Figure 2.

Skeletal muscle histopathological abnormalities associated with pathogenic mtDNA mutations. The histological and histochemical assessments of skeletal muscle may provide useful clues in determining mtDNA involvement in disease pathology. Shown is a sequential series of transverse-orientated muscle biopsy sections from a patient with CPEO due to a mitochondria tRNA gene point mutation, reacted for the following stains or enzyme activities: (a) modified Gomori trichome stain highlighting classical ragged-red muscle fibres, in which abnormal mitochondrial accumulate around the subsarcolemmal region; (b) SDH, which further accentuates the subsarcolemmal accumulation of mitochondrial enzyme activity; (c) COX histochemistry showing pale-reacting COX-deficient fibres within a population of normal fibres, a typical “mosaic” distribution; (d) sequential COX/SDH histochemistry highlighting individual COX-deficient fibres which retain SDH activity (blue) against a background of fibres with normal COX activity (brown).