Fatal infantile mitochondrial myopathy due to cytochrome c oxidase deficiency

Effect of bezafibrate treatment on late-onset mitochondrial myopathy in mice

Mitochondrial dysfunction is an important cause of metabolic disorders of children and adults, with no effective therapy options. Recently, induction of mitochondrial biogenesis, by transgenic overexpression of PGC1-alpha [peroxisome proliferator-activated receptor (PPAR)-gamma coactivator 1-alpha], was reported to delay progression of early-onset cytochrome-c-oxidase (COX) deficiency in skeletal muscle of two mouse models: a muscle-specific knock-out of COX10 (COX10-mKO) and a constitutive knock-out of Surf1 (Surf1-KO). A pan-PPAR agonist, bezafibrate, could similarly delay myopathy progression in COX10-mKOs, but not in SURF1-KOs. We asked whether bezafibrate affected disease progression in late-onset adult-type mitochondrial myopathy mice. These 'Deletor mice' express a dominant patient mutation in Twinkle-helicase, leading to accumulation of multiple mtDNA deletions and subsequent progressive respiratory chain (RC) deficiency with COX-negative muscle fibers at 12 months of age. The primary and secondary molecular findings in Deletor mice mimic closely those in patients with Twinkle myopathy. We applied 0.5% bezafibrate diet to Deletors for 22 weeks, starting at disease manifestation, mimicking patient treatment after diagnosis. Bezafibrate delayed significantly the accumulation of COX-negative fibers and multiple mtDNA deletions. However, mitochondrial biogenesis was not induced: mitochondrial DNA copy number, transcript and RC protein amounts decreased in both Deletors and wild-type mice. Furthermore, bezafibrate induced severe lipid oxidation effects, with hepatomegaly and loss of adipose tissue, the mechanism involving lipid mobilization by high hepatic expression of FGF21 cytokine. However, as bezafibrate has been tolerated well by humans, the beneficial muscle findings in Deletor mice support consideration of bezafibrate trials on adult patients with mitochondrial myopathy.

Mitochondrial dysfunction and neuromuscular disease

Mitochondrial diseases are a heterogeneous group of disorders with widely varying clinical features, due to defects in mitochondrial function. Involvement of both muscle and nerve is common in mitochondrial disease. In some cases, this involvement is subclinical or a minor part of a multisystem disorder, but myopathy and neuropathy are a major, often presenting, feature of a number of mitochondrial syndromes. In addition, mitochondrial dysfunction may play a role in a number of classic neuromuscular diseases. This article reviews the role of mitochondrial dysfunction in neuromuscular disease and discusses a rational approach to diagnosis and treatment of patients presenting with a neuromuscular syndrome due to mitochondrial disease.

Human cytochrome oxidase deficiency

The human cytochrome oxidase complex is a multisubunit assembly in the inner mitochondrial membrane responsible for the terminal event in electron transport in which molecular oxygen is reduced. Various phenotypic forms of cytochrome oxidase deficiency have been recognized, the major varieties involving degeneration of the brain stem and basal ganglia (Leigh syndrome) and lactic acidemia. Others include a fatal infantile form, a benign reversible form, and forms with cardiomyopathy. Early recognition of complementation groups within, for instance, the Leigh syndrome group has recently been followed up with a description of the gene defect for three of the nuclear-encoded forms of cytochrome c oxidase (COX) deficiency. The three genes indicted, SURF1 for Leigh syndrome, COX 10 for leukodystrophy and tubulopathy, and SCO2 for the cardiomyopathic form, all have a role in the assembly of the mature cytochrome oxidase complex. The description of these gene defects and the role these genes play are discussed in terms of what can be learned about COX assembly and about the etiology of the different phenotypic forms of the disease.

A case of mitochondrial cytopathy with a typical point mutation for MELAS, presenting with severe focal-segmental glomerulosclerosis as main clinical manifestation

A 27-year-old female with short stature and mild hearing loss was diagnosed as having focal-segmental glomerulosclerosis by renal biopsy at our hospital. One year later she developed progressive renal dysfunction and cardiac failure and was admitted again to our hospital for evaluation. Though her only neurological disorder was mild hearing loss, her short stature and elevated lactate and pyruvate values in cerebrospinal fluid suggested mitochondrial cytopathy. A muscle biopsy specimen of the left biceps brachii, using modified Gomori trichrome stain, showed a typical image of ragged-red fibers, and an increased number of giant mitochondria with paracrystalline inclusions were visible by electron microscopy. Mitochondrial DNA from the skeletal muscle showed an A-to-G transition at 3243 of transfer RNALeu(UUR), the common point mutation for mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes. These data confirmed the diagnosis of atypical mitochondrial cytopathy with renal and heart involvement. Mitochondrial cytopathies are often associated with hypertrophic cardiomyopathy but rarely with renal disease. Among the few reported cases with associated renal disease, most included renal tubular disorders; few cases with focal glomerular sclerosis are known. The present case of atypical mitochondrial cytopathy was characterized by a unique clinical course and rare complications with focal-segmental glomerulosclerosis.

Tissue-specific expression and mapping of the Cox7ah gene in mouse

We have isolated and examined the gene for the heart isoform of cytochrome c oxidase subunit VIIa (COX VIIa-H) in mouse, an isoform gene previously thought to be lacking in rodents. Interspecies amino acid comparisons indicate that mouse COX VIIa-H protein displays 82.5 and 70.9% identity with the bovine and human heart isoforms of COX VIIa, but only 53.7% identity with the paralogous mouse liver isoform (COX VIIa-L). Expression in adult mouse tissues is limited to heart and skeletal muscle, as found in other species. In the early mouse embryo, Cox7al was the exclusive isoform expressed and Cox7ah mRNA was not detectable until day 17 postcoitum. That the mouse Cox7ah gene characterized in this study is orthologous to the human COX7AH gene was also suggested by its mapping to mouse chromosome 7, to a conserved region syntenic with the human chromosome location of COX7AH, 19q13.1. As a result, all three COX heart isoform genes in mouse group to chromosome 7. Interestingly, mapping of the mouse Cox7al to chromosome 9 suggests a new syntenic region between the mouse and the human genomes.

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.

Clinical and molecular heterogeneity of cytochrome c oxidase deficiency in the newborn

We report 8 cases of severe cytochrome c oxidase deficiency with onset in the neonatal period. Clinical symptoms were heterogeneous: antenatal cerebral malformations, neurological distress with ketoacidosis, severe myopathy, or isolated respiratory control failure. Lactic acid was elevated in blood and/or CSF in 7 cases. Muscle biopsy (7 patients), liver biopsy (4 patients), and cultured skin fibroblasts (7 patients) were used to assess the cytochrome c oxidase deficiency. Among the patients, the enzymatic defect differed in the level of residual activity, expression in different tissues and subunit composition in muscle (as analysed by immunohistochemistry). Southern blot analysis of the mitochondrial DNA was normal in 7 patients. The heterogeneity of cytochrome c oxidase deficiency was therefore demonstrated by these clinical presentations and by the biochemical assessment of the enzyme defect. This reflects, most probably, the diverse nature of the causal mutations.

Renal amino acid transport in adults with oxidative phosphorylation diseases

The clinical manifestations of mitochondrial DNA (mtDNA) mutations depend on a variety of factors including ratios of normal to abnormal mtDNA and tissue-specific differences in ATP production by oxidative phosphorylation (OXPHOS). In order to investigate the effects of OXPHOS defects on renal tubule function, we characterized sodium-coupled transport processes in six individuals with OXPHOS diseases. Pathogenic mtDNA mutations were identified in five of these individuals. Sodium coupled transport processes were evaluated by determining fractional excretions of amino acids, glucose, lactate, urate, and phosphate in patients and controls. Four of the six individuals had high fractional excretions of neutral amino acids, indicating abnormal renal tubule reabsorbtion of these amino acids. Abnormalities in fractional excretions of lactate, glucose, urate, and phosphate were less pronounced. These results demonstrate that sodium-coupled transport processes in the kidney are sensitive to OXPHOS impairment. When abnormalities in these processes are encountered, an OXPHOS disease should be included in the differential diagnosis.

Immunohistochemical analysis of muscle cytochrome c oxidase deficiency in children

Despite the demonstration of a clear biochemical defect, the genetic alterations causing childhood forms of cytochrome c oxidase (COX) deficiency remain unknown. The double genetic origin (nuclear and mitochondrial DNA), and the complexity of COX enzyme structure and regulation, indicate the need for genetic investigations of the molecular structure of individual COX subunits. In the present study a new monoclonal antibody, which reacts exclusively with heart-type human COX subunit VIIa (VIIa-H), and other monoclonal antibodies against human COX subunits, were used in the immunohistochemical analysis of skeletal muscle from children with different forms of mitochondrial myopathy with COX deficiency. By immunohistochemical investigation a normal reaction was seen with antibodies to COX subunits IV, Va+Vb, and VIa+VIc in all four cases, and in two cases with antibodies to COX VIIa-H and VIIa+VIIb. In muscle from a fatal infantile case with cardiac and skeletal muscle involvement, no immunohistochemical reaction was seen with the monoclonal antibody against the tissue-specific subunit VIIa-H. In muscle from an 11-year-old boy with exclusive muscular symptoms and signs, immunohistological reactions were absent with COX subunit VIIa-H and COX subunits VIIa+VIIb, and slightly decreased with COX subunit II, thus demonstrating a different molecular mechanism in each case. It is concluded that the molecular basis of COX deficiency in childhood may vary greatly between patients.

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.

Steady-state transcript levels of cytochrome c oxidase genes during human myogenesis indicate subunit switching of subunit VIa and co-expression of subunit VIIa isoforms

Steady-state levels of the mitochondrial rRNAs, of mRNAs for mitochondrially and nuclear-encoded subunits of cytochrome c oxidase and for the beta subunit of ATP synthase were assessed by Northern blot hybridizations during the in vitro differentiation of human myoblasts. Transcript levels of the so-called liver-type form of subunit VIa of cytochrome c oxidase diminished during the course of differentiation, while transcription of the so-called heart-type form was induced. Transcripts for the liver-type form and for the heart-type form of subunit VIIa of cytochrome c oxidase were detected in all myogenic cultures; the levels of the heart-type form progressively increased during the course of differentiation. The levels of the other transcripts studied did not change substantially. The results suggest subunit switching of subunit VIa and co-expression of subunit VIIa isoforms during myogenesis. The differential changes in mRNA levels of the heart-type subunits VIa and VIIa and the differential changes in mRNA levels of the liver-type subunits VIa and VIIa demonstrate that different transcriptional regulation mechanisms are present for both heart-type genes as well as for both liver-type genes.

Defects of the mitochondrial respiratory chain complexes in three pediatric cases with hypotonia and cardiac involvement

Three children displaying hypotonia, cardiac involvement and defects of the mitochondrial respiratory chain complexes are reported. The first case showed severe neonatal hypotonia, failure to thrive, hepatomegaly, dilation of the right cardiac cavities, profound lactic acidosis and amino aciduria. The boy died at the age of 7 weeks. In the second case hypotonia, severe cardiomyopathy, cyclic neutropenia, lactic acidosis and 3-methylglutaconic aciduria occurred. The boy died at the age of 27 months. The third case presented at the age of 16 months as an acute hypokinetic hypertrophic cardiomyopathy with transient hypotonia and mild lactic acidosis. Spontaneous clinical remission occurred. In all cases muscle biopsy was performed. Morphological studies failed to show ragged-red fibers but there was lipid storage myopathy and decreased cytochrome c oxidase activity. Biochemical studies confirmed the cytochrome c oxidase deficiency in muscle in all cases. It was associated with complex I III deficiency in case 1 and with severe deficits of all respiratory chain complexes in case 2. Post-mortem studies in case 1 indicated that complex IV was reduced in the liver but not in the heart and quantitative analysis of mtDNA revealed a depletion in muscle. Cases 1 and 2 shared some clinical features with fatal infantile myopathy associated with cytochrome c oxidase deficiency, while case 3 displayed a very unusual clinical presentation. The histochemical enzyme reaction of cytochrome c oxidase is useful for the diagnosis of mitochondrial myopathy because ragged-red fibers may be lacking. Finally, biochemical measurement of the different mitochondrial respiratory chain complexes is required because multiple defects are frequent and occasionally related to mtDNA depletion.

Organic acidurias: a review. Part 1

Organic acidemias are disorders of intermediary metabolism that lead to accumulation of organic acids in biologic fluids, disturb acid-base balance, and derange intracellular biochemical pathways. Their clinical presentation reflects the resultant systemic disease and progressive encephalopathy. While in some organic acidemias, disturbed acid-base metabolism is the predominant presenting feature, in others it is less prominent or even absent. The etiologies of the more than 50 different phenotypes include impaired metabolism of branched-chain amino acids, vitamins, glucose, lipids, glutathione, and gamma-aminobutyric acid and defects of oxidative phosphorylation. Most organic acidemias present with neurologic manifestations, which include acutely or subacutely progressive encephalopathy that involves different parts of the nervous system. The age of presentation and the associated systemic, hematologic, and immune findings provide additional guidelines for differential diagnosis. We summarize major organic acidemias, while emphasizing their usual and unusual neurologic presentations.

Adult onset lipid storage in gastric mucosa and skeletal muscle fibers associated with gastric pain, progressive muscle weakness and partial deficiency of cytochrome C oxidase

We report on the first case, a 21-year-old man, with partial deficiency of cytochrome c oxidase, lipid storage myopathy and concomitant lipid storage in the gastric mucosa affecting chief, parietal, and argentaffine cells as well as interstitial macrophages. The clinical symptoms consisted of increasing muscle weakness, cramps of the legs, and severe gastric pain that was resistant to treatment. Muscle biopsy specimens showed severe lipid storage in muscle fibers. Enzyme histochemistry revealed partial deficiency of cytochrome c oxidase (COX) with scattered non-reactive fibers among a majority of COX-positive fibers whereas biochemical analysis of muscle homogenates resulted in no corresponding defect of mitochondrial enzymes. Gastric biopsy specimens showed similarly to muscle fibers an extensive accumulation of lipid droplets in the chief cells, HCl producing parietal cells, macrophages, neutrophilic and eosinophilic leucocytes, and to a lesser degree also in argentaffine cells and unmyelinated axons of the gastric mucosa. The lipid droplets were associated with an insignificant increase in the number and size of mitochondria although paracristalline mitochondrial inclusions were neither noted in muscle fibers nor in cells of the gastric mucosa. These findings resemble those in multisystem triglyceride storage disease although the clinical signs were not reminiscent of this disease, and indicate that among the clinically heterogeneous group of cytochrome c oxidase deficiencies lipid storage may not be confined to muscle, but can affect the gastric mucosa as well.

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.

[Myopathy due to succinate cytochrome C oxidoreductase deficiency: possible defect of complex II of the respiratory chain]

The case of a 24 years-old woman with weakness since the teens and progressive loss of muscle strength is reported. The muscle biopsy showed increased number of mitochondria. In two occasions the respiratory chain enzymes showed important reduction of the succinate-cytochrome-C-reductase, suggesting a possible defect in the complex II of the respiratory chain. Large doses of vitamins C and K were prescribed. There was improvement of muscle strength. A discussion about the most common syndromes marked by mitochondrial abnormalities in muscle is made, as well as about the type of work-up that should be done in suspect cases of respiratory chain defects.

Infantile cytochrome c oxidase deficiency with neonatal death

A newborn male presented with severe respiratory insufficiency, generalized muscle weakness, and lactic acidemia. Immediately after admission, he was placed on a respirator because of respiratory arrest. He deteriorated rapidly and died 75 hours after birth. There was notable variation in fiber size and an increased number of type 2C fibers in the quadriceps femoris muscle obtained at autopsy; however, no ragged-red fibers were observed with modified Gomori trichrome staining. Markedly decreased cytochrome c oxidase activity was demonstrated in skeletal muscle by biochemical and histochemical studies, while cardiac muscle demonstrated normal cytochrome c oxidase activity. Mitochondrial myopathy should be considered in the differential diagnosis of patients with neonatal respiratory distress syndrome.

Mitochondrial myopathy and cardiomyopathy in siblings

Two siblings with infantile lactic acidosis and mitochondrial myopathy are described. The first child, a girl, died at 5 months of age from severe lactic acidosis after about 3 weeks of progressive muscular hypotonia. The younger brother had congenital lactic acidosis but no other symptoms until 6 months of age when progressive muscle weakness appeared. Treatment with dichloroacetate lowered the serum lactic acid level but did not affect his clinical condition. At 13 months of age, cardiomyopathy was diagnosed and he died at the age of 29 months of circulatory failure. Both children had mitochondrial myopathy. Postmortem examination of the boy revealed marked morphologic changes of the mitochondria in both skeletal muscle and the myocardium; biochemical investigation of skeletal muscle mitochondria demonstrated deficiencies in both complex I (NADH ferricyanide reductase) and complex IV (cytochrome c oxidase). The disease in these siblings differs in several respects from previously reported patients with mitochondrial myopathy and cytochrome c oxidase deficiency.

Mitochondrial myopathy: a genetic study of 71 cases

Of 71 index cases with histologically defined mitochondrial myopathy, 13 (18%) had relatives who were definitely affected with a similar disorder. Eight familial cases from four families were confined to a single generation. In five families maternal transmission to offspring occurred. There were no instances of paternal transmission, but one patient had an affected cousin in the paternal line. No consistent clinical syndrome or pattern of inheritance emerged for any identified defect of the mitochondrial respiratory chain, localised biochemically in 41 cases. Overall, the recurrence rate was 3% for sibs and 5.5% for offspring of index cases. Review of published reports of familial cases of mitochondrial myopathy suggests that the ratio of maternal to paternal transmission is about 9:1. We conclude that these disorders may be caused by mutations of either nuclear or mitochondrial genes.

Molecular defects in cytochrome oxidase in mitochondrial diseases

Defects of cytochrome c oxidase (COX) show remarkable clinical, biochemical, and genetic heterogeneity. Clinically, there are two main groups of disorders, one dominated by muscle involvement, the other by brain dysfunction. Biochemically, the enzyme defect may be confined to one or a few tissues (reflecting the existence of tissue-specific isozymes) or affect all tissues. Immunologically reactive enzyme protein is decreased in some forms of COX deficiency but not in others. Because COX is encoded both by nuclear and by mitochondrial genes, COX deficiencies may be due to mutations of either genome and may offer useful models to study the communication between nuclei and mitochondria. We have isolated full-length cDNA clones encoding human COX subunits IV, Vb, and VIII and a partial-length clone for subunit Va. These clones are being used as probes to analyze the DNA and RNA of patients with COX deficiency.

de Toni-Fanconi-Debré syndrome with Leigh syndrome revealing severe muscle cytochrome c oxidase deficiency

We describe a patient with severe muscle cytochrome c oxidase deficiency who had de Toni-Fanconi-Debré syndrome and acute neurologic deterioration resembling Leigh syndrome, without clear evidence of muscle abnormality. Metabolic investigations revealed elevated cerebrospinal fluid lactate values contrasting with normal blood lactate, and high 3-hydroxybutyrate/acetoacetate ratio with normal lactate/pyruvate ratio. This case emphasizes the importance of performing metabolic and biochemical investigations in every patient with Leigh syndrome, even in the absence of hyperlactatemia or myopathy.

A mitochondrial encephalomyopathy with a partial cytochrome c oxidase deficiency of muscle

A 16 year old girl showed delayed psychomotor development. In infancy, exercise intolerance, cerebellar signs, deteriorated with increasing intercurrent infections, and disturbances of breathing and cardiac rhythm became manifest. From the age of 7 years there was chronic progressive psychomotor deterioration, with hypotonia, a bilateral pyramidal and cerebellar syndrome, and mild epilepsy. CSF pyruvate and lactate levels were elevated, and lactate content was elevated in the urine. There was an abnormally high rise of lactate levels on moderate exercise and an abnormal response to pyruvate loading. Quadriceps muscle biopsies obtained at age 10 and 16 years showed ragged-red fibres, and a decreased cytochrome c oxidase activity and cytochrome aa3 content. Cytochrome c oxidase activity in fibroblasts was normal. Clinical signs and symptoms in association with a disturbance of mitochondrial energy metabolism led us to diagnosis of probable Leigh syndrome.

The biochemical basis of mitochondrial diseases

Dysfunctioning of human mitochondria is found in a rapidly increasing number of patients. The mitochondrial system for energy transduction is very vulnerable to damage by genetic and environmental factors. A primary mitochondrial disease is caused by a genetic defect in a mitochondrial enzyme or translocator. More than 60 mitochondrial enzyme deficiencies have been reported. Secondary mitochondrial defects are caused by lack of compounds to enable a proper mitochondrial function or by inhibition of that function. This may result from malnutrition, circulatory or hormonal disturbances, viral infection, poisoning, or an extramitochondrial error of metabolism. Once mitochondrial ATP synthesis decreases, secondary mitochondrial lesions may be generated further, due to changes in synthesis and degradation of mitochondrial phospholipids and proteins, to mitochondrial antibody formation following massive degradation, to accumulation of toxic products as excess acyl-CoA, to the depletion of Krebs cycle intermediates, and to the increase of free radical formation and lipid peroxidation.

A morphometric study of muscle mitochondria in cytochrome c oxidase deficiency

Quantitative analysis of mitochondrial size and its percentage of total fibre volume in different muscle fibre types was performed on biceps brachii muscles of controls aged from 9 months to 10 years, and patients aged from 8 months to 14 years, with cytochrome c oxidase (CCO) deficiency confirmed by both histochemical and biochemical analyses. The disease was classified into 2 subgroups: one not containing ragged-red fibres (RRF) (group I), and one containing RRF (group II). Relationship between type 1 and 2 fibres in mitochondrial size and percentages of total fibre volume showed significant differences in the controls and group I. A comparison of the controls and group I did not show significant differences in mitochondrial size, but abnormally enlarged mitochondria were occasionally observed in the latter. In group I, statistical differences were observed in mitochondrial percentage of total fibre volume, though these differences remained in the control range, suggesting the presence of mild morphological changes in mitochondria on electron microscopy. In group II, mitochondrial size and its percentage of total fibre volume were markedly increased in both type 1 and 2 fibres, with no statistical differences observed between the 2 fibre types.

Defects in muscle fiber growth in fatal infantile cytochrome c oxidase deficiency

In addition to numerous ragged-red fibers in the muscle from a female infant with fetal infantile cytochrome c oxidase deficiency, the muscle fibers were small in caliber with electron microscopic characteristics of immaturity; the satellite cells were significantly increased in number to 31.3% as compared with those in controls, 8.4 +/- 1.6% (p less than 0.001). In the culture system, the biopsied muscle showed markedly reduced growth despite the presence of numerous satellite cells which are known to act as myoblasts in muscle regeneration, and formed fewer numbers of myotubes containing poorly organized myofibrils and mitochondria with no cytochrome c oxidase activity. A defect in myogenesis and a paucity in repair process in severe form may account for the progressive course and a fatal outcome.

Cytochrome c oxidase deficiency in Leigh syndrome

We studied 6 mitochondrial enzymes in crude extracts and isolated mitochondria from 5 children with pathologically proven subacute necrotizing encephalomyelopathy (Leigh syndrome). Samples were taken from brain (5 patients), skeletal muscle (4 patients), liver (4 patients), kidney (4 patients), heart (1 patient), and cultured fibroblasts (3 patients). An isolated defect of cytochrome c oxidase (COX) activity was found in brain (decrease of activity to 15 to 39% of the normal mean), muscle (9 to 20%), kidney (1 to 67%), and in the 1 available heart (4%) from a patient with cardiopathy. COX activity was also decreased in liver of 3 patients (2 to 13% of normal) and in cultured fibroblasts of 2 patients (18 and 27%), but it was normal in both liver and fibroblasts from 1 patient. Immunotitration using polyclonal antibodies against human heart COX showed essentially normal amounts of cross-reacting enzyme protein in various tissues from different patients. Electrophoresis of COX immunoprecipitated from brain mitochondrial extracts showed normal patterns of COX subunits in 2 patients. This study confirms the theory that COX deficiency is an important cause of Leigh syndrome.

Myo-, neuro-, gastrointestinal encephalopathy (MNGIE syndrome) due to partial deficiency of cytochrome-c-oxidase. A new mitochondrial multisystem disorder

A 42-year-old woman had a 10-year history of external ophthalmoplegia, malabsorption resulting in chronic malnutrition, muscle atrophy and polyneuropathy. Computer tomography revealed hypodensity of her cerebral white matter. A metabolic disturbance consisted of lactic acidosis after moderate glucose loads with increased excretion of hydroxybutyric and fumaric acids. Post-mortem studies revealed gastrointestinal scleroderma as the morphological manifestation of her malabsorption syndrome, ocular and skeletal myopathy with ragged red fibers, peripheral neuropathy, vascular abnormalities of meningeal and peripheral nerve vessels. Biochemical examination of the liver and muscle tissues revealed a partial defect of cytochrome-c-oxidase (complex IV of the respiratory chain). This mitochondrial multisystem disorder may represent a separate entity to be classified between the spectrum of myoencephalopathies and oculo-gastrointestinal muscular dystrophy.

Mitochondrial myopathies

The mitochondrial myopathies or encephalomyopathies with known biochemical defects can be divided into 5 groups: (1) defects of mitochondrial transport, such as CPT deficiency or carnitine deficiencies; (2) defects of substrate utilization, such as PDHC deficiency or defects of beta-oxidation; (3) defects of the Krebs cycle, such as fumarase deficiency; (4) defects of oxidation-phosphorylation coupling, such as Luft disease, and (5) defects of the respiratory chain. These disorders are reviewed, with particular emphasis on the defects of the respiratory chain. Defects of complex I, III and IV show remarkable clinical and biochemical heterogeneity. All 3 complexes contain some subunits encoded by mtDNA and others encoded by nuclear DNA. At least some of the cytoplasmically made subunits appear to be tissue specific and may be developmentally regulated, thus explaining the genetic heterogeneity of these disorders.

Cytochrome c oxidase deficiency in subacute necrotizing encephalomyelopathy

Two new patients with Leigh's syndrome (subacute necrotizing encephalomyelopathy) due to deficiency of cytochrome c oxidase are presented and their data are compared with those of the four Leigh's syndrome patients previously reported with this deficiency. It is not possible to distinguish between the various biochemical aetiologies of Leigh's syndrome on clinical grounds. Investigation of pyruvate metabolism and of the respiratory chain will reveal the enzymatic defect in some of the patients. It has now been firmly established that a relationship exists between Leigh's syndrome and deficiency of cytochrome c oxidase. There are, however, other syndromes which are also associated with a deficiency of this enzyme. In Leigh's syndrome, the enzyme deficiency has been reported in many organ systems and in cultured fibroblasts. In the liver, however, decreased, intermediate or normal values of cytochrome c oxidase activity have been found. Selective or more widespread involvement of organ systems, due to mutations of either the nuclear or the mitochondrial DNA encoding for different subunits of the enzyme molecule (some of which may be organ- or tissue-specific), could explain the clinical and biochemical heterogeneity of syndromes associated with a cytochrome c oxidase deficiency.

Two bovine genes for cytochrome c oxidase subunit IV: a processed pseudogene and an expressed gene

We have isolated and analyzed 17 clones from a bovine genomic library in phage lambda Charon28 probed with a bovine liver cDNA for cytochrome c oxidase subunit IV. Restriction enzyme mapping and Southern analysis indicated that these clones represent only two genomic regions. One region was shown by nucleotide sequencing to contain a subunit IV pseudogene of the processed type. The other class of clones contained the 5' region of a putative expressed gene; the region consists of two exons and two introns, with one exon encoding exclusively the domain representing the presequence present on newly synthesized subunit-IV polypeptides. Genomic Southern analysis indicated that these two clones probably represent the only sequences in the bovine nucleus that share nucleotide sequence identity with the liver subunit IV cDNA when utilizing moderately stringent hybridization conditions.

Myopathies due to enzyme deficiencies

After the discovery in 1959 of myophosphorylase deficiency, at least 15 myopathies due to deficiency of enzymes involved in energy substrate utilization have been described. In this review two main categories of enzymopathies, glycogenosis and mitochondrial disorders, are discussed. Clinically, the patients with these categories of enzyme defects present two major syndromes: acute recurrent muscle impairment, generally related to exercise, associated with cramps and/or myoglobinuria; progressive muscular weakness and wasting eventually associated with signs of affected organs other than skeletal muscle. Defects of glycogen breakdown and of the first step of glycolysis are more frequently associated with acute exercise intolerance, such as in myophosphorylase and phosphofructokinase deficiencies, but may be associated with progressive muscle weakness and wasting, such as in acid maltase and debrancher enzyme deficiency. Clinical heterogeneity is common in these disorders, but a biochemical explanation for their different clinical expression is still lacking. Defects of the second step of glycolysis, phosphoglycerate kinase, phosphoglycerate mutase and lactate dehydrogenase deficiencies, have been discovered recently and are associated with exercise intolerance. The reason for muscle weakness and atrophy in glycogenosis is still unclear, although it has been suggested that excessive protein catabolism occurs in myophosphorylase, debrancher and acid maltase deficiencies. Myopathies due to deficiencies of mitochondrial enzymes are less well defined, as a group, than the glycogenoses. They are currently considered to fall into three main groups: defects of substrate utilization, such as carnitine palmitoyltransferase deficiency; defects of respiratory chain complexes, such as cytochrome-c-oxidase deficiency and defects of phosphorylation-respiration coupling, such as Luft's disease. Again, severe and benign exercise intolerance or progressive life-threatening myopathic syndromes may be the clinical expression of these disorders. Detailed biochemical and morphological studies of muscle biopsies are needed in these patients to obtain a definite diagnosis and prognosis, and to decide on eventual treatment.

Mitochondrial myopathies

Mitochondrial myopathies are clinically heterogeneous disorders that can affect multiple systems besides skeletal muscle (mitochondrial encephalomyopathies or cytopathies) and are usually defined by morphological abnormalities of muscle mitochondria. There are a few distinctive syndromes, such as the Kearns-Sayre syndrome; myoclonus epilepsy with ragged-red fibers; and mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes. Biochemically, mitochondrial myopathies can be divided into defects of substrate utilization, oxidation-phosphorylation coupling, and the respiratory chain. Because mitochondria have their own DNA and their own translation and transcription apparatuses, mitochondrial myopathies can be due to defects of either a nuclear or mitochondrial genome and can be transmitted by mendelian or maternal inheritance.

Isolation and properties of cytochrome c oxidase from rat liver and quantification of immunological differences between isozymes from various rat tissues with subunit-specific antisera

Cytochrome c oxidase was isolated from rat liver either by affinity chromatography on cytochrome-c--Sepharose 4B or by chromatography on DEAE-Sepharose. Dodecyl sulfate gel electrophoresis of both preparations showed the same subunit pattern consisting of 13 different polypeptides. Kinetic analysis of the two preparations gave a higher Vmax for the enzyme isolated by chromatography on DEAE-Sephacel. Specific antisera were raised in rabbits against nine of the ten nuclear endoded subunits. A monospecific reaction of each antiserum with its corresponding subunit was obtained by Western blot analysis, thus excluding artificial bands in the gel electrophoretic pattern of the isolated enzyme due to proteolysis, aggregation or conformational modification of subunits. With an antiserum against rat liver holocytochrome c oxidase a different reactivity was found by Western blot analysis for subunits VIa and VIII between isolated cytochrome c oxidases from pig liver or kidney and heart or skeletal muscle. For a quantitative analysis of immunological differences a nitrocellulose enzyme-linked immunosorbent assay was developed. Monospecific antisera against 12 of the 13 subunits of rat liver cytochrome c oxidase were titrated with increasing amounts of total mitochondrial proteins from different rat tissues dissolved in dodecyl sulfate and dotted on nitrocellulose. The absorbance of a soluble dye developed by the second peroxidase-conjugated antibody was measured. From the data the following conclusions were obtained: (a) The mitochondrial encoded catalytic subunits I-III of cytochrome c oxidase are probably identical in all rat tissues. (b) All nine investigated nuclear encoded subunits of cytochrome c oxidase showed immunological differences between two or more tissues. Large immunological differences were found between liver, kidney or brain and heart or skeletal muscle. Minor but significant differences were observed for some subunits between heart and skeletal muscle and between liver, kidney and brain. (c) Between corresponding nuclear encoded subunits of cytochrome c oxidase from fetal and adult tissues of liver, heart and skeletal muscle apparent immunological differences were observed. The data could explain cases of fatal infantile myopathy due to cytochrome c oxidase deficiency.

Fatal infantile mitochondrial myopathy and renal dysfunction caused by cytochrome c oxidase deficiency: immunological studies in a new patient

A 3-month-old female infant had profound generalized weakness, de Toni-Fanconi-Debre syndrome, and lactic acidosis. She required assisted ventilation and died at the age of 8 months. Muscle biopsy showed accumulation of mitochondria, glycogen, and lipid droplets. Histochemical reaction and immunocytochemical stain for cytochrome c oxidase showed very weak results, but both reactions were normal in intrafusal fibers of the muscle spindle. In crude extracts of the patient's muscle, cytochrome c oxidase activity was undetectable and enzyme-linked immunosorbent assay showed decreased reaction at all dilutions of antiserum. These data indicate that the amount of immunoreactive enzyme protein is markedly decreased in muscle of patients with fatal infantile cytochrome c oxidase deficiency and renal dysfunction.

Muscle pathology in cytochrome c oxidase deficiency

Muscle biopsies from 16 patients with cytochrome c oxidase (CCO) deficiency were examined morphologically. Two siblings had the fatal infantile form. The muscle of the older sister at the age of 5 months had numerous ragged-red fibers (RRF) and increased numbers of lipid droplets; at 28 days the brother had no RRF suggesting that the RRF formed later than 28 days. The muscle pathology in two patients with the benign infantile form improved as they grew older; numbers of RRF, lipid droplets and glycogen particles decreased and CCO activity increased in the second biopsy. In the encephalomyopathic form, RRF were seen in 5 of 12 muscles mostly in patients more than 6 years of age. Muscle spindles and blood vessel walls in the biopsies from three patients with rapid clinical aggravation had no CCO activity, suggesting that enzyme activity differed from tissue to tissue (tissue specificity).