CNM in Labrador Retrievers

CNM (Centronuclear Myopathy) or also HMLR (Hereditary Myopathy in Labrador Retrievers), are two names used for the same disease. It is a genetically conditioned defect in the development of muscle fibres occurring in the field line and the show line in Europe, USA, Canada and Australia. The autosomal recessive centronuclear myopathy in Labradors is caused by insertion SINE in exon 2 of PTPLA-gene (Pelé et al. 2005).

At birth, the affected pups are indistinguishable from their healthy littermates, but by 2 weeks of age there is a significant progressive loss of weight. By one month of age the pups with CNM have lost tendon reflexes and this can be used for early and reliable diagnostics. By 2 to 5 months, the muscle atrophy starts to develop that becomes evident by awkward gait, very wobbly walking and provided the dog is able to remain on its feet, by decreased tolerance to exercise, associated with a general muscle weakness. The muscle atrophy also affects swallowing muscles and in consequence thereof food may be breathed in and recurrent pneumonia may occur. The affected dog cannot stand the cold (as known, faced with a cold environment, the body tries to protect itself by shivering to increase muscle heat production and due to it the body becomes warm) and might even collapse. There is no cure to CNM disease. And therefore the affected dogs are very early euthanized. However, it can be prevented by a genetic test that reveals potential carriers of the disease. By suitable mating of the carriers of this disease with healthy individuals the CNM is gradually eliminated.

Dogs that inherit one mutated allele from each parent have two copies of the mutated gene and are affected by CNM and the typical symptoms may be present to a different extent. Dogs with one copy of the mutated gene show no symptoms affecting their health, but are carriers of the disease. The molecular-genetic test enables to detect the presence or absence of the mutation and to identify the carriers of the disease.

References:
Manuel Pele et al.: SINE exonic insertion in the PTPLA gene leads to multiple splicing defects and segregates with the autosomal recessive centronuclear myopathy in dogs; Human Molecular Genetics; 2005