Fatal neonatal hepatocellular deficiency with lactic acidosis: a defect of the respiratory chain

Orthotopic liver transplantation for mitochondrial respiratory chain disorders: a study of 5 children

BACKGROUND

Liver involvement in mitochondrial respiratory chain disorders (MRCD) frequently ends in liver failure and death. Because of the high risk of extrahepatic, particularly neuromuscular, manifestations of the disease, the indication of orthotopic liver transplantation (OLT) in these patients remains controversial. We report on 5 such children in whom OLT was carried out, in an attempt to help clarify the matter.

PATIENTS

Patients 1 and 2 presented with fulminant liver failure at ages 7 and 6 months respectively. Emergency liver transplantation was performed before etiological investigations were completed. Retrospective examination of the explanted livers showed defects in complexes I, III and IV. In patient 1, severe neurological deterioration occurred 2 months after OLT with fatal outcome 9 months later. Patient 2 is alive 22 months after OLT with moderate motor impairment. Patients 3, 4 and 5 presented with progressive liver failure before 6 months of age. Surgical liver biopsies displayed a 50% defect in complex IV (patient 3), a defect in complexes I, IV (patient 4) and in complexes I, III, IV (patient 5). Because there was no clinical extrahepatic involvement on investigations, OLT was carried out in these patients. Patient 3 died of multiple organ failure soon after OLT, patients 4 and 5 are alive respectively 21 months and 12 months after OLT with normal neurological examination.

CONCLUSION

OLT may be a valid therapeutic option in infants with delayed liver cell failure due to MRCD, only after performing in emergency a thorough inves tigation to exclude clinically significant extrahepatic, especially neuromuscular, involvement.

Mitochondrial respiratory chain disorders and the liver

Mitochondrial respiratory chain disorders are an established cause of liver failure in early childhood but they are probably under-diagnosed, partly due to under-recognition and partly due to the difficulty of investigation. It is particularly important to look for mitochondrial disorders if the liver disease presents with hypoglycaemia and lactic acidaemia or if it is accompanied by neurological, muscle or renal tubular abnormalities. Respiratory chain defects have been demonstrated in a number of patients who die of liver failure following severe epilepsy; this includes at least some cases of Alpers syndrome or 'progressive neuronal degeneration of childhood'. In mitochondrial liver disease, histology usually shows steatosis, often accompanied by fibrosis, cholestasis and loss of hepatocytes. Unless the clinical picture suggests a particular syndrome, such as Pearson syndrome, biochemical assays and histochemistry should be the initial investigations. Ideally, investigations should be carried out on liver as well as more standard tissues, such as muscle, since defects can be tissue-specific. Nuclear defects and mtDNA point mutations are probably responsible for many cases of mitochondrial liver disease but, as yet, the only identified molecular abnormalities are mtDNA rearrangements and mtDNA depletion. Treatment of mitochondrial liver disease is unsatisfactory. If the disease is confined to the liver, transplantation may be appropriate but in several patients transplantation has been followed by the appearance of disease in other organs, particularly the brain.

Microvesicular steatosis, hemosiderosis and rapid development of liver cirrhosis in a patient with Pearson's syndrome

BACKGROUND/AIMS

Pearson's marrow-pancreas syndrome consists of refractory sideroblastic anemia with vacuolization of marrow precursors and exocrine pancreas dysfunction. Patients with this disease usually have large deletions of the mitochondrial genome. We report a patient with Pearson's syndrome who had predominantly hepatic manifestations such as microvesicular steatosis, hemosiderosis and rapidly developing cirrhosis.

METHODS

Analysis of the mitochondrial and nuclear genomes, determination of enzyme activities and of the hepatic iron content were performed using standard techniques of molecular biology and biochemistry.

RESULTS

The patient had typical ringed sideroblasts in a bone marrow smear and a 7436-bp deletion of the mitochondrial genome in all tissues investigated, compatible with Pearson's syndrome. He died within 3 months after birth due to liver failure. Histopathological analysis of the liver revealed complete cirrhosis with signs of chronic cholestasis, microvesicular steatosis and massive hemosiderosis. In addition, the patient was heterozygous for the C282Y and H63D mutations of the hemochromatosis gene.

CONCLUSIONS

Pearson's syndrome should be added to the list of neonatal diseases which can cause microvesicular steatosis, hepatic accumulation of iron and liver cirrhosis.

Neonatal presentations of mitochondrial metabolic disorders

Because of the high energy requirements of the growing neonate, disorders of mitochondrial metabolism caused by defects in fatty acid oxidation, pyruvate metabolism, and the respiratory chain may often present in the neonatal period. Common neonatal presentations are hypotonia, lethargy, feeding and respiratory difficulties, failure to thrive, psychomotor delay, seizures, and vomiting. Laboratory clues include alterations in the levels of lactate, pyruvate (and the lactate/pyruvate ratio), glucose, and ketone bodies. Diagnosis usually depends on specific enzyme assays or on molecular genetic analysis. Without treatment, most infants die in the first few days or months of life. In the last decade, there have been significant advances in the understanding of the molecular basis of these disorders. This review discusses the major subgroups of mitochondrial disorders, focusing on defects of pyruvate oxidation, the Krebs cycle, and the respiratory chain. Disorders caused by respiratory chain defects may involve nuclear DNA, mitochondrial DNA, or intergenomic signaling. Recognition and early diagnosis of these conditions are important in the genetic counseling of these families.

Severe complex I deficiency in a case of neonatal-onset lactic acidosis and fatal liver failure

We report a newborn admitted to our service on the 2nd day of life because of hypotonia and metabolic acidosis. A progressive hepatocellular dysfunction dominated the clinical picture and the patient died at 13 months of age because of severe hepatic failure. Persistent lactic acidosis, high ketone bodies levels and high-normal lactate/pyruvate and 3-hydroxybutyrate/acetoacetate molar ratios in plasma were found. Investigation of a liver biopsy revealed low activities of all the mitochondrial respiratory chain enzymes but in particular a marked decrease of complex I (NADH cytochrome c reductase) activity. All respiratory chain enzyme activities were normal in cultured skin fibroblasts. Mitochondrial DNA analysis failed to detect any major rearrangements. Although only a few cases have been reported so far, it is becoming clear that liver should be considered as one of the organs involved in oxidative phosphorylation disorders. The finding of unexplained progressive liver failure with poor neurological conditions, lactic acidaemia and ketonuria strongly warrants investigation for a respiratory chain disorder. Moreover, the finding of normal respiratory enzyme activities in a tissue other than liver does not rule out the existence of an oxidative phosphorylation disorder in patients with hepatocellular disease of unexplained origin.

Depletion of mitochondrial deoxyribonucleic acid in a family with fatal neonatal liver disease

We describe a family in which three children of consanguineous parents died of hepatic failure before the age of 3 months. The first child had clinical symptoms of liver disease with hypoglycemia that were evident at birth. The second child was healthy and has normal development. The third child had severe liver dysfunction noted a few days after birth. Liver failure also developed in the fourth child soon after birth. Recently a mitochondrial disorder was considered as a possible cause. Deficiency of respiratory chain enzymes that contain polypeptides encoded by mitochondrial DNA (mtDNA) and depletion of mtDNA were found in the liver of the fourth child, but mitochondrial abnormalities were absent in muscle of the third child. The similarities in clinical presentation suggest that liver-specific depletion of mtDNA was the cause of the hepatic failure in all three children. We conclude that liver dysfunction with onset in the perinatal period can be caused by depletion of mtDNA.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

Liver cytochrome c oxidase deficiency in a case of neonatal-onset hepatic failure

In the last few years, inborn errors of oxidative phosphorylation have been recognized as possible causes of hepatic failure in infancy and respiratory enzyme deficiencies have been described in several tissues of affected individuals. Here, we report on cytochrome c oxidase deficiency in the liver but not in the skeletal muscle of a 5-month-old girl who presented hepatic failure in early infancy. Persistent hyperlactatemia (> 4 mM, normal < 2.4) with high lactate/pyruvate (L/P) molar ratios in plasma, and their further elevation in the post-absorptive period were suggestive of an inborn error of oxidative phosphorylation. However, no mutation in the coding sequences of the liver-specific subunits of cytochrome c oxidase (VIa and VIIa) has been detected and no major rearrangement or depletion of the mitochondrial DNA has been observed. Based on this observation we suggest that inborn errors of oxidative phosphorylation be considered in the diagnosis of severe hepatocellular dysfunction of unknown origin, especially when an abnormal oxidation-reduction status is found in the plasma and even if normal respiratory enzyme activities are found in peripheral tissues. The findings of normal respiratory enzyme activities in skeletal muscle, circulating lymphocytes or cultured skin fibroblasts does not rule out this diagnosis. Instead, the negativity of these tests should prompt one to carry out the specific enzyme assays in the tissue which expresses the disease, namely the liver.

Valproate-induced hepatic failure in a case of cytochrome c oxidase deficiency

We report a 3 year-old girl with a myoclonic epilepsy. A fatal hepatic failure occurred after 3 months of valproate (VPA) therapy. In this patient, a defect of cytochrome c oxidase (COX) was demonstrated in her circulating lymphocytes. The enzyme was also found to be deficient in post-mortem liver and in cultured skin fibroblasts. However, a fully functional respiratory chain was found in muscle. VPA administration apparently triggered the hepatic failure, given this patient's background of partial COX deficiency.

Fatal neonatal lactic acidosis with respiratory insufficiency due to complex I and IV deficiency

We present a newborn boy who died after 53 days of life in respiratory failure with lactic acidosis. Analysis of skeletal muscle mitochondria demonstrated a combined defect in complexes I and IV of the respiratory chain. The boy had severe muscle hypotonia but no signs of encephalopathy, illustrating the variation in multi-organ presentation of mitochondrial defects.

Fatal neonatal liver failure and mitochondrial cytopathy (oxidative phosphorylation deficiency): a light and electron microscopic study of the liver

Mitochondrial cytopathies are multisystemic disorders of extremely variable expression due to a deficiency in oxidative phosphorylation. Cases have recently been reported in which fatal liver failure with neonatal onset was the major clinical and biochemical syndrome. In this series we reviewed the liver histology of 10 such patients who died in the first weeks of life (from 3 days to 6 mo). In six cases the diagnosis was confirmed by study of the mitochondrial respiratory chain in the muscle, liver or both; in the other four, appropriate tests were not available for diagnosis but symptoms were identical and all other diagnoses were ruled out. In all 10 cases we noted significant steatosis, mostly microvesicular; widespread hepatocytic, canalicular and bile duct cholestasis with bile thrombi and cholangiolar proliferation; and different degrees of hepatosiderosis and glycogen depletion. Fibrosis took varying forms: perisinusoidal, periportal with the formation of septa, even precirrhosis. In the two cases of infants who died, one at 5 and one 6 mo, micronodular cirrhosis was also present. Mitochondria, either densely or loosely packed, were abnormal-pleiomorphic with few or no cristae and a granular fluffy matrix. Dense, large granules were seen in two cases. The association of neonatal liver failure and hyperlactacidemia should lead to immediate examination of the respiratory chain. The expression of this mitochondrial cytopathy can be lethal, associated with severe liver damage due to the deficiency in oxidative phosphorylation.

Alterations in mitochondrial function and morphology in chronic liver disease: pathogenesis and potential for therapeutic intervention

Studies assessing mitochondrial function and structure in livers from humans or experimental animals with chronic liver disease, including liver cirrhosis, revealed a variety of alterations in comparison with normal subjects or control animals. Depending on the etiology of chronic liver disease, the function of the electron transport chain and/or ATP synthesis was found to be impaired, leading to decreased oxidative metabolism of various substrates and to impaired recovery of the hepatic energy state after a metabolic insult. Changes in mitochondrial structure include megamitochondria with reduced cristae, dilatation of mitochondrial cristae and crystalloid inclusions in the mitochondrial matrix. The most important strategies to maintain an adequate mitochondrial function per liver are mitochondrial proliferation and increases in the activity of critical enzymes or in the content of cofactors per mitochondrion. Possibilities to assess hepatic mitochondrial function and to treat mitochondrial dysfunction in patients with chronic liver disease are discussed.

Fatal infantile liver failure associated with mitochondrial DNA depletion

A 3-month-old girl was admitted to the hospital because of hypotonia and frequent vomiting. She had severe metabolic acidosis and her liver function was abnormal. Hepatomegaly and rapidly progressive liver failure developed, and she died at 4 months of age. Two half-siblings from a different mother had died in infancy of an undiagnosed myopathy. The liver was fatty and hepatocytes were filled with large and small lipid droplets. Other tissues were morphologically normal. The respiratory chain enzymes containing subunits encoded by mitochondrial DNA were markedly decreased in liver, partially decreased in muscle, but normal in other tissues. Southern blot analysis showed 90% depletion of mitochondrial DNA in liver, 53% depletion in muscle, and normal amounts in other tissues. This is the second case of fatal infantile liver failure associated with mitochondrial DNA depletion. This pathogenetic mechanism should be considered in infants with multiple respiratory chain defects and variable tissue expression.

Fatal neonatal liver failure and mitochondrial cytopathy: an observation with antenatal ascites

Mitochondrial cytopathies are multisystemic diseases of extremely variable expression caused by a deficiency in oxidative phosphorylation. Only five cases of neonatal liver failure in the context of mitochondrial cytopathy have been reported, with incomplete morphological data of the liver in three. In the case presented here, ascites had been diagnosed prenatally and liver failure was particularly severe (factor V less than 15% with fatal coma the fourth day). Histologically there were incomplete cirrhosis, microvesicular steatosis, major canalicular cholestasis with proliferative neocholangioles, and bile duct thrombi. There were also some iron pigments in the periportal area and partial glycogen depletion. By electron microscopy, mitochondria in numerous hepatocytes appeared abnormal with occasional cristae in a fluffy matrix, some containing dense inclusions. Study of respiratory chain activity showed a defect in cytochrome c oxidase (complex IV), revealed by oxygraphic measurement on fresh muscle biopsy and confirmed by spectrophotometric enzymatic assays performed on muscle and liver homogenates. The association of neonatal liver failure with hyperlactacidemia warrants investigation into a deficiency in oxidative phosphorylation.

Clinical aspects of mitochondrial disorders

Mitochondrial disorders have long been regarded as neuromuscular diseases only. In fact, owing to the ubiquitous nature of the oxidative phosphorylation, a broad spectrum of clinical features should be expected in mitochondrial disorders. Here, we present eight puzzling observations which give support to the view that a disorder of oxidative phosphorylation can give rise to any symptom in any organ or tissue with any apparent mode of inheritance. Consequently, we suggest giving consideration to the diagnosis of a mitochondrial disorder when dealing with an unexplained association of symptoms, with an early onset and a rapidly progressive course involving seemingly unrelated organs. Determination of lactate/pyruvate and ketone body molar ratios in plasma can help to select patients at risk for this condition.