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Centronuclear Myopathy      CNM Test      Code 352

For breeds: Lab/Golden Cross, Labradoodle (including Australian variety), Labradoodle/Goldendoodle Cross, and Labrador Retriever

Clinical signs/Disease Description: 

Centronuclear Myopathy (CNM), also known as type II muscle fiber deficiency, is a distinct form of inherited muscular myopathy in the Labrador Retriever. Clinical signs of the disease in affected puppies include a progressive significant weight loss starting at two weeks of age, the absence of tendon reflexes at about one month of age, followed by the development of an awkward gait and decreased exercise tolerance due to generalized muscle weakness between 2 to 5 months. In adults, the most striking feature of the disease progression is the atrophy of temporal, cervical and leg muscles, leading to abnormal postures and movements, as well as a predisposition to respiratory complications. On a histological level, this type of myopathy is characterized by a progressive centralization of nuclei in muscular cells, as it is reflected in the descriptive name of the disease, i.e. centronuclear myopathy (1).  

CNM mutation test
 

A small insertion in the PTPLA gene has been identified as the mutation that causes the CNM in Labrador Retrievers [2]. The mutation has a worldwide distribution with an average carrier frequency of 13.9 %, with the highest frequency found in Labrador retrievers from the UK (19%), the USA (13%) and Canada (11.5%) [3].
  The DNA-based test is designed to determine the genetic status of a tested dog as being homozygous normal, carrier or homozygous affected in regard to the CNM mutation.    

Testing/Breeding Recommendations:
 

The Centronuclear Myopathy is inherited in an autosomal recessive mode with both sexes equally affected when a dog receives two copied of the mutated gene. Carriers of one copy of the insertion do not develop clinical symptoms but they transmit the mutation to about 50% of their progeny. In order to avoid producing CNM affected offspring, at least one parent of any litter should be DNA tested and shown to be Normal/Clear of the PTPLA mutation.

References:

1. Tiret L., Blot S., Kessler JL, Gaillot H., Breen M., and Panthier JJ. 2003. The cnm locus, a canine homologue of human autosomal forms of centronuclear myopathy, maps to chromosome 2. Hum Genet, 113:297-306.

2. Pelé M, L. Tiret, JL Kessler, S Blot, JJ Panthier. 2005. 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 14(11):1417-1427.

3. Maurer M, J Mary, L Guillaud et al. 2012. Centronuclear myopathy in Labrador Retrievers: A recent founder mutation in the PTPLA gene has rapidly disseminated worldwide. Plos One 7(10): e46408.


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