Degenerative Myelopathy (DM) Testing in Dogs: What Breeders Need to Know

Degenerative Myelopathy (DM) is a progressive, fatal neurological disease affecting the spinal cord of dogs. It is caused by a mutation in the SOD1 gene and has a relatively simple autosomal recessive inheritance pattern — though the disease's penetrance is incomplete, meaning not all at-risk dogs develop clinical disease. Testing is available from OFA and most major DNA labs.

What Is Degenerative Myelopathy?

DM begins with hind limb weakness and progresses to full paralysis, typically appearing in middle-aged to older dogs (6–14 years). There is no treatment and no cure. The disease is clinically similar to ALS in humans. Affected dogs typically require euthanasia within 6 months to 3 years of clinical onset.

The SOD1 mutation associated with DM was identified in 2009, enabling DNA testing that identifies at-risk dogs before any clinical signs appear.

DM Test Results and What They Mean

DM Clear (N/N): The dog has two normal copies of SOD1. It is not at risk for DM and cannot pass the DM mutation to offspring. Two clear dogs will never produce an at-risk puppy.

DM Carrier (N/A): One copy of the normal gene, one copy of the mutation. Carriers are not expected to develop DM themselves but can pass the mutation to offspring. Two carriers bred together produce an expected 25% at-risk offspring.

DM At-Risk (A/A): Two copies of the DM mutation. These dogs have a significantly elevated risk of developing DM, though not all at-risk dogs develop clinical disease — penetrance is incomplete. At-risk dogs should not be used for breeding if other options exist.

Breeds Affected by DM

DM affects many breeds. The mutation is particularly prevalent in:

Breeding Recommendations

The goal is to eliminate DM from breeding lines without eliminating genetic diversity. A practical approach: