Centronuclear myopathy (CNM) is a hereditary myopathy. This condition is also known as: type II muscle fiber deficiency, autosomal recessive muscular dystrophy and hereditary myopathy. The disease affects males and females equally, and symptoms include loss of muscle tone and control, exercise intolerance, weakness, irregular gait, and loss of patellar reflex. Age of onset is 2-5 months. The carrier and affected population world-wide for the labrador retriever breed is considered to be moderately high (10-16% estimates) meaning that it is recommended that owners and breeders test carefully, and include some carriers + clear tested dogs in their breeding plans to maintain genetic diversity and a balance of other desireable traits.