Mitochondrial myopathy with lactic acidaemia, Fanconi-De Toni-Debré syndrome and a disturbed succinate: cytochrome c oxidoreductase activity

Mitochondrial DNA mutations in renal disease: an overview

Kidneys have a high energy demand to facilitate the reabsorption of the glomerular filtrate. For this reason, renal cells have a high density of mitochondria. Mitochondrial cytopathies can be the result of a mutation in both mitochondrial and nuclear DNA. Mitochondrial dysfunction can lead to a variety of renal manifestations. Examples of tubular manifestations are renal Fanconi Syndrome, which is often found in patients diagnosed with Kearns-Sayre and Pearson's marrow-pancreas syndrome, and distal tubulopathies, which result in electrolyte disturbances such as hypomagnesemia. Nephrotic syndrome can be a glomerular manifestation of mitochondrial dysfunction and is typically associated with focal segmental glomerular sclerosis on histology. Tubulointerstitial nephritis can also be seen in mitochondrial cytopathies and may lead to end-stage renal disease. The underlying mechanisms of these cytopathies remain incompletely understood; therefore, current therapies focus mainly on symptom relief. A better understanding of the molecular disease mechanisms is critical in order to improve treatments.

Mitochondria in Acute Kidney Injury

Acute kidney injury (AKI) continues to be a significant contributor to morbidity, mortality, and health care expenditure. In the United States alone, it is estimated that more than $10 billion is spent on AKI every year. Currently, there are no available therapies to treat established AKI. The mitochondrion is positioned to be a critical player in AKI with its dual role as the primary source of energy for each cell and as a key regulator of cell death. This review aims to cover the current state of research on the role of mitochondria in AKI, while also proposing potential therapeutic targets and future therapies.

[Renal involvement in mitochondrial cytopathies]

Mitochondrial disorders are genetic defects of oxidative phosphorylation. Oxidative phosphorylation takes place in the mitochondrial inner membrane and consists of the oxidation of fuel molecules by oxygen and the concomitant energy transduction into ATP. The mitochondrial respiratory chain is a complex metabolic pathway. It is made of approximately 100 polypeptides, most of which are encoded in the nucleus whereas 13 are encoded in the mitochondria. Mitochondrial DNA is maternally inherited and its mutations are transmitted by the mother. During cell division, mitochondria are randomly partitioned in daughter cells. Therefore, in case normal and mutant DNA are present in the mother's cells, some lineage may have only mutant mitochondrial DNA or normal mitochondrial DNA while others may have both mutant and normal DNA, a condition named heteroplasmy. Renal involvement in mitochondrial cytopathies is rare. Patients most often present with a more or less complete de Toni-Debré-Fanconi syndrome. A few patients present with a nephrotic syndrome or with chronic tubulointerstitial nephritis. The investigation of patients with mitochondrial disorders include metabolic screening for abnormal oxidoreduction status in plasma, investigation of the mitochondrial respiratory chain, including polarographic and spectrophotometric studies, histopathologic studies and genetic studies.

Focal segmental glomerulosclerosis associated with mitochondrial cytopathy: report of two cases with special emphasis on podocytes

We report two children with focal segmental glomerulosclerosis (FSGS) associated with mitochondrial cytopathy (MC). Case 1 was diagnosed as MC with the findings of ptosis, ophthalmoplegia, failure to thrive, high serum lactate and pyruvate levels, ragged red fibers in muscle biopsy and the common 4.9 kb deletion in mtDNA when she was four years old. She subsequently developed FSGS four years later. Case 2 was a four month-old girl presenting with feeding difficulty from birth, with vomiting, seizures and nystagmoid eye movements, nephrotic proteinuria and hematuria. Renal biopsy revealed FSGS. Ultrastructural study demonstrated markedly pleomorphic mitochondria in podocytes with a severe effacement of foot processes. The analyses of muscle biopsy and skin fibroblasts for respiratory chain enzymes were found to be normal, while mitochondrial DNA analysis revealed the population of a single deleted mtDNA in the heteroplasmic state. The present cases illustrate FSGS as a rare renal complication of mitochondrial disease and provide further evidence of podocytes possessing abnormal mitochondria which may cause glomerular epithelial cell damage leading to glomerulosclerosis.

Renal pathology in children with mitochondrial diseases

We studied renal involvement in 42 children with mitochondrial diseases (MDs). The diagnosis of MD was established by morphological, biochemical, and molecular genetic criteria. Renal disease was considered when patients had renal failure, nephrotic syndrome, Fanconi's syndrome or any symptomatic renal alteration. Mild tubular disorder was established if they had abnormal laboratory findings with no apparent clinical symptom. Renal involvement was found in 21 children (50%), of whom 8 had an apparent clinical picture and 13 a mild tubular disorder. Five patients with renal disease showed Debré-Toni-Fanconi's syndrome, 2 of them with decreased glomerular filtration rate (GFR). One case had nephrotic syndrome, another one presented decreased GFR, and the last one had a neurogenic bladder and bilateral hydronephrosis. Patients with mild renal disease showed tubular dysfunction with normal GFR. Renal involvement is frequent and present in about half of the children with MD. Thus, studies for evaluating kidney function should be performed on children with MD. Conversely, patients with tubulopathy of unknown origin or progressive renal disease should be investigated for the existence of MD, especially if associated with involvement of other organs or tissues. Southern blot analysis to search for large-scale mitochondrial DNA (mtDNA) rearrangements should be performed for patients with MD and kidney involvement.

Renal manifestations of congenital lactic acidosis

Congenital lactic acidoses (CLAs) constitute a group of rare inborn errors of mitochondrial metabolism in which cellular energy failure is the defining biochemical abnormality. We report the principal manifestations of renal dysfunction in 35 children with CLA caused by defects in either the pyruvate dehydrogenase multienzyme complex or one or more components of the respiratory chain. The most prominent renal abnormalities included bicarbonaturia, phosphaturia, hypercalciuria, complete Fanconi's syndrome, proteinuria, and decreased glomerular filtration rate. These data were compared with those from 79 previously published cases. Clinical manifestations of renal dysfunction in CLA are common and may be the first presenting sign of the disease. The glomerulus and proximal renal tubule appear to be the anatomic sites most vulnerable to abnormal mitochondrial energy transduction. We propose that the primary defect in mitochondrial energy metabolism, together with the consequent intracellular accumulation of lactate and hydrogen ions, precipitates a state of tissue injury that, unless interrupted, becomes self-perpetuating and ultimately leads to renal cell death.

Mitochondrial cytopathy combined with Fanconi's syndrome

Severe muscle weakness in Fanconi's syndrome is rarely the result of mitochondrial cytopathy. We describe a rare case of a 9-year-old male with early onset of Fanconi's syndrome. He developed severe proximal muscle weakness exacerbated by hypokalemia and hypophosphatemia in childhood. The muscle biopsy revealed increased accumulation of abnormal mitochondria and fat droplets in histochemical stains and electron microscopy. Mitochondrial cytopathy cannot be excluded in Fanconi's syndrome with late onset of muscular impairment. Long-term follow-up of his clinical course is suggested to understand the natural history of this unusual case.

Clinical heterogeneity in respiratory chain complex III deficiency in childhood

Six children are presented with an isolated complex III deficiency in muscle tissue. More specifically, oxidation rates and ATP+CrP production rates from both pyruvate and succinate as substrates and/or the activity of decylubiquinol:cytochrome c oxidoreductase were all markedly reduced. Complex III deficiency was also present in liver of two patients tested, but could not be demonstrated in cultured fibroblasts of four patients tested. Mitochondrial DNA, extracted from muscle, was analyzed; no deletions or common point mutations were found. Four patients presented with a multi-organ disorder. Among these patients three presented at neonatal age with neurological signs and lactate elevation in blood and CSF, of whom two had severe neonatal Fanconi syndrome. One child, aged seven years, had encephalomyopathy, ophthalmoplegia, retinopathy and Wolff-Parkinson-White syndrome. The remaining two patients exhibited myopathy only, within the first year of life. Thus, like in other respiratory chain disorders, patients with complex III deficiency may present at any age and show variable symptoms and outcome, ranging from neonatal death to failure to thrive only. Apparently there are no clinical findings which are specific for complex III deficiency.

Gas chromatographic-mass spectrometric metabolic profiling of patients with fatal infantile mitochondrial myopathy with de Toni-Fanconi-Debré syndrome

The metabolic profiles of three patients with fatal infantile mitochondrial myopathy with de Toni-Fanconi-Debré syndrome were studied by simultaneous analysis, after urease treatment of urinary organic acids, carbohydrates, polyols and amino acids using gas chromatography/mass spectrometry (GC/MS). All three patients persistently showed lactic aciduria, phosphaturia, glucosuria and generalized amino aciduria. This abnormal urinary metabolic profile was observed before the onset of any clinical symptoms, indicating that chemical diagnosis may be done presymptomatically. In one patient, the concentration of lactate increased in parallel with the severity of the clinical condition, whereas the urinary levels of 3-hydroxybutyrate, amino acids and glucose fluctuated and showed only a general tendency to increase with the clinical course. The above results suggest that simultaneous GC/MS analyses, without fractionation, of urinary metabolites facilitate not only the early chemical diagnosis either before or after the first onset, but also follow-up studies, providing an important index for the evaluation of the severity and clinical course in patients with this disorder.

Renal involvement in mitochondrial cytopathies

Mitochondrial cytopathies have long been regarded as neuromuscular diseases. However, an oxidative phosphorylation disorder may give rise to various symptoms in other organs or tissues which are dependent upon mitochondrial energy supply. A broad spectrum of clinical symptoms have been described in these patients, including renal symptoms. The most frequent is proximal tubular dysfunction with a more or less complete de Toni-Debré-Fanconi syndrome. A few patients have been reported with tubular acidosis, Bartter syndrome, chronic tubulointerstitial nephritis, or nephrotic syndrome. The diagnosis of a respiratory chain deficiency is difficult when only renal symptoms are present but should be easier when another seemingly unrelated symptom is observed. Metabolic screening for abnormal oxidoreduction status in plasma, including lactate/pyruvate and ketone body molar ratios, can help to identify patients for further investigations. These include the measurement of oxygen consumption by mitochondria, the assessment of mitochondrial respiratory enzyme activities by spectrophotometric studies, and, when possible, the molecular analysis of mitochondrial DNA. Any mode of inheritance can be observed: sporadic, autosomal dominant or recessive, or maternal inheritance. No satisfactory therapy is presently available for mitochondrial disorders.

Neonatal De Toni-Debré-Fanconi syndrome due to a defect in complex III of the respiratory chain

A patient with neonatal expression of severe De Toni-Debré-Fanconi syndrome is presented. Because of early signs of renal tubulopathy together with a large urinary excretion of lactate, 3-hydroxybutyrate and citric acid cycle intermediates, a mitochondrial disorder was suspected and muscle and liver biopsies were performed. Biochemical investigations in both tissues revealed a defect in the respiratory chain at the level of complex III. In this patient renal dysfunction was the primary symptom, and hyperlactataemia, an important clue for a mitochondrial disorder, was lacking. CONCLUSION. Complex III deficiency should be included in the differential diagnosis of neonatal De Toni-Debré-Fanconi syndrome.

Mutation of a nuclear succinate dehydrogenase gene results in mitochondrial respiratory chain deficiency

We now report a mutation in the nuclear-encoded flavoprotein (Fp) subunit gene of the succinate dehydrogenase (SDH) in two siblings with complex II deficiency presenting as Leigh syndrome. Both patients were homozygous for an Arg554Trp substitution in the Fp subunit. Their parents (first cousins) were heterozygous for the mutation that occurred in a conserved domain of the protein and was absent from 120 controls. The deleterious effect of the Arg to Trp substitution on the catalytic activity of SDH was observed in a SDH- yeast strain transformed with mutant Fp cDNA. The Fp subunit gene is duplicated in the human genome (3q29; 5p15), with only the gene on chromosome 5 expressed in human-hamster somatic cell hybrids. This is the first report of a nuclear gene mutation causing a mitochondrial respiratory chain deficiency in humans.

Neonatal Fanconi syndrome due to deficiency of complex III of the respiratory chain

Fanconi syndrome is an important presentation of respiratory chain disease. We report three patients who presented in the neonatal period with Fanconi syndrome, lactic acidosis and intrauterine growth retardation. In all three patients the major biochemical defect was in complex III of the mitochondrial respiratory chain, a relatively uncommon defect. The diagnosis could only be made by muscle biopsy as the defect was not expressed in cultured skin fibroblasts. Treatment with vitamins C and K3 and ubiquinone did not alter the course of the disease and all patients died before the age of 4 months.

Deletion of the mitochondrial DNA in a case of de Toni-Debré-Fanconi syndrome and Pearson syndrome

We report a patient with Pearson syndrome with failure to thrive, exocrine pancreas insufficiency, growth hormone deficiency and severe tubular dysfunction. The patient had no signs of liver involvement. Normal respiratory chain enzyme activity was found in the lymphocytes, but a mitochondrial DNA deletion was demonstrated in lymphocytes and in the kidney. Polymerase chain reaction amplification and sequence analysis revealed the presence of the 4,977 base pair "common" deletion in the mitochondrial genome. Our findings support the view that tubulopathies of unknown origin may be related to mitochondrial respiratory chain deficiency.

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.

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.

The expanding clinical spectrum of mitochondrial diseases

The mitochondrion is the only extranuclear organelle containing DNA (mtDNA). As such, genetically determined mitochondrial diseases may result from a molecular defect involving the mitochondrial or the nuclear genome. The first is characterized by maternal inheritance and the second by Mendelian inheritance. Ragged-red fibers (RRF) are commonly seen with primary lesions of mtDNA, but this association is not invariant. Conversely, RRF are seldom associated with primary lesions of nuclear DNA. Large-scale rearrangements (deletions and insertions) and point mutations of mtDNA are commonly associated with RRF and lactic acidosis, e.g. Kearns-Sayre syndrome (KSS) (major large-scale rearrangements), Pearson syndrome (large-scale rearrangements), myoclonus epilepsy with RRF (MERRF) (point mutation affecting tRNA(lys) gene), mitochondrial myopathy, lactic acidosis, and stroke-like episodes (MELAS) (two point mutations affecting tRNA(leu)(UUR) gene) and a maternally-inherited myopathy with cardiac involvement (MIMyCa) (point mutation affecting tRNA(leu)(UUR) gene). However, RRF and lactic acidosis are absent in Leber hereditary optic neuropathy (LHON) (one point mutation affecting ND4 gene, two point mutations affecting ND1 gene, and one point mutation affecting the apocytochrome b subunit of complex III), and the condition associated with maternally inherited sensory neuropathy (N), ataxia (A), retinitis pigmentosa (RP), developmental delay, dementia, seizures, and limb weakness (NARP) (point mutation affecting ATPase subunit 6 gene). The point mutations in MELAS, MIMyCa, and MERRF, and the large-scale mtDNA rearrangements in KSS and Pearson syndrome have a broader biochemical impact since these molecular defects involve the translational sequence of mitochondrial protein synthesis. The nuclear defects involving mitochondrial function generally are not associated with RRF. The biochemical classification of mitochondrial diseases principally catalogues these nuclear defects. This classification divides mitochondrial diseases into five categories. Primary and secondary deficiencies of carnitine are examples of a substrate transport defect. A lipid storage myopathy is often present. Disturbances of pyruvate or fatty acid metabolism are examples of substrate utilization defects. Only four defects of the Krebs cycle are known: fumarase deficiency, dihydrolipoyl dehydrogenase deficiency, alpha-ketoglutarate dehydrogenase deficiency, and combined defects of muscle succinate dehydrogenase and aconitase. Luft disease is the singular example of a defect in oxidation-phosphorylation coupling. Defects of respiratory chain function are manifold. Two clinical syndromes predominate, one involving limb weakness, and the other primarily affecting brain function. Leigh syndrome may result from different enzyme defects, most notably pyruvate dehydrogenase complex deficiency, cytochrome c oxidase deficiency, complex I deficiency, and complex V deficiency associated with the recently described NARP point mutation. A new group of mitochondrial diseases has emerged.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzyme activities of the mitochondrial energy generating system in skeletal muscle tissue of preterm and fullterm neonates

Quadriceps muscle specimens from autopsy of 28 neonates (gestational age 25-42 weeks) were investigated to determine pyruvate and malate oxidation rates and several enzymes of the mitochondrial oxidative process. In general, the levels of all mitochondrial parameters measured, including carnitine levels, were lower in the neonates who died within the first week of life than those in the control group (age > 5 years). Pyruvate and malate oxidation rates (P < 0.05), activities of pyruvate dehydrogenase complex (P < 0.10) and succinate: cytochrome c oxidoreductase (P < 0.05) increased significantly with gestational age. Pyruvate oxidation rates (P < 0.05) as well as activities of citrate synthase (P < 0.05) and NADH:Q1 oxidoreductase (P < 0.05) were significantly lower in the group of very preterm infants at an age of 1-7 days compared with very preterm infants at an age between 3-8 weeks. We conclude from our study that special reference values are necessary for a correct biochemical diagnosis of mitochondrial encephalomyopathies in the neonatal period. Differences between preterm and fullterm children of the same age (1 week) indicate a maturational process in human muscle tissue during gestation. Comparison of two different age groups within the very preterm neonates point to a postnatal maturation of the mitochondrial energy metabolism, at least in preterm neonates.

Deficiency in complex II of the respiratory chain, presenting as a leukodystrophy in two sisters with Leigh syndrome

We report 2 sisters with a degenerative neurological disorder presenting clinically as a leukodystrophy. CT scan and MRI demonstrated small symmetrical foci of necrosis in the substentia nigra and in the basal ganglia typical of Leigh syndrome and diffuse cerebral white matter abnormalities. In these patients a deficiency in complex II of the respiratory chain was demonstrated in isolated mitochondria from muscle, as well as in fibroblasts and lymphocytes.

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.

Deficiency of skeletal muscle succinate dehydrogenase and aconitase. Pathophysiology of exercise in a novel human muscle oxidative defect

We evaluated a 22-yr-old Swedish man with lifelong exercise intolerance marked by premature exertional muscle fatigue, dyspnea, and cardiac palpitations with superimposed episodes lasting days to weeks of increased muscle fatigability and weakness associated with painful muscle swelling and pigmenturia. Cycle exercise testing revealed low maximal oxygen uptake (12 ml/min per kg; healthy sedentary men = 39 +/- 5) with exaggerated increases in venous lactate and pyruvate in relation to oxygen uptake (VO2) but low lactate/pyruvate ratios in maximal exercise. The severe oxidative limitation was characterized by impaired muscle oxygen extraction indicated by subnormal systemic arteriovenous oxygen difference (a-v O2 diff) in maximal exercise (patient = 4.0 ml/dl, normal men = 16.7 +/- 2.1) despite normal oxygen carrying capacity and Hgb-O2 P50. In contrast maximal oxygen delivery (cardiac output, Q) was high compared to sedentary healthy men (Qmax, patient = 303 ml/min per kg, normal men 238 +/- 36) and the slope of increase in Q relative to VO2 (i.e., delta Q/delta VO2) from rest to exercise was exaggerated (delta Q/delta VO2, patient = 29, normal men = 4.7 +/- 0.6) indicating uncoupling of the normal approximately 1:1 relationship between oxygen delivery and utilization in dynamic exercise. Studies of isolated skeletal muscle mitochondria in our patient revealed markedly impaired succinate oxidation with normal glutamate oxidation implying a metabolic defect at the level of complex II of the mitochondrial respiratory chain. A defect in Complex II in skeletal muscle was confirmed by the finding of deficiency of succinate dehydrogenase as determined histochemically and biochemically. Immunoblot analysis showed low amounts of the 30-kD (iron-sulfur) and 13.5-kD proteins with near normal levels of the 70-kD protein of complex II. Deficiency of succinate dehydrogenase was associated with decreased levels of mitochondrial aconitase assessed enzymatically and immunologically whereas activities of other tricarboxylic acid cycle enzymes were increased compared to normal subjects. The exercise findings are consistent with the hypothesis that this defect impairs muscle oxidative metabolism by limiting the rate of NADH production by the tricarboxylic acid cycle.

Renal tubular involvement mimicking Bartter syndrome in a patient with Kearns-Sayre syndrome

A 10-year-old boy had short stature, external ophthalmoplegia, atypical retinal pigmentary degeneration, and sensorineural hearing loss (Kearns-Sayre syndrome). In addition to ragged-red fibers observed on modified Gomori trichrome staining, there were scattered fibers exhibiting no cytochrome c oxidase activity, indicating a focal deficiency. Cytochrome c oxidase and other respiratory chain enzyme activities were normal biochemically. The patient also had renal tubular dysfunction, including isosthenuria, decreased urine-concentrating ability, and excessive excretion of potassium and magnesium. In addition, he had hyperreninemia and hyperaldosteronism but no hypertension. The renal dysfunction was thought to have resulted from a primary defect in the thick ascending limb of the loop of Henle, mimicking Bartter syndrome. In contrast to previously described cases of cytochrome c oxidase deficiency with de Toni-Fanconi Debré syndrome, the patient had less intensive muscle abnormalities. A renal biopsy specimen showed ultrastructural changes in mitochondria that were similar to those seen in biopsy specimens of muscle. A large-scale deletion (8.8 kilobases) in mitochondrial DNA was found in biopsy specimens of muscle and kidney.

Glycogen storage disease, Fanconi nephropathy, abnormal galactose metabolism and mitochondrial myopathy

We present a 4-year-old male suffering from profound muscular weakness, enzymatically undefined glycogen storage disease. Fanconi nephropathy and impaired galactose utilization. Distorted mitochondria, intramitochondrial fat droplets and partial deficiencies of pyruvate dehydrogenase complex, succinate: cytochrome c oxidoreductase, and cytochrome c oxidase have been found in muscle tissue. The causal relationship between mitochondrial myopathy, glycogen storage disease, Fanconi nephropathy and impaired utilization of galactose is discussed.