DURING the past ten years several myopathies with unusual microscopic changes in muscle have been described.1-3 Shy and Magee presented the original report of a familial myopathy, "central core disease," characterized by weakness and hypotonia from birth and a characteristic morphologic abnormality in the center of muscle fibers. Shy and co-workers later described "nemaline myopathy," a congenital muscle disease marked by collections of small rod-shaped structures within muscle fibers. Enlarged and numerous mitochondria, referred to as "megaconial" and "pleoconial" respectively, have recently been demonstrated in the electron microscopic study of muscle in sporadic cases with clinical signs of myopathy.4
This report is a clinical and pathologic study of two sisters with diffuse muscular weakness and growth retardation, with enlarged and abundant muscle mitochondria.
Report of Cases
CASE 1.—This 15-year-old girl was referred for the study of muscle weakness, growth failure, and seizures. She weighed 1,531 gm (3