Congenital myopathy with arrest of myogenesis prior to formation of myotubes

We report a novel type of congenital myopathy, which is characterized by an early arrest of muscle formation prior to formation of myotubes. A female infant born prematurely at 32 weeks of gestational age died after six weeks of continuous ventilatory support. Various muscle specimens including quadriceps, deltoid, pectoral, neck, psoas, tongue, and diaphragm musculature were studied. Light and electron microscopy revealed well-demarcated fascicular structures interspersed with undifferentiated, mononuclear myogenic cells. Multinucleated myotubes and muscle fibres were not detectable, pointing towards a defect prior to the generation of myotubes during myogenesis. Immunohistochemistry identified the absence of dystrophin, N-CAM, MyoD and myogenin expression in these myogenic cells, compatible with a block of the complex transcriptional network necessary for correct embryonic muscle formation at an early stage of muscle development. These myopathological findings were absent in cardiac muscle, indicating that the defect exclusively affects skeletal muscle formation.

Leukoencephalopathy with ataxia, hypodontia, and hypomyelination

The authors describe four unrelated girls with a distinctive neurologic disorder with early-onset progressive ataxia and hypodontia with a characteristic pattern of delayed dentition. Cerebral MRI shows hypomyelinated white matter and cerebellar atrophy; 1H-MRS of white matter reveals a marked elevation of myo-inositol.