Mitochondrial disorders: clinical presentation and diagnostic dilemmas

Glutamine metabolism in diseases associated with mitochondrial dysfunction

Mitochondrial dysfunction can arise from genetic defects or environmental exposures and impact a wide range of biological processes. Among these are metabolic pathways involved in glutamine catabolism, anabolism, and glutamine-glutamate cycling. In recent years, altered glutamine metabolism has been found to play important roles in the pathologic consequences of mitochondrial dysfunction. Glutamine is a pleiotropic molecule, not only providing an alternate carbon source to glucose in certain conditions, but also playing unique roles in cellular communication in neurons and astrocytes. Glutamine consumption and catabolic flux can be significantly altered in settings of genetic mitochondrial defects or exposure to mitochondrial toxins, and alterations to glutamine metabolism appears to play a particularly significant role in neurodegenerative diseases. These include primary mitochondrial diseases like Leigh syndrome (subacute necrotizing encephalopathy) and MELAS (mitochondrial myopathy with encephalopathy, lactic acidosis, and stroke-like episodes), as well as complex age-related neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Pharmacologic interventions targeting glutamine metabolizing and catabolizing pathways appear to provide some benefits in cell and animal models of these diseases, indicating glutamine metabolism may be a clinically relevant target. In this review, we discuss glutamine metabolism, mitochondrial disease, the impact of mitochondrial dysfunction on glutamine metabolic processes, glutamine in neurodegeneration, and candidate targets for therapeutic intervention.

Knowledge and awareness of mitochondrial diseases among physicians in the tertiary hospitals in Ghana

BACKGROUND

Mitochondrial diseases/disorders (MDs), for decades, have been identified as a key underlying condition for many chronic diseases globally. However, data on the knowledge and prevalence of MDs in many countries in sub-Saharan Africa are lacking. This study assessed the knowledge, and awareness, of MDs among senior medical doctors in the five tertiary hospitals in Ghana.

METHOD

Data were collected from one hundred and twenty-eight (128) medical doctors in the five Tertiary Hospitals in Ghana using both closed and open-ended questionnaires and analysed using descriptive statistics.

RESULTS

Of the 128 respondents, 70.32% were senior medical officers and above, 87% of them indicated that they were aware of MDs and over 90% said physicians do not often diagnose MDs in Ghana. About 81% indicated that MDs are associated with chronic illnesses whilst 72% said the disease is diagnosed in both males and females. About 45% of the respondents alluded to the fact that MDs are difficult to diagnose, are associated with mutations in both the mitochondrial and the nuclear DNA, and are non-infectious diseases. Approximately 85% said nervous system dysfunction and muscle weakness are some of the symptoms associated with MDs whilst 77% said fatigue is also one of the symptoms. About 38% of the respondents specified that they encounter myopathies. A majority (70%) did not know about the availability of any consensus or standard diagnostic procedure and/or drugs for MDs.

CONCLUSION

There is a high level of knowledge and awareness of MDs among the respondents. However, there is a low disease encounter, which could be due to a lack of diagnostic protocols or a low disease prevalence. It is, therefore recommend that a patient perspective study, which looks at clinical records and laboratory data be conducted to fully ascertain the prevalence of MDs in Ghana and that appropriate educational strategies and interventions aimed at improving the diagnosis of mitochondrial diseases in Ghana be put in place.

A case for genomic medicine in South African paediatric patients with neuromuscular disease

Paediatric neuromuscular diseases are under-recognised and under-diagnosed in Africa, especially those of genetic origin. This may be attributable to various factors, inclusive of socioeconomic barriers, high burden of communicable and non-communicable diseases, resource constraints, lack of expertise in specialised fields and paucity of genetic testing facilities and biobanks in the African population, making access to and interpretation of results more challenging. As new treatments become available that are effective for specific sub-phenotypes, it is even more important to confirm a genetic diagnosis for affected children to be eligible for drug trials and potential treatments. This perspective article aims to create awareness of the major neuromuscular diseases clinically diagnosed in the South African paediatric populations, as well as the current challenges and possible solutions. With this in mind, we introduce a multi-centred research platform (ICGNMD), which aims to address the limited knowledge on NMD aetiology and to improve genetic diagnostic capacities in South African and other African populations.

Current progress in the therapeutic options for mitochondrial disorders

Mitochondrial disorders manifest enormous genetic and clinical heterogeneity - they can appear at any age, present with various phenotypes affecting any organ, and display any mode of inheritance. What mitochondrial diseases do have in common, is impairment of respiratory chain activity, which is responsible for more than 90% of energy production within cells. While diagnostics of mitochondrial disorders has been accelerated by introducing Next-Generation Sequencing techniques in recent years, the treatment options are still very limited. For many patients only a supportive or symptomatic therapy is available at the moment. However, decades of basic and preclinical research have uncovered potential target points and numerous compounds or interventions are now subjects of clinical trials. In this review, we focus on current and emerging therapeutic approaches towards the treatment of mitochondrial disorders. We focus on small compounds, metabolic interference, such as endurance training or ketogenic diet and also on genomic approaches.

Defined neuronal populations drive fatal phenotype in a mouse model of Leigh syndrome

Mitochondrial deficits in energy production cause untreatable and fatal pathologies known as mitochondrial disease (MD). Central nervous system affectation is critical in Leigh Syndrome (LS), a common MD presentation, leading to motor and respiratory deficits, seizures and premature death. However, only specific neuronal populations are affected. Furthermore, their molecular identity and their contribution to the disease remains unknown. Here, using a mouse model of LS lacking the mitochondrial complex I subunit Ndufs4, we dissect the critical role of genetically-defined neuronal populations in LS progression. Ndufs4 inactivation in Vglut2-expressing glutamatergic neurons leads to decreased neuronal firing, brainstem inflammation, motor and respiratory deficits, and early death. In contrast, Ndufs4 deletion in GABAergic neurons causes basal ganglia inflammation without motor or respiratory involvement, but accompanied by hypothermia and severe epileptic seizures preceding death. These results provide novel insight in the cell type-specific contribution to the pathology, dissecting the underlying cellular mechanisms of MD.

Selective galactose culture condition reveals distinct metabolic signatures in pyruvate dehydrogenase and complex I deficient human skin fibroblasts

INTRODUCTION

A decline in mitochondrial function represents a key factor of a large number of inborn errors of metabolism, which lead to an extremely heterogeneous group of disorders.

OBJECTIVES

To gain insight into the biochemical consequences of mitochondrial dysfunction, we performed a metabolic profiling study in human skin fibroblasts using galactose stress medium, which forces cells to rely on mitochondrial metabolism.

METHODS

Fibroblasts from controls, complex I and pyruvate dehydrogenase (PDH) deficient patients were grown under glucose or galactose culture condition. We investigated extracellular flux using Seahorse XF24 cell analyzer and assessed metabolome fingerprints using NMR spectroscopy.

RESULTS

Incubation of fibroblasts in galactose leads to an increase in oxygen consumption and decrease in extracellular acidification rate, confirming adaptation to a more aerobic metabolism. NMR allowed rapid profiling of 41 intracellular metabolites and revealed clear separation of mitochondrial defects from controls under galactose using partial least squares discriminant analysis. We found changes in classical markers of mitochondrial metabolic dysfunction, as well as unexpected markers of amino acid and choline metabolism. PDH deficient cell lines showed distinct upregulation of glutaminolytic metabolism and accumulation of branched-chain amino acids, while complex I deficient cell lines were characterized by increased levels in choline metabolites under galactose.

CONCLUSION

Our results show the relevance of selective culture methods in discriminating normal from metabolic deficient cells. The study indicates that untargeted fingerprinting NMR profiles provide physiological insight on metabolic adaptations and can be used to distinguish cellular metabolic adaptations in PDH and complex I deficient fibroblasts.

Feeding difficulties, a key feature of the Drosophila NDUFS4 mitochondrial disease model

Mitochondrial diseases are associated with a wide variety of clinical symptoms and variable degrees of severity. Patients with such diseases generally have a poor prognosis and often an early fatal disease outcome. With an incidence of 1 in 5000 live births and no curative treatments available, relevant animal models to evaluate new therapeutic regimes for mitochondrial diseases are urgently needed. By knocking down ND-18, the unique Drosophila ortholog of NDUFS4, an accessory subunit of the NADH:ubiquinone oxidoreductase (Complex I), we developed and characterized several dNDUFS4 models that recapitulate key features of mitochondrial disease. Like in humans, the dNDUFS4 KD flies display severe feeding difficulties, an aspect of mitochondrial disorders that has so far been largely ignored in animal models. The impact of this finding, and an approach to overcome it, will be discussed in the context of interpreting disease model characterization and intervention studies.This article has an associated First Person interview with the first author of the paper.

Mitochondrial disorders in children: toward development of small-molecule treatment strategies

This review presents our current understanding of the pathophysiology and potential treatment strategies with respect to mitochondrial disease in children. We focus on pathologies due to mutations in nuclear DNA‐encoded structural and assembly factors of the mitochondrial oxidative phosphorylation (OXPHOS) system, with a particular emphasis on isolated mitochondrial complex I deficiency. Following a brief introduction into mitochondrial disease and OXPHOS function, an overview is provided of the diagnostic process in children with mitochondrial disorders. This includes the impact of whole‐exome sequencing and relevance of cellular complementation studies. Next, we briefly present how OXPHOS mutations can affect cellular parameters, primarily based on studies in patient‐derived fibroblasts, and how this information can be used for the rational design of small‐molecule treatment strategies. Finally, we discuss clinical trial design and provide an overview of small molecules that are currently being developed for treatment of mitochondrial disease.

A review of anaesthetic outcomes in patients with genetically confirmed mitochondrial disorders

Mitochondrial disorders are a clinically and biochemically diverse group of disorders which may involve multiple organ systems. General anaesthesia (GA) poses a potential risk of decompensation in children with mitochondrial disorders, and there is little guidance for anaesthetists and other clinicians regarding the optimal anaesthetic agents and perioperative management to provide to patients with mitochondrial disease[15]. The aim of this review was to document adverse events and perioperative complications from GA in patients with genetically confirmed mitochondrial disorders. A retrospective chart review of patients with genetically confirmed mitochondrial disorders who had undergone GA was undertaken. The indication for GA, anaesthetic agents utilised, length of admission and post anaesthetic complications were documented and analysed. Twenty-six patients with genetically proven mitochondrial disease underwent 65 GAs. Thirty-four (52%), received propofol as their induction agent. Thirty-three (51%) patients received sevoflurane for the maintenance of anaesthesia, while 8 (12%) received isoflurane and 24 (37%) received propofol. The duration of most GAs was short with 57 (87%) lasting less than 1 h. Perioperative complications occurred in five patients while under GA including ST segment depression, hypotension and metabolic acidosis in one. All five patients were stabilised successfully and none required ICU admission as a consequence of their perioperative complications. The duration of hospital stay post GA was <24 h in 25 (38%) patients.

CONCLUSION

No relationship between choice of anaesthetic agent and subsequent perioperative complication was observed. It is likely that individual optimisation on a case-by-case basis is more important overall than choice of any one particular technique. What is Known: • General anaesthesia (GA) poses a potential risk of decompensation in children with mitochondrial disorders. • There is a great diversity in the anaesthetic approaches undertaken in this cohort, and little guidance exists for anaesthetists and other clinicians regarding the optimal anaesthetic agents and perioperative management to provide to patients with mitochondrial disease. What is New: • In this study of 26 patients with genetically confirmed mitochondrial disease who underwent 65 GAs, no relationship between choice of anaesthetic agent and subsequent perioperative complication was observed • It is likely that individual optimisation on a case-by-case basis is more important overall than choice of any one particular technique.

Metabolic and mitochondrial disorders associated with epilepsy in children with autism spectrum disorder

Autism spectrum disorder (ASD) affects a significant number of individuals in the United States, with the prevalence continuing to grow. A significant proportion of individuals with ASD have comorbid medical conditions such as epilepsy. In fact, treatment-resistant epilepsy appears to have a higher prevalence in children with ASD than in children without ASD, suggesting that current antiepileptic treatments may be suboptimal in controlling seizures in many individuals with ASD. Many individuals with ASD also appear to have underlying metabolic conditions. Metabolic conditions such as mitochondrial disease and dysfunction and abnormalities in cerebral folate metabolism may affect a substantial number of children with ASD, while other metabolic conditions that have been associated with ASD such as disorders of creatine, cholesterol, pyridoxine, biotin, carnitine, γ-aminobutyric acid, purine, pyrimidine, and amino acid metabolism and urea cycle disorders have also been associated with ASD without the prevalence clearly known. Interestingly, all of these metabolic conditions have been associated with epilepsy in children with ASD. The identification and treatment of these disorders could improve the underlying metabolic derangements and potentially improve behavior and seizure frequency and/or severity in these individuals. This paper provides an overview of these metabolic disorders in the context of ASD and discusses their characteristics, diagnostic testing, and treatment with concentration on mitochondrial disorders. To this end, this paper aims to help optimize the diagnosis and treatment of children with ASD and epilepsy. This article is part of a Special Issue entitled "Autism and Epilepsy".

Mitochondrial disease associated with complex I (NADH-CoQ oxidoreductase) deficiency

Mitochondrial diseases due to a reduced capacity for oxidative phosphorylation were first identified more than 20 years ago, and their incidence is now recognized to be quite significant. In a large proportion of cases the problem can be traced to a complex I (NADH-CoQ oxidoreductase) deficiency (Phenotype MIM #252010). Because the complex consists of 44 subunits, there are many potential targets for pathogenic mutations, both on the nuclear and mitochondrial genomes. Surprisingly, however, almost half of the complex I deficiencies are due to defects in as yet unidentified genes that encode proteins other than the structural proteins of the complex. This review attempts to summarize what we know about the molecular basis of complex I deficiencies: mutations in the known structural genes, and mutations in an increasing number of genes encoding "assembly factors", that is, proteins required for the biogenesis of a functional complex I that are not found in the final complex I. More such genes must be identified before definitive genetic counselling can be applied in all cases of affected families.

Irritable bowel syndrome may be associated with maternal inheritance and mitochondrial DNA control region sequence variants

BACKGROUND AND AIM

Mitochondrial dysfunction has been implicated in various functional disorders that are co-morbid to irritable bowel syndrome (IBS) such as migraine, depression and chronic fatigue syndrome. The aim of the current case-control pilot study was to determine if functional symptoms in IBS show a maternal inheritance bias, and if the degree of this maternal inheritance is related to mitochondrial DNA (mtDNA) polymorphisms.

METHODS

Pedigrees were obtained from 308 adult IBS patients, 102 healthy controls, and 36 controls with inflammatory bowel disease (IBD), all from Caucasian heritage, to determine probable maternal inheritance. Two mtDNA polymorphisms (16519T and 3010A), which have previously been implicated in other functional disorders, were assayed in mtDNA haplogroup H IBS subjects and compared to genetic data from 344 published haplogroup H controls.

RESULTS

Probable maternal inheritance was found in 17.5 % IBS, 2 % healthy controls and 0 % IBD controls (p < .0001). No difference was found between IBS and control for 3010A, and a trend was found for 16519T (p = 0.05). IBS with maternal inheritance were significantly more likely to have the 16519T than controls (OR 5.8; 95 % CI 1.5-23.1) or IBS without maternal inheritance (OR 5.2; 95 % CI 1.2-22.6).

CONCLUSIONS

This small pilot study shows that a significant minority (1/6) of IBS patients have pedigrees suggestive of maternal inheritance. The mtDNA polymorphism 16519T, which has been previously implicated in other functional disorders, is also associated with IBS patients who display maternal inheritance. These findings suggest that mtDNA-related mitochondrial dysfunction may constitute a sub-group within IBS. Future replication studies in larger samples are needed.

Association of fibroblast growth factor (FGF-21) as a biomarker with primary mitochondrial disorders, but not with secondary mitochondrial disorders (Friedreich Ataxia)

Mitochondrial respiratory chain deficiencies are a group of more than 100 disorders of adults and children, with highly variable phenotypes. The high prevalence of mitochondrial disorders (MIDs) urges the clinician to diagnose these disorders accurately, which is difficult in the light of highly variable and overlapping phenotypes, transmission patterns and molecular backgrounds. Fibroblast growth factor 21 (FGF-21) is an important endocrine and paracrine regulator of metabolic homeostasis. The FGF-21 transcript is reported to be abundantly expressed in liver, but little is known about the regulation of FGF-21 expression in other tissues. FGF-21 could play a role in the metabolic alterations that are often associated with mitochondrial diseases. The aim of this study was to show the association of the FGF-21 biomarker with human primary MIDs and secondary MIDs in suspected patients in Iran. Serum FGF-21 levels were determined using ELISA in 47 mitochondrial patients, including 32 with primary MIDs, 15 patients with Friedreich ataxia as a secondary MID and 30 control subjects. Serum FGF-21 levels were significantly higher in subjects with the primary MIDs (p < 0.05), compared to subjects without MIDs. However, serum FGF-21 levels did not show significant increase in subjects with FA as a secondary MID. There is an association between increasing concentrations of FGF-21 with mitochondrial diseases, suggesting FGF-21 as a biomarker for diagnosis of primary MIDs in humans. However, this biomarker is not appropriate for the diagnosis of FA.

Generation of a hypomorphic model of propionic acidemia amenable to gene therapy testing

Propionic acidemia (PA) is a recessive genetic disease that results in an inability to metabolize certain amino acids and odd-chain fatty acids. Current treatment involves restricting consumption of these substrates or liver transplantation. Deletion of the Pcca gene in mice mimics the most severe forms of the human disease. Pcca(-) mice die within 36 hours of birth, making it difficult to test intravenous systemic therapies in them. We generated an adult hypomorphic model of PA in Pcca(-) mice using a transgene bearing an A138T mutant of the human PCCA protein. Pcca(-/-)(A138T) mice have 2% of wild-type PCC activity, survive to adulthood, and have elevations in propionyl-carnitine, methylcitrate, glycine, alanine, lysine, ammonia, and markers associated with cardiomyopathy similar to those in patients with PA. This adult model allowed gene therapy testing by intravenous injection with adenovirus serotype 5 (Ad5) and adeno-associated virus 2/8 (AAV8) vectors. Ad5-mediated more rapid increases in PCCA protein and propionyl-CoA carboxylase (PCC) activity in the liver than AAV8 and both vectors reduced propionylcarnitine and methylcitrate levels. Phenotypic correction was transient with first generation Ad whereas AAV8-mediated long-lasting effects. These data suggest that this PA model may be a useful platform for optimizing systemic intravenous therapies for PA.

Stoffwechselerkrankungen

Entsprechend ihrer Wanderung bei isoelektrischer Fokussierung werden die allelen Varianten des α1-AT als Proteinaseinhibitorphänotypen (Pi) klassifiziert. Die dominierende Isoform ist der normale Phänotyp M, daneben gibt es die Mangelvarianten S und Z sowie eine 0-Variante.

Increased nuclear factor-κB and loss of p53 are key mechanisms in Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Fukuda's criteria are adequate to make a distinction between Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) and chronic fatigue (CF), but ME/CFS patients should be subdivided into those with (termed ME) and without (termed CFS) post exertional malaise [Maes et al. 2012]. ME/CFS is considered to be a neuro-immune disease. ME/CFS is characterized by activated immuno-inflammatory pathways, including increased levels of pro-inflammatory cytokines, nuclear factor κB (NF-κB) and aberrations in mitochondrial functions, including lowered ATP. These processes may explain typical symptoms of ME/CFS, e.g. fatigue, malaise, hyperalgesia, and neurologic and autonomic symptoms. Here we hypothesize that increased NF-κB together with a loss of p53 are key phenomena in ME/CFS that further explain ME/CFS symptoms, such as fatigue and neurocognitive dysfunction, and explain ME symptoms, such as post-exertional malaise following mental and physical activities. Inactivation of p53 impairs aerobic mitochondrial functions and causes greater dependence on anaerobic glycolysis, elevates lactate levels, reduces mitochondrial density in skeletal muscle and reduces endurance during physical exercise. Lowered p53 and increased NF-κB are associated with elevated reactive oxygen species. Increased NF-κB induces the production of pro-inflammatory cytokines, which increase glycolysis and further compromise mitochondrial functions. All these factors together may contribute to mitochondrial exhaustion and indicate that the demand for extra ATP upon the commencement of increased activity cannot be met. In conditions of chronic inflammation and oxidative stress, high NF-κB and low p53 may conspire to promote neuron and glial cell survival at a price of severely compromised metabolic brain function. Future research should examine p53 signaling in ME/CFS.

Diagnostic accuracy of blood and CSF lactate in identifying children with mitochondrial diseases affecting the central nervous system

OBJECTIVE

To determine the diagnostic accuracy of blood and cerebrospinal fluid (CSF) lactate and pyruvate concentrations in identifying children with mitochondrial diseases (MD) affecting the central nervous system (CNS).

METHODS

We studied lactate and pyruvate concentrations in paired samples of blood and CSF collected concurrently from 17 patients with MD (Leigh encephalomyelopathy 10, MELAS 5, Pearson disease 1, PDH deficiency 1) and those from control patients (n=49).

RESULTS

Although blood and CSF variables (lactate, pyruvate concentrations and lactate/pyruvate ratio) were significantly higher in the mitochondrial group than in the control group, there was considerable overlap of individual values between these two groups. The maximum value of the area under the receiver operating characteristic curve (AUC) was observed for the CSF lactate concentration (0.994, optimal cut-off value 19.9 mg/dl, sensitivity 0.941 and specificity 1.00), followed by the CSF pyruvate level (0.983). There was an inverse relationship between blood lactate and lactate CSF/blood ratio. For blood lactate concentrations between 20 and 40 mg/dl, a significant difference was also noted in the lactate CSF/blood ratio between the two groups (AUC 1.0, optimal cut-off value 0.91, sensitivity 1.0 and specificity 1.0).

CONCLUSIONS

Our study suggests that that CSF lactate level>19.9 mg/dl is the most reliable variable for identifying patients with MD affecting the CNS. When blood lactate concentrations are marginally elevated (20-40 mg/dl), lactate CSF/blood ratio>0.91 may also provide diagnostic information.

Beyond the serotonin hypothesis: mitochondria, inflammation and neurodegeneration in major depression and affective spectrum disorders

For many years, a deficiency of monoamines including serotonin has been the prevailing hypothesis on depression, yet research has failed to confirm consistent relations between brain serotonin and depression. High degrees of overlapping comorbidities and common drug efficacies suggest that depression is one of a family of related conditions sometimes referred to as the "affective spectrum disorders", and variably including migraine, irritable bowel syndrome, chronic fatigue syndrome, fibromyalgia and generalized anxiety disorder, among many others. Herein, we present data from many different experimental modalities that strongly suggest components of mitochondrial dysfunction and inflammation in the pathogenesis of depression and other affective spectrum disorders. The three concepts of monoamines, energy metabolism and inflammatory pathways are inter-related in many complex manners. For example, the major categories of drugs used to treat depression have been demonstrated to exert effects on mitochondria and inflammation, as well as on monoamines. Furthermore, commonly-used mitochondrial-targeted treatments exert effects on mitochondria and inflammation, and are increasingly being shown to demonstrate efficacy in the affective spectrum disorders. We propose that interactions among monoamines, mitochondrial dysfunction and inflammation can inspire explanatory, rather than mere descriptive, models of these disorders.

An overview of a cohort of South African patients with mitochondrial disorders

Mitochondrial disorders are frequently encountered inherited diseases characterized by unexplained multisystem involvement with a chronic, intermittent, or progressive nature. The objective of this paper is to describe the profile of patients with mitochondrial disorders in South Africa. Patients with possible mitochondrial disorders were accessed over 10 years. Analyses for respiratory chain and pyruvate dehydrogenase complex enzymes were performed on muscle. A diagnosis of a mitochondrial disorder was accepted only if an enzyme activity was deficient. Sixty-three patients were diagnosed with a mitochondrial disorder, including 40 African, 20 Caucasian, one mixed ancestry, and two Indian patients. The most important findings were the difference between African patients and other ethnicities: respiratory chain enzyme complexes CI+III or CII+III deficiencies were found in 52.5% of African patients, being of statistical significance (p value = 0.0061). They also presented predominantly with myopathy (p value = 0.0018); the male:female ratio was 1:1.2. Twenty-five (62.5%) African patients presented with varying degrees of a myopathy accompanied by a myopathic face, high palate, and scoliosis. Fourteen of these 25 also had ptosis and/or progressive external ophthalmoplegia. No patients of other ethnicities presented with this specific myopathic phenotype. Caucasian patients (16/20) presented predominantly with central nervous system involvement. Of the South African pediatric neurology patients, Africans are more likely to present with myopathy and CII+III deficiency, and Caucasian patients are more likely to present with encephalopathy or encephalomyopathy.

Aerobic exercise in children with oxidative phosphorylation defects

Fatigue and exercise intolerance are symptoms in children with metabolic myopathy. Frequently this is combined with muscle pain in children with mitochondrial myopathy. Offering therapeutic advice remains challenging in this patient group. Here we describe five children above the age of four years, with normal intelligence, myopathy, exercise intolerance, motor developmental delay, and fatigue, who were diagnosed with a mitochondrial dysfunction. Based on the positive experience of condition training in adults with mitochondrial disease and inactivity, aerobic exercise training was advised for all the children. Because of the lack of clear protocols for individualized mitochondrial myopathies, regular training was initiated. The Movement Assessment Battery of Children, the Jamar dynamometer for grip force, and the Bruce protocol treadmill test were applied for evaluation. No patient showed significant disease progression on a weekly scheme of strength training or on aerobic training during periods varying between 6 and 18 months. Only one out of the five patients has shown an improvement after a period of structured, aerobic training, demonstrating good compliance and motivation over the course of 18 months. Some patients developed severe muscle pain after explosive exercise. Even in a relatively homogenous, intelligent group of patients and motivated parents, we could not reach full compliance. With our case studies, we would like to draw attention to the importance and pitfalls of movement therapy in children with mitochondrial disease.

Gene expression in a Drosophila model of mitochondrial disease

Background

A point mutation in the Drosophila gene technical knockout (tko), encoding mitoribosomal protein S12, was previously shown to cause a phenotype of respiratory chain deficiency, developmental delay, and neurological abnormalities similar to those presented in many human mitochondrial disorders, as well as defective courtship behavior.

Methodology/Principal Findings

Here, we describe a transcriptome-wide analysis of gene expression in tko^25t mutant flies that revealed systematic and compensatory changes in the expression of genes connected with metabolism, including up-regulation of lactate dehydrogenase and of many genes involved in the catabolism of fats and proteins, and various anaplerotic pathways. Gut-specific enzymes involved in the primary mobilization of dietary fats and proteins, as well as a number of transport functions, were also strongly up-regulated, consistent with the idea that oxidative phosphorylation OXPHOS dysfunction is perceived physiologically as a starvation for particular biomolecules. In addition, many stress-response genes were induced. Other changes may reflect a signature of developmental delay, notably a down-regulation of genes connected with reproduction, including gametogenesis, as well as courtship behavior in males; logically this represents a programmed response to a mitochondrially generated starvation signal. The underlying signalling pathway, if conserved, could influence many physiological processes in response to nutritional stress, although any such pathway involved remains unidentified.

Conclusions/Significance

These studies indicate that general and organ-specific metabolism is transformed in response to mitochondrial dysfunction, including digestive and absorptive functions, and give important clues as to how novel therapeutic strategies for mitochondrial disorders might be developed.

Phenotypic suppression of the Drosophila mitochondrial disease-like mutant tko(25t) by duplication of the mutant gene in its natural chromosomal context

A mutation in the Drosophila gene technical knockout (tko(25t)), encoding mitoribosomal protein S12, phenocopies human mitochondrial disease. We isolated three spontaneous X-dominant suppressors of tko(25t) (designated Weeble), exhibiting almost wild-type phenotype and containing overlapping segmental duplications including the mutant allele, plus a second mitoribosomal protein gene, mRpL14. Ectopic, expressed copies of tko(25t) and mRpL14 conferred no phenotypic suppression. When placed over a null allele of tko, Weeble retained the mutant phenotype, even in the presence of additional transgenic copies of tko(25t). Increased mutant gene dosage can thus compensate the mutant phenotype, but only when located in its normal chromosomal context.

[Clinical variability and diagnosis steps in childhood mitochondrial disease]

OBJECTIVES

Mitochondrial respiratory chain deficiencies are known for their high clinical variability. Difficult to diagnose, the prevalence of these diseases is probably underestimated.

METHODS

We report 18 children diagnosed with respiratory chain deficiency at the Tours University Hospital over the past 10 years.

RESULTS

Three clinical profiles can be distinguished depending on the age at onset of the first symptoms: the neonatal period (4 cases), between 1 month and 2 years of age (10 cases), and after 10 years (4 cases). However, no clinical feature appears specific of any age group. In contrast, respiratory chain analysis on liver biopsy was very informative for all our patients at any age and with any clinical presentation, even with predominant neurological symptoms.

CONCLUSIONS

These biochemical analyses support the diagnosis of mitochondrial disorders in view of molecular analysis, which nevertheless frequently remains inconclusive. These investigations should benefit from the new molecular screening technologies based on DNA chips that can identify the genomic mutations responsible for these severe and relatively frequent diseases.

Neuromuscular and mitochondrial disorders: what is relevant to the anaesthesiologist?

PURPOSE OF REVIEW

The review provides an up-to-date information to the anaesthesiologist about the more frequent and important neuromuscular disorders for which new basic insights or clinical implications have been reported.

RECENT FINDINGS

The findings include the mechanisms of the hyperkalemia after succinylcholine in patients with upregulation of acetylcholine receptors. New insights into the mechanism of malignant hyperthermia-like reactions such as rhabdomyolysis during anaesthesia in patients with Duchenne muscular dystrophy have been published. The importance of mitochondrial defects and the effect of agents used in anaesthesia on mitochondrial function are also highlighted.

SUMMARY

The increased understanding of the genetics and pathophysiology of common muscle disorders may lead to a decrease in life-threatening complications related to surgery and anaesthesia. However, there is still a lack of prospective clinical studies to determine which is the safest anaesthetic technique for these patients.

Anesthesia-related morbidity and mortality after surgery for muscle biopsy in children with mitochondrial defects

BACKGROUND

Children with mitochondrial defects (MD) may have an increased risk for cardiorespiratory and neurological complications from anesthesia. The aim of this study was to determine the incidence of perioperative complications and adverse events in children with MD.

METHODS

We performed a retrospective review of the anesthesia, surgical and medical records of 155 children up to 10 years who underwent a diagnostic surgical muscle biopsy for suspected mitochondrial and muscle disorders between 1999 and 2003. The data of the 122 patients where a definite MD diagnosis was found were analyzed. Anesthesia was conducted according to the discretion of the attending staff. In children with MD the activity of the different complexes of the oxidative phosphorylation system was measured.

RESULTS

From the preoperative assessment, signs of encephalopathy were most frequent (n = 93), followed by muscle weakness (n = 32), lactic acidosis (n = 15), cardiomyopathy and/or conduction defects (n = 10) and chronic respiratory problems (n = 7). The mean age of the children with MD was 32.4 months (SD = 26.9). The mean duration of anesthesia was 36.0 min (SD = 12.6) and the mean length of stay in the recovery room was 33.0 min (SD = 24.0). There were no major changes in heart rate or blood pressure which required pharmacological intervention during anesthesia or postanesthesia care unit (PACU) stay. A short episode of SpO2 <80% with airway obstruction occurred once in the PACU. Biochemical analysis in the children with a MD showed an isolated deficiency of one of the five protein complexes of oxidative phosphorylation in 42 children, a combination of complex deficiencies in 41 and no definite localization in 39 children.

CONCLUSION

With standard preoperative assessment, monitoring and anesthesia management, there were no major peroperative and postoperative anesthesia-related complications in children undergoing surgical muscle biopsy with a MD diagnosis.

Neurosurgical treatment of tremor in mitochondrial encephalopathy

A 53-year-old woman underwent several ischemic stroke-like episodes and later developed incomplete, bilateral ophthalmoplegia, left vision deterioration, and bilateral tremor. The clinical course, laboratory data, and muscle histology led to a diagnosis of mitochondrial encephalomyopathy. No other etiology could be identified in the background of her disabling bilateral postural-kinetic tremor. As this tremor did not respond to pharmacological therapy, left thalamotomy and subsequently right thalamic deep brain stimulator (DBS) implantation were performed, which resulted in an excellent clinical outcome. The Fahn-Tolosa-Marin Tremor Rating Scale improved from 110 to 11 points. This case suggests that the rare tremor caused by mitochondrial encephalopathy may be treated long-term with either thalamotomy or thalamic DBS implantation.

Comparative analysis of the pathogenic mechanisms associated with the G8363A and A8296G mutations in the mitochondrial tRNA(Lys) gene

Two mutations (G8363A and A8296G) in the mtDNA (mitochondrial DNA) tRNA(Lys) gene have been associated with severe mitochondrial diseases in a number of reports. Their functional significance, however, remains unknown. We have already shown that homoplasmic cybrids harbouring the A8296G mutation display normal oxidative phosphorylation, although the possibility of a subtle change in mitochondrial respiratory capacity remains an open issue. We have now investigated the pathogenic mechanism of another mutation in the tRNA(Lys) gene (G8363A) by repopulating an mtDNA-less human osteosarcoma cell line with mitochondria harbouring either this genetic variant alone or an unusual combination of the two mutations (A8296G+G8363A). Cybrids homoplasmic for the single G8363A or the A8296G+G8363A mutations have defective respiratory-chain enzyme activities and low oxygen consumption, indicating a severe impairment of the oxidative phosphorylation system. Generation of G8363A cybrids within a wild-type or the A8296G mtDNA genetic backgrounds resulted in an important alteration in the conformation of the tRNA(Lys), not affecting tRNA steady-state levels. Moreover, mutant cybrids have an important decrease in the proportion of amino-acylated tRNA(Lys) and, consequently, mitochondrial protein synthesis is greatly decreased. Our results demonstrate that the pathogenicity of the G8363A mutation is due to a change in the conformation of the tRNA that severely impairs aminoacylation in the absence of changes in tRNA stability. The only effect detected in the A8296G mutation is a moderate decrease in the aminoacylation capacity, which does not affect mitochondrial protein biosynthesis.

Diagnostic value of immunostaining in cultured skin fibroblasts from patients with oxidative phosphorylation defects

In the last decades, a large variety of oxidative phosphorylation (OXPHOS) defects have been reported, expressed as an increasing variety of clinical phenotypes. With the expanding number of genes and proteins involved, new screening techniques leading to more effective diagnostic routes are in ever-increasing demand. Cultured skin fibroblasts from a cohort of patients with various OXPHOS defects, previously recognized by enzyme activity studies and blue native PAGE, were investigated with an immunocytochemical technique. Cytospins of cultured fibroblasts were air dried, fixed, and stained with antibodies specifically directed against subunits of each OXPHOS complex. Control cells stained homogeneously and strongly. In fibroblasts from five out of seven patients with a severe deficiency of one of the OXPHOS complexes, a homogeneous reduction of cytoimmunoreactivity of the affected complex was observed. In five out of seven fibroblast strains harboring a mitochondrial tRNA mutation, a mosaic pattern of staining was observed for both complexes I and IV, reflecting the heteroplasmic nature of the defect. The proportion of deficient fibroblasts varied considerably between cell strains from different subjects. The method described offers a convenient and rapid approach to first-line screening of OXPHOS defects. In association with routine assays of enzyme activity, the technique is helpful in orienting molecular investigation further.

Mitochondrial medicine: a metabolic perspective on the pathology of oxidative phosphorylation disorders

The final steps in the production of adenosine triphosphate (ATP) in mitochondria are executed by a series of multisubunit complexes and electron carriers, which together constitute the oxidative phosphorylation (OXPHOS) system. OXPHOS is under dual genetic control, with communication between the nuclear and mitochondrial genomes essential for optimal assembly and function of the system. We describe the current understanding of the metabolic consequences of pathological OXPHOS defects, based on analyses of patients and of genetically engineered model systems. Understanding the metabolic consequences of OXPHOS disease is of key importance for elucidating pathogenic mechanisms, guiding diagnosis and developing therapies.

Long-term follow-up of neonatal mitochondrial cytopathies: a study of 57 patients

OBJECTIVES

We sought to determine the long-term clinical and biochemical outcome of newborns with mitochondrial cytopathies (MCs) and to identify possible prognostic factors that may modify the course of these diseases.

MATERIAL AND METHODS

Fifty-seven newborns with MCs were identified in a retrospective review (1983-2002). We defined 2 different outcome categories: clinical (neurologic, hepatic, myopathic, and multiorganic) and biochemical (lactate level normalization or initially normal remaining unchanged, decreased but not normalized, and persistently high). We used 2 different statistical approaches: (1) survival studies depending on the initial symptoms and lactate and enzymatic deficiencies using the Kaplan-Meier method; and (2) the same variables compared with different survival age groups and clinical and biochemical outcome categories using the chi2 test.

RESULTS

Thirty-three patients died (57.8%), 12 remain alive (21%), and 12 were lost in the follow-up; 6 of them are currently older than 4 years. Most of the patients manifested multiorganic disease (64.8%) and high lactate level (77.1%) over time. Children surviving to 2.5 to 3 years of age were more likely to survive for a long period of time. Initial neurologic and hepatic presentation increased the risk to develop neurologic disease and severe persistent hyperlactacidemia, respectively. Initial severe hyperlactacidemia and combined enzyme deficiencies were significant risk factors for higher mortality and multiorganic disorders. Two patients with exclusively myopathic outcome are alive and cognitively normal at 12 years of life.

CONCLUSIONS

Children with neonatal-onset MCs have very high mortality and poor prospects. However, some with life-threatening presentations may gradually improve, giving rise to less severe diseases. Those with exclusively myopathic symptoms have a better prognosis.

Risperidone-induced psychosis and depression in a child with a mitochondrial disorder

OBJECTIVE

To our knowledge, this is the first published case report of an adolescent girl with a mitochondrial disorder and depression who displayed both new-onset psychotic and increased mood symptoms during treatment with risperidone.

DATA

A 16-year-old girl was treated with risperidone for mood lability and impulsivity at a community hospital. Within days, she developed paranoid ideation, profound psychomotor retardation, increased depression, and fatigue. She was transferred to an inpatient psychiatric hospital, where she was taken off risperidone. Within 48 hours after discontinuation of the medication, she had complete resolution of psychotic symptoms, fatigue, and psychomotor retardation, and her depression improved.

CONCLUSIONS

This observation of "on-off" risperidone treatment suggests that risperidone may have worsened both psychiatric and physical manifestations of the mitochondrial disorder in this adolescent. These findings are consistent with recent in vitro literature, which implicate a series of neuroleptic medications with mitochondrial dysfunction. Furthermore, the authors provide diagnostic and treatment options that are available for mitochondrial disorders, which are of interest to child psychiatrists due to the central nervous system manifestations of these disorders.

Molecular genetics of complex I-deficient Chinese hamster cell lines

The work from our laboratory on complex I-deficient Chinese hamster cell mutants is reviewed. Several complementation groups with a complete defect have been identified. Three of these are due to X-linked mutations, and the mutated genes for two have been identified. We describe null mutants in the genes for the subunits MWFE (gene: NDUFA1) and ESSS. They represent small integral membrane proteins localized in the Ialpha (Igamma) and Ibeta subcomplexes, respectively [J. Hirst, J. Carroll, I.M. Fearnley, R.J. Shannon, J.E. Walker. The nuclear encoded subunits of complex I from bovine heart mitochondria. Biochim. Biophys. Acta 1604 (7-10-2003) 135-150.]. Both are absolutely essential for assembly and activity of complex I. Epitope-tagged versions of these proteins can be expressed from a poly-cistronic vector to complement the mutants, or to be co-expressed with the endogenous proteins in other hamster cell lines (mutant or wild type), or human cells. Structure-function analyses can be performed with proteins altered by site-directed mutagenesis. A cell line has been constructed in which the MWFE subunit is conditionally expressed, opening a window on the kinetics of assembly of complex I. Its targeting, import into mitochondria, and orientation in the inner membrane have also been investigated. The two proteins have recently been shown to be the targets for a cAMP-dependent kinase [R. Chen, I.M. Fearnley, S.Y. Peak_Chew, J.E. Walker. The phosphorylation of subunits of complex I from bovine heart mitochondria. J. Biol. Chem. xx (2004) xx-xx.]. The epitope-tagged proteins can be cross-linked with other complex I subunits.

Mitochondrial DNA analysis in clinical laboratory diagnostics

Mitochondrial disorders are increasingly being diagnosed, especially among patients with multiple, seemingly unrelated, neuromuscular and multi-sytem disorders. The genetics are complex, in particular as the primary mutation can be either on the nuclear or the mitochondrial DNA (mtDNA). mtDNA mutations are often maternally inherited, but can be sporadic or secondary to autosomally inherited mutations in nuclear genes that regulate mtDNA biosynthesis. mtDNA mutations demonstrate extreme variable expressivity in terms of clinical manifestations and severity, even within a family. Disease is often episodic. Several well-defined clinical syndromes associated with specific mutations are described, yet the genotype-phenotype correlation is fair at best and most patients do not fit within any defined syndrome and have rare or novel mutations. In most patients, mutant and wild-type mtDNA coexist ("heteroplasmy"), although homoplasmic mtDNA mutations also are known. "Standard" mtDNA clinical diagnostics usually consists of a PCR-based assay to detect a small number of relatively common point mutations and Southern blotting (or PCR) for large (>500 bp) rearrangements. In selected cases testing negative, additional analyses can include real-time PCR for mtDNA depletion, and full mtDNA genome screening for the detection of rare and novel point mutations by a variety of methods. Prenatal diagnosis is problematic in most cases.

Application of the yeast Yarrowia lipolytica as a model to analyse human pathogenic mutations in mitochondrial complex I (NADH:ubiquinone oxidoreductase)

While diagnosis and genetic analysis of mitochondrial disorders has made remarkable progress, we still do not understand how given molecular defects are correlated to specific patterns of symptoms and their severity. Towards resolving this dilemma for the largest and therefore most affected respiratory chain enzyme, we have established the yeast Yarrowia lipolytica as a eucaryotic model system to analyse respiratory chain complex I. For in vivo analysis, eYFP protein was attached to the 30-kDa subunit to visualize complex I and mitochondria. Deletions strains for nuclear coded subunits allow the reconstruction of patient alleles by site-directed mutagenesis and plasmid complementation. In most of the pathogenic mutations analysed so far, decreased catalytic activities, elevated K(M) values, and/or elevated I(50) values for quinone-analogous inhibitors were observed, providing plausible clues on the pathogenic process at the molecular level. Leigh mutations in the 49-kDa and PSST homologous subunits are found in regions that are at the boundaries of the ubiquinone-reducing catalytic core. This supports the proposed structural model and at the same time identifies novel domains critical for catalysis. Thus, Y. lipolytica is a useful lower eucaryotic model that will help to understand how pathogenic mutations in complex I interfere with enzyme function.