Mitochondrial mosaics in the liver of 3 infants with mtDNA defects

<p>Abstract</p> <p>Background</p> <p>In muscle cytochrome oxidase (COX) negative fibers (mitochondrial mosaics) have often been visualized.</p> <p>Methods</p> <p>COX activity staining of liver for light and electron microscopy, muscle stains, blue native gel electrophoresis and activity assays of respiratory chain proteins, their immunolocalisation, mitochondrial and nuclear DNA analysis.</p> <p>Results</p> <p>Three unrelated infants showed a mitochondrial mosaic in the liver after staining for COX activity, i.e. hepatocytes with strongly reactive mitochondria were found adjacent to cells with many negative, or barely reactive, mitochondria. Deficiency was most severe in the patient diagnosed with Pearson syndrome. Ragged-red fibers were absent in muscle biopsies of all patients. Enzyme biochemistry was not diagnostic in muscle, fibroblasts and lymphocytes. Blue native gel electrophoresis of liver tissue, but not of muscle, demonstrated a decreased activity of complex IV; in both muscle and liver subcomplexes of complex V were seen. Immunocytochemistry of complex IV confirmed the mosaic pattern in two livers, but not in fibroblasts. MRI of the brain revealed severe white matter cavitation in the Pearson case, but only slight cortical atrophy in the Alpers-Huttenlocher patient, and a normal image in the 3rd. MtDNA in leucocytes showed a common deletion in 50% of the mtDNA molecules of the Pearson patient. In the patient diagnosed with Alpers-Huttenlocher syndrome, mtDNA was depleted for 60% in muscle. In the 3rd patient muscular and hepatic mtDNA was depleted for more than 70%. Mutations in the nuclear encoded gene of <it>POLG </it>were subsequently found in both the 2nd and 3rd patients.</p> <p>Conclusion</p> <p>Histoenzymatic COX staining of a liver biopsy is fast and yields crucial data about the pathogenesis; it indicates whether mtDNA should be assayed. Each time a mitochondrial disorder is suspected and muscle data are non-diagnostic, a liver biopsy should be recommended. Mosaics are probably more frequent than observed until now. A novel pathogenic mutation in <it>POLG </it>is reported.</p> <p>Tentative explanations for the mitochondrial mosaics are, in one patient, unequal partition of mutated mitochondria during mitoses, and in two others, an interaction between products of several genes required for mtDNA maintenance.</p

Liver pathology and immunocytochemistry in congenital peroxisomal diseases : a review

Diagnostic and pathogenetic investigations of peroxisomal disorders should include the study of the macroscopic and microscopic pathology of the liver, in addition to careful clinical observations, skeletal X-ray and brain CT scan, assays of very long-chain fatty acids and bile acid intermediates, and selected enzyme activities. This review of the literature also contains novel observations about the following syndromes: cerebro-hepato-renal (Zellweger) syndrome, X-linked and neonatal adrenoleukodystrophies (ALD, NALD), NALD-like syndromes, infantile phytanic acid storage, classical Refsum disease, rhizomelic and other forms of chondrodysplasia punctata (XD, XR, AR), hyperpipecolic acidaemia, primary hyperoxaluria I, pseudo-Zellweger and Zellweger-like syndromes, and single enzyme deficiencies. Microscopic data include catalase staining and morphometry of peroxisomes, immunolocalization of beta-oxidation enzymes, detection of trilamellar, polarizing inclusions in PAS-positive macrophages, fibrosis and iron storage. Peroxisomal enlargement appears to be related to functional deficit in beta-oxidation disorders as well as in rhizomelic chondrodysplasia punctata. Because normal peroxisomal localization of active beta-oxidation enzymes can accompany a C26 beta-oxidation deficit, other mechanisms such as impaired transport of metabolites should be investigated. 'Ghost'-like organelles are shown in the liver of an infantile Refsum patient and in an NALD-like case; immuno-gold labelling of membrane proteins did not reveal ghosts in Zellweger livers