Myopathy with abnormal structure and function of muscle mitochondria.

Abstract
A case of myopathy involving the proximal muscles is described in a 27-month-old girl. Light microscope study revealed the presence of muscle fibers of very small diameter containing fine, granulated material. High activity of oxidative enzymes was seen in these small fibers. Electron microscopic study revealed numerous mitochondria. Many of these were abnormal in shape and in size. Biochemical studies of isolated mitochondrial fractions showed loose coupling of oxidative phosphorylation.