Centronuclear myopathy (CNM; Labrador muscular myopathy) is an autosomal-recessive genetic disease of dogs characterized by early-onset muscular atrophy.
This disease is caused by a missense mutation in the PTPLA gene.
Centronuclear myopathy is a recessively inherited muscular disease. At birth, affected puppies are indistinguishable from their control littermates but as from two weeks of age, a progressive significant weight loss is observed. At one month of age, the absence of tendon reflexes is noticed and used as an early and reliable diagnosis. The age of onset of the disabling phenotype varies between 2 to 5 months, with an awkward gait and a decreased exercise tolerance and difficulty eating associated with a generalized muscle weakness. The pup will never recover from this disabling disease.
Clinical signs become apparent within the first year of life (usually from 6 weeks to 7 months) and are variable degrees of exercise-induced weakness and collapse, particularly the hindlimbs, as well as neurological deficits such as ataxia, bunny-hopping and ventroflexion of the neck. As the condition progresses, generalized atrophy of the skeletal muscles develops.
A tentative diagnosis can be established based on muscle tissue biopsy, with histopathology showing centronuclear myopathy in type II muscle fibres, but a definitive diagnosis requires molecular testing using PCR-based DNA assays. This also allows for identification of asymptomatic heterozygous carrier dogs. This information is particularly relevant for breeders, enabling them to produce healthy litters.
Some dogs may respond to supportive medications such as L-carnitine, co-enzyme Q10 and vitamin B compounds.
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