Mitochondrial respiratory chain disorders are an established cause of liver failure in early childhood. In some patients, the levels of mitochondrial DNA are markedly reduced, a condition referred to as mtDNA depletion syndrome (MDS). We report here on the ultrastructural changes in the livers of 10 infants with the hepatic form of this syndrome. All patients displayed progressive liver failure, neurological abnormalities, hypoglycemia, and lactic acidosis that warranted investigation of respiratory chain disorder in liver tissue, specifically expressing the disease. Decreased activity of respiratory chain complexes containing mtDNA-encoded subunits (complexes I, III, IV) was shown in 5 patients. Mitochondrial DNA depletion was confirmed by Southern blot analysis in the livers of 6 patients. We found hepatocytes filled with mitochondria having aspects of "oncocytic transformation," associated with numerous changes in shape, size, cristae, and matrix. The changes were virtually identical in all specimens. In many hepatocytes, microvesicular steatosis was the salient feature. Additional findings included cholestasis and focal cytoplasmic biliary necrosis (CBN), as well as cytosiderosis in hepatocytes and sinusoidal cells. In some hepatocytes the damage appeared extreme, but fibrosis was identified only in the few patients who died beyond 6 months of age. Although individual ultrastructural findings are not specific, when taken together, they show a diagnostic pattern highly suggestive of a respiratory chain disorder. In the appropriate clinical context, these findings can direct the clinician towards the diagnosis of hepatic MDS.
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Abbreviations: mtDNA, mitochondrial DNA; MDS, mitochondrial DNA depletion syndrome; COX, cytochrome c oxidase; OXPHOS, oxidative phosphorylation; CBN, cytoplasmic biliary necrosis; ATP, adenosine triphosphate; NADH, nicotinamide adenine dinucleotide (reduced); FADH2, flavin adenine dinucleotide (reduced). From the1Metabolic Disease Unit, and 2Pediatric Gastroenterology Unit, Rambam Medical Center; the 3Metabolic Disease Unit, Shaare Zedek Medical Center, Jerusalem; and the 4Electron Microscopy Unit, B. Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel. Received March 20, 2001; accepted July 2, 2001. The electron-microscopic work was supported in part by The Milman Fund for Pediatric Research (grant 12-99), Dr. I. Manov was supported in part by the Giladi Fund (1999-2000). The metabolic studies were supported in part by the Joseph Elias Fund, Technion VPR Fund (grant #181-421). Address reprint requests to: Theodore C. Iancu, M.D., Pediatric Research and Electron Microscopy Unit, B. Rappaport Faculty of Medicine, P.O.Box 9649, Haifa, 31096, Israel. E-mail: email@example.com; fax: (972) 4-851-4285. Copyright © 2001 by the American Association for the Study of Liver Diseases. 0270-9139/01/3404-0022$35.00/0 doi:10.1053/jhep.2001.27664
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