Degenerative Myelopathy DM (Exon 1) Health Testing for Bernese Mountain Dogs

The Bernese mountain dog puppies are a large breed in the Kennel Club’s working group, historically used for herding and cattle tending in Switzerland. Recognisable by their tall, stocky stature, these dogs combine an impressive appearance with gentle, loyal temperaments that make them beloved companions.

Known for patience and calmness, Bernese mountain dogs generally get on well with children but require ample exercise to maintain health. Their thick, heavy coats shed extensively, necessitating regular grooming and brushing to manage. Investing in a powerful hoover and grooming tools is a wise choice for owners.

Large breeds like the Bernese mountain dog have shorter life expectancies than smaller dogs, averaging seven to eight years. They are also predisposed to several inherited health conditions that may impact their quality of life and longevity.

One such condition unique to this breed is Degenerative Myelopathy (DM) associated with a specific mutation in the SOD1 gene exon 1, termed DM (Exon 1). This neurodegenerative disorder gradually damages the spinal cord, usually manifesting in dogs over eight years old, and can lead to progressive paralysis.

What is Degenerative Myelopathy DM (Exon 1)?

Degenerative myelopathy is a progressive and chronic spinal cord disease that exists in multiple genetic variants. The Bernese mountain dog is particularly affected by a unique mutation in exon 1 of the SOD1 gene, distinct from the more common exon 2 mutation found in several breeds.

Clinically, the condition starts with hind limb ataxia—loss of muscle coordination affecting walking and movement. Over months or years, this progresses to full paralysis of the hind limbs and may eventually affect the forelimbs. Urinary and faecal incontinence often occur in advanced stages.

Unfortunately, there is no cure or treatment to reverse this condition. Once hindrance to mobility and quality of life become severe, euthanasia is usually considered to prevent suffering.

How is Degenerative Myelopathy Inherited in Bernese Mountain Dogs?

This type of DM follows an autosomal recessive inheritance pattern. Dogs must inherit two copies of the mutated gene to be at significant risk of developing the disease. Importantly, some dogs with two copies may not develop symptoms due to incomplete penetrance.

• If both parents are tested affected, all puppies will be affected.
• Two clear parents will only produce clear pups.
• Two carrier parents usually produce a mix: 50% carriers, 25% clear, and 25% affected.
• A pairing of a clear and an affected parent results in all carrier puppies.
• A clear parent bred with a carrier gives about 50% clear and 50% carriers.
• A carrier and affected pairing yields 50% carriers and 50% affected puppies.

Importance of DNA Testing for Degenerative Myelopathy

Because clinical symptoms appear late, often after breeding age, DNA testing is crucial for informed breeding decisions. The test categorises dogs as:

• Clear: No copies of the exon 1 or exon 2 mutations;
• Carrier: One copy of the mutation, usually asymptomatic;
• Affected/At risk: Two copies of mutations or one copy of each exon 1 and exon 2 mutation, at high risk of DM.

UK breeders and owners should ask their vets to perform DNA testing before mating decisions. Samples are sent to accredited labs specialising in SOD1 gene mutation analysis.

Genetic testing helps reduce disease transmission and supports the health and welfare of future litters. However, it is not a definitive diagnosis of DM as clinical signs also need assessment, and other neurological issues must be ruled out.

Promoting Responsible Breeding and Ownership

Responsible ownership includes understanding health issues specific to the Bernese mountain dog and cooperating with breed clubs and vets to prioritise health screenings. Selecting breeding pairs without combined risks of DM (Exon 1) will help lower disease incidence gradually.

Prospective owners considering a Bernese mountain dog puppy should seek reputable breeders who provide health clearances, including DM testing. This ensures stronger, healthier dogs and a more enjoyable companionship experience.

Conclusion

Degenerative Myelopathy DM (Exon 1) in Bernese mountain dogs is a serious hereditary neurological disease linked to a specific gene mutation unique to the breed. It causes progressive paralysis, typically in eight-year-olds and older. DNA testing is essential for breeders and owners to manage the condition responsibly and safeguard the breed's health.

By prioritising genetic screening, responsible breeding, and early awareness, the Bernese mountain dog community can work towards reducing the impact of this disease and improving dogs' quality of life.