X-linked recessive myotubular myopathy: II. Muscle morphology and human myogenesis.

The classification of centronuclear myotubular myopathies is controversial. Within this group of disorders, congenital X-linked recessive myotubular myopathy (XLMTM), characterized by marked cell hypotrophy and structural resemblance to fetal myotubes, represents a distinct entity. The histologic findings in verified and probable cases of XLMTM are reviewed. In addition, the ultrastructural features of muscle in one case of XLMTM are compared with those of normal fetal muscle at various developmental ages. In XLMTM both muscle and nerve show evidence of immaturity. Proliferation of the sarcotubular organelles in XLMTM, not observed in normal fetal muscle, may be due to impaired innervation.