Centronuclear Myopathy (CNM) in Labrador Retrievers: Breeding Guidance

Centronuclear Myopathy (CNM) is an inherited neuromuscular disease affecting Labrador Retrievers. Caused by a recessive mutation in the PTPLA gene, CNM produces progressive muscle weakness from early puppyhood. DNA testing identifies carriers and affected dogs before breeding, allowing responsible breeders to prevent producing affected puppies entirely.

Clinical Signs of CNM

CNM affects muscle function — the muscles themselves develop and contract abnormally. Signs typically appear at 2–5 months of age:

• Progressive weakness, especially in the hind quarters
• Exercise intolerance — the puppy tires easily and may collapse
• Abnormal gait — stiff, stilted movement
• Difficulty holding the head up (neck muscle weakness)
• Abnormal swallowing, regurgitation
• Muscle atrophy

There is no treatment. Affected puppies that survive have permanent significant disability. Many are euthanised for quality of life reasons.

Inheritance and DNA Testing

CNM is autosomal recessive — two copies of the mutant allele produce an affected dog. Carriers (one copy) are clinically normal.

Clear (N/N): Two normal PTPLA alleles — will not develop CNM, cannot pass the mutation to offspring

Carrier (N/CNM): One normal, one mutant — clinically normal, but passes the mutation to 50% of offspring on average. Carrier x carrier pairings produce 25% affected puppies.

Affected (CNM/CNM): Two mutant alleles — will develop the disease

Prevalence and Where to Test

CNM carrier frequency is estimated at approximately 20% in Labrador Retrievers, which means one in five Labs in some populations carries one copy. This is high enough that testing both breeding dogs — not just one — is important.

DNA testing for CNM is available from PawPrint Genetics, Embark, and the Laboklin lab. OFA publishes CNM results when submitted. Verify at ofa.org by searching the dog's registered name.

Breeding Strategy

Do not breed two carriers together. A carrier x clear pairing produces no affected puppies. Over generations, selecting toward clear dogs gradually reduces the mutation's frequency in the breeding population.