Electron cytochemistry of crystalline inclusions in human skeletal muscle mitochondria

Limb muscle biopsies from a patient with idiopathic progressive ophthalmoplegia and a patient with a slowly progressive neuromuscular disorder since infancy revealed by conventional electron microscopy the presence of crystalline inclusions in the mitochondria as the most prominent morphological finding. Electron cytochemical studies on fresh tissue blocks showed no cytochrome C oxidase or carnitine acetyl transferase activity within the crystalline inclusions. The study of respiration linked accumulation of electron dense strontium supported by either NAD or flavoprotein linked substrates on freshly isolated mitochondrial fractions showed no electron dense strontium within the crystalline inclusions. These electron cytochemical findings suggest that the crystalline inclusions are space occupying structures that do not have an active functional role within the mitochondrion.