Centronuclear Myopathy (CNM), formerly called Labrador Muscular Myopathy or Hereditary Myopathy of the Labrador Retriever (HMLR) as well as many other names, segregates in Labrador Retrievers. The disease was first observed in the 1970’s. By the 1990’s, the incidence had increased significantly. This increase is globally due to famous successful Labradors who are carriers being used extensively for breeding.
At this time, there is little on the disease in handbooks and clinical manuals typically used by veterinary clinics. This is due to the documents being published perhaps every five years, and because this myopathy is a breed-specific disease. There are extensive efforts to notify the thousands of veterinary clinics that there is now a simple DNA test, but it is a slow process.
CNM is a hereditary disease where the muscles of the Labrador do not develop properly. Affected pups are obvious by the time they are between three and six months of age. The pup will begin to stumble and fall when trying to walk. There are difficulties in swallowing since the muscles in the esophagus are often affected. There is no cure for the disease. See video 1 or video 2 for a picture of an affected pup. CNM is a simple autosomal recessive. Consider the charts before planning a breeding. (See my chart below)
Diagnosing CNM Affected, Carrier, and Clean Labrador Retrievers.
The CNM DNA test is highly reliable in identifying the disease. It can determine affected, carriers, and clean CNM Labradors. It is inexpensive and involves a non-painful collection of cells from the inside of the canine’s cheek. The owner can easily do the test themselves, or can choose to go to a veterinarian. The CNM Project provides kits and e-forms with very specific easy directions.
The only other way to determine if a parent in a Labrador litter is a known carrier would be if an affected pup had been produced. At one time biopsies were also used, but these have been abandoned as a method since they do not identify carriers and are expensive and invasive.
CNM clear Labradors are placed on an International Registry.