Fig. 2
From: The natural history of infantile mitochondrial DNA depletion syndrome due to RRM2B deficiency
Histopathological findings associated with RRM2B deficiency. The images show the histochemical and ultrastructural features of patients C, D, G, and I. On hematoxylin and eosin (HE) staining (a–d), there were myopathic features, increased variation in fiber size with excess small fibers, and vacuoles. On Gömöri trichrome (GT) staining (e–h), there was accumulation of mitochondria in the vacuolated fibers and there were some ragged-red fibers. Lipid staining with oil red O (i–l) showed marked excess lipid in the vacuolated fibers. Succinate dehydrogenase (SDH) histochemistry showed fibers with increased staining (m–p). Cytochrome c oxidase showed frequent negative fibers in all four patients (q–t). Electron microscopy was available in patients D, G, and I and showed clusters of enlarged atypical mitochondria (u–w). Nemaline rods were also present (not illustrated) in patients G and I. Patient D had two muscle biopsies 4 months apart, the second taken after a low-fat diet. The two biopsies were similar except for reduced lipid following the low-fat diet. All the images of this patient show the first biopsy except for (n), which is from the second. The table summarizes muscle biopsy findings for 8/9 new patients for whom this was available. CoQ coenzyme Q, COX cytochrome c oxidase, EM electron microscopy, NADH reduced nicotinamide adenine dinucleotide, ND not done, RBF ragged-blue fibers, RRF ragged-red fiber. Scale Bars: a–t: 50 µm, u–w: 2 µm.
