so dangerous to your dog it is advisable to have the dog tested so you know whether it is sensitive before it receives any of the listed drugs.

What do the MDR1 test results mean?
This is a DNA mutation test. It will determine whether or not a dog has the MDR1 mutation and, if it does, whether it has one copy or two. The test report will provide you with the genotype for your dog, generally listed as Normal/Normal, Normal/Mutant or Mutant/Mutant.

Dogs with even one copy of the mutation should be considered sensitive to listed drugs. If your dog carries the mutation, provide a copy of the test results and a copy of the listed drugs to every veterinarian who treats your dog and let them know your dog cannot have those drugs.

What dogs should be tested and how often?
Since this is a DNA test, a dog only needs to be tested once. Due to the high frequency of the mutation in the breed and the variety of drugs to which dogs with the mutation can react, all dogs, including rescues of unknown parentage and Aussie-mixes should be tested. Their lives could depend on it.

The only exception is as follows: If both parents of a dog have tested Normal/Normal, they cannot pass on the gene and their offspring will not need to be tested. However, if a Normal/Normal dog is bred to one of unknown status or one that has even a single copy of the mutation, the offspring must be tested.

How do I get the test done?
For those in North America, The test is available through Washington State University. Information can be found on their website: 
http://vcpl.vetmed.wsu.edu/

Or through Paw Print Genetics where all of our dogs have been tested.  Contact us to take advantage of our discount with PPG.

Does the MDR1 mutation cause epilepsy?
MDR1 drug reactions are not a form of epilepsy, nor are they in any way related to epilepsy, which is caused by different and as yet unidentified genes. The MDR1 mutation is one of the many things that can cause non-epileptic seizures. The drug reaction is very different from primary epilepsy. The dog will only seize if the chemicals build up in its brain. Treatment is different, prognosis is different and the seizures themselves may be different in presentation. MDR1-related seizures only occur if a susceptible dog is given one of the listed drugs. Once the drugs finally clear from the dog's system, the seizing will stop. If the dog does not receive those drugs, it will not have seizures due to the MDR1 gene.             

DM FAQ's

What is Degenerative Myelopathy (DM)?

Degenerative myelopathy (DM) is a progressive disease of the spinal cord in older dogs. The disease has an insidious onset typically between 8 and 14 years of age. It begins with a loss of coordination (ataxia) in the hind limbs. The affected dog will wobble when walking, knuckle over or drag the feet. This can first occur in one hind limb and then affect the other. As the disease progresses, the limbs become weak and the dog begins to buckle and has difficulty standing. The weakness gets progressively worse until the dog is unable to walk. The clinical course can range from 6 months to 1 year before dogs become paraplegic. If signs progress for a longer period of time, loss of urinary and fecal continence may occur and eventually weakness will develop in the front limbs. Another key feature of DM is that it is not a painful disease.

 New research has identified a gene that is associated with a major increase in risk of the disease.  Results for testing DM will appear as N/N (Normal), N/M (Carrier of 1 copy), or M/M (Carrier of 2 copies).  Just because a dog carries both copies does not guarantee they will develop DM.  In the same way, dogs can develop DM without having a single copy of the gene.  Testing for Degenerative Myelopathy is only a guideline to use in breeding as it tells us if a dog possesses a gene associated with DM. 

What causes Degenerative Myelopathy?

Degenerative myelopathy begins with the spinal cord in the thoracic (chest) region. If we look under the microscope at that area of the cord from a dog that has died from DM, we see degeneration of the white matter of the spinal cord. The white matter contains fibers that transmit movement commands from the brain to the limbs and sensory information from the limbs to the brain.

This degeneration consists of both demyelination (stripping away the insulation of these fibers) and axonal loss (loss of the actual fibers), and interferes with the communication between the brain and limbs. Recent research has identified a mutation in a gene that confers a greatly increased risk of developing the disease.

How is degenerative myelopathy clinically diagnosed?

Degenerative myelopathy is a diagnosis of elimination. We look for other causes of the weakness using diagnostic tests like myelography and MRI. When we have ruled them out, we end up with a presumptive diagnosis of DM. The only way to confirm the diagnosis is to examine the spinal cord under the microscope when a necropsy (autopsy) is performed. There are degenerative changes in the spinal cord characteristic for DM and not typical for some other spinal cord disease.

What else can look like degenerative myelopathy?

Any disease that affects the dog’s spinal cord can cause similar signs of loss of coordination and weakness. Since many of these diseases can be treated effectively, it is important to pursue the necessary tests to be sure that the dog doesn’t have one of these diseases. The most common cause of hind limb weakness is herniated intervertebral disks. The disks are shock absorbers between the vertebrae in the back. When herniated, they can cause pressure on the spinal cord and weakness or paralysis. Short-legged, long back dogs are prone to slipped disks. A herniated disk can usually be detected with X-rays of the spine and myelogram or by using more advanced imaging such as CT scan or MRI. Other diseases we should consider include tumors, cysts, infections, injuries and stroke. Similar diagnostic procedures will help to diagnose most of these diseases. If necessary, your veterinarian can refer you to a board-certified neurologist who can aid in diagnosing degenerative myelopathy.

How do we treat degenerative myelopathy?

There are no treatments that have been clearly shown to stop or slow progression of DM. Although there are several approaches that have been tried or recommended on the internet, no scientific evidence exists that they work. The outlook for a dog with DM is still grave. The discovery of a gene that identifies dogs at risk for developing degenerative myelopathy could pave the way for therapeutic trials to prevent the disease from developing. Meanwhile, the quality of life of an affected dog can be improved by measures such as good nursing care, physical rehabilitation, pressure sore prevention, monitoring for urinary infections, and ways to increase mobility through use of harnesses and carts.

Source: http://www.caninegeneticdiseases.net/DM/basicDM.htm