Treatment of complex I deficiency with riboflavin

The Ubiquinone-Ubiquinol Redox Cycle and Its Clinical Consequences: An Overview

Coenzyme Q10 (CoQ10) plays a key role in many aspects of cellular metabolism. For CoQ10 to function normally, continual interconversion between its oxidised (ubiquinone) and reduced (ubiquinol) forms is required. Given the central importance of this ubiquinone-ubiquinol redox cycle, this article reviews what is currently known about this process and the implications for clinical practice. In mitochondria, ubiquinone is reduced to ubiquinol by Complex I or II, Complex III (the Q cycle) re-oxidises ubiquinol to ubiquinone, and extra-mitochondrial oxidoreductase enzymes participate in the ubiquinone-ubiquinol redox cycle. In clinical terms, the outcome of deficiencies in various components associated with the ubiquinone-ubiquinol redox cycle is reviewed, with a particular focus on the potential clinical benefits of CoQ10 and selenium co-supplementation.

Recent advances in small molecules for improving mitochondrial disorders

Mitochondrial disorders are observed in various human diseases, including rare genetic disorders and complex acquired pathologies. Recent advances in molecular biological techniques have dramatically expanded the understanding of multiple pathomechanisms involving mitochondrial disorders. However, the therapeutic methods for mitochondrial disorders are limited. For this reason, there is increasing interest in identifying safe and effective strategies to mitigate mitochondrial impairments. Small-molecule therapies hold promise for improving mitochondrial performance. This review focuses on the latest advances in developing bioactive compounds for treating mitochondrial disease, aiming to provide a broader perspective of fundamental studies that have been carried out to evaluate the effects of small molecules in regulating mitochondrial function. Novel-designed small molecules ameliorating mitochondrial functions are urgent for further research.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

Personalized Medicine in Mitochondrial Health and Disease: Molecular Basis of Therapeutic Approaches Based on Nutritional Supplements and Their Analogs

Mitochondrial diseases (MDs) may result from mutations affecting nuclear or mitochondrial genes, encoding mitochondrial proteins, or non-protein-coding mitochondrial RNA. Despite the great variability of affected genes, in the most severe cases, a neuromuscular and neurodegenerative phenotype is observed, and no specific therapy exists for a complete recovery from the disease. The most used treatments are symptomatic and based on the administration of antioxidant cocktails combined with antiepileptic/antipsychotic drugs and supportive therapy for multiorgan involvement. Nevertheless, the real utility of antioxidant cocktail treatments for patients affected by MDs still needs to be scientifically demonstrated. Unfortunately, clinical trials for antioxidant therapies using α-tocopherol, ascorbate, glutathione, riboflavin, niacin, acetyl-carnitine and coenzyme Q have met a limited success. Indeed, it would be expected that the employed antioxidants can only be effective if they are able to target the specific mechanism, i.e., involving the central and peripheral nervous system, responsible for the clinical manifestations of the disease. Noteworthily, very often the phenotypes characterizing MD patients are associated with mutations in proteins whose function does not depend on specific cofactors. Conversely, the administration of the antioxidant cocktails might determine the suppression of endogenous oxidants resulting in deleterious effects on cell viability and/or toxicity for patients. In order to avoid toxicity effects and before administering the antioxidant therapy, it might be useful to ascertain the blood serum levels of antioxidants and cofactors to be administered in MD patients. It would be also worthwhile to check the localization of mutations affecting proteins whose function should depend (less or more directly) on the cofactors to be administered, for estimating the real need and predicting the success of the proposed cofactor/antioxidant-based therapy.

Current and Emerging Clinical Treatment in Mitochondrial Disease

Primary mitochondrial disease (PMD) is a group of complex genetic disorders that arise due to pathogenic variants in nuclear or mitochondrial genomes. Although PMD is one of the most prevalent inborn errors of metabolism, it often exhibits marked phenotypic variation and can therefore be difficult to recognise. Current treatment for PMD revolves around supportive and preventive approaches, with few disease-specific therapies available. However, over the last decade there has been considerable progress in our understanding of both the genetics and pathophysiology of PMD. This has resulted in the development of a plethora of new pharmacological and non-pharmacological therapies at varying stages of development. Many of these therapies are currently undergoing clinical trials. This review summarises the latest emerging therapies that may become mainstream treatment in the coming years. It is distinct from other recent reviews in the field by comprehensively addressing both pharmacological non-pharmacological therapy from both a bench and a bedside perspective. We highlight the current and developing therapeutic landscape in novel pharmacological treatment, dietary supplementation, exercise training, device use, mitochondrial donation, tissue replacement gene therapy, hypoxic therapy and mitochondrial base editing.

Mitochondrial DNA mutations in renal disease: an overview

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

Therapeutical Management and Drug Safety in Mitochondrial Diseases-Update 2020

Mitochondrial diseases (MDs) are a group of genetic disorders that may manifest with vast clinical heterogeneity in childhood or adulthood. These diseases are characterized by dysfunctional mitochondria and oxidative phosphorylation deficiency. Patients are usually treated with supportive and symptomatic therapies due to the absence of a specific disease-modifying therapy. Management of patients with MDs is based on different therapeutical strategies, particularly the early treatment of organ-specific complications and the avoidance of catabolic stressors or toxic medication. In this review, we discuss the therapeutic management of MDs, supported by a revision of the literature, and provide an overview of the drugs that should be either avoided or carefully used both for the specific treatment of MDs and for the management of comorbidities these subjects may manifest. We finally discuss the latest therapies approved for the management of MDs and some ongoing clinical trials.

Riboflavin Deficiency-Implications for General Human Health and Inborn Errors of Metabolism

As an essential vitamin, the role of riboflavin in human diet and health is increasingly being highlighted. Insufficient dietary intake of riboflavin is often reported in nutritional surveys and population studies, even in non-developing countries with abundant sources of riboflavin-rich dietary products. A latent subclinical riboflavin deficiency can result in a significant clinical phenotype when combined with inborn genetic disturbances or environmental and physiological factors like infections, exercise, diet, aging and pregnancy. Riboflavin, and more importantly its derivatives, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), play a crucial role in essential cellular processes including mitochondrial energy metabolism, stress responses, vitamin and cofactor biogenesis, where they function as cofactors to ensure the catalytic activity and folding/stability of flavoenzymes. Numerous inborn errors of flavin metabolism and flavoenzyme function have been described, and supplementation with riboflavin has in many cases been shown to be lifesaving or to mitigate symptoms. This review discusses the environmental, physiological and genetic factors that affect cellular riboflavin status. We describe the crucial role of riboflavin for general human health, and the clear benefits of riboflavin treatment in patients with inborn errors of metabolism.

Mitochondria in migraine pathophysiology - does epigenetics play a role?

The approximately three times higher rate of migraine prevalence in women than men may result from the mitochondrial transmission of this disease. Studies with imaging techniques suggest disturbances in mitochondrial metabolism in specific regions of the brain in migraine patients. Migraine shares some clinical features with several mitochondrial diseases and many other disorders include migraine headaches. Epigenetic regulation of mitochondrial DNA (mtDNA) is a matter of debate and there are some conflicting results, especially on mtDNA methylation. Micro RNAs (miRNAs) and long-noncoding RNA (lncRNAs) have been detected in mitochondria. The regulation of the miRNA-lncRNA axis can be important for mitochondrial physiology and its impairment can result in a disease phenotype. Further studies on the role of mitochondrial epigenetic modifications in migraine are needed, but they require new methods and approaches.

Flavin Imbalance as an Important Player in Diabetic Retinopathy

The retina and RPE together constitute the most metabolically active ecosystem in the body, harboring high levels of flavins. Although diabetic patients have been reported to suffer from riboflavin deficiency and use of flavins as nutritional interventions to combat diabetic insult on other tissues have been investigated, such attempts have never been tested for the retina to avoid diabetic retinopathy. Furthermore, the role of flavins in pathophysiology of the retina and RPE has mostly been overlooked. Herein, we review the impact of flavins on various clinical manifestations of diabetic retinopathy and discuss possible ways to address them.

Current and Emerging Therapies for Mitochondriopathies

Mitochondrial diseases are a clinically and genetically heterogeneous group of disorders. The underlying dysfunction of the mitochondrial electron transport chain and oxidative phosphorylation is caused by variants of genes encoding mitochondrial proteins. Despite substantial advances in the understanding of the mechanism of these diseases, there are still no satisfactory therapies available. Therapeutic strategies include the use of antioxidants, inducers of mitochondrial biogenesis, enhancers of electron transfer chain function, energy buffers, amino acids restoring NO production, nucleotide bypass therapy, liver transplantation, and gene therapy. Although there are some promising projects underway, to date satisfactory therapies are missing.

Feeding mitochondria: Potential role of nutritional components to improve critical illness convalescence

Persistent physical impairment is frequently encountered after critical illness. Recent data point towards mitochondrial dysfunction as an important determinant of this phenomenon. This narrative review provides a comprehensive overview of the present knowledge of mitochondrial function during and after critical illness and the role and potential therapeutic applications of specific micronutrients to restore mitochondrial function. Increased lactate levels and decreased mitochondrial ATP-production are common findings during critical illness and considered to be associated with decreased activity of muscle mitochondrial complexes in the electron transfer system. Adequate nutrient levels are essential for mitochondrial function as several specific micronutrients play crucial roles in energy metabolism and ATP-production. We have addressed the role of B vitamins, ascorbic acid, α-tocopherol, selenium, zinc, coenzyme Q10, caffeine, melatonin, carnitine, nitrate, lipoic acid and taurine in mitochondrial function. B vitamins and lipoic acid are essential in the tricarboxylic acid cycle, while selenium, α-tocopherol, Coenzyme Q10, caffeine, and melatonin are suggested to boost the electron transfer system function. Carnitine is essential for fatty acid beta-oxidation. Selenium is involved in mitochondrial biogenesis. Notwithstanding the documented importance of several nutritional components for optimal mitochondrial function, at present, there are no studies providing directions for optimal requirements during or after critical illness although deficiencies of these specific micronutrients involved in mitochondrial metabolism are common. Considering the interplay between these specific micronutrients, future research should pay more attention to their combined supply to provide guidance for use in clinical practise. REVISION NUMBER: YCLNU-D-17-01092R2.

Mitochondrial Agents for Bipolar Disorder

Background

Bipolar disorder is a chronic and often debilitating illness. Current treatment options (both pharmaco- and psychotherapy) have shown efficacy, but for many leave a shortfall in recovery. Advances in the understanding of the pathophysiology of bipolar disorder suggest that interventions that target mitochondrial dysfunction may provide a therapeutic benefit.

Methods

This review explores the current and growing theoretical rationale as well as existing preclinical and clinical data for those therapies aiming to target the mitochondrion in bipolar disorder. A Clinicaltrials.gov and ANZCTR search was conducted for complete and ongoing trials on mitochondrial agents used in psychiatric disorders. A PubMed search was also conducted for literature published between January 1981 and July 2017. Systematic reviews, randomized controlled trials, observational studies, case series, and animal studies with an emphasis on agents affecting mitochondrial function and its role in bipolar disorder were included. The search was augmented by manually searching the references of key papers and related literature. The results were presented as a narrative review.

Results

Mitochondrial agents offer new horizons in mood disorder treatment. While some negative effects have been reported, most compounds are overall well tolerated and have generally benign side-effect profiles.

Conclusions

The study of neuroinflammation, neurodegeneration, and mitochondrial function has contributed the understanding of bipolar disorder's pathophysiology. Agents targeting these pathways could be a potential therapeutic strategy. Future directions include identification of novel candidate mitochondrial modulators as well as rigorous and well-powered clinical trials.

Nutritional Interventions for Mitochondrial OXPHOS Deficiencies: Mechanisms and Model Systems

Multisystem metabolic disorders caused by defects in oxidative phosphorylation (OXPHOS) are severe, often lethal, conditions. Inborn errors of OXPHOS function are termed primary mitochondrial disorders (PMDs), and the use of nutritional interventions is routine in their supportive management. However, detailed mechanistic understanding and evidence for efficacy and safety of these interventions are limited. Preclinical cellular and animal model systems are important tools to investigate PMD metabolic mechanisms and therapeutic strategies. This review assesses the mechanistic rationale and experimental evidence for nutritional interventions commonly used in PMDs, including micronutrients, metabolic agents, signaling modifiers, and dietary regulation, while highlighting important knowledge gaps and impediments for randomized controlled trials. Cellular and animal model systems that recapitulate mutations and clinical manifestations of specific PMDs are evaluated for their potential in determining pathological mechanisms, elucidating therapeutic health outcomes, and investigating the value of nutritional interventions for mitochondrial disease conditions.

Therapies for mitochondrial diseases and current clinical trials

Mitochondrial diseases are a clinically and genetically heterogeneous group of disorders that result from dysfunction of the mitochondrial oxidative phosphorylation due to molecular defects in genes encoding mitochondrial proteins. Despite the advances in molecular and biochemical methodologies leading to better understanding of the etiology and mechanism of these diseases, there are still no satisfactory therapies available for mitochondrial disorders. Treatment for mitochondrial diseases remains largely symptomatic and does not significantly alter the course of the disease. Based on limited number of clinical trials, several agents aiming at enhancing mitochondrial function or treating the consequences of mitochondrial dysfunction have been used. Several agents are currently being evaluated for mitochondrial diseases. Therapeutic strategies for mitochondrial diseases include the use of agents enhancing electron transfer chain function (coenzyme Q₁₀, idebenone, riboflavin, dichloroacetate, and thiamine), agents acting as energy buffer (creatine), antioxidants (vitamin C, vitamin E, lipoic acid, cysteine donors, and EPI-743), amino acids restoring nitric oxide production (arginine and citrulline), cardiolipin protector (elamipretide), agents enhancing mitochondrial biogenesis (bezafibrate, epicatechin, and RTA 408), nucleotide bypass therapy, liver transplantation, and gene therapy. Although, there is a lack of curative therapies for mitochondrial disorders at the current time, the increased number of clinical research evaluating agents that target different aspects of mitochondrial dysfunction is promising and is expected to generate more therapeutic options for these diseases in the future.

Riboflavin Has Neuroprotective Potential: Focus on Parkinson's Disease and Migraine

With the huge negative impact of neurological disorders on patient's life and society resources, the discovery of neuroprotective agents is critical and cost-effective. Neuroprotective agents can prevent and/or modify the course of neurological disorders. Despite being underestimated, riboflavin offers neuroprotective mechanisms. Significant pathogenesis-related mechanisms are shared by, but not restricted to, Parkinson's disease (PD) and migraine headache. Those pathogenesis-related mechanisms can be tackled through riboflavin proposed neuroprotective mechanisms. In fact, it has been found that riboflavin ameliorates oxidative stress, mitochondrial dysfunction, neuroinflammation, and glutamate excitotoxicity; all of which take part in the pathogenesis of PD, migraine headache, and other neurological disorders. In addition, riboflavin-dependent enzymes have essential roles in pyridoxine activation, tryptophan-kynurenine pathway, and homocysteine metabolism. Indeed, pyridoxal phosphate, the active form of pyridoxine, has been found to have independent neuroprotective potential. Also, the produced kynurenines influence glutamate receptors and its consequent excitotoxicity. In addition, methylenetetrahydrofolate reductase requires riboflavin to ensure normal folate cycle influencing the methylation cycle and consequently homocysteine levels which have its own negative neurovascular consequences if accumulated. In conclusion, riboflavin is a potential neuroprotective agent affecting a wide range of neurological disorders exemplified by PD, a disorder of neurodegeneration, and migraine headache, a disorder of pain. In this article, we will emphasize the role of riboflavin in neuroprotection elaborating on its proposed neuroprotective mechanisms in opposite to the pathogenesis-related mechanisms involved in two common neurological disorders, PD and migraine headache, as well as, we encourage the clinical evaluation of riboflavin in PD and migraine headache patients in the future.

Therapeutic strategies for mitochondrial disorders

OBJECTIVES

There is currently no curative therapy for mitochondrial disorders, although symptomatic measures can be highly effective and greatly improve the quality of life and outcome of these patients. This review highlights potential strategies for the therapeutic management of mitochondrial disorders.

METHODS

Data for this review were identified by searches of MEDLINE, Current Contents, using various relevant search terms.

RESULTS

Strategies to establish a therapeutic regimen aim to enhance respiratory chain function, eliminate noxious compounds, shift the heteroplasmy rate, alter mitochondrial dynamics, transfer cytoplasm, and promote gene therapy. Symptomatic measures rely on drugs (e.g., antiepileptics), avoidance of mitochondrion-toxic agents, substitution of blood cells, hemodialysis, invasive measures (such as a pacemaker), surgery (e.g., ptosis correction), physiotherapy, speech therapy, occupational therapy, dietary measures (e.g., ketogenic diet, anaplerotic diet), and the avoidance of mitochondrion-toxic agents (e.g., ozone). With the increasing awareness of mitochondrial disorders, the number of treatment studies is growing and its quality is improving. If high quality studies (high Jadad score) yield statistical significance for end points, a treatment is more reliable than with lower quality studies.

CONCLUSIONS

Despite the lack of a proven treatment for mitochondrial disorders, a nihilistic attitude toward treatment is not justified. A number of studies are seeking targeted therapies, and highly effective symptomatic measures are available.

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.

Treatment of mitochondrial disorders: antioxidants and beyond

Although mitochondrial disorders are among the most common inherited conditions that cause neurologic impairment, there are currently no U.S. Food and Drug Administration (FDA)-approved medications designed to treat primary mitochondrial disease. This is in part related to the lack of biomarkers to monitor disease status or response to treatment and the paucity of randomized, controlled clinical trials focused on mitochondrial disease therapies. Despite this discouraging historical precedent, a number of new approaches to mitochondrial disease therapy are on the horizon. By studying metabolites central to redox chemistry, investigators are gaining new insights into potential noninvasive biomarkers. Controlled clinical trials designed to study the effects of novel redox-modulating therapies, such as EPI-743, in patients with inherited mitochondrial disease are also underway. Furthermore, several new compounds with potential effects on inner mitochondrial membrane function and mitochondrial biogenesis are in development. Such advances are providing the foundation for a new era in mitochondrial disease therapeutics.

New treatments for mitochondrial disease-no time to drop our standards

Mitochondrial dysfunction is a common cause of inherited multisystem disease that often involves the nervous system. Despite major advances in our understanding of the pathophysiology of mitochondrial diseases, clinical management of these conditions remains largely supportive. Using a systematic approach, we identified 1,039 publications on treatments for mitochondrial diseases, only 35 of which included observations on more than five patients. Reports of a positive outcome on the basis of a biomarker of unproven clinical significance were more common in nonrandomized and nonblinded studies, suggesting a publication bias toward positive but poorly executed studies. Although trial design is improving, there is a critical need to develop new biomarkers of mitochondrial disease. In this Perspectives article, we make recommendations for the design of future treatment trials in mitochondrial diseases. Patients and physicians should no longer rely on potentially biased data, with the associated costs and risks.

Treatment for mitochondrial disorders

BACKGROUND

Mitochondrial respiratory chain disorders are the most prevalent group of inherited neurometabolic diseases. They present with central and peripheral neurological features usually in association with other organ involvement including the eye, the heart, the liver, and kidneys, diabetes mellitus and sensorineural deafness. Current treatment is largely supportive and the disorders progress relentlessly causing significant morbidity and premature death. Vitamin supplements, pharmacological agents and exercise therapy have been used in isolated cases and small clinical trials, but the efficacy of these interventions is unclear. The first review was carried out in 2003, and identified six clinical trials. This major update was carried out to identify new studies and grade the original studies for potential bias in accordance with revised Cochrane Collaboration guidelines.

OBJECTIVES

To determine whether there is objective evidence to support the use of current treatments for mitochondrial disease.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (4 July 2011), CENTRAL (2011, Issue 2, MEDLINE (1966 to July 2011), and EMBASE (January 1980 to July 2011), and contacted experts in the field.

SELECTION CRITERIA

We included randomised controlled trials (including cross-over studies). Two of the authors independently selected abstracts for further detailed review. Further review was performed independently by all five authors to decide which trials fit the inclusion criteria and graded risk of bias. Participants included males and females of any age with a confirmed diagnosis of mitochondrial disease based upon muscle histochemistry, respiratory chain complex analysis of tissues or cell lines or DNA studies. Interventions included any pharmacological agent, dietary modification, nutritional supplement, exercise therapy or other treatment. The review authors excluded studies at high risk of bias in any category. The primary outcome measures included an change in muscle strength and/or endurance, or neurological clinical features. Secondary outcome measures included quality of life assessments, biochemical markers of disease and negative outcomes.

DATA COLLECTION AND ANALYSIS

Two of the authors (GP and PFC) independently identified studies for further evaluation from all abstracts within the search period. For those studies identified for further review, all five authors then independently assessed which studies met the entry criteria. For the included studies, we extracted details of the number of randomised participants, treatment, study design, study category, allocation concealment and other risk of bias criteria, and participant characteristics. Analysis was based on intention-to-treat data. We planned to use meta-analysis, but this did not prove necessary.

MAIN RESULTS

The authors reviewed 1335 abstracts, and from these identified 21 potentially eligible abstracts. Upon detailed review, 12 studies fulfilled the entry criteria. Of these, eight were new studies that had been published since the previous version of this review. Two studies which were included in the previous version of this review were excluded because of potential for bias. The comparability of the included studies is extremely low because of differences in the specific diseases studied, differences in the therapeutic agents used, dosage, study design, and outcomes. The methodological quality of included studies was generally high, although risk of bias was unclear in random sequence generation and allocation concealment for most studies. Otherwise, the risk of bias was low for most studies in the other categories. Serious adverse events were uncommon, except for peripheral nerve toxicity in a long-term trial of dichloroacetate (DCA) in adults.One trial studied high-dose coenzyme Q10 without clinically meaningful improvement (although there were multiple biochemical, physiologic, and neuroimaging outcomes, in 30 participants). Three trials used creatine monohydrate alone, with one reporting evidence of improved measures of muscle strength and post-exercise lactate, but the other two reported no benefit (total of 38 participants). One trial studied the effects of a combination of coenzyme Q10, creatine monohydrate, and lipoic acid and reported a statistically significant improvement in biochemical markers and peak ankle dorsiflexion strength, but overall no clinical improvement in 16 participants. Five trials studied the effects of DCA: three trials in children showed a statistically significant improvement in secondary outcome measures of mitochondrial metabolism (venous lactate in three trials, and magnetic resonance spectroscopy (MRS) in one trial; total of 63 participants). One trial of short-term DCA in adults demonstrated no clinically relevant improvement (improved venous lactate but no change in physiologic, imaging, or questionnaire findings, in eight participants). One longer-term DCA trial in adults was terminated prematurely due to peripheral nerve toxicity without clinical benefit (assessments included the GATE score, venous lactate and MRS, in 30 participants). One trial using dimethylglycine showed no significant effect (measurements of venous lactate and oxygen consumption (VO(2)) in five participants). One trial using a whey-based supplement showed statistically significant improvement in markers of free radical reducing capacity but no clinical benefit (assessments included the Short Form 36 Health Survey (SF-36) questionnaire and UK Medical Research Council (MRC) muscle strength, in 13 participants).

AUTHORS' CONCLUSIONS

Despite identifying eight new trials there is currently no clear evidence supporting the use of any intervention in mitochondrial disorders. Further research is needed to establish the role of a wide range of therapeutic approaches. We suggest further research should identify novel agents to be tested in homogeneous study populations with clinically relevant primary endpoints.

Convergent mechanisms in etiologically-diverse dystonias

INTRODUCTION

Dystonia is a neurological disorder associated with twisting motions and abnormal postures, which compromise normal movements and can be both painful and debilitating. It can affect a single body part (focal), several contiguous regions (segmental), or the entire body (generalized), and can arise as a result of numerous causes, both genetic and acquired. Despite the diversity of causes and manifestations, shared clinical features suggest that common mechanisms of pathogenesis may underlie many dystonias.

AREAS COVERED

Shared themes in etiologically-diverse dystonias exist at several biological levels. At the cellular level, abnormalities in the dopaminergic system, mitochondrial function and calcium regulation are often present. At the anatomical level, the basal ganglia and the cerebellum are frequently implicated. Global CNS dysfunction, specifically aberrant neuronal plasticity, inhibition and sensorimotor integration, are also observed in a number of dystonias. Using clinical data and data from animal models, this article seeks to highlight shared pathways that may be critical in understanding mechanisms and identifying novel therapeutic strategies in dystonia.

EXPERT OPINION

Identifying shared features of pathogenesis can provide insight into the biological processes that underlie etiologically diverse dystonias, and can suggest novel targets for therapeutic intervention that may be effective in a broad group of affected individuals.

A modern approach to the treatment of mitochondrial disease

The treatment of mitochondrial disease varies considerably. Most experts use a combination of vitamins, optimize patients' nutrition and general health, and prevent worsening of symptoms during times of illness and physiologic stress. We agree with this approach, and we agree that therapies using vitamins and cofactors have value, though there is debate about the choice of these agents and the doses prescribed. Despite the paucity of high-quality scientific evidence, these therapies are relatively harmless, may alleviate select clinical symptoms, and theoretically may offer a means of staving off disease progression. Like many other mitochondrial medicine physicians, we have observed significant (and at times life-altering) clinical responses to such pharmacologic interventions. However, it is not yet proven that these therapies truly alter the course of the disease, and some experts may choose not to use these medications at all. At present, the evidence of their effectiveness does not rise to the level required for universal use. Based on our clinical experience and judgment, however, we agree that a therapeutic trial of coenzyme Q10, along with other antioxidants, should be attempted. Although individual specialists differ as to the exact drug cocktail, a common approach involves combinations of antioxidants that may have a synergistic effect. Because almost all relevant therapies are classified as medical foods or over-the-counter supplements, most physicians also attempt to balance the apparent clinical benefit of mitochondrial cocktails with the cost burden that these supplements pose for the family.

A neurological perspective on mitochondrial disease

Disruption of the most fundamental cellular energy process, the mitochondrial respiratory chain, results in a diverse and variable group of multisystem disorders known collectively as mitochondrial disease. The frequent involvement of the brain, nerves, and muscles, often in the same patient, places neurologists at the forefront of the interesting and challenging process of diagnosing and caring for these patients. Mitochondrial diseases are among the most frequently inherited neurological disorders, and can be caused by mutations in mitochondrial or nuclear DNA. Substantial progress has been made over the past decade in understanding the genetic basis of these disorders, with important implications for the general neurologist in terms of the diagnosis, investigation, and multidisciplinary management of these patients.

Flavin adenine dinucleotide rescues the phenotype of frataxin deficiency

BACKGROUND

Friedreich ataxia is a neurodegenerative disease caused by the lack of frataxin, a mitochondrial protein. We previously demonstrated that frataxin interacts with complex II subunits of the electronic transport chain (ETC) and putative electronic transfer flavoproteins, suggesting that frataxin could participate in the oxidative phosphorylation.

METHODS AND FINDINGS

Here we have investigated the effect of riboflavin and its cofactors flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) in Saccharomyces cerevisiae and Caenorhabditis elegans models of frataxin deficiency. We used a S. cerevisiae strain deleted for the yfh1 gene obtained by homologous recombination and we assessed growth in fermentable and non-fermentable cultures supplemented with either riboflavin or its derivates. Experiments with C. elegans were performed in transient knock-down worms (frh-1[RNAi]) generated by microinjection of dsRNA frh-1 into the gonads of young worms. We observed that FAD rescues the phenotype of both defective organisms. We show that cell growth and enzymatic activities of the ETC complexes and ATP production of yfh1Delta cells were improved by FAD supplementation. Moreover, FAD also improved lifespan and other physiological parameters in the C. elegans knock-down model for frataxin.

CONCLUSIONS/SIGNIFICANCE

We propose that rescue of frataxin deficiency by FAD supplementation could be explained by an improvement in mitochondrial respiration. We suggest that riboflavin may be useful in the treatment of Friedreich ataxia.

Effects of riboflavin in children with complex II deficiency

Isolated complex II deficiency is a rare cause of mitochondrial disease in infancy and childhood. No satisfactory treatment is currently available, and affected patients undergo a relentlessly progressive motor and mental deterioration. We report on three complex II-deficient children treated with riboflavin per os, who were followed-up for a mean period of 4.5 years. In two patients with early-onset leukoencephalopathy, neurological condition remained stable or even moderately improved. In the third child, presenting in the first year of life with poor somatic growth and severe hyperlactacidemia, plasma lactate decreased to near-normal levels, and he did not develop signs of neurological involvement. Riboflavin supplementation to the growth medium of cultured fibroblasts resulted in a 2-fold increase of complex II activity in patients, but not in controls.

Diminished FAD binding in the Y459H and V492E Antley-Bixler syndrome mutants of human cytochrome P450 reductase

Numerous mutations/polymorphisms of the POR gene, encoding NADPH:cytochrome P450 oxidoreductase (CYPOR), have been described in patients with Antley-Bixler syndrome (ABS), presenting with craniofacial dysmorphogenesis, and/or disordered steroidogenesis, exhibiting ambiguous genitalia. CYPOR is the obligate electron donor to 51 microsomal cytochromes P450 that catalyze critical steroidogenic and xenobiotic reactions, and to two heme oxygenase isoforms, among other redox partners. To address the molecular basis of CYPOR dysfunction in ABS patients, the soluble catalytic domain of human CYPOR was bacterially expressed. WT enzyme was green, due to air-stable FMN semiquinone (blue) and oxidized FAD (yellow). The ABS mutant V492E was blue-gray. Flavin analysis indicated that WT had a protein:FAD:FMN ratio of approximately 1:1:1, whereas approximately 1:0.1:0.9 was observed for V492E, which retained 9% of the WT k(cat)/K(m) in NADPH:cytochrome c reductase assays. V492E was reconstituted upon addition of FAD, post-purification, as shown by flavin analysis, activity assay, and near UV-visible CD. Both Y459H and V492E were expressed as membrane anchor-containing proteins, which also exhibited FAD deficiency. CYP4A4-catalyzed omega-hydroxylation of prostaglandin E1 was supported by WT CYPOR but not by either of the ABS mutants. Hydroxylation activity was rescued for both Y459H and V492E upon addition of FAD to the reaction. Based on these findings, decreased FAD-binding affinity is proposed as the basis of the observed loss of CYPOR function in the Y459H and V492E POR mutations in ABS.

Treatment for mitochondrial disorders

BACKGROUND

Mitochondrial respiratory chain disorders are the most prevalent group of inherited neurometabolic diseases. They present with central and peripheral neurological features usually in association with other organ involvement including the eye, the heart, the liver, and kidneys, diabetes mellitus and sensorineural deafness. Current treatment is largely supportive and the disorders progress relentlessly causing significant morbidity and premature death. Vitamin supplements, pharmacological agents and exercise therapy have been used in isolated cases and small clinical trials, but the efficacy of these interventions is unclear.

OBJECTIVES

To determine whether there is objective evidence to support the use of current treatments for mitochondrial disease.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (searched September 2003), the Cochrane Central Register of Controlled Trials, MEDLINE (January 1966 to October 3 2003), EMBASE (January 1980 to October 3 2003) and the European Neuromuscular Centre (ENMC) clinical trials register, and contacted experts in the field.

SELECTION CRITERIA

We included randomised controlled trials (including crossover studies) and quasi-randomised trials comparing pharmacological treatments, and non-pharmacological treatments (vitamins and food supplements), and physical training in individuals with mitochondrial disorders. The primary outcome measures included an improvement in muscle strength and/or endurance, or neurological clinical features. Secondary outcome measures included quality of life assessments, biochemical markers of disease and negative outcomes.

DATA COLLECTION AND ANALYSIS

Details of the number of randomised patients, treatment, study design, study category, allocation concealment and patient characteristics were extracted. Analysis was based on intention to treat data. We planned to use meta-analysis, but this did not prove necessary.

MAIN RESULTS

Six hundred and seventy-eight abstracts were reviewed, and six fulfilled the entry criteria. Two trials studied the effects of co-enzyme Q10 (ubiquinone), one reporting a subjective improvement and a significant increase in a global scale of muscle strength, but the other trial did not show any benefit. Two trials used creatine, with one reporting improved measures of muscle strength and post-exercise lactate, but the other reported no benefit. One trial of dichloroacetate showed an improvement in secondary outcome measures of mitochondrial metabolism, and one trial using dimethylglycine showed no significant effect.

AUTHORS' CONCLUSIONS

There is currently no clear evidence supporting the use of any intervention in mitochondrial disorders. Further research is needed to establish the role of a wide range of therapeutic approaches.

Targeting cellular energy production in neurological disorders

The concepts of energy dysregulation and oxidative stress and their complicated interdependence have rapidly evolved to assume primary importance in understanding the pathophysiology of numerous neurological disorders. Therefore, neuroprotective strategies addressing specific bioenergetic defects hold particular promise in the treatment of these conditions (i.e., amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease, Friedreich's ataxia, mitochondrial cytopathies and other neuromuscular diseases), all of which, to some extent, share 'the final common pathway' leading to cell death through either necrosis or apoptosis. Compounds such as creatine monohydrate and coenzyme Q(10) offer substantial neuroprotection against ischaemia, trauma, oxidative damage and neurotoxins. Miscellaneous agents, including alpha-lipoic acid, beta-OH-beta-methylbutyrate, riboflavin and nicotinamide, have also been shown to improve various metabolic parameters in brain and/or muscle. This review will highlight the biological function of each of the above mentioned compounds followed by a discussion of their utility in animal models and human neurological disease. The balance of this work will be comprised of discussions on the therapeutic applications of creatine and coenzyme Q(10).

Effect of high-dose vitamins, coenzyme Q and high-fat diet in paediatric patients with mitochondrial diseases

We reviewed the medical records of all patients with confirmed mitochondrial diseases treated with any or all of thiamin, riboflavin, coenzyme Q, vitamin C (approximately 10 mg/kg per day) and a high-fat diet (50-60% of caloric intake) between 1997 and 2003. There were 15 patients (9 male): 10 had enzymatic deficiency and 10 had a molecular diagnosis. Age at diagnosis was 11 months to 17 years 10 months. Treatment was commenced at time of clinical diagnosis in 12 patients. Follow-up period was 3 days to 7 years (median 22 months). Improvement was reported in 9 patients, of whom 4 attained further developmental skills, but this was only temporary in 6 patients. Five patients died during the follow-up period (3 days to 7 years). Patients with the 3243A > G mutation showed no significant change in the course of their disease, except for fewer migraine attacks. Of the six patients who had seizures, one has had a significant reduction in the severity of the seizures and one has had no further seizures. Plasma lactate levels were noncontributory. We conclude that high-dose vitamin and cofactor treatment and, where applicable, high-fat diet, are well tolerated and possibly effective in the short term, but ineffective in the longer term.

Nutritional cofactor treatment in mitochondrial disorders

Mitochondrial disorders are degenerative diseases characterized by a decrease in the ability of mitochondria to supply cellular energy requirements. Substantial progress has been made in defining the specific biochemical defects and underlying molecular mechanisms, but limited information is available about the development and evaluation of effective treatment approaches. The goal of nutritional cofactor therapy is to increase mitochondrial adenosine 5'-triphosphate production and slow or arrest the progression of clinical symptoms. Accumulation of toxic metabolites and reduction of electron transfer activity have prompted the use of antioxidants, electron transfer mediators (which bypass the defective site), and enzyme cofactors. Metabolic therapies that have been reported to produce a positive effect include Coenzyme Q(10) (ubiquinone); other antioxidants such as ascorbic acid, vitamin E, and lipoic acid; riboflavin; thiamin; niacin; vitamin K (phylloquinone and menadione); creatine; and carnitine. A literature review of the use of these supplements in mitochondrial disorders is presented.

Nutritional and exercise-based therapies in the treatment of mitochondrial disease

PURPOSE OF REVIEW

This review will critically summarize the nutritional and exercise-based interventions that have been used to treat mitochondrial disease, with a focus on the biochemical or molecular rationale for their use as well as recent advances in the field.

RECENT FINDINGS

Many nutritional-based treatment strategies have been used in an attempt to target energy impairment and its sequelae. Recently, coenzyme Q10, idebenone and triacylglycerol have been shown to bypass defective respiratory enzymes or scavenge free radicals, whereas creatine monohydrate has provided an alternative energy source. Thiamine has been used to decrease lactate levels and increase flux through aerobic metabolism, and riboflavin has been used as a precursor to complexes I and II. Several therapies employing various antioxidants in combination with other supplements have been effective at targeting several of the final common pathways of mitochondrial disease. Miscellaneous supplements, such as L-arginine and uridine, have also had recent success. However, although positive responses have been reported with these agents, many reports have shown no benefit, and there is widespread disparity in the literature. An alternative approach to treatment is exercise training. Both resistance and endurance exercise training have had positive outcomes in patients with mitochondrial disease, although several questions remain to be answered.

SUMMARY

There is no currently recognized treatment for mitochondrial disease. Future clinical trials are needed, as well as research into the potential for in-vitro screening of various compounds within affected cells from patients. Until this time, an accurate diagnosis will facilitate treatment on a case-by-case basis.

Current concepts of mitochondrial disorders in childhood

Respiratory chain deficiencies have long been regarded as rare neuromuscular diseases mostly originating from mutations in the mitochondrial genome. Research in the last years has created quite a different picture. The clinical spectrum has expanded to multiorgan disease manifestation, with an estimated minimum incidence in children of 1:11,000. Mutations in the nuclear genome have been discovered in recent years, thereby adding mendelian genetics to the broadened spectrum of mitochondrial disease. This review summarizes recent advances in mitochondrial disorders with a special focus on childhood presentation and therapeutic approaches that may prove useful in the future.

High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased K(m)): relevance to genetic disease and polymorphisms

As many as one-third of mutations in a gene result in the corresponding enzyme having an increased Michaelis constant, or K(m), (decreased binding affinity) for a coenzyme, resulting in a lower rate of reaction. About 50 human genetic dis-eases due to defective enzymes can be remedied or ameliorated by the administration of high doses of the vitamin component of the corresponding coenzyme, which at least partially restores enzymatic activity. Several single-nucleotide polymorphisms, in which the variant amino acid reduces coenzyme binding and thus enzymatic activity, are likely to be remediable by raising cellular concentrations of the cofactor through high-dose vitamin therapy. Some examples include the alanine-to-valine substitution at codon 222 (Ala222-->Val) [DNA: C-to-T substitution at nucleo-tide 677 (677C-->T)] in methylenetetrahydrofolate reductase (NADPH) and the cofactor FAD (in relation to cardiovascular disease, migraines, and rages), the Pro187-->Ser (DNA: 609C-->T) mutation in NAD(P):quinone oxidoreductase 1 [NAD(P)H dehy-drogenase (quinone)] and FAD (in relation to cancer), the Ala44-->Gly (DNA: 131C-->G) mutation in glucose-6-phosphate 1-dehydrogenase and NADP (in relation to favism and hemolytic anemia), and the Glu487-->Lys mutation (present in one-half of Asians) in aldehyde dehydrogenase (NAD + ) and NAD (in relation to alcohol intolerance, Alzheimer disease, and cancer).

Epidemiology and treatment of mitochondrial disorders

The last ten years have seen a huge increase in the number of different genetic defects found in patients with mitochondrial disorders, but the true impact of mitochondrial disease is only just becoming apparent. Mitochondrial diseases are far more common than was anticipated. Although there have also been major advances in our understanding of mitochondrial pathology, the clinical management of patients with mitochondrial disease is largely supportive. In this article, we focus on primary disorders of the mitochondrial respiratory chain and mtDNA defects. We review the available epidemiological data, outline current strategies for the management of mitochondrial disease, and highlight new therapeutic approaches that may prove useful in the future.

Mitochondrial Disease

Mitochondrial diseases are disorders of energy metabolism that include defects of pyruvate metabolism, Krebs cycle, respiratory chain (RC), and fatty acid oxidation (FAO). Treatment of pyruvate metabolism, Krebs cycle, and RC disorders is, in general, disappointing. Therapeutic approaches consist of electron acceptors, enzyme activators, vitamins, coenzymes, free-radical scavengers, dietary measures, and supportive therapy. These treatment assumptions are based on current understanding of the pathophysiology, on anecdotal clinical reports, and on a few controlled clinical trials, which have not been encouraging. Although it is difficult to perform clinical trials in these conditions due to their rarity and genotypic and phenotypic heterogeneity, there is a great need for well-performed double-blind placebo- controlled clinical trials with comparable groups of patients and with sufficient follow-up periods. Treatment options for FAO disorders are, in general, satisfactory and are mainly based on diet, lifestyle recommendations, and administration of L-carnitine and, in some cases, riboflavin. Special conditions that involve primary deficiencies of L-carnitine, coenzyme Q(10), and cofactor- and vitamin-responsive enzyme defects must be systematically considered, because supplementation with these substances may be curative or produce dramatic improvements. While awaiting more specific therapies for mitochondrial disorders, it is useful to reach a consensus regarding the management of these patients. The expected outcome is a slowing of the disease process and stabilization of the clinical syndrome. More definitive treatments hopefully will follow in the near future.

Riboflavin therapy. Biochemical heterogeneity in two adult lipid storage myopathies

Two unrelated adult males, aged 36 (patient 1) and 25 (patient 2) years, presented with subacute carnitine-deficient lipid storage myopathy that was totally and partly responsive to riboflavin supplementation in the two patients, respectively. Plasma acyl-carnitine and urinary organic acid profiles indicated multiple acyl coenzyme A dehydrogenase deficiency, which was mild in patient 1 and severe in patient 2. The activities of short-chain and medium-chain acyl coenzyme A dehydrogenases in mitochondrial fractions were decreased, especially in patient 2. This was in agreement with Western blotting results. Flavin-dependent complexes I and II were studied by immunoblotting and densitometric quantification of two-dimensional electrophoresis with comparable results. Complex I was present in normal amounts in both patients, whereas complex II was decreased only in the pretherapy muscle of patient 2. Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) concentrations in muscle and isolated mitochondria, and the activity of mitochondrial FAD pyrophosphatase, showed that patient 1 had low levels of FAD (46%) and FMN (49%) in mitochondria, with a significant increase (P < 0.01) in mitochondrial FAD pyrophosphatase (273%) compared with controls. Patient 2 had similar low levels of FAD and FMN in both total muscle (FAD and FMN 22% of controls) and mitochondria (FAD 26%; FMN 16%) and normal activity of mitochondrial FAD pyrophosphatase. All of these biochemical parameters were either totally or partly corrected after riboflavin therapy.

Mitochondrial respiratory chain disorders and the liver

Mitochondrial respiratory chain disorders are an established cause of liver failure in early childhood but they are probably under-diagnosed, partly due to under-recognition and partly due to the difficulty of investigation. It is particularly important to look for mitochondrial disorders if the liver disease presents with hypoglycaemia and lactic acidaemia or if it is accompanied by neurological, muscle or renal tubular abnormalities. Respiratory chain defects have been demonstrated in a number of patients who die of liver failure following severe epilepsy; this includes at least some cases of Alpers syndrome or 'progressive neuronal degeneration of childhood'. In mitochondrial liver disease, histology usually shows steatosis, often accompanied by fibrosis, cholestasis and loss of hepatocytes. Unless the clinical picture suggests a particular syndrome, such as Pearson syndrome, biochemical assays and histochemistry should be the initial investigations. Ideally, investigations should be carried out on liver as well as more standard tissues, such as muscle, since defects can be tissue-specific. Nuclear defects and mtDNA point mutations are probably responsible for many cases of mitochondrial liver disease but, as yet, the only identified molecular abnormalities are mtDNA rearrangements and mtDNA depletion. Treatment of mitochondrial liver disease is unsatisfactory. If the disease is confined to the liver, transplantation may be appropriate but in several patients transplantation has been followed by the appearance of disease in other organs, particularly the brain.

[Leigh syndrome and leukodystrophy due to partial succinate dehydrogenase deficiency: regression with riboflavin]

Succinate dehydrogenase (SDH) deficiency is rare. Clinical manifestations can appear in infancy with a marked impairment of psychomotor development with pyramidal signs and extrapyramidal rigidity.

CASE REPORT

A 10-month-old boy developed severe neurological features, evoking a Leigh syndrome; magnetic resonance imaging showed features of leukodystrophy. A deficiency in the complex II respiratory chain (succinate dehydrogenase [SDH]) was shown. The course was remarkable by the regression of neurological impairment under treatment by riboflavin. The delay of psychomotor development, mainly involving language, was moderate at the age of 5 years.

CONCLUSION

The relatively good prognosis of this patient, despite severe initial neurological impairment, may be due to the partial enzyme deficiency and/or riboflavin administration.

Biochemical and genetic studies in a family with mitochondrial myopathy

We present a family with severe exercise intolerance, progressive proximal weakness, and lactic acidemia. Fifteen of 24 family members in five generations were affected. Since the affected males do not have offspring at this time, the family pedigree is consistent with either maternal or autosomal dominant inheritance. Muscle histochemistry showed ragged-red fibers and electron microscopy showed globular mitochondrial inclusions. Biochemical analysis showed reduced muscle activities of mitochondrial NADH-cytochrome c reductase (1 of 2 patients), succinate-cytochrome c reductase (2 patients), and cytochrome c oxidase (2 patients). For 1 patient, sequence analysis of 44% of the muscle mitochondrial DNA including all 22 transfer RNA regions showed no point mutation with pathogenic significance. Southern blot analysis showed no deletion. Six affected members of the family were treated with methylprednisolone (0.25 mg/kg) for 3 months. Muscle strength, serum lactate, and energy metabolism at rest (measured by 31P magnetic resonance spectroscopy) significantly improved with treatment.

Treatment of mitochondrial disease

Defects of the mitochondrial genome are widely recognized as important causes of disease in man. Patients may present at any age with clinical symptoms that vary from acute episodes of lactic acidosis in infancy to severe neurodegenerative illness in adulthood. While modern molecular genetic techniques have facilitated major advances in the diagnosis and characterization of specific molecular defects, treatment for the majority of patients remains supportive in the absence of definitive biochemical therapies. As a consequence, the possibilities for mitochondrial DNA gene therapy must be considered. In this review, we will evaluate the current biochemical strategies available to clinicians for the management of patients with mitochondrial disease and examine the possible approaches to the gene therapy of mitochondrial DNA defects.

Mitochondrial myopathy with tRNA(Leu(UUR)) mutation and complex I deficiency responsive to riboflavin

Deficiency of complex I (reduced nicotinamide adenine dinucleotide dehydrogenase-ubiquinone oxidoreductase) of the mitochondrial respiratory chain may be seen as a pure myopathy or as a neuromuscular disorder at presentation. Efficacy of long- term therapy for these disorders is yet to be established. We report the case of a female patient with complex I deficiency and skeletal myopathy, who has had a sustained clinical response to riboflavin during 3 years of therapy. Molecular studies found no mutations in the putative flavin mononucleotide binding site in the 51 kd subunit of complex I, but a T-to-C transition at nucleotide 3250 in the mitochondrial DNA tRNA(Leu(UUR)) gene was identified. This mutation has been reported in one other family in that five members had fatigue with or without muscle weakness. There were also five cases of unexplained infant deaths in that family and two cases in the family reported here. Riboflavin therapy should be attempted in all patients with complex I deficiency when the clinical presentation is one of isolated skeletal myopathy.