Light-cored dense particles in mitochondria of a patient with skeletal muscle and myocardial disease.

A 15-year-old boy with skeletal muscle and myocardial disease was found to have large numbers of abnormal muscle mitochondria, the distinguishing feature of which was the presence of many light-cored dense particles. These particles bore a marked resemblance to those seen in situations where mitochondria accumulate calcium. If that is what they were, it remains to be determined whether such an accumulation of calcium, or other mitochondrial abnormality, played a role in the patient's muscle weakness. Alternatively, the granules might have represented evidence of virus involvement of the mitochondria, but this seems less likely.