Myotubular myopathy: arrest of morphogenesis of myofibres associated with persistence of fetal vimentin and desmin. Four cases compared with fetal and neonatal muscle.

Vastus lateralis muscle biopsies of four unrelated male neonates showing myotubular (i.e. centronuclear) myopathy (MM) were compared with muscle from four human fetuses in the myotubular stage of development, a 31 week preterm infant and four term neonates. The perimysium, blood vessels, spindles, myelinated intramuscular nerves, and motor end-plates in MM are as well developed as in term neonatal muscle. The cytoarchitecture of myofibres in MM is more mature than that of fetal myotubes in the spacing of central nuclei, Z-band registry, development of the sarcotubular system, and in the condensation of nuclear chromatin and nucleoli. Triads in MM may retain an immature oblique or longitudinal orientation. Myofibrillar ATPase shows normal differentiation of fibre types, consistent with normal innervation. Spinal motor neurons are normal in number and in RNA fluorescence. Immunoreactivity for vimentin and desmin in myofibres of MM is uniformly strong, as in fetal myotubes and unlike mature neonatal muscle. Maternal muscle biopsies of two cases also showed scattered small centronuclear myofibres reactive for vimentin and desmin. The arrest in morphogenesis of fibre architecture in MM is not a general arrest in muscle development. Persistence of fetal cytoskeletal proteins that preserve the immature central positions of nuclei and mitochondria may be important in pathogenesis. Vimentin/desmin studies of the infant and maternal muscle biopsies are useful in establishing the diagnosis.