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Reversible infantile respiratory chain deficiency, previously termed reversible infantile cytochrome c oxidase (COX) deficiency myopathy, is a rare mitochondrial disorder that is characterized by severe hypotonia and generalized muscle weakness in infancy that is associated with lactic acidosis. Affected infants will spontaneously recover, if they survive the first months of life. Here, we present the case of a 4-week-old girl who initially presented with hyperammonemia, hypotonia, and failure to thrive, for which she was referred for genetic evaluation. After several tests, a distinct genetic syndrome could not be identified and she continued to deteriorate. A muscle biopsy was performed and demonstrated severe mitochondrial myopathy with abundant COX-negative fibers. Ultrastructural abnormalities of the mitochondria, diagnostic of mitochondrial myopathy, were identified on electron microscopy. Molecular studies revealed the classic homoplasmic disease causing mutation, m.14674 T>C in the MT-TE gene, associated with reversible COX deficiency. Although hyperammonemia is an unusual presentation for mitochondrial myopathies, specifically reversible infantile respiratory chain deficiency, it should be included in the list of possible presenting symptoms for this condition.

A term girl infant delivered following foetal distress presented with early respiratory distress syndrome and lactic acidaemia. She subsequently underwent detailed investigation for primary lactic acidaemia and was identified as homozygous for the c.515A>G,p.(Tyr172Cys) missense variant in the LRPPRC gene. Variants in this gene are known to cause French-Canadian type Leigh syndrome. Both parents were confirmed to be heterozygous for this mutation. This is the first case report of mitochondrial respiratory chain complex IV deficiency presenting as foetal distress and neonatal respiratory distress syndrome., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2019. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Leigh syndrome, French Canadian type is a rare neurodegenerative disease. To our knowledge, there have been no studies based on ocular findings published for this disease. The purpose of this study is to describe ophthalmic findings in these patients., Patients: Six patients genetically identified as having the syndrome were included in this study., Methods: Four patients had an ophthalmic examination with an ophthalmologist including evaluation of visual acuity, extraocular motility and lid position, orthoptic workup, evaluation of stereopsis, refraction, evaluation of pupils, color vision, slit-lamp biomicroscopy, measurement of intraocular pressure, and fundoscopy. Two patients had a chart review., Results: Visual acuity ranged from 0.00 logmar to 1.55 logmar. Extraocular motility abnormalities and ptosis were noted in half of the patients. Strabismus was present in the entire cohort, and stereopsis was absent in half of these patients. Amblyopia was noted in 83% of individuals and suppression in 33%. Only one patient had nystagmus. Refraction varied throughout patients. It included severe hyperopia, myopia, astigmatism, and significant anisometropia. Pupils, anterior segment, fundus, and color vision were normal in all patients. Intraocular pressure was slightly elevated in one patient., Conclusion: Patients with Leigh syndrome, French Canadian type display a variety of ophthalmic findings, and screening at a young age is recommended.

Background: Cytochrome oxidase IV complex regulates energy production in mitochondria. Therefore, we determined the relation of COX genes with atherosclerosis in mice and pigs., Methods and Results: First, we compared atherosclerosis in the aortic arch of age-matched (24 weeks) C57BL/6J control (n = 10), LDL-receptor deficient (n = 8), leptin-deficient ob/ob (n = 10), and double knock-out (lacking LDL-receptor and leptin) mice (n = 12). Low aortic mitochondria-encoded cytochrome oxidase 1 in obese diabetic double knock-out mice was associated with a larger plaque area and higher propensity of M1 macrophages and oxidized LDL. Caloric restriction increased mitochondria-encoded cytochrome oxidase 1 and reduced plaque area and oxidized LDL. This was associated with a reduction of titer of anti-oxidized LDL antibodies, a proxy of systemic oxidative stress. Low of mitochondria-encoded cytochrome oxidase 1 was related to low expression of peroxisome proliferative activated receptors α, δ, and γ and of peroxisome proliferative activated receptor, gamma, co-activator 1 alpha reflecting mitochondrial dysfunction. Caloric restriction increased them. To investigate if there was a diabetic/obesity requirement for mitochondria-encoded cytochrome oxidase 1 to be down-regulated, we then studied atherosclerosis in LAD of hypercholesterolemic pigs (n = 37). Pigs at the end of the study were divided in three groups based on increasing LAD plaque complexity according to Stary (Stary I: n = 12; Stary II: n = 13; Stary III: n = 12). Low mitochondria-encoded cytochrome oxidase 1 in isolated plaque macrophages was associated with more complex coronary plaques and oxidized LDL. Nucleus-encoded cytochrome oxidase 4I1 and cytochrome oxidase 10 did not correlate with plaque complexity and oxidative stress. In mice and pigs, MT-COI was inversely related to insulin resistance., Conclusions: Low MT-COI is related to mitochondrial dysfunction, oxidative stress and atherosclerosis and plaque complexity., Competing Interests: The authors have declared that no competing interests exist.

Objectives: Isolated complex IV (cytochrome c oxidase) deficiency is one of the most frequent respiratory chain defects in mitochondrial disorders (MIDs) and usually occurs together with severe pediatric or rarely adult multisystem disease. Here we report an adult with isolated complex IV deficiency with unusually mild clinical manifestations., Case Report: A 50-year-old man had developed generalized muscle aches and occasional twitching and stiffness of the musculature since age 48 years. He had a previous history of diabetes, acute hearing loss, hyperlipidemia, hyperuricemia, arterial hypertension, polyarthrosis, hypogonadism, and hypothyroidism. The family history was positive for diabetes (mother), CK elevation (brother), myalgias (brother), and proximal weakness of the upper limbs (mother). Work-up revealed hypoacusis, postural tremor and reduced tendon reflexes, recurrent mild hyper-CK-emia, neurogenic needle electromyography, and a muscle biopsy with mild non-specific changes. Biochemical investigations of the muscle homogenate revealed an isolated complex IV defect and reduced amounts of coenzyme Q (CoQ). He profited from CoQ supplementation, low-carbohydrate diet, and gluten-free diet., Conclusions: Isolated complex IV deficiency may present with only mild muscular, endocrine, or cardiac manifestations in adults. Coenzyme Q supplementation, low-carbohydrate diet, and gluten-free diet may have a beneficial effect at least on some of the manifestations.

Mitochondrial dysfunction is a significant factor in human disease, ranging from systemic disorders of childhood to cardiomyopathy, ischaemia and neurodegeneration. Cytochrome oxidase, the terminal enzyme of the mitochondrial respiratory chain, is a frequent target. Lower eukaryotes possess alternative respiratory-chain enzymes that provide non-proton-translocating bypasses for respiratory complexes I (single-subunit reduced nicotinamide adenine dinucleotide dehydrogenases, e.g. Ndi1 from yeast) or III + IV [alternative oxidase (AOX)], under conditions of respiratory stress or overload. In previous studies, it was shown that transfer of yeast Ndi1 or Ciona intestinalis AOX to Drosophila was able to overcome the lethality produced by toxins or partial knockdown of complex I or IV. Here, we show that AOX can provide a complete or substantial rescue of a range of phenotypes induced by global or tissue-specific knockdown of different cIV subunits, including integral subunits required for catalysis, as well as peripheral subunits required for multimerization and assembly. AOX was also able to overcome the pupal lethality produced by muscle-specific knockdown of subunit CoVb, although the rescued flies were short lived and had a motility defect. cIV knockdown in neurons was not lethal during development but produced a rapidly progressing locomotor and seizure-sensitivity phenotype, which was substantially alleviated by AOX. Expression of Ndi1 exacerbated the neuronal phenotype produced by cIV knockdown. Ndi1 expressed in place of essential cI subunits produced a distinct residual phenotype of delayed development, bang sensitivity and male sterility. These findings confirm the potential utility of alternative respiratory chain enzymes as tools to combat mitochondrial disease, while indicating important limitations thereof.

Leigh syndrome (LS) is a severe neurodegenerative disorder with characteristic bilateral lesions, typically in the brainstem and basal ganglia. It usually presents in infancy and is genetically heterogeneous, but most individuals with mitochondrial complex IV (or cytochrome c oxidase) deficiency have mutations in the biogenesis factor SURF1. We studied eight complex IV-deficient LS individuals from six families of Lebanese origin. They differed from individuals with SURF1 mutations in having seizures as a prominent feature. Complementation analysis suggested they had mutation(s) in the same gene but targeted massively parallel sequencing (MPS) of 1,034 genes encoding known mitochondrial proteins failed to identify a likely candidate. Linkage and haplotype analyses mapped the location of the gene to chromosome 19 and targeted MPS of the linkage region identified a homozygous c.3G>C (p.Met1?) mutation in C19orf79. Abolishing the initiation codon could potentially still allow initiation at a downstream methionine residue but we showed that this would not result in a functional protein. We confirmed that mutation of this gene was causative by lentiviral-mediated phenotypic correction. C19orf79 was recently renamed PET100 and predicted to encode a complex IV biogenesis factor. We showed that it is located in the mitochondrial inner membrane and forms a ∼300 kDa subcomplex with complex IV subunits. Previous proteomic analyses of mitochondria had overlooked PET100 because its small size was below the cutoff for annotating bona fide proteins. The mutation was estimated to have arisen at least 520 years ago, explaining how the families could have different religions and different geographic origins within Lebanon., (Copyright © 2014 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Mitochondrial aminoacyl-tRNA synthetases (aaRSs) are essential enzymes in protein synthesis since they charge tRNAs with their cognate amino acids. Mutations in the genes encoding mitochondrial aaRSs have been associated with a wide spectrum of human mitochondrial diseases. Here we report the identification of pathogenic mutations (a partial genomic deletion and a highly conserved p. Asp325Tyr missense variant) in FARS2, the gene encoding mitochondrial phenylalanyl-tRNA synthetase, in a patient with early-onset epilepsy and isolated complex IV deficiency in muscle. The biochemical defect was expressed in myoblasts but not in fibroblasts and associated with decreased steady state levels of COXI and COXII protein and reduced steady state levels of the mt-tRNA(Phe) transcript. Functional analysis of the recombinant mutant p. Asp325Tyr FARS2 protein showed an inability to bind ATP and consequently undetectable aminoacylation activity using either bacterial tRNA or human mt-tRNA(Phe) as substrates. Lentiviral transduction of cells with wildtype FARS2 restored complex IV protein levels, confirming that the p.Asp325Tyr mutation is pathogenic, causing respiratory chain deficiency and neurological deficits on account of defective aminoacylation of mt-tRNA(Phe)., (© 2013. Published by Elsevier B.V. All rights reserved.)

Mitochondrial disorders are a heterogeneous group of disorders resulting from primary dysfunction of the respiratory chain. Muscle tissue is highly metabolically active, and therefore myopathy is a common element of the clinical presentation of these disorders, although this may be overshadowed by central neurological features. This review is aimed at a general medical and neurologist readership and provides a clinical approach to the recognition, investigation, and treatment of mitochondrial myopathies. Emphasis is placed on practical management considerations while including some recent updates in the field.

Renal manifestations of mitochondrial cytopathies have been described, but nephrotic syndrome with respiratory-chain disorders have been described extremely rarely. We report a 9-month-old boy with a mitochondrial cytopathy preceded by a 2-month history of steroid-resistant nephrotic syndrome. Percutaneous renal biopsy revealed diffuse mesangial sclerosis, and mutational analysis was compatible with PLCE1 mutation. However, electron microscopic findings of renal tissue, sensorineural hearing loss, and other ocular and neurologic findings led us to suspect mitochondrial cytopathy. Muscle tissue analysis showed a deficiency of the respiratory chain complex IV. The clinical presentation of our patient is not typical for primary cytochrome oxidase (COX) deficiency but showed similarities with patients carrying AR mutations in COX10. This was the first case in the literature with both PLCE1 mutation and COX deficiency. We could not identify pathogenic mutations in the COX10 gene, suggesting that PLCE1 deficiency could be the cause of the secondary deficiency of COX. Another, more likely, possibility is that the mitochondriopathy phenotype is caused by another mutation homozygous by descent in a yet unidentified recessive gene.

Autism is the prototype of generalized developmental disorders or what today are called autism spectrum disorders. In most cases it is impossible to detect a specific etiology. It is estimated that a causative diagnosis may be shown in approximately 10-37% of the cases, including, congenital rubella, tuberous sclerosis, chromosome abnormalities such as fragile X syndrome and 22q13.3 deletion syndrome, Angelman, Williams, Smith-Magenis, Sotos, Cornelia de Lange, Möbius, Joubert and Goldenhar syndromes, Ito's hypomelanosis, as well as certain cerebral malformations and several inherited metabolic disorders. The case of a 3-year old girl is described, who was considered as autistic according to the criteria established by the DSM-IV manual for psychiatric disorders. She showed a delay in psychomotor development since she was 18 months old; she pronounces very few words (10), points to some objects, does not look up and it is hard to establish eye contact with her. She has paradoxical deafness and therefore, does not respond when called or when she is given orders, she is beginning to walk. She has not convulsions. Laboratory tests showed an anion gap of 31.6 mEq/L, lactate: 2.55: mmol/L, pyruvate: 0.06 mmol/L, and elevated lactate to/pyruvate ratio: 42.5. Under optical microscopy a muscular biopsy showed a reduction of the diameter of muscular fibers. The study of energy metabolism showed a partial deficiency of complexes III and IV of the respiratory chain, which allowed us to conclude that this was a mitochondrial dysfunction with an autistic clinical spectrum.

The multiple dysfunctional changes associated with a brain affected with Alzheimer's disease (AD) makes the understanding of primary pathogenic mechanisms challenging. Mitochondrial dysfunction has been associated with almost every neurodegenerative disease and neurodegenerative-related event. Alzheimer's disease is no exception with data suggesting mitochondrial malfunctions ranging from improper organelle dynamics, defective oxidative phosphorylation (OXPHOS), oxidative stress, and harmful beta amyloid (Abeta) associations with the mitochondria. A major change often associated with AD is impairment of the electron transport chain at complex IV: cytochrome c oxidase (COX). This mini-review concentrates on recent work by our group that sheds light on the role COX deficiency plays in the pathophysiology of AD using a transgenic mouse model. Results suggest that neuronal COX deficiency does not increase oxidative stress and nor increases amyloidal formations in vivo. Conclusions from this work also suggest that Abeta formation is a cause of COX deficiency as opposed to the consequence.

Background: Pathogenic mutations of the human mitochondrial genome are associated with well-characterized, progressive neurological syndromes, with mutations in the transfer RNA genes being particularly prominent., Objective: To describe a novel mitochondrial transfer RNA(Pro) gene mutation in a woman with a myoclonic epilepsy with ragged-red fibers-like disease. Design, Setting, and Patient Case report of a 49-year-old woman presenting with a myoclonic epilepsy with ragged-red fibers-like disease comprising myoclonic jerks, cerebellar ataxia, and proximal muscle weakness., Results: Histochemical analysis of a muscle biopsy revealed numerous cytochrome-c oxidase-deficient, ragged-red fibers, while biochemical studies indicated decreased activity of respiratory chain complex I. Molecular investigation of mitochondrial DNA revealed a new heteroplasmic mutation in the TpsiC stem of the mitochondrial transfer RNA(Pro) gene that segregated with cytochrome-c oxidase deficiency in single muscle fibers., Conclusions: Our case serves to illustrate the ever-evolving phenotypic spectrum of mitochondrial DNA disease and the importance of performing comprehensive mitochondrial genetic studies in the absence of common mitochondrial DNA mutations.

Mitochondrial respiratory chain deficiencies can present as fulminant liver failure or disease, and the prognosis when associated with severe neonatal lactic acidosis is frequently guarded. We report the case of a neonate who presented with acute liver failure and fulminant lactic acidosis with profound complex IV deficiency documented in muscle and liver biopsies. The neonate subsequently experienced clinical resolution by 3 months of age, and was observed to have reversibility of the biochemical deficiency noted in muscle. This case illustrates that resolution of this severe neonatal phenotype does occur, of importance for accurate prognostic and genetic counseling for such affected neonates.

Background: Motor neuron diseases (amyotrophic lateral sclerosis [ALS] and spinal muscular atrophy [SMA]) have been rarely associated with mitochondrial respiratory chain defects., Objectives: To describe a patient with typical ALS and the finding of ragged-red fibers in muscle biopsy specimens and to review the literature on respiratory chain defects in ALS and SMA., Design: Case report and review of the literature., Setting: Collaboration between tertiary care academic hospitals., Patient: A 65-year-old man with typical ALS., Main Outcome Measures: The patient had 10% ragged-red fibers and 3% cytochrome-c oxidase-negative fibers in muscle biopsy specimens but no biochemical defects of respiratory chain enzymes or alterations of mitochondrial DNA (mtDNA)., Results: Amyotrophic lateral sclerosis with ragged-red fibers has been reported in 5 families and is associated with mtDNA mutations in some subjects. Spinal muscular atrophy without mutations in the survival motor neuron gene (SMN; OMIM 600354) has been associated with mtDNA depletion or with mutations in the cytochrome-c oxidase assembly gene (SCO2; OMIM 604377)., Conclusion: Respiratory chain defects can mimic ALS or SMA and should be considered in the differential diagnosis.

Background: MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is one of the more common mitochondrial encephalomyopathies. About 80% of MELAS cases are caused by transition 3243A-->G in the mitochondrial tRNA(Leu(UUR)) gene (MT-TL1). Other mutations in MT-TL1, other mitochondrial tRNA genes and mitochondrial-encoded subunits of respiratory complex I account for the remainder of cases., Objective: To characterise the molecular basis of a MELAS case without a mutation in any recognised MELAS target gene., Results and Methods: Deletion of a single nucleotide (7630delT) within MT-CO2, the gene of subunit II of cytochrome c oxidase (COX), was identified by mitochondrial DNA (mtDNA) sequencing. The deletion-induced frameshift results in a stop codon close to the 5' end of the reading frame. The lack of subunit II (COII) precludes the assembly of COX and leads to the degradation of unassembled subunits, even those not directly affected by the mutation. Despite mitochondrial proliferation and transcriptional upregulation of nuclear and mtDNA-encoded COX genes (including MT-CO2), a severe COX deficiency was found with all investigations of the muscle biopsy (histochemistry, biochemistry, immunoblotting)., Conclusions: The 7630delT mutation in MT-CO2 leads to a lack of COII with subsequent misassembly and degradation of respiratory complex IV despite transcriptional upregulation of its subunits. The causal association of the resulting isolated COX deficiency with MELAS is at odds with current concepts of the biochemical deficits underlying this common mitochondrial disease, and indicates that the genetic and pathobiochemical heterogeneity of MELAS is greater than previously appreciated.

The authors report on a patient with mild cranio-facial abnormalities observed at birth and growth hormone deficiency, which later developed a typical Kearns-Sayre syndrome. Facial abnormalities are similar to those reported in the fetal alcohol syndrome (a typical neural crest syndrome). In the authors' opinion, they could be an abnormality of neural crest cell development or migration, due to expression of antenatal oxidative phosphorylation deficiency in neural crest cells or to an interference of defective oxidative phosphorylation with neural crest cells signal(s). On this ground, the Kearns-Sayre syndrome can be considered a neurocristopathy and the studies on this syndrome should take into account those diseases commonly associated with neurocristopathies (i.e. facial, endocrine, osseous, cardiovascular and of peripheral nerve system).

Unlabelled: Fatal infantile cardioencephalomyopathy (OMIM No. 604377) is a disorder of the mitochondrial respiratory chain and is characterised by neonatal progressive muscular hypotonia and cardiomyopathy because of severe Cytochrome c oxidase deficiency. Here we report a novel mutation in the Cytochrome c oxidase assembly gene SCO2 in an infant with fatal infantile cardioencephalomyopathy despite normal initial metabolic screening., Conclusion: In newborns with unexplained muscular hypotonia and cardiomyopathy genetic testing of mitochondrial respiratory chain disorders might be helpful to establish a final diagnosis and guide treatment decisions.

Leigh syndrome is an inherited, progressive neurodegenerative disorder of infancy and childhood. Mutations in the nuclear SURF-1 gene are specifically associated with cytochrome C oxidase-deficient Leigh syndrome. This report describes two patients with similar facial features. One of them was a 2(1/2)-year-old male, and the other was a 3-year-old male with a mutation in SURF-1 gene and facial dysmorphism including frontal bossing, brachycephaly, hypertrichosis, lateral displacement of inner canthi, esotropia, maxillary hypoplasia, hypertrophic gums, irregularly placed teeth, upturned nostril, low-set big ears, and retrognathi. The first patient's magnetic resonance imaging at 15 months of age indicated mild symmetric T2 prolongation involving the subthalamic nuclei. His second magnetic resonance imaging at 2 years old revealed a symmetric T2 prolongation involving the subthalamic nuclei, substantia nigra, and medulla lesions. In the second child, at the age of 2 the first magnetic resonance imaging documented heavy brainstem and subthalamic nuclei involvement. A second magnetic resonance imaging, performed when he was 3 years old, revealed diffuse involvement of the substantia nigra and hyperintense lesions of the central tegmental tract in addition to previous lesions. Facial dysmorphism and magnetic resonance imaging findings, observed in these cases, can be specific findings in Leigh syndrome patients with cytochrome C oxidase deficiency. SURF-1 gene mutations must be particularly reviewed in such patients.

Mitochondrial DNA (mtDNA) disease is a common cause of myopathy and the presence of histochemically demonstrated cytochrome c oxidase (COX) deficiency is an extremely useful diagnostic feature. However, there is currently no quantitative information regarding the variability of COX deficiency within or between muscles. This study addresses this issue by studying a number of skeletal muscle samples obtained at post-mortem from three patients with mitochondrial disease due to established mitochondrial DNA defects. COX deficient muscle fibres were enumerated in sections of these muscles and analysed according to patient, individual muscle, position within a particular muscle and sample size. Descriptive statistics were generated followed by an analysis of variance (ANOVA) to assess the effect of these parameters on the mean percentage of COX deficient fibres. We observed statistically significant variation in the percentage of COX deficient fibres within individual muscles from each patient for samples sizes of between 100 and 400 fibres. Our results have implications for the way in which biopsies of skeletal muscle are used for the assessment of disease severity, progression and response to treatment.

Mutations in the SURF1 gene are the most frequent causes of Leigh disease with cytochrome c oxidase deficiency. We describe four children with novel SURF1 mutations and unusual features: three had prominent renal symptoms and one had ragged red fibers in the muscle biopsy. We identified five pathogenic mutations in SURF1: two mutations were novel, an in-frame nonsense mutation (834G-->A) and an out-of-frame duplication (820-824dupTACAT). Although renal manifestations have not been described in association with SURF1 mutations, they can be part of the clinical presentation. Likewise, mitochondrial proliferation in muscle (with ragged red fibers) is most unusual in Leigh disease but might be part of an emerging phenotype.

Cytochrome c oxidase (COX) deficiency is the most commonly recognized respiratory chain defect in childhood. The disease is clinically heterogeneous with phenotypes including Leigh syndrome, hepatic failure and myopathies. COX deficiency has been associated with mitochondrial DNA mutations in COX I, II, and III with large-scale deletions of the mitochondrial genome and with point mutations in mitochondrial tRNA genes. Here we report on a 3.5-year-old girl with a rare type of isolated myopathy due to COX deficiency.

We describe a lethal mitochondrial disease in a 10-month-old child who presented with encephalomyopathy. Histochemical and electron microscopy examinations of skeletal muscle biopsy revealed abnormal mitochondria associated with a combined deficiency of complexes I and IV. After excluding mitochondrial DNA deletions and depletion, direct sequencing was used to screen for mutation in all transfer RNA (tRNA) genes. A T-to-C substitution at position 5693 in the tRNA(Asn) gene was found in blood and muscle. Microdissection of muscle biopsy and its analysis revealed the highest level of this mutation in cytochrome c oxidase (COX)-negative fibres. We suggest that this novel mutation would affect the anticodon loop structure of the tRNA(Asn) and cause a fatal mitochondrial disease.

The authors report 3 cases of cytochrome-c-oxidase deficiency (2 cases of Kearns-Sayre syndrome and 1 case of chronic progressive external ophthalmoplegia) with Central Nervous System alterations and facial anomalies. The facial anomalies are high forehead, wide nasal bridge, upturned nose, long and flat philtrum (alterations depending on frontal-nasal-premaxillary structures which derive from prosencephalic neural crests), hypoplastic maxilla and mandible, ophthalmoplegia (alterations of maxilla and III-VI cranial nerve nuclei, which derive on the mesencefalic neural crests), low set ears, short neck (alterations of the 3rd, 4th branchial arch derivatives, which arise from rhombencephalic neural crests). The authors conclude that cytochrome-c-oxidase deficiency in embryonic stage can injure, in Kearns-Sayre syndrome and chronic progressive external ophthalmoplegia, distal tissues of face and Central Nervous System depending on neural crests, and that the symptomatology of these diseases can be ascribed to dysneurulation.

Background: Doxorubicin induces a self-perpetuating nephropathy characterized by early glomerular and late-onset tubular lesions in rats. We investigated the potential role of mitochondrial injury in the onset of these lesions., Methods: Rats were treated with intravenous doxorubicin (1 mg kg(-1) week(-1)) for 7 weeks and were sacrificed either 1 week ('short-term') or 30 weeks ('long-term') following the last dose. Additional rats received a single dose either 6 days or 2 h prior to euthanasia. All rats were killed at 48 weeks of age. Glomerular and tubular injury was monitored and correlated to the activity or expression of respiratory chain components. Finally, we quantified both nuclear and mitochondrial DNA (mtDNA) as well as superoxide production and the 4834 base pair 'common' mtDNA deletion., Results: The 'long-term' group had significant glomerular and tubular lesions, depressed activities of mtDNA-encoded NADH dehydrogenase and cytochrome-c oxidase (COX) and increased citrate synthase activity. In addition, expression of the mtDNA-encoded COX subunit I was reduced and mtDNA levels were decreased. In 'short-term' rats, there were fewer tubular lesions, but similar numbers of glomerular lesions activity. Among all animals, glomerular and tubular injury were inversely correlated with mtDNA levels, mtDNA-encoded respiratory chain activities and with the expression of the mtDNA-encoded respiratory chain subunit COX-I. Injury was positively correlated with superoxide production and the activities of nucleus-encoded mitochondrial or cytoplasmic enzymes. Kidneys from the 'long-term' group showed more mtDNA deletions than in 'short-term' animals and these were not observed in the other groups., Conclusions: These results suggest an important role for quantitative and qualitative mtDNA alterations through the reduction of mtDNA-encoded respiratory chain function and induction of superoxide in doxorubicin-induced renal lesions.

Leigh syndrome (LS) is one of the most frequent forms of mitochondrial disease in infancy and childhood. Mutations in SURF1 have been shown to be an important cause of LS with cytochrome c oxidase (COX) deficiency. The authors have identified four pathogenic mutations including a novel, in-frame, 15-bp tandem duplication (806-820) in exon 8 and a novel 751+1G>A splice site mutation in SURF1 in three cases of LS with COX deficiency.

We studied the accumulation of cytochrome c oxidase (COX)-negative skeletal muscle fibres in six patients with a myopathy due to a mitochondrial DNA (mtDNA) defect. Each patient was biopsied on two or more occasions over a period of 3-15 years. Progressive proximal weakness was associated with an increase in the proportion of COX-negative fibres. These fibres were arranged randomly, indicating that each fibre became COX negative independently of the status of neighbouring fibres. The clinical progression of mtDNA myopathy is therefore a consequence of a biochemical defect that develops independently within individual muscle fibres. It is likely that this is due to the clonal expansion of mutant mtDNA.

We report a nine-year-old boy with the features of Leigh syndrome (LS) and a severe cytochrome-c oxidase (COX) deficiency with a single thymidine insertion at nucleotide position 5537 (T 5537i) in the tRNA Trp gene of mitochondrial DNA. During infancy the boy was irritable and hypotonus was noticed. Early motor development was delayed, although mental development seemed normal until eight months of age. Early neurological signs were nystagmus, hypertonus and optic atrophy. Severe seizures and mental retardation developed subsequently. Major findings on neuroradiological investigation were from the brainstem, thalami and white matter compatible with LS. Spectrophotometric analysis of skeletal muscle mitochondria showed a profound COX deficiency and a marked complex I deficiency. Enzyme-histochemical analysis showed reduced COX activity in the majority of the muscle fibres. There were no ragged red fibres. The T 5537i mutation was found in a high proportion (> 95 %) in blood, liver and muscle tissue of the patient and in blood of the patient's mother (81 %). This mutation has previously been described in one family in which one child had a very high proportion of the T 5537i mutation and clinical features of LS. We conclude that, although mtDNA mutations are considered to be rare in LS with COX deficiency, the T 5537i mutation should be screened for in cases of LS with COX deficiency when SURF1 gene mutations have been excluded, especially when complex I activity is also decreased.

We report an unusual case of encephalo-entero-myopathy associated with the A8344G mutation in the tRNA(Lys) gene of mitochondrial DNA (mtDNA). This patient had mitochondrial myopathy, multiple lipomatosis, mild hearing loss, stroke-like episodes, and paralytic ileus, but she lacked the canonical clinical features of MERRF, myoclonus, epilepsy, or ataxia. We conducted genetic, biochemical, histochemical, and immunohistochemical studies in skeletal muscle, brain, intestine, and lipoma tissue. The mutation was abundant in all tissues, and cytochrome c oxidase (COX) activity was selectively decreased in brain and small intestine. COX deficiency was also documented histochemically and immunohistochemically in the small intestine, suggesting that mitochondrial dysfunction played a role in the pathogenesis of paralytic ileus. This case illustrates an unusual and dramatic clinical phenotype of the A8344G mutation, characterized by stroke-like episodes and acute ileus.

We report on a patient with complex IV deficiency who in later clinical course was diagnosed as a Lowe syndrome. Mitochondrial abnormalities can be present in Lowe syndrome and might lead to misdiagnosis, additionally because clinical features can be overlapping.

Cytochrome-c oxidase (COX) is the most common respiratory chain complex involved in liver failure, either as a single enzyme deficiency or as part of multiple enzyme deficiencies. We describe an infant who presented with fulminant lactic acidosis in the neonatal period. The lactic acidosis resolved spontaneously but liver and pancreatic insufficiency ensued. Isolated cytochrome-c oxidase deficiency was found in liver but not in muscle and fibroblasts. mtDNA rearrangements or depletion were ruled out. By the age of one year, liver and pancreatic functions have normalized completely and neurodevelopment is normal.

We have identified a novel heteroplasmic C6489A missense mutation in the mitochondrial DNA (mtDNA) CO I gene encoding the cytochrome c oxidase (COX) subunit I in a 17-year-old girl with epilepsia partialis continua. This point mutation leads to an exchange of the highly conserved Leu196 to Ileu196. Muscle biopsy showed in single fibers decreased COX activity and lowered binding of COX antibodies, indicating decreased stability of the mutated enzyme. The analysis of blood mtDNA revealed about 30% mutant mtDNA in the patients blood but about 90% mutant mtDNA in the blood of two non-affected family members. Quantitative analysis of the mutation gene dose effect on COX activity on single muscle fiber level revealed a very high threshold-a COX deficiency was observed only in fibers containing >95% mutant mtDNA. In apparent contrast to this high mutation gene dose threshold, in vivo investigations of mitochondrial function in saponin-permeabilized muscle fibers of the index patient containing approximately 90% mutated mtDNA showed decreased maximal rates of respiration and an increased sensitivity of fiber respiration to cyanide. This is due to a 2-fold increase of COX flux control on muscle fiber respiration and a 30% decrease of COX metabolic threshold, supporting the concept of tight COX control of oxidative phosphorylation in skeletal muscle.

We report a 16-month-old boy with psychomotor regression, muscle hypotonia, peripheral neuropathy, and lactic acidosis. Brain magnetic resonance imaging showed a bilateral abnormal signal in the substantia nigra and in the subthalamic nucleus, suggestive of Leigh disease. Histochemical analysis of skeletal muscle showed decreased cytochrome-c oxidase activity. Biochemical analysis of respiratory chain enzymes in muscle homogenate and in cultured fibroblasts showed isolated cytochrome-c oxidase deficiency. Western blot analysis in fibroblasts showed the absence of Surf1 protein. Genetic analysis of the SURF1 gene revealed that the patient was compound heterozygous for a previously reported mutation at the splice-junction site of intron 3 (240 + 1G > T), and for a novel 4-bp deletion in exon 6 (531_534delAAAT). Our data further enlarge the spectrum of mutations in SURF1 gene in patients with Leigh disease and cytochrome-c oxidase deficiency, contributing to better characterization of the clinical and neuroradiologic features of this group of patients for genotype-phenotype correlations.