Muscle maturation delay in infantile myotonic dystrophy.

Specimens of the quadriceps femoris muscle from four infants with neonatal myotonic dystrophy had features of muscle fiber immaturity. Delayed establishment of major fiber subtypes and persistent myotubes, seen in the youngest infant, resolved in a repeated specimen obtained at the age of 4 months. Prominence of satellite cells, central nuclei, acid phosphatase activity sites, and Golgi zones diminished with age at biopsy. All four infants had type 1 fiber-size disproportion. These results substantiate the concept of delayed muscle fiber maturation in myotonic dystrophy.