The myopathic form of coenzyme Q10 deficiency is caused by mutations in the electron-transferring-flavoprotein dehydrogenase (ETFDH) gene

Elucidation of the mechanism of atorvastatin-induced myopathy in a rat model

Myopathy is among the well documented and the most disturbing adverse effects of statins. The underlying mechanism is still unknown. Mitochondrial dysfunction related to coenzyme Q10 decline is one of the proposed theories. The present study aimed to investigate the mechanism of atorvastatin-induced myopathy in rats. In addition, the mechanism of the coenzyme Q10 protection was investigated with special focus of mitochondrial alterations. Sprague-Dawely rats were treated orally either with atorvastatin (100mg/kg) or atorvastatin and coenzyme Q10 (100mg/kg). Myopathy was assessed by measuring serum creatine kinase (CK) and myoglobin levels together with examination of necrosis in type IIB fiber muscles. Mitochondrial dysfunction was evaluated by measuring muscle lactate/pyruvate ratio, ATP level, pAkt as well as mitochondrial ultrastructure examination. Atorvastatin treatment resulted in a rise in both CK (2X) and myoglobin (6X) level with graded degrees of muscle necrosis. Biochemical determinations showed prominent increase in lactate/pyruvate ratio and a decline in both ATP (>80%) and pAkt (>50%) levels. Ultrastructure examination showed mitochondrial swelling with disrupted organelle membrane. Co-treatment with coenzyme Q10 induced reduction in muscle necrosis as well as in CK and myoglobin levels. In addition, coenzyme Q10 improved all mitochondrial dysfunction parameters including mitochondrial swelling and disruption. These results presented a model for atorvastatin-induced myopathy in rats and proved that mitochondrial dysfunction is the main contributor in statin-myopathy pathophysiology.

Riboflavin-Responsive and -Non-responsive Mutations in FAD Synthase Cause Multiple Acyl-CoA Dehydrogenase and Combined Respiratory-Chain Deficiency

Multiple acyl-CoA dehydrogenase deficiencies (MADDs) are a heterogeneous group of metabolic disorders with combined respiratory-chain deficiency and a neuromuscular phenotype. Despite recent advances in understanding the genetic basis of MADD, a number of cases remain unexplained. Here, we report clinically relevant variants in FLAD1, which encodes FAD synthase (FADS), as the cause of MADD and respiratory-chain dysfunction in nine individuals recruited from metabolic centers in six countries. In most individuals, we identified biallelic frameshift variants in the molybdopterin binding (MPTb) domain, located upstream of the FADS domain. Inasmuch as FADS is essential for cellular supply of FAD cofactors, the finding of biallelic frameshift variants was unexpected. Using RNA sequencing analysis combined with protein mass spectrometry, we discovered FLAD1 isoforms, which only encode the FADS domain. The existence of these isoforms might explain why affected individuals with biallelic FLAD1 frameshift variants still harbor substantial FADS activity. Another group of individuals with a milder phenotype responsive to riboflavin were shown to have single amino acid changes in the FADS domain. When produced in E. coli, these mutant FADS proteins resulted in impaired but detectable FADS activity; for one of the variant proteins, the addition of FAD significantly improved protein stability, arguing for a chaperone-like action similar to what has been reported in other riboflavin-responsive inborn errors of metabolism. In conclusion, our studies identify FLAD1 variants as a cause of potentially treatable inborn errors of metabolism manifesting with MADD and shed light on the mechanisms by which FADS ensures cellular FAD homeostasis.

Metabolic Myoglobinuria

One large group of hereditary myopathies characterized by recurrent myoglobinuria, almost invariably triggered by exercise, comprises metabolic disorders of two main fuels, glycogen and long-chain fatty acids, or mitochondrial diseases of the respiratory chain. Differential diagnosis is required to distinguish the three conditions, although all cause a crisis of muscle energy. Muscle biopsy may be useful when performed well after the episode of rhabdomyolysis. Molecular genetics is increasingly the diagnostic test of choice to discover the underlying genetic basis.

Genome-wide association study of serum coenzyme Q10 levels identifies susceptibility loci linked to neuronal diseases

Coenzyme Q₁₀ (CoQ₁₀) is a lipophilic redox molecule that is present in membranes of almost all cells in human tissues. CoQ₁₀ is, amongst other functions, essential for the respiratory transport chain and is a modulator of inflammatory processes and gene expression. Rare monogenetic CoQ₁₀ deficiencies show noticeable symptoms in tissues (e.g. kidney) and cell types (e.g. neurons) with a high energy demand. To identify common genetic variants influencing serum CoQ₁₀ levels, we performed a fixed effects meta-analysis in two independent cross-sectional Northern German cohorts comprising 1300 individuals in total. We identified two genome-wide significant susceptibility loci. The best associated single nucleotide polymorphism (SNP) was rs9952641 (P value = 1.31 × 10 ^-8, β = 0.063, CI_0.95 [0.041, 0.085]) within the COLEC12 gene on chromosome 18. The SNP rs933585 within the NRXN-1 gene on chromosome 2 also showed genome wide significance (P value = 3.64 × 10 ^-8, β = -0.034, CI_0.95 [-0.046, -0.022]). Both genes have been previously linked to neuronal diseases like Alzheimer's disease, autism and schizophrenia. Among our 'top-10' associated variants, four additional loci with known neuronal connections showed suggestive associations with CoQ₁₀ levels. In summary, this study demonstrates that serum CoQ₁₀ levels are associated with common genetic loci that are linked to neuronal diseases.

Multiple acyl-CoA dehydrogenase deficiency (MADD) as a cause of late-onset treatable metabolic disease

INTRODUCTION

Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare, treatable, beta-oxidation disorder responsible for neuromuscular symptoms in adults. This case series describes the clinical and biochemical features of 13 French patients with late-onset MADD.

METHODS AND RESULTS

Thirteen ambulant patients (eight women, five men), with a median age at onset of 27 years, initially experienced exercise intolerance (n=9), isolated muscle weakness (n=1) and a multisystemic pattern with either central nervous system or hepatic dysfunction (n=3). During the worsening period, moderate rhabdomyolysis (n=5), a pseudomyasthenic pattern (n=5) and acute respiratory failure (n=1) have been observed. Weakness typically affected the proximal limbs and axial muscles, and there was sometimes facial asymmetry (n=3). Moderate respiratory insufficiency was noted in one case. Median baseline creatine kinase was 190IU/L. Lactacidemia was sometimes moderately increased at rest (3/10) and after exercise (1/3). The acylcarnitine profile was characteristic, with increases in all chain-length acylcarnitine species. Electromyography revealed a myogenic pattern, while muscle biopsy showed lipidosis, sometimes with COX-negative fibers (n=2). The mitochondrial respiratory chain was impaired in five cases, with coenzyme Q10 decreased in two cases. All patients harbored mutations in the ETFDH gene (four homozygous, seven compound heterozygous, two single heterozygous), with nine previously unidentified mutations. All patients were good responders to medical treatment, but exercise intolerance and/or muscular weakness persisted in 11 of them.

CONCLUSION

Late-onset forms of MADD may present as atypical beta-oxidation disorders. Acylcarnitine profiling and muscle biopsy remain the most decisive investigations for assessing the diagnosis. These tests should thus probably be performed more widely, particularly in unexplained cases of neuromuscular and multisystemic disorders.

Coenzyme Q biosynthesis and its role in the respiratory chain structure

Coenzyme Q (CoQ) is a unique electron carrier in the mitochondrial respiratory chain, which is synthesized on-site by a nuclear encoded multiprotein complex. CoQ receives electrons from different redox pathways, mainly NADH and FADH2 from tricarboxylic acid pathway, dihydroorotate dehydrogenase, electron transfer flavoprotein dehydrogenase and glycerol-3-phosphate dehydrogenase that support key aspects of the metabolism. Here we explore some lines of evidence supporting the idea of the interaction of CoQ with the respiratory chain complexes, contributing to their superassembly, including respirasome, and its role in reactive oxygen species production in the mitochondrial inner membrane. We also review the current knowledge about the involvement of mitochondrial genome defects and electron transfer flavoprotein dehydrogenase mutations in the induction of secondary CoQ deficiency. This mechanism would imply specific interactions coupling CoQ itself or the CoQ-biosynthetic apparatus with the respiratory chain components. These interactions would regulate mitochondrial CoQ steady-state levels and function. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

Coenzyme Q10 defects may be associated with a deficiency of Q10-independent mitochondrial respiratory chain complexes

BACKGROUND

Coenzyme Q10 (CoQ10 or ubiquinone) deficiency can be due either to mutations in genes involved in CoQ10 biosynthesis pathway, or to mutations in genes unrelated to CoQ10 biosynthesis. CoQ10 defect is the only oxidative phosphorylation disorder that can be clinically improved after oral CoQ10 supplementation. Thus, early diagnosis, first evoked by mitochondrial respiratory chain (MRC) spectrophotometric analysis, then confirmed by direct measurement of CoQ10 levels, is of critical importance to prevent irreversible damage in organs such as the kidney and the central nervous system. It is widely reported that CoQ10 deficient patients present decreased quinone-dependent activities (segments I + III or G3P + III and II + III) while MRC activities of complexes I, II, III, IV and V are normal. We previously suggested that CoQ10 defect may be associated with a deficiency of CoQ10-independent MRC complexes. The aim of this study was to verify this hypothesis in order to improve the diagnosis of this disease.

RESULTS

To determine whether CoQ10 defect could be associated with MRC deficiency, we quantified CoQ10 by LC-MSMS in a cohort of 18 patients presenting CoQ10-dependent deficiency associated with MRC defect. We found decreased levels of CoQ10 in eight patients out of 18 (45 %), thus confirming CoQ10 disease.

CONCLUSIONS

Our study shows that CoQ10 defect can be associated with MRC deficiency. This could be of major importance in clinical practice for the diagnosis of a disease that can be improved by CoQ10 supplementation.

Molecular diagnosis of coenzyme Q10 deficiency

Coenzyme Q10 (CoQ) deficiency syndromes comprise a growing number of neurological and extraneurological disorders. Primary-genetic but also secondary CoQ deficiencies have been reported. The biochemical determination of CoQ is a good tool for the rapid identification of CoQ deficiencies but does not allow the selection of candidate genes for molecular diagnosis. Moreover, the metabolic pathway for CoQ synthesis is an intricate and not well-understood process, where a large number of genes are implicated. Thus, only next-generation sequencing techniques (either genetic panels of whole-exome and -genome sequencing) are at present appropriate for a rapid and realistic molecular diagnosis of these syndromes. The potential treatability of CoQ deficiency strongly supports the necessity of a rapid molecular characterization of patients, since primary CoQ deficiencies may respond well to CoQ treatment.

Spectrum of combined respiratory chain defects

Inherited disorders of mitochondrial energy metabolism form a large and heterogeneous group of metabolic diseases. More than 250 gene defects have been reported to date and this number continues to grow. Mitochondrial diseases can be grouped into (1) disorders of oxidative phosphorylation (OXPHOS) subunits and their assembly factors, (2) defects of mitochondrial DNA, RNA and protein synthesis, (3) defects in the substrate-generating upstream reactions of OXPHOS, (4) defects in relevant cofactors and (5) defects in mitochondrial homeostasis. Deficiency of more than one respiratory chain enzyme is a common finding. Combined defects are found in 49 % of the known disease-causing genes of mitochondrial energy metabolism and in 57 % of patients with OXPHOS defects identified in our diagnostic centre. Combined defects of complexes I, III, IV and V are typically due to deficiency of mitochondrial DNA replication, RNA metabolism or translation. Defects in cofactors can result in combined defects of various combinations, and defects of mitochondrial homeostasis can result in a generalised decrease of all OXPHOS enzymes. Noteworthy, identification of combined defects can be complicated by different degrees of severity of each affected enzyme. Furthermore, even defects of single respiratory chain enzymes can result in combined defects due to aberrant formation of respiratory chain supercomplexes. Combined OXPHOS defects have a great variety of clinical manifestations in terms of onset, course severity and tissue involvement. They can present as classical encephalomyopathy but also with hepatopathy, nephropathy, haematologic findings and Perrault syndrome in a subset of disorders.

Redox signalling and mitochondrial stress responses; lessons from inborn errors of metabolism

Mitochondria play a key role in overall cell physiology and health by integrating cellular metabolism with cellular defense and repair mechanisms in response to physiological or environmental changes or stresses. In fact, dysregulation of mitochondrial stress responses and its consequences in the form of oxidative stress, has been linked to a wide variety of diseases including inborn errors of metabolism. In this review we will summarize how the functional state of mitochondria -- and especially the concentration of reactive oxygen species (ROS), produced in connection with the respiratory chain -- regulates cellular stress responses by redox regulation of nuclear gene networks involved in repair systems to maintain cellular homeostasis and health. Based on our own and other's studies we re-introduce the ROS triangle model and discuss how inborn errors of mitochondrial metabolism, by production of pathological amounts of ROS, may cause disturbed redox signalling and induce chronic cell stress with non-resolving or compromised cell repair responses and increased susceptibility to cell stress induced cell death. We suggest that this model may have important implications for those inborn errors of metabolism, where mitochondrial dysfunction plays a major role, as it allows the explanation of oxidative stress, metabolic reprogramming and altered signalling growth pathways that have been reported in many of the diseases. It is our hope that the model may facilitate novel ideas and directions that can be tested experimentally and used in the design of future new approaches for pre-symptomatic diagnosis and prognosis and perhaps more effective treatments of inborn errors of metabolism.

A case of late-onset riboflavin responsive multiple acyl-CoA dehydrogenase deficiency (MADD) with a novel mutation in ETFDH gene

We report a novel mutation in the electron transfer flavoprotein dehydrogenase (EFTDH) gene in an adolescent Chinese patient with late-onset riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency (MADD) characterized by muscle weakness as early symptom. At the age of 9 years, the patient experienced progressive muscle weakness. Blood creatine kinase level and aminotransferase were higher than normal. The muscle biopsy revealed lipid storage myopathy. Serum acylcarnitine and urine organic acid analyses were consistent with MADD. Genetic mutation analysis revealed a compound heterozygous mutation in EFTDH gene. The patients showed good response to riboflavin and l-carnitine treatment.

The investigation and management of metabolic myopathies

Metabolic myopathies (MM) are rare inherited primary muscle disorders that are mainly due to abnormalities of muscle energy metabolism resulting in skeletal muscle dysfunction. These diseases include disorders of fatty acid oxidation, glyco(geno)lytic muscle disorders and mitochondrial respiratory chain (MRC) disease. Clinically these disorders present with a range of symptoms including infantile hypotonia, myalgia/exercise tolerance, chronic or acute muscle weakness, cramps/spasms/stiffness or episodic acute rhabdomyolysis. The precipitant may be fasting, infection, general anaesthesia, heat/cold or most commonly, exercise. However, the differential diagnosis includes a wide range of both acquired and inherited conditions and these include exposure to drugs/toxins, inflammatory myopathies, dystrophies and channelopathies. Streamlining of existing diagnostic protocols has now become a realistic prospect given the availability of second-generation sequencing. A diagnostic pathway using a ‘rhabdomyolysis’ gene panel at an early stage of the diagnostic process is proposed. Following detailed clinical evaluation and first-line investigations, some patients will be identified as candidates for McArdle disease/glycogen storage disease type V or MRC disease and these will be referred directly to the specialised services. However, for the majority of patients, second-line investigation is best undertaken through next-generation sequencing using a ‘rhabdomyolysis’ gene panel. Following molecular analysis and careful evaluation of the findings, some patients will receive a clear diagnosis. Further functional or specific targeted testing may be required in other patients to evaluate the significance of uncertain/equivocal findings. For patients with no clear diagnosis, further investigations will be required through a specialist centre.

Metabolic and mitochondrial myopathies

Metabolic and mitochondrial myopathies encompass a heterogeneous group of disorders that result in impaired energy production in skeletal muscle. Symptoms of premature muscle fatigue, sometimes leading to myalgia, rhabdomyolysis, and myoglobinuria, typically occur with exercise that would normally depend on the defective metabolic pathway. But in another group of these disorders, the dominant muscle symptom is weakness. This article reviews the clinical features, diagnosis, and management of these diseases with emphasis on the recent literature.

Glutaric aciduria type II presenting as myopathy and rhabdomyolysis in a teenager

Late-onset glutaric aciduria type II has been described recently as a rare but treatable cause of proximal myopathy in teenagers and adults. It is an autosomal recessive disease affecting fatty acid, amino acid, and choline metabolism. This is usually a result of 2 defective flavoproteins: either electron transfer flavoprotein (ETF) or electron transfer flavoprotein-ubiquinone oxidoreductase (ETF:QO). We present a 14-year-old boy with a background of autistic spectrum disorder who presented with severe muscle weakness and significant rhabdomyolysis. Before the onset of muscle weakness, he was very active but was completely bedridden at presentation. Diagnosis was established quickly by urine organic acid and plasma acylcarnitine analysis. He has shown significant improvement after starting oral riboflavin supplementation and is now fully mobile. This case highlights that late-onset glutaric aciduria type II is an important differential diagnosis to consider in teenagers presenting with proximal myopathy and rhabdomyolysis and it may not be associated with hypoglycemia.

Genetic bases and clinical manifestations of coenzyme Q10 (CoQ 10) deficiency

Coenzyme Q(10) is a remarkable lipid involved in many cellular processes such as energy production through the mitochondrial respiratory chain (RC), beta-oxidation of fatty acids, and pyrimidine biosynthesis, but it is also one of the main cellular antioxidants. Its biosynthesis is still incompletely characterized and requires at least 15 genes. Mutations in eight of them (PDSS1, PDSS2, COQ2, COQ4, COQ6, ADCK3, ADCK4, and COQ9) cause primary CoQ(10) deficiency, a heterogeneous group of disorders with variable age of onset (from birth to the seventh decade) and associated clinical phenotypes, ranging from a fatal multisystem disease to isolated steroid resistant nephrotic syndrome (SRNS) or isolated central nervous system disease. The pathogenesis is complex and related to the different functions of CoQ(10). It involves defective ATP production and oxidative stress, but also an impairment of pyrimidine biosynthesis and increased apoptosis. CoQ(10) deficiency can also be observed in patients with defects unrelated to CoQ(10) biosynthesis, such as RC defects, multiple acyl-CoA dehydrogenase deficiency, and ataxia and oculomotor apraxia.Patients with both primary and secondary deficiencies benefit from high-dose oral supplementation with CoQ(10). In primary forms treatment can stop the progression of both SRNS and encephalopathy, hence the critical importance of a prompt diagnosis. Treatment may be beneficial also for secondary forms, although with less striking results.In this review we will focus on CoQ(10) biosynthesis in humans, on the genetic defects and the specific clinical phenotypes associated with CoQ(10) deficiency, and on the diagnostic strategies for these conditions.

Diagnosis and management of mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society

PURPOSE

The purpose of this statement is to review the literature regarding mitochondrial disease and to provide recommendations for optimal diagnosis and treatment. This statement is intended for physicians who are engaged in diagnosing and treating these patients.

METHODS

The Writing Group members were appointed by the Mitochondrial Medicine Society. The panel included members with expertise in several different areas. The panel members utilized a comprehensive review of the literature, surveys, and the Delphi method to reach consensus. We anticipate that this statement will need to be updated as the field continues to evolve.

RESULTS

Consensus-based recommendations are provided for the diagnosis and treatment of mitochondrial disease.

CONCLUSION

The Delphi process enabled the formation of consensus-based recommendations. We hope that these recommendations will help standardize the evaluation, diagnosis, and care of patients with suspected or demonstrated mitochondrial disease.

Heart mitochondrial proteome study elucidates changes in cardiac energy metabolism and antioxidant PRDX3 in human dilated cardiomyopathy

Background

Dilated cardiomyopathy (DCM) is a public health problem with no available curative treatment, and mitochondrial dysfunction plays a critical role in its development. The present study is the first to analyze the mitochondrial proteome in cardiac tissue of patients with DCM to identify potential molecular targets for its therapeutic intervention.

Methods and Results

16 left ventricular (LV) samples obtained from explanted human hearts with DCM (n = 8) and control donors (n = 8) were extracted to perform a proteomic approach to investigate the variations in mitochondrial protein expression. The proteome of the samples was analyzed by quantitative differential electrophoresis and Mass Spectrometry. These changes were validated by classical techniques and by novel and precise selected reaction monitoring analysis and RNA sequencing approach increasing the total heart samples up to 25. We found significant alterations in energy metabolism, especially in molecules involved in substrate utilization (ODPA, ETFD, DLDH), energy production (ATPA), other metabolic pathways (AL4A1) and protein synthesis (EFTU), obtaining considerable and specific relationships between the alterations detected in these processes. Importantly, we observed that the antioxidant PRDX3 overexpression is associated with impaired ventricular function. PRDX3 is significantly related to LV end systolic and diastolic diameter (r = 0.73, p value<0.01; r = 0.71, p value<0.01), fractional shortening, and ejection fraction (r = −0.61, p value<0.05; and r = −0.62, p value<0.05, respectively).

Conclusion

This work could be a pivotal study to gain more knowledge on the cellular mechanisms related to the pathophysiology of this disease and may lead to the development of etiology-specific heart failure therapies. We suggest new molecular targets for therapeutic interventions, something that up to now has been lacking.

Coenzyme q10 therapy

For a number of years, coenzyme Q10 (CoQ10) was known for its key role in mitochondrial bioenergetics; later studies demonstrated its presence in other subcellular fractions and in blood plasma, and extensively investigated its antioxidant role. These 2 functions constitute the basis for supporting the clinical use of CoQ10. Also, at the inner mitochondrial membrane level, CoQ10 is recognized as an obligatory cofactor for the function of uncoupling proteins and a modulator of the mitochondrial transition pore. Furthermore, recent data indicate that CoQ10 affects the expression of genes involved in human cell signaling, metabolism and transport, and some of the effects of CoQ10 supplementation may be due to this property. CoQ10 deficiencies are due to autosomal recessive mutations, mitochondrial diseases, aging-related oxidative stress and carcinogenesis processes, and also statin treatment. Many neurodegenerative disorders, diabetes, cancer, and muscular and cardiovascular diseases have been associated with low CoQ10 levels as well as different ataxias and encephalomyopathies. CoQ10 treatment does not cause serious adverse effects in humans and new formulations have been developed that increase CoQ10 absorption and tissue distribution. Oral administration of CoQ10 is a frequent antioxidant strategy in many diseases that may provide a significant symptomatic benefit.

Clinical presentations of coenzyme q10 deficiency syndrome

Coenzyme Q10 (CoQ10) deficiency is a clinically and genetically heterogeneous syndrome which has been associated with 5 major clinical phenotypes: (1) encephalomyopathy, (2) severe infantile multisystemic disease, (3) nephropathy, (4) cerebellar ataxia, and (5) isolated myopathy. Of these phenotypes, cerebellar ataxia and syndromic or isolated nephrotic syndrome are the most common. CoQ10 deficiency predominantly presents in childhood. To date, causative mutations have been identified in a small proportion of patients, making it difficult to identify a phenotype-genotype correlation. Identification of CoQ10 deficiency is important because the disease, in particular muscle symptoms and nephropathy, frequently responds to CoQ10 supplementation.

Genetics of coenzyme q10 deficiency

Coenzyme Q10 (CoQ10) is an essential component of eukaryotic cells and is involved in crucial biochemical reactions such as the production of ATP in the mitochondrial respiratory chain, the biosynthesis of pyrimidines, and the modulation of apoptosis. CoQ10 requires at least 13 genes for its biosynthesis. Mutations in these genes cause primary CoQ10 deficiency, a clinically and genetically heterogeneous disorder. To date mutations in 8 genes (PDSS1, PDSS2, COQ2, COQ4, COQ6, ADCK3, ADCK4, and COQ9) have been associated with CoQ10 deficiency presenting with a wide variety of clinical manifestations. Onset can be at virtually any age, although pediatric forms are more common. Symptoms include those typical of respiratory chain disorders (encephalomyopathy, ataxia, lactic acidosis, deafness, retinitis pigmentosa, hypertrophic cardiomyopathy), but some (such as steroid-resistant nephrotic syndrome) are peculiar to this condition. The molecular bases of the clinical diversity of this condition are still unknown. It is of critical importance that physicians promptly recognize these disorders because most patients respond to oral administration of CoQ10.

Invertebrate models for coenzyme q10 deficiency

The human syndrome of coenzyme Q (CoQ) deficiency is a heterogeneous mitochondrial disease characterized by a diminution of CoQ content in cells and tissues that affects all the electron transport processes CoQ is responsible for, like the electron transference in mitochondria for respiration and ATP production and the antioxidant capacity that it exerts in membranes and lipoproteins. Supplementation with external CoQ is the main attempt to address these pathologies, but quite variable results have been obtained ranging from little response to a dramatic recovery. Here, we present the importance of modeling human CoQ deficiencies in animal models to understand the genetics and the pathology of this disease, although the election of an organism is crucial and can sometimes be controversial. Bacteria and yeast harboring mutations that lead to CoQ deficiency are unable to grow if they have to respire but develop without any problems on media with fermentable carbon sources. The complete lack of CoQ in mammals causes embryonic lethality, whereas other mutations produce tissue-specific diseases as in humans. However, working with transgenic mammals is time and cost intensive, with no assurance of obtaining results. Caenorhabditis elegans and Drosophila melanogaster have been used for years as organisms to study embryonic development, biogenesis, degenerative pathologies, and aging because of the genetic facilities and the speed of working with these animal models. In this review, we summarize several attempts to model reliable human CoQ deficiencies in invertebrates, focusing on mutant phenotypes pretty similar to those observed in human patients.

Pathomechanisms in coenzyme q10-deficient human fibroblasts

Primary coenzyme Q10 (CoQ10) deficiency is a rare mitochondrial disorder associated with 5 major clinical phenotypes: (1) encephalomyopathy, (2) severe infantile multisystemic disease, (3) cerebellar ataxia, (4) isolated myopathy, and (5) steroid-resistant nephrotic syndrome. Growth retardation, deafness and hearing loss have also been described in CoQ10-deficient patients. This heterogeneity in the clinical presentations suggests that multiple pathomechanisms may exist. To investigate the biochemical and molecular consequences of CoQ10 deficiency, different laboratories have studied cultures of skin fibroblasts from patients with CoQ10 deficiency. In this review, we summarize the results obtained in these studies over the last decade.

Clinical and genetical heterogeneity of late-onset multiple acyl-coenzyme A dehydrogenase deficiency

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an autosomal recessive disorder caused by deficiency of electron transfer flavoprotein or electron transfer flavoprotein dehydrogenase. The clinical picture of late-onset forms is highly variable with symptoms ranging from acute metabolic decompensations to chronic, mainly muscular problems or even asymptomatic cases.

METHODS

All 350 cases of late-onset MADD reported in the literature to date have been analyzed and evaluated with respect to age at presentation, diagnostic delay, biochemical features and diagnostic parameters as well as response to treatment.

RESULTS

Mean age at onset was 19.2 years. The mean delay between onset of symptoms and diagnosis was 3.9 years. Chronic muscular symptoms were more than twice as common as acute metabolic decompensations (85% versus 33% of patients, respectively). 20% had both acute and chronic symptoms. 5% of patients had died at a mean age of 5.8 years, while 3% of patients have remained asymptomatic until a maximum age of 14 years. Diagnosis may be difficult as a relevant number of patients do not display typical biochemical patterns of urine organic acids and blood acylcarnitines during times of wellbeing. The vast majority of patients carry mutations in the ETFDH gene (93%), while mutations in the ETFA (5%) and ETFB (2%) genes are the exceptions. Almost all patients with late-onset MADD (98%) are clearly responsive to riboflavin.

CONCLUSIONS

Late-onset MADD is probably an underdiagnosed disease and should be considered in all patients with acute or chronic muscular symptoms or acute metabolic decompensation with hypoglycemia, acidosis, encephalopathy and hepatopathy. This may not only prevent patients from invasive diagnostic procedures such as muscle biopsies, but also help to avoid fatal metabolic decompensations.

EXOSC8 mutations alter mRNA metabolism and cause hypomyelination with spinal muscular atrophy and cerebellar hypoplasia

The exosome is a multi-protein complex, required for the degradation of AU-rich element (ARE) containing messenger RNAs (mRNAs). EXOSC8 is an essential protein of the exosome core, as its depletion causes a severe growth defect in yeast. Here we show that homozygous missense mutations in EXOSC8 cause progressive and lethal neurological disease in 22 infants from three independent pedigrees. Affected individuals have cerebellar and corpus callosum hypoplasia, abnormal myelination of the central nervous system or spinal motor neuron disease. Experimental downregulation of EXOSC8 in human oligodendroglia cells and in zebrafish induce a specific increase in ARE mRNAs encoding myelin proteins, showing that the imbalanced supply of myelin proteins causes the disruption of myelin, and explaining the clinical presentation. These findings show the central role of the exosomal pathway in neurodegenerative disease.

The exosome is responsible for mRNA degradation, which is an important step in the regulation of gene expression. Here the authors report that homozygous missense mutations in the exosome subunit, EXOSC8, may cause neurodegenerative disease in infants through the dysregulation of myelin expression.

Primary coenzyme Q10 (CoQ 10) deficiencies and related nephropathies

Oxidative phosphorylation (OXPHOS) is a metabolic pathway that uses energy released by the oxidation of nutrients to generate adenosine triphosphate (ATP). Coenzyme Q10 (CoQ10), also known as ubiquinone, plays an essential role in the human body not only by generating ATP in the mitochondrial respiratory chain but also by providing protection from reactive oxygen species (ROS) and functioning in the activation of many mitochondrial dehydrogenases and enzymes required in pyrimidine nucleoside biosynthesis. The presentations of primary CoQ10 deficiencies caused by genetic mutations are very heterogeneous. The phenotypes related to energy depletion or ROS production may depend on the content of CoQ10 in the cell, which is determined by the severity of the mutation. Primary CoQ10 deficiency is unique among mitochondrial disorders because early supplementation with CoQ10 can prevent the onset of neurological and renal manifestations. In this review I summarize primary CoQ10 deficiencies caused by various genetic abnormalities, emphasizing its nephropathic form.

Treatment of mitochondrial disorders

OPINION STATEMENT

While numerous treatments for mitochondrial disorders have been suggested, relatively few have undergone controlled clinical trials. Treatment of these disorders is challenging, as only symptomatic therapy is available. In this review we will focus on newer drugs and treatment trials in mitochondrial diseases, with a special focus on medications to avoid in treating epilepsy and ICU patient with mitochondrial disease, which has not been included in such a review. Readers are also referred to the opinion statement in A Modern Approach to the Treatment of Mitochondrial Disease published in Current Treatment Options in Neurology 2009. Many of the supplements used for treatment were reviewed in the previous abstract, and dosing guidelines were provided. The focus of this review is on items not previously covered in depth, and our discussion includes more recently studied compounds as well as any relevant updates on older compounds . We review a variety of vitamins and xenobiotics, including dichloroacetate (DCA), arginine, coenzyme Q10, idebenone, EPI-743, and exercise training. Treatment of epilepsy, which is a common feature in many mitochondrial phenotypes, warrants special consideration due to the added toxicity of certain medications, and we provide a discussion of these unique treatment challenges. Interesting, however, with only a few exceptions, the treatment strategies for epilepsy in mitochondrial cytopathies are the same as for epilepsy without mitochondrial dysfunction. We also discuss intensive care management, building upon similar reviews, adding new dimensions, and demonstrating the complexity of overall care of these patients.

Cellular consequences of oxidative stress in riboflavin responsive multiple acyl-CoA dehydrogenation deficiency patient fibroblasts

Mitochondrial dysfunction and oxidative stress are central to the molecular pathology of many human diseases. Riboflavin responsive multiple acyl-CoA dehydrogenation deficiency (RR-MADD) is in most cases caused by variations in the gene coding for electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). Currently, patients with RR-MADD are treated with high doses of riboflavin resulting in improvements of the clinical and biochemical profiles. However, in our recent studies of RR-MADD, we have shown that riboflavin treatment cannot fully correct the molecular defect in patient cells producing increased reactive oxygen species (ROS). In the current study, we aim to elucidate the cellular consequences of increased ROS by studying the cellular ROS adaption systems including antioxidant system, mitochondrial dynamics and metabolic reprogramming. We have included fibroblasts from six unrelated RR-MADD patients and two control fibroblasts cultivated under supplemented and depleted riboflavin conditions and with coenzyme Q10 (CoQ10) treatment. We demonstrated inhibition of mitochondrial fusion with increased fractionation and mitophagy in the patient fibroblasts. Furthermore, we indicated a shift in the energy metabolism by decreased protein levels of SIRT3 and decreased expression of fatty acid β-oxidation enzymes in the patient fibroblasts. Finally, we showed that CoQ10 treatment has a positive effect on the mitochondrial dynamic in the patient fibroblasts, indicated by increased mitochondrial fusion marker and reduced mitophagy. In conclusion, our results indicate that RR-MADD patient fibroblasts suffer from a general mitochondria dysfunction, probably initiated as a rescue mechanism for the patient cells to escape apoptosis as a result of the oxidative stress.

Disorders of fatty acid oxidation

Recognition of fatty acid oxidation (FAO) disorders is important for the pediatric neurologist as they present with a spectrum of clinical disorders, including progressive lipid storage myopathy, recurrent myoglobinuria, neuropathy, progressive cardiomyopathy, recurrent hypoglycemic hypoketotic encephalopathy or Reye-like syndrome, seizures, and mental retardation. They constitute a critical group of diseases because they are potentially rapidly fatal and a source of major morbidity. There is frequently a family history of sudden infant death syndrome in siblings. Early recognition and prompt institution of therapy and appropriate preventive measures, and in certain cases specific therapy, may be life-saving and may significantly decrease long-term morbidity, particularly with respect to CNS sequelae. All currently known conditions are inherited as autosomal recessive traits. There are now at least 25 enzymes and specific transport proteins in the β-oxidation pathway and 18 have been associated with human disease. The most common defect is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which had an incidence of 1 in 8930 live births in one series. The identification of serum acylcarnitines by electrospray ionization-tandem mass spectrometry of dried blood spots on filter paper in newborn screening programs has significantly enhanced the early recognition of these disorders.

[Muscle weakness and early stages of liver failure in a 22-year-old man]

A 22-year-old man without pre-existing medical conditions presented to our hospital with a progressive reduction of his physical overall performance, muscle weakness of the extremities, and diarrhea for the last 2 months concomitant with elevated liver enzymes and creatine kinase activity. After ruling out infectious diseases, neoplasia, and autoimmune disorders as a cause of these symptoms, the histology of liver and muscle samples led us to suspect a diagnosis of a rare lipid metabolism disorder. Molecular biologic testing provided the diagnosis of multiple acyl-coA dehydrogenase deficiency with ubiquinone deficiency and late onset. The course of disease was complicated by liver failure and severe pneumonia requiring ventilatory assistance. With the substitution of riboflavin and ubiquinone, the patient showed a gradual recovery of his clinical presentation and an improvement of his laboratory tests. A congenital lipid metabolic disorder might be a rare cause of severe myopathy and hepatopathy in a young adult.

Characterization of CoQ₁₀ biosynthesis in fibroblasts of patients with primary and secondary CoQ₁₀ deficiency

Primary coenzyme Q₁₀ (CoQ₁₀) deficiencies are associated with mutations in genes encoding enzymes important for its biosynthesis and patients are responsive to CoQ₁₀ supplementation. Early treatment allows better prognosis of the disease and therefore, early diagnosis is desirable. The complex phenotype and genotype and the frequent secondary CoQ₁₀ deficiencies make it difficult to achieve a definitive diagnosis by direct quantification of CoQ₁₀. We developed a non-radioactive methodology for the quantification of CoQ₁₀ biosynthesis in fibroblasts that allows the identification of primary deficiencies. Fibroblasts were incubated 72 h with 28 μmol/L (2)H₃-mevalonate or 1.65 mmol/L (13)C₆-p-hydroxybenzoate. The newly synthesized (2)H₃- and (13)C₆- labelled CoQ₁₀ were analysed by high performance liquid chromatography-tandem mass spectrometry. The mean and the reference range for (13)C₆-CoQ₁₀ and (2)H₃-CoQ₁₀ biosynthesis were 0.97 (0.83-1.1) and 0.13 (0.09-0.17) nmol/Unit of citrate synthase, respectively. We validated the methodology through the study of one patient with COQ2 mutations and six patients with CoQ₁₀ deficiency secondary to other inborn errors of metabolism. Afterwards we investigated 16 patients' fibroblasts and nine showed decreased CoQ₁₀ biosynthesis. Therefore, the next step is to study the COQ genes in order to reach a definitive diagnosis in these nine patients. In the patients with normal rates the deficiency is probably secondary. In conclusion, we have developed a non-invasive non-radioactive method suitable for the detection of defects in CoQ₁₀ biosynthesis, which offers a good tool for the stratification of patients with these treatable mitochondrial diseases.

Genomics and genetics in the biology of adaptation to exercise

This article is devoted to the role of genetic variation and gene-exercise interactions in the biology of adaptation to exercise. There is evidence from genetic epidemiology research that DNA sequence differences contribute to human variation in physical activity level, cardiorespiratory fitness in the untrained state, cardiovascular and metabolic response to acute exercise, and responsiveness to regular exercise. Methodological and technological advances have made it possible to undertake the molecular dissection of the genetic component of complex, multifactorial traits, such as those of interest to exercise biology, in terms of tissue expression profile, genes, and allelic variants. The evidence from animal models and human studies is considered. Data on candidate genes, genome-wide linkage results, genome-wide association findings, expression arrays, and combinations of these approaches are reviewed. Combining transcriptomic and genomic technologies has been shown to be more powerful as evidenced by the development of a recent molecular predictor of the ability to increase VO2max with exercise training. For exercise as a behavior and physiological fitness as a state to be major players in public health policies will require that the role of human individuality and the influence of DNA sequence differences be understood. Likewise, progress in the use of exercise in therapeutic medicine will depend to a large extent on our ability to identify the favorable responders for given physiological properties to a given exercise regimen.

Clinical and functional characterisation of the combined respiratory chain defect in two sisters due to autosomal recessive mutations in MTFMT

Exome sequencing identified compound heterozygous mutations in the recently discovered mitochondrial methionyl-tRNA formyltransferase (MTFMT) gene in two sisters with mild Leigh syndrome and combined respiratory chain deficiency. The mutations lead to undetectable levels of the MTFMT protein. Blue native polyacrylamide gel electrophoresis showed decreased complexes I and IV, and additional products stained with complex V antibodies, however the overall steady state level of mt-tRNA(Met) was normal. Our data illustrate that exome sequencing is an excellent diagnostic tool, and its value in clinical medicine is enormous, however it can only be optimally exploited if combined with detailed phenotyping and functional studies.

Early myoclonic epilepsy, hypertrophic cardiomyopathy and subsequently a nephrotic syndrome in a patient with CoQ10 deficiency caused by mutations in para-hydroxybenzoate-polyprenyl transferase (COQ2)

BACKGROUND

Primary coenzyme Q10 (CoQ10) deficiencies are heterogeneous autosomal recessive disorders. CoQ2 mutations have been identified only rarely in patients. All affected individuals presented with nephrotic syndrome in the first year of life.

METHODS

An infant is studied with myoclonic seizures and hypertrophic cardiomyopathy in the first months of life and developed a nephrotic syndrome in a later stage.

RESULTS

At three weeks of age, the index patient developed myoclonic seizures. In addition, he had hypertrophic cardiomyopathy and increased CSF lactate. A skeletal muscle biopsy performed at two months of age disclosed normal activities of the oxidative phosphorylation complexes. The child was supplemented with CoQ10 (5 mg/kg/day). At the age of four months, brain MR images showed bilateral increased signal intensities in putamen and cerebral cortex. After that age, he developed massive proteinuria. The daily dose of CoQ10 was increased to 30 mg/kg. Renal biopsy showed focal segmental glomerulosclerosis. Biochemical analyses of a kidney biopsy sample revealed a severely decreased activity of succinate cytochrome c reductase [complex II + III] suggesting ubiquinone depletion. Incorporation of labelled precursors necessary for CoQ10 synthesis was significantly decreased in cultured skin fibroblasts. His condition deteriorated and he died at the age of five months. A novel homozygous mutation c.326G > A (p.Ser109Asn) was found in COQ2.

CONCLUSIONS

In contrast to previously reported patients with CoQ2 the proband presented with early myoclonic epilepsy, hypertrophic cardiomyopathy and only in a later stage developed a nephrotic syndrome. The phenotype of this patient enlarges the phenotypical spectrum of the multisystem infantile variant.

Pathophysiology of fatty acid oxidation disorders and resultant phenotypic variability

Fatty acids are a major fuel for the body and fatty acid oxidation is particularly important during fasting, sustained aerobic exercise and stress. The myocardium and resting skeletal muscle utilise long-chain fatty acids as a major source of energy. Inherited disorders affecting fatty acid oxidation seriously compromise the function of muscle and other highly energy-dependent tissues such as brain, nerve, heart, kidney and liver. Such defects encompass a wide spectrum of clinical disease, presenting in the neonatal period or infancy with recurrent hypoketotic hypoglycaemic encephalopathy, liver dysfunction, hyperammonaemia and often cardiac dysfunction. In older children, adolescence or adults there is often exercise intolerance with episodic myalgia or rhabdomyolysis in association with prolonged aerobic exercise or other exacerbating factors. Some disorders are particularly associated with toxic metabolites that may contribute to encephalopathy, polyneuropathy, axonopathy and pigmentary retinopathy. The phenotypic diversity encountered in defects of fat oxidation is partly explained by genotype/phenotype correlation and certain identifiable environmental factors but there remain many unresolved questions regarding the complex interaction of genetic, epigenetic and environmental influences that dictate phenotypic expression. It is becoming increasingly clear that the view that most inherited disorders are purely monogenic diseases is a naive concept. In the future our approach to understanding the phenotypic diversity and management of patients will be more realistically achieved from a polygenic perspective.

Increased muscle coenzyme Q10 in riboflavin responsive MADD with ETFDH gene mutations due to secondary mitochondrial proliferation

Multiple acyl-coenzyme A dehydrogenation deficiency (MADD) has a wide range of phenotypic variation ranging from a neonatal lethal form to a mild late-onset form. Our previous data showed that in a group of Chinese patients, a mild type of MADD characterized by myopathy with clinically no other systemic involvement was caused by mutations in electron transfer flavoprotein dehydrogenase (ETFDH) gene, which encodes electron transfer flavoprotein: ubiquinone oxidoreductase (ETF:QO). Coenzyme Q10 (CoQ10), a downstream electron receptor of ETF:QO was first reported deficient in muscle of MADD patients with ETFDH gene mutations. Nevertheless, this result was not confirmed in a recently published study. Therefore to elucidate muscle CoQ10 level in a large group of MADD patients may provide further insight into the pathomechanism and therapeutic strategies. In this study, we found that 34 riboflavin responsive patients with ETFDH gene mutations had an elevated CoQ10 pool in muscle by high performance liquid chromatography (HPLC). However, when CoQ10 levels were normalized to citrate synthase, a marker of mitochondrial mass, there was no significant difference between patients and normal controls. Meanwhile, the increased mitochondrial DNA copy number in muscle also supported that the elevated CoQ10 pool was mainly due to mitochondrial mass proliferation. The expression of CoQ10 biosynthesis genes showed no significant changes whereas genes involved in lipid metabolism, such as PPARα, were marked up regulated. Our results suggested that CoQ10 seems not to be a primary factor in riboflavin responsive MADD and the apparent increase in CoQ10 may be secondary to mitochondrial proliferation.

Secondary coenzyme Q10 deficiency and oxidative stress in cultured fibroblasts from patients with riboflavin responsive multiple Acyl-CoA dehydrogenation deficiency

Coenzyme Q10 (CoQ10) is essential for the energy production of the cells and as an electron transporter in the mitochondrial respiratory chain. CoQ10 links the mitochondrial fatty acid β-oxidation to the respiratory chain by accepting electrons from electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). Recently, it was shown that a group of patients with the riboflavin responsive form of multiple acyl-CoA dehydrogenation deficiency (RR-MADD) carrying inherited amino acid variations in ETF-QO also had secondary CoQ10 deficiency with beneficial effects of CoQ10 treatment, thus adding RR-MADD to an increasing number of diseases involving secondary CoQ10 deficiency. In this study, we show that moderately decreased CoQ10 levels in fibroblasts from six unrelated RR-MADD patients were associated with increased levels of mitochondrial reactive oxygen species (ROS). Treatment with CoQ10, but not with riboflavin, could normalize the CoQ10 level and decrease the level of ROS in the patient cells. Additionally, riboflavin-depleted control fibroblasts showed moderate CoQ10 deficiency, but not increased mitochondrial ROS, indicating that variant ETF-QO proteins and not CoQ10 deficiency are the causes of mitochondrial ROS production in the patient cells. Accordingly, the corresponding variant Rhodobacter sphaeroides ETF-QO proteins, when overexpressed in vitro, bind a CoQ10 pseudosubstrate, Q10Br, less tightly than the wild-type ETF-QO protein, suggesting that molecular oxygen can get access to the electrons in the misfolded ETF-QO protein, thereby generating superoxide and oxidative stress, which can be reversed by CoQ10 treatment.

Cyclic vomiting syndrome masking a fatal metabolic disease

Disorders of fatty acid oxidation are rare but can be fatal. Hypoglycaemia with acidosis is a cardinal feature. Cases may present during early childhood or can be delayed into adolescence or beyond. We present a case of multiple acyl-coenzyme A dehydrogenase deficiency (MADD), an extremely rare disorder of fatty acid oxidation. Our 20-year-old patient presented with cardiovascular collapse, raised anion gap metabolic acidosis and non-ketotic hypoglycaemia. She subsequently developed multi-organ failure and sadly died. She had a previous diagnosis of cyclic vomiting syndrome (CVS) for more than 10 years, warranting frequent hospital admissions. The association between CVS and MADD has been made before though the exact relationship is unclear. All patients with persistent severe CVS should have metabolic investigations to exclude disorders of fatty acid oxidation. In case of non-ketotic hypoglycaemia with acidosis, the patient should be urgently referred to a specialist in metabolic diseases. All practitioners should be aware of these rare disorders as a cause of unexplained acidosis.

[Metabolic and mitochondrial myopathies]

Metabolic myopathies include a broad group of diseases involving inherited enzyme defects in the various metabolic pathways and skeletal musculature. They show an extensive phenotypic variability of symptoms and different ages of manifestation. Symptoms often included intolerance to duress or permanent paresis. Some forms of metabolic myopathy, in particular mitochondriopathy, are associated with multsystemic organ participation. The diagnostics must be adjusted to individual cases and carried out in stages. Primary investigations should include blood parameters (e.g. creatine kinase measurement, muscle load tests and determination of the acylcarnitine spectrum) and a second step includes muscle biopsy for histological and enzyme investigations and special molecular genetic tests although the causative enzyme defect cannot be clarified in every case. On the other hand by means of a thorough investigation it is particularly important in patients with load intolerance to differentiate between other causes, in particular psychosomatic diseases. If this is not done there is a danger of classifying the symptoms of a metabolic myopathy as a somatoform disorder. Therapy is mostly symptom-oriented as Pompe disease is the only one which can be treated with enzyme replacement therapy.

Survival transcriptome in the coenzyme Q10 deficiency syndrome is acquired by epigenetic modifications: a modelling study for human coenzyme Q10 deficiencies

OBJECTIVES

Coenzyme Q10 (CoQ10) deficiency syndrome is a rare condition that causes mitochondrial dysfunction and includes a variety of clinical presentations as encephalomyopathy, ataxia and renal failure. First, we sought to set up what all have in common, and then investigate why CoQ10 supplementation reverses the bioenergetics alterations in cultured cells but not all the cellular phenotypes. DESIGN MODELLING STUDY: This work models the transcriptome of human CoQ10 deficiency syndrome in primary fibroblast from patients and study the genetic response to CoQ10 treatment in these cells.

SETTING

Four hospitals and medical centres from Spain, Italy and the USA, and two research laboratories from Spain and the USA.

PARTICIPANTS

Primary cells were collected from patients in the above centres.

MEASUREMENTS

We characterised by microarray analysis the expression profile of fibroblasts from seven CoQ10-deficient patients (three had primary deficiency and four had a secondary form) and aged-matched controls, before and after CoQ10 supplementation. Results were validated by Q-RT-PCR. The profile of DNA (CpG) methylation was evaluated for a subset of gene with displayed altered expression.

RESULTS

CoQ10-deficient fibroblasts (independently from the aetiology) showed a common transcriptomic profile that promotes cell survival by activating cell cycle and growth, cell stress responses and inhibiting cell death and immune responses. Energy production was supported mainly by glycolysis while CoQ10 supplementation restored oxidative phosphorylation. Expression of genes involved in cell death pathways was partially restored by treatment, while genes involved in differentiation, cell cycle and growth were not affected. Stably demethylated genes were unaffected by treatment whereas we observed restored gene expression in either non-methylated genes or those with an unchanged methylation pattern.

CONCLUSIONS

CoQ10 deficiency induces a specific transcriptomic profile that promotes cell survival, which is only partially rescued by CoQ10 supplementation.

Diagnosis and treatment of mitochondrial myopathies

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.

Primary and secondary coenzyme Q10 deficiency: the role of therapeutic supplementation

Coenzyme Q10 (CoQ10) is the only lipid-soluble antioxidant that animal cells synthesize de novo. It is found in cell membranes and is particularly well known for its role in the electron transport chain in mitochondrial membranes during aerobic cellular respiration. A deficiency in either its bioavailability or its biosynthesis can lead to one of several disease states. Primary deficiency has been well described and results from mutations in genes involved in CoQ10 biosynthesis. Secondary deficiency may be linked to hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), which are used for the treatment of hypercholesterolemia. Dietary contributions of CoQ10 are very small, but supplementation is effective in increasing plasma CoQ10 levels. It has been clearly demonstrated that treatment with CoQ10 is effective in numerous disorders and deficiency states and that supplementation has a favorable outcome. However, CoQ10 is not routinely prescribed in clinical practice. This review explores primary as well as statin-induced secondary deficiency and provides an overview of the benefits of CoQ10 supplementation.