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In Reply.—
I regret that the report of Karpati et al ("Infantile Myotonic Dystrophy," Neurology 23:1066-1077, 1973) was inadvertently overlooked in our review. Their article indeed is relevant and important to understanding the range of infantile myotonic dystrophy.Their patients differed from ours in having minimal or no arthrogryposis at birth and in surviving. The assumption that the muscle fibers in their patients had been less mature at birth, and had progressed in development during the months and years before muscle biopsies were performed, is not necessarily a justified conclusion. We emphasized in our patients that the state of immaturity of the muscle corresponded to the degree of clinical involvement; the least mature muscles were those associated with arthrogrypotic joints, and other muscles were minimally involved both clinically and pathologically. We chose to regard the pathologic condition of severely involved muscles as maturational arrest because all stages of development, from satellite cell