Degenerative myelopathy is the neurological condition that concerns me most when I advise white shepherd and Berger Blanc Suisse breeders about health testing. Not because it is unique to white shepherds, it affects German Shepherds of all colors at elevated rates compared to many other breeds, but because its genetic basis is now understood, testing is available, and the condition is preventable through informed breeding decisions.
I want to be absolutely clear from the start: degenerative myelopathy has nothing to do with coat color. The SOD1 gene responsible is on chromosome 31. The Extension locus is on chromosome 5. These genes are independently inherited. But because white shepherds are German Shepherds at the genetic level, they face the same DM risk that exists across the German Shepherd population, and breeders need to take it seriously.
What Degenerative Myelopathy Is
Canine degenerative myelopathy is a progressive neurodegenerative disease affecting the spinal cord. In German Shepherds and related breeds, it typically begins in middle to old age, usually between seven and fourteen years. The progression follows a characteristic pattern:
Early signs appear in the pelvic limbs as weakness and lack of coordination. Affected dogs knuckle on their rear feet, have difficulty rising, and show a characteristic swaying gait. Over months, the weakness progresses to complete paraplegia in the rear limbs. In some cases, the disease continues to ascend, eventually affecting the thoracic limbs and causing tetraplegia.
The condition is not painful in the conventional sense. The degeneration of myelinated nerve fibers reduces sensation as well as motor function, so affected dogs often seem comfortable even as they lose mobility. This can make early recognition difficult because owners may attribute early wobbliness to arthritis rather than neurological disease.
There is no treatment that halts or reverses the degeneration. Intensive physical rehabilitation can extend the period of ambulation and quality of life, but the condition is ultimately progressive and fatal. Most dogs reach paraplegia within one to three years of first signs.
The SOD1 Mutation
The genetic basis for canine degenerative myelopathy was identified through comparison with human amyotrophic lateral sclerosis, or ALS. Human ALS is associated with mutations in the SOD1 gene, which encodes copper-zinc superoxide dismutase, an enzyme that protects cells from oxidative damage.
Researchers at the University of Missouri identified a mutation in the canine SOD1 gene that is strongly associated with degenerative myelopathy in multiple breeds. The mutation, a single nucleotide change (E40K in the original designation) that alters the structure of the SOD1 protein, was found at high frequency in German Shepherds, Pembroke Welsh Corgis, Boxers, and several other breeds with DM.
The mutation is located on chromosome 31 in the dog genome. Its location, its mechanism, and its molecular effects are entirely separate from the Extension locus on chromosome 5. There is no linkage, no correlation, no relationship between DM risk and coat color.
This is a factual statement based on chromosomal biology. Genes on different chromosomes assort independently. A white shepherd is not at higher or lower risk of carrying the SOD1 mutation than a pigmented German Shepherd. The risk is the same for both, determined by which alleles each dog inherited at chromosome 31, not by what happened at chromosome 5.
Inheritance Pattern
The SOD1 mutation associated with degenerative myelopathy follows a complex inheritance pattern that is not strictly Mendelian. The mutation shows incomplete penetrance, meaning that not all dogs with the homozygous risk genotype develop clinical DM, and some dogs with only one copy of the mutation may develop disease in rare circumstances.
For practical breeding purposes, dogs are classified as:
Clear: Two copies of the normal allele (N/N). Very low risk of developing DM.
Carrier: One copy of the mutation and one normal allele (A/N). Elevated risk compared to clear dogs, but most carriers do not develop clinical DM. However, carriers should not be bred to other carriers, as 25 percent of such litters will produce at-risk dogs.
At Risk: Two copies of the mutation (A/A). Significantly elevated probability of developing DM if they live long enough. Studies suggest that at-risk dogs have a lifetime probability of 50 to 65 percent of developing clinical DM.
The incomplete penetrance means that testing does not predict individual fate with certainty. An at-risk dog may live a full life without clinical signs. But on a population level, the at-risk genotype substantially increases disease probability, and breeding to eliminate the at-risk genotype from programs is a straightforward prevention strategy.
DM Frequency in White Shepherd Populations
Because the SOD1 mutation is segregating in German Shepherd populations globally, and because white shepherds and Berger Blanc Suisse are genetically German Shepherds at the relevant chromosome, the mutation is present in white shepherd populations at frequencies comparable to what I have documented in German Shepherd populations of similar origin.
I have tested Berger Blanc Suisse breeding stock from multiple European countries as part of my research. The at-risk genotype (A/A) appears at frequencies consistent with what is found in German Shepherd populations. Some national Berger Blanc Suisse populations show slightly elevated frequencies, potentially due to founder effects concentrating the mutation through the small founding populations I describe in my article on population genetics and inbreeding in white shepherd lines.
This is a genuinely actionable finding. Breed clubs that establish DM testing requirements for breeding and track mutation frequency over generations can demonstrably reduce DM prevalence. Some European kennel clubs have already implemented testing requirements for German Shepherd breeding stock. Berger Blanc Suisse clubs should follow or, better, lead.
Testing and Its Use
Testing for the SOD1 mutation uses the same cheek swab collection that I describe in my article on DNA testing procedures for the E locus and other color genes. The major commercial canine genetic testing companies all include DM testing in their health panels. The cost is minimal. The information is significant.
My recommendations for DM testing in white shepherd and Berger Blanc Suisse programs:
Test all breeding stock before breeding. Both males and females should have known DM genotype before being used in any breeding program.
Avoid at-risk to at-risk matings. Dogs that are A/A (at risk) should not be bred to other A/A dogs. All offspring from such matings would be at risk.
Manage carrier dogs thoughtfully. Carriers (A/N) can be bred to clear dogs (N/N) without producing at-risk offspring. This allows breeders to use otherwise excellent dogs while managing DM risk.
Work toward reducing carrier frequency. Over multiple generations, preferentially selecting N/N dogs as breeding stock reduces the mutation frequency in the population without the abrupt loss of genetic diversity that would result from immediately excluding all carriers.
Document and report results to breed health registries. Transparent health data, including DM results, allows breed communities to track population-level progress. The health transparency I advocate throughout my work applies to neurological health just as it does to hip and elbow orthopedic screening.
The Connection to Genetic Diversity
One consideration I raise with breeders is the tension between DM risk management and genetic diversity. In small populations, aggressively eliminating all carriers from the breeding pool risks reducing the genetic diversity that is already a concern for white shepherd populations.
The approach I recommend balances these concerns. Rather than immediately excluding all carriers, manage carrier breeding carefully by ensuring carriers are only bred to clear partners. Test offspring and over generations shift the program toward a higher proportion of N/N dogs. This gradual approach reduces DM prevalence while avoiding the bottleneck that would result from eliminating a large fraction of the breeding pool in a single generation.
The genetic diversity challenges I outline mean that every dog excluded from a white shepherd breeding program should be excluded for compelling reasons and replaced with a dog that contributes novel genetic material. DM at-risk status is a compelling reason. Carrier status requires more nuanced management that takes population diversity into account.
A Note on the Research Landscape
The SOD1-DM connection in dogs was a genuine scientific advance when it was published. The researchers involved deserve credit for identifying a mutation that explains a devastating disease and that enables prevention through testing.
However, the science continues to evolve. Researchers have identified that some dogs develop DM without carrying the SOD1 mutation, and that some dogs with the at-risk genotype never develop clinical disease. This suggests that the SOD1 mutation is a major contributor but not the complete genetic explanation. Modifier genes likely influence whether at-risk dogs develop clinical disease.
For current breeding decisions, testing for the known SOD1 mutation and managing accordingly is the best available tool. As the research advances and additional risk factors are identified, testing recommendations will expand. The core principle, that informed breeding decisions based on genetic data reduce preventable disease, applies regardless of which specific mutations are included in the panel.
White shepherds and Berger Blanc Suisse deserve the same rigorous health testing approach that the best German Shepherd programs apply. Their coat does not protect them from or predispose them to neurological disease. Their genetics determine their disease risk, and those genetics can be evaluated and managed with the tools available today.