The DM test can be obtained directly from OFA for $65
Understanding the DNA test for Degenerative Myelopathy
What is Degenerative Myelopathy?
Degenerative myelopathy (DM) is a progressive neurological disease that results in destruction of tissue within the spinal cord, usually in middle aged or older dogs. It is similiar to Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig’s Disease) in humans. The disease’s onset usually occurs between 8 and 14 years of age.
The spinal cord is wrapped in a protecive membrane called the mylin sheath. Like insulation around an electrical cord, it protects the electral pathway of the nerves running down the dog’s spine. When this membrane becomes weak and starts to deterioate, it is known as a myelopathy (myelo=myelin sheath, pathy=disease). Once this protective layer deteriorates, the nerves themselves are at risk of degeneration. DM consists of both myelin and spinal cord nerve fiber degenration.
Since one of the most important functions of the spinal cord is to conduct signals from the brain to the nerves controlling the hind limbs, the principal clinical feature (visible symptom) of degenerative myelopathy is poor control over hindlimb function. Dogs with degenerative myelopathy show a lack of coordination in both hind limbs, together with a degree of muscle weakness.
DM starts slowly and affects the rear legs first. Early signs may go unnoticed by the owner. Slight dragging of a back foot, wearing of the toenails on the affected foot or feet can be an early sign. More advanced signs are dogs that might knuckle over on both paws, cross hind limbs (especially when turning in tight circles) and swing hind limbs wide or take abnormally long strides. Over time, the hindquarters become progressively weaker, until the dog can no longer support its own weight. Eventually, the disease leads to complete paralysis.
It is difficult to accurately diagnose DM as many other conditions can have similiar early symptoms. Injuries, bulging or ruptured vertebral disks, hip dysplasia, cruciate ligament ruptures, and many other things can show as a slight draggng of a hind foot, or wobbling when walking. To properly diagnose DM, all these other issues must be ruled out first before DM is considered. Diagnosis of the disease is only possible through magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) tap, or through autopsy. Even an MRI diagnosis can be incorrect as it does not pinpoint DM. An MRI only rules out other similiar diseases.
There is currently no available cure for DM. The disease inevitably progresses over a variable period of time – anywhere from 6 months to 3 years. Ultimately, affected dogs lose the ability to walk in both hind limbs and at this point, most owners elect for euthanasia.
How do Chesapeakes get DM?
What is a Polygenic Trait?
A New Problem in Chesapeake Bay Retrievers?
Veterinary neurologists are familiar with DM because it is a common problem inGerman Shepherd dogs. From time to time sporadic cases have also been seen inother breeds. We are now seeing a growing number of Chesapeake BayRetrievers with the condition.
Knowing that this disease is strongly associatedwith particular breeds, it is possible that DM has a strong genetic component inCBRs as well. As yet we do not understand the cause; meaning, we do not haveenough data to ascertain whether the problem is due to a defect within a singlegene or defects in multiple genes acting in concert. More data and pedigrees needto be collected from dogs affected with DM to ascertain whether the problem isworth investigating further to try and locate a genetic component in the CBRbreed.
Trying to Eliminate the Disease