Fatal reducing body myopathy. Ultrastructural and immunohistochemical observations.

Two female infants who developed normally during infancy began to have progressive muscle hypotonia and weakness from 2 years 10 months and 2 years 3 months of ages, respectively. Both patients had rapidly progressive muscle weakness with death from respiratory failure at 4 years 11 months and 3 years 9 months, respectively. In addition to mild inflammation in their muscle biopsies, the most striking finding was the presence of numerous reducing bodies (RB) in almost all degenerating fibers. By electron microscopy, these bodies consisted of fine granular material, usually located around the degenerating nucleus. These bodies showed no immunohistochemical reaction to antibodies against structural, cytoskeletal and membrane proteins and a histone-specific antibody against nuclei and chromosomes. They were occasionally positively stained with a ubiquitin antibody. Although the origin of these bodies remains unknown, they appeared to be related to active myofibrillar degeneration, probably resulting from primary nuclear degeneration.