http://www.mdausa.org/publications/mitochondrial_myopathies.html
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Muscular Dystrophy Association
Just as some diseases are named for the part of the body they affect (like heart disease), mitochondrial diseases are so-named because they affect a specific part of the cells of which our bodies are made. Specifically, mitochondrial diseases affect the mitochondria — tiny energy factories found inside almost all our cells.