Change in fiber size in Duchenne muscular dystrophy

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Abstract
A curve representing changes in mean diameter of gastrocnemius muscle fibers with age was constructed from measurements of 72 control muscle specimens. The rate of diameter increase was greatest in the neonate and decreased with age. The coefficient of variation for these specimens remained relatively constant with increasing age and mean fiber size, which suggested that all fibers in normal muscle grew at the same proportionate rate and reacted uniformly to the same growth stimuli. Biopsies from young dystrophic children had mean fiber diameters greater than those of corresponding control samples. This fact suggested that a true hypertrophy of muscle fibers contributes to the clinically observable calf enlargement seen in many of these children. At approximately 5 to 7 yr. of age, the increase in mean fiber diameter ceased in the dystrophic biopsies, and there was an accelerated increase in the degree of fiber size variation. These occurrences were due to an increased replacement of normal and large fibers by abnormally small fibers.