Hereditary myopathy of the diaphragmatic muscles in Holstein-Friesian cattle.

We describe a family line with an autosomal recessive disease of muscular dystrophy of the diaphragmatic muscles in Holstein-Friesian cattle. Histopathological examination in the present cases revealed various degenerative changes in the diaphragmatic and other thoracic muscles as follows: variation in muscle fiber diameter, fiber splitting, sarcoplasmic masses, ring fiber, vacuolar and hyalinized degeneration of muscle fibers. In addition, central core-like structures were the prominent features in the diaphragmatic muscles, occupying the center of the fiber or scattered within the fiber. These pathological alterations are consistent with the diaphragmatic myopathy previously reported in Meuse-Rhine-Yssel cattle in the Netherlands. The fibers containing core-like structures consisted of three distinct zones which could be well distinguished by NADH-tetrazolium reductase activity. This activity was absent in the innermost zone, decreased in the intermediate zone, and normal or increased in the periphery. Electron microscopically, this structure appeared to be composed of focal myofibrillar degeneration beginning with streaming or disintegration of the Z disk. We discuss here the similarity between this core-like structure and the other alternative organelles that have been reported previously, and a possible defect or storage in the cytoskeleton from the findings of the Z disk abnormalities.