We studied a family with four neonatal deaths due to X-linked myotubular myopathy. The cardinal features of the two index patients included low Apgar scores, weak respiratory efforts requiring intubation and positive pressure ventilation, flaccidity, lethargy, hypotonia, reduced muscle mass, no spontaneous movements, poor grasp, suck, and Moro reflexes, absent deep tendon reflexes, cephalohematomata, narrow chest with thin ribs, undescended testes, and various minor congenital anomalies.

Light microscopy studies revealed variation in cell size and fiber hypotrophy. Fiber typing showed that the small fibers were both Type I and II cells; 90% of larger fibers were Type II A and B. Muscle nuclei appeared prominent and were located centrally in both large and small muscle cells. Small fibers showed prominent hollow centers with thin marginal rims of myofibrils. Larger fibers also had altered myofibril-free centers.

Electron microscopy examinations also noted fiber size variation and central nuclei. The myofibril-free areas contained glycogen and vacuoles. Complex stacks of cylinders comprised of membranes with granular material resembling junctional complexes abutted the central pale regions. Both rough endoplasmic reticulum and ribosomes aligned along the myofilaments were observed.

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Pueschel, S., Ambler, M., Neave, C. et al. X-LINKED RECESSIVE MYOTUBULAR MYOPATHY. Pediatr Res 18, 224 (1984). https://doi.org/10.1203/00006450-198404001-00786

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