Muscle regeneration in mitochondrial myopathies

Mitochondrial myopathies cover a diverse group of disorders in which ragged red and COX-negative fibers are common findings on muscle morphology. In contrast, muscle degeneration and regeneration, typically found in muscular dystrophies, are not considered characteristic features of mitochondrial myopathies. We investigated regeneration in muscle biopsies from 61 genetically well-defined patients affected by mitochondrial myopathy. Our results show that the perturbed energy metabolism in mitochondrial myopathies causes ongoing muscle regeneration in a majority of patients, and some were even affected by a dystrophic morphology. The results add to the complexity of the pathogenesis underlying mitochondrial myopathies, and expand the knowledge about the impact of energy deficiency on another aspect of muscle structure and function.

► Muscle regeneration is a significant feature in mitochondrial myopathy.
► Muscle regeneration is not correlated to mtDNA mutation load or age.
► No correlation between regenerating and ragged red or COX-negative fibers.
► Structural compensation appears related to muscle histopathology.
► Apoptosis appears in a very small fraction of muscle fibers in all mutation types.