This inherited (autosomal recessive) condition is characterized by a type 2 muscle fiber deficiency and is now called centronuclear myopathy. Clinical signs are seen at <5 months of age and include skeletal muscle atrophy, stunted growth, ataxia, and weakness. Signs are progressive until the animal reaches maturity, when they stabilize. Animals may have a normal life span. Diagnosis is by creatinuria, muscle biopsy, and electromyography. Histology reveals increased connective tissue around muscle fibers and staining deficiency of type II fibers. Myotonic discharges are seen with electromyography. There is no effective treatment, although warm housing and L-carnitine supplementation may make affected dogs more comfortable. This condition has different clinical features than exercised-induced collapse in Labrador Retrievers.