Succinate in dystrophic white matter: a proton magnetic resonance spectroscopy finding characteristic for complex II deficiency

Human microbiota from drug-naive patients with obsessive-compulsive disorder drives behavioral symptoms and neuroinflammation via succinic acid in mice

Emerging evidence suggests that the gut microbiota is closely related to psychiatric disorders. However, little is known about the role of the gut microbiota in the development of obsessive-compulsive disorder (OCD). Here, to investigate the contribution of gut microbiota to the pathogenesis of OCD, we transplanted fecal microbiota from first-episode, drug-naive OCD patients or demographically matched healthy individuals into antibiotic-treated specific pathogen-free (SPF) mice and showed that colonization with OCD microbiota is sufficient to induce core behavioral deficits, including abnormal anxiety-like and compulsive-like behaviors. The fecal microbiota was analyzed using 16 S rRNA full-length sequencing, and the results demonstrated a clear separation of the fecal microbiota of mice colonized with OCD and control microbiota. Notably, microbiota from OCD-colonized mice resulted in injured neuronal morphology and function in the mPFC, with inflammation in the mPFC and colon. Unbiased metabolomic analyses of the serum and mPFC region revealed the accumulation of succinic acid (SA) in OCD-colonized mice. SA impeded neuronal activity and induced an inflammatory response in both the colon and mPFC, impacting intestinal permeability and brain function, which act as vital signal mediators in gut microbiota-brain-immune crosstalk. Manipulations of dimethyl malonate (DM) have been reported to exert neuroprotective effects by suppressing the oxidation of accumulated succinic acid, attenuating the downstream inflammatory response and neuronal damage, and can help to partly improve abnormal behavior and reduce neuroinflammation and intestinal inflammation in OCD-colonized mice. We propose that the gut microbiota likely regulates brain function and behaviors in mice via succinic acid signaling, which contributes to the pathophysiology of OCD through gut-brain crosstalk and may provide new insights into the treatment of this disorder.

Enhanced ROS Production in Mitochondria from Prematurely Aging mtDNA Mutator Mice

An increase in mitochondrial DNA (mtDNA) mutations and an ensuing increase in mitochondrial reactive oxygen species (ROS) production have been suggested to be a cause of the aging process ("the mitochondrial hypothesis of aging"). In agreement with this, mtDNA-mutator mice accumulate a large amount of mtDNA mutations, giving rise to defective mitochondria and an accelerated aging phenotype. However, incongruously, the rates of ROS production in mtDNA mutator mitochondria have generally earlier been reported to be lower - not higher - than in wildtype, thus apparently invalidating the "mitochondrial hypothesis of aging". We have here re-examined ROS production rates in mtDNA-mutator mice mitochondria. Using traditional conditions for measuring ROS (succinate in the absence of rotenone), we indeed found lower ROS in the mtDNA-mutator mitochondria compared to wildtype. This ROS mainly results from reverse electron flow driven by the membrane potential, but the membrane potential reached in the isolated mtDNA-mutator mitochondria was 33 mV lower than that in wildtype mitochondria, due to the feedback inhibition of succinate oxidation by oxaloacetate, and to a lower oxidative capacity in the mtDNA-mutator mice, explaining the lower ROS production. In contrast, in normal forward electron flow systems (pyruvate (or glutamate) + malate or palmitoyl-CoA + carnitine), mitochondrial ROS production was higher in the mtDNA-mutator mitochondria. Particularly, even during active oxidative phosphorylation (as would be ongoing physiologically), higher ROS rates were seen in the mtDNA-mutator mitochondria than in wildtype. Thus, when examined under physiological conditions, mitochondrial ROS production rates are indeed increased in mtDNA-mutator mitochondria. While this does not prove the validity of the mitochondrial hypothesis of aging, it may no longer be said to be negated in this respect. This paper is dedicated to the memory of Professor Vladimir P. Skulachev.

Expert Panel Curation of 113 Primary Mitochondrial Disease Genes for the Leigh Syndrome Spectrum

OBJECTIVE

Primary mitochondrial diseases (PMDs) are heterogeneous disorders caused by inherited mitochondrial dysfunction. Classically defined neuropathologically as subacute necrotizing encephalomyelopathy, Leigh syndrome spectrum (LSS) is the most frequent manifestation of PMD in children, but may also present in adults. A major challenge for accurate diagnosis of LSS in the genomic medicine era is establishing gene-disease relationships (GDRs) for this syndrome with >100 monogenic causes across both nuclear and mitochondrial genomes.

METHODS

The Clinical Genome Resource (ClinGen) Mitochondrial Disease Gene Curation Expert Panel (GCEP), comprising 40 international PMD experts, met monthly for 4 years to review GDRs for LSS. The GCEP standardized gene curation for LSS by refining the phenotypic definition, modifying the ClinGen Gene-Disease Clinical Validity Curation Framework to improve interpretation for LSS, and establishing a scoring rubric for LSS.

RESULTS

The GDR with LSS across the nuclear and mitochondrial genomes was classified as definitive for 31 of 114 GDRs curated (27%), moderate for 38 (33%), limited for 43 (38%), and disputed for 2 (2%). Ninety genes were associated with autosomal recessive inheritance, 16 were maternally inherited, 5 were autosomal dominant, and 3 were X-linked.

INTERPRETATION

GDRs for LSS were established for genes across both nuclear and mitochondrial genomes. Establishing these GDRs will allow accurate variant interpretation, expedite genetic diagnosis of LSS, and facilitate precision medicine, multisystem organ surveillance, recurrence risk counseling, reproductive choice, natural history studies, and determination of eligibility for interventional clinical trials. ANN NEUROL 2023;94:696-712.

Neuroimaging in Primary Coenzyme-Q10-Deficiency Disorders

Coenzyme Q10 (CoQ10) is an endogenously synthesized lipid molecule. It is best known for its role as a cofactor within the mitochondrial respiratory chain where it functions in electron transfer and ATP synthesis. However, there are many other cellular pathways that also depend on the CoQ10 supply (redox homeostasis, ferroptosis and sulfide oxidation). The CoQ10 biosynthesis pathway consists of several enzymes, which are encoded by the nuclear DNA. The majority of these enzymes are responsible for modifications of the CoQ-head group (benzoquinone ring). Only three enzymes (PDSS1, PDSS2 and COQ2) are required for assembly and attachment of the polyisoprenoid side chain. The head-modifying enzymes may assemble into resolvable domains, representing COQ complexes. During the last two decades, numerous inborn errors in CoQ10 biosynthesis enzymes have been identified. Thus far, 11 disease genes are known (PDSS1, PDSS2, COQ2, COQ4, COQ5, COQ6, COQ7, COQ8A, COQ8B, COQ9 and HPDL). Disease onset is highly variable and ranges from the neonatal period to late adulthood. CoQ10 deficiency exerts detrimental effects on the nervous system. Potential consequences are neuronal death, neuroinflammation and cerebral gliosis. Clinical features include encephalopathy, regression, movement disorders, epilepsy and intellectual disability. Brain magnetic resonance imaging (MRI) is the most important tool for diagnostic evaluation of neurological damage in individuals with CoQ10 deficiency. However, due to the rarity of the different gene defects, information on disease manifestations within the central nervous system is scarce. This review aims to provide an overview of brain MRI patterns observed in primary CoQ10 biosynthesis disorders and to highlight disease-specific findings.

Leigh syndrome

Leigh syndrome, or subacute necrotizing encephalomyelopathy, was initially recognized as a neuropathological entity in 1951. Bilateral symmetrical lesions, typically extending from the basal ganglia and thalamus through brainstem structures to the posterior columns of the spinal cord, are characterized microscopically by capillary proliferation, gliosis, severe neuronal loss, and relative preservation of astrocytes. Leigh syndrome is a pan-ethnic disorder usually with onset in infancy or early childhood, but late-onset forms occur, including in adult life. Over the last six decades it has emerged that this complex neurodegenerative disorder encompasses more than 100 separate monogenic disorders associated with enormous clinical and biochemical heterogeneity. This chapter discusses clinical, biochemical and neuropathological aspects of the disorder, and postulated pathomechanisms. Known genetic causes, including defects of 16 mitochondrial DNA (mtDNA) genes and approaching 100 nuclear genes, are categorized into disorders of subunits and assembly factors of the five oxidative phosphorylation enzymes, disorders of pyruvate metabolism and vitamin and cofactor transport and metabolism, disorders of mtDNA maintenance, and defects of mitochondrial gene expression, protein quality control, lipid remodeling, dynamics, and toxicity. An approach to diagnosis is presented, together with known treatable causes and an overview of current supportive management options and emerging therapies on the horizon.

In vivo Human MR Spectroscopy Using a Clinical Scanner: Development, Applications, and Future Prospects

MR spectroscopy (MRS) is a unique and useful method for noninvasively evaluating biochemical metabolism in human organs and tissues, but its clinical dissemination has been slow and often limited to specialized institutions or hospitals with experts in MRS technology. The number of 3-T clinical MR scanners is now increasing, representing a major opportunity to promote the use of clinical MRS. In this review, we summarize the theoretical background and basic knowledge required to understand the results obtained with MRS and introduce the general consensus on the clinical utility of proton MRS in routine clinical practice. In addition, we present updates to the consensus guidelines on proton MRS published by the members of a working committee of the Japan Society of Magnetic Resonance in Medicine in 2013. Recent research into multinuclear MRS equipped in clinical MR scanners is explained with an eye toward future development. This article seeks to provide an overview of the current status of clinical MRS and to promote the understanding of when it can be useful. In the coming years, MRS-mediated biochemical evaluation is expected to become available for even routine clinical practice.

A pioneer study on human 3-nitropropionic acid intoxication: Contributions from metabolomics

The neurotoxin 3-nitropropionic acid (3-NPA) is an inhibitor of succinate dehydrogenase, an enzyme participating both in the citric acid cycle and the mitochondrial respiratory chain. In human intoxications, it produces symptoms such as vomiting and stomach ache in mild cases, and dystonia, coma, and sometimes death in severe cases. We report the results from a liquid chromatography-Orbitrap mass spectrometry metabolomics study mapping the metabolic impacts of 3-NPA intoxication in plasma, urine, and cerebrospinal fluid (CSF) samples of a Norwegian boy initially suspected to suffer from a mitochondrial disease. In addition to the identification of 3-NPA, our findings included a large number of annotated/identified altered metabolites (80, 160, and 62 in plasma, urine, and CSF samples, respectively) belonging to different compound classes, for example, amino acids, fatty acids, and purines and pyrimidines. Our findings indicated protective mechanisms to attenuate the toxic effects of 3-NPA (e.g., decreased oleamide), occurrence of increased oxidative stress in the patient (such as increased free fatty acids and hypoxanthine) and energy turbulence caused by the intoxication (e.g., increased succinate). To our knowledge, this is the first case of 3-NPA intoxication reported in Norway and the first published metabolomics study of human 3-NPA intoxication worldwide. The unexpected identification of 3-NPA illustrates the importance for health care providers to consider intake-related intoxications during diagnostic evaluations, treatment and follow-up examinations for neurotoxicity and a wide range of metabolic derangements.

Diagnosis of primary mitochondrial disorders -Emphasis on myopathological aspects

Mitochondrial disorders are one of the most common neurometabolic disorders affecting all age groups. The phenotype-genotype heterogeneity in these disorders can be attributed to the dual genetic control on mitochondrial functions, posing a challenge for diagnosis. Though the advancement in the high-throughput sequencing and other omics platforms resulted in a "genetics-first" approach, the muscle biopsy remains the benchmark in most of the mitochondrial disorders. This review focuses on the myopathological aspects of primary mitochondrial disorders. The utility of muscle biopsy is not limited to analyse the structural abnormalities; rather it also proves to be a potential tool to understand the deranged sub-cellular functions.

MR spectroscopy in pediatric neuroradiology

Magnetic resonance spectroscopy (MRS), being able to identify and measure some brain components (metabolites) in pathologic lesions and in normal-appearing tissue, offers a valuable additional diagnostic tool to assess several pediatric neurological diseases. In this review we will illustrate the basic principles and clinical applications of brain proton (H¹; hydrogen) MRS (H¹MRS), by now the only MRS method widely available in clinical practice. Performing H¹MRS in the brain is inherently less complicated than in other tissues (e.g., liver, muscle), in which spectra are heavily affected by magnetic field inhomogeneities, respiration artifacts, and dominating signals from the surrounding adipose tissues. H¹MRS in pediatric neuroradiology has some advantages over acquisitions in adults (lack of motion due to children sedation and lack of brain iron deposition allow optimal results), but it requires a deep knowledge of pediatric pathologies and familiarity with the developmental changes in spectral patterns, particularly occurring in the first two years of life. Examples from our database, obtained mainly from a 1.5 Tesla clinical scanner in a time span of 15 years, will demonstrate the efficacy of H¹MRS in the diagnosis of a wide range of selected pediatric pathologies, like brain tumors, infections, neonatal hypoxic-ischemic encephalopathy, metabolic and white matter disorders.

Neuroimaging of Mitochondrial Cytopathies

Mitochondrial diseases are a complex and heterogeneous group of genetic disorders that occur as a result of either nuclear DNA or mitochondrial DNA pathogenic variants, leading to a decrease in oxidative phosphorylation and cellular energy (ATP) production. Increasing knowledge about molecular, biochemical, and genetic abnormalities related to mitochondrial dysfunction has expanded the neuroimaging phenotypes of mitochondrial disorders. As a consequence of this growing field, the imaging recognition patterns of mitochondrial cytopathies are continually evolving. In this review, we describe the main neuroimaging characteristics of pediatric mitochondrial diseases, ranging from classical to more recent and challenging features. Due to the increased knowledge about the imaging findings of mitochondrial cytopathies, the pediatric neuroradiologist plays a crucial role in the diagnosis and evaluation of these patients.

Myopathology of Adult and Paediatric Mitochondrial Diseases

Mitochondria are dynamic organelles ubiquitously present in nucleated eukaryotic cells, subserving multiple metabolic functions, including cellular ATP generation by oxidative phosphorylation (OXPHOS). The OXPHOS machinery comprises five transmembrane respiratory chain enzyme complexes (RC). Defective OXPHOS gives rise to mitochondrial diseases (mtD). The incredible phenotypic and genetic diversity of mtD can be attributed at least in part to the RC dual genetic control (nuclear DNA (nDNA) and mitochondrial DNA (mtDNA)) and the complex interaction between the two genomes. Despite the increasing use of next-generation-sequencing (NGS) and various omics platforms in unravelling novel mtD genes and pathomechanisms, current clinical practice for investigating mtD essentially involves a multipronged approach including clinical assessment, metabolic screening, imaging, pathological, biochemical and functional testing to guide molecular genetic analysis. This review addresses the broad muscle pathology landscape including genotype–phenotype correlations in adult and paediatric mtD, the role of immunodiagnostics in understanding some of the pathomechanisms underpinning the canonical features of mtD, and recent diagnostic advances in the field.

Metabolic flexibility of mitochondrial respiratory chain disorders predicted by computer modelling

Mitochondrial respiratory chain dysfunction causes a variety of life-threatening diseases affecting about 1 in 4300 adults. These diseases are genetically heterogeneous, but have the same outcome; reduced activity of mitochondrial respiratory chain complexes causing decreased ATP production and potentially toxic accumulation of metabolites. Severity and tissue specificity of these effects varies between patients by unknown mechanisms and treatment options are limited. So far most research has focused on the complexes themselves, and the impact on overall cellular metabolism is largely unclear. To illustrate how computer modelling can be used to better understand the potential impact of these disorders and inspire new research directions and treatments, we simulated them using a computer model of human cardiomyocyte mitochondrial metabolism containing over 300 characterised reactions and transport steps with experimental parameters taken from the literature. Overall, simulations were consistent with patient symptoms, supporting their biological and medical significance. These simulations predicted: complex I deficiencies could be compensated using multiple pathways; complex II deficiencies had less metabolic flexibility due to impacting both the TCA cycle and the respiratory chain; and complex III and IV deficiencies caused greatest decreases in ATP production with metabolic consequences that parallel hypoxia. Our study demonstrates how results from computer models can be compared to a clinical phenotype and used as a tool for hypothesis generation for subsequent experimental testing. These simulations can enhance understanding of dysfunctional mitochondrial metabolism and suggest new avenues for research into treatment of mitochondrial disease and other areas of mitochondrial dysfunction.

Leukoencephalopathy due to Complex II Deficiency and Bi-Allelic SDHB Mutations: Further Cases and Implications for Genetic Counselling

Isolated complex II deficiency is a rare cause of mitochondrial disease and bi-allelic mutations in SDHB have been identified in only a few patients with complex II deficiency and a progressive neurological phenotype with onset in infancy. On the other hand, heterozygous SDHB mutations are a well-known cause of familial paraganglioma/pheochromocytoma and renal cell cancer. Here, we describe two additional patients with respiratory chain deficiency due to bi-allelic SDHB mutations. The patients' clinical, neuroradiological, and biochemical phenotype is discussed according to current knowledge on complex II and SDHB deficiency and is well in line with previously described cases, thus confirming the specific neuroradiological presentation of complex II deficiency that recently has emerged. The patients' genotype revealed one novel SDHB mutation, and one SDHB mutation, which previously has been described in heterozygous form in patients with familial paraganglioma/pheochromocytoma and/or renal cell cancer. This is only the second example in the literature where one specific SDHx mutation is associated with both recessive mitochondrial disease in one patient and familial paraganglioma/pheochromocytoma in others. Due to uncertainties regarding penetrance of different heterozygous SDHB mutations, we argue that all heterozygous SDHB mutation carriers identified in relation to SDHB-related leukoencephalopathy should be referred to relevant surveillance programs for paraganglioma/pheochromocytoma and renal cell cancer. The diagnosis of complex II deficiency due to SDHB mutations therefore raises implications for genetic counselling that go beyond the recurrence risk in the family according to an autosomal recessive inheritance.

Magnetic resonance imaging spectrum of succinate dehydrogenase-related infantile leukoencephalopathy

OBJECTIVE

Succinate dehydrogenase-deficient leukoencephalopathy is a complex II-related mitochondrial disorder for which the clinical phenotype, neuroimaging pattern, and genetic findings have not been comprehensively reviewed.

METHODS

Nineteen individuals with succinate dehydrogenase deficiency-related leukoencephalopathy were reviewed for neuroradiological, clinical, and genetic findings as part of institutional review board-approved studies at Children's National Health System (Washington, DC) and VU University Medical Center (Amsterdam, the Netherlands).

RESULTS

All individuals had signal abnormalities in the central corticospinal tracts and spinal cord where imaging was available. Other typical findings were involvement of the cerebral hemispheric white matter with sparing of the U fibers, the corpus callosum with sparing of the outer blades, the basis pontis, middle cerebellar peduncles, and cerebellar white matter, and elevated succinate on magnetic resonance spectroscopy (MRS). The thalamus was involved in most studies, with a predilection for the anterior nucleus, pulvinar, and geniculate bodies. Clinically, infantile onset neurological regression with partial recovery and subsequent stabilization was typical. All individuals had mutations in SDHA, SDHB, or SDHAF1, or proven biochemical defect.

INTERPRETATION

Succinate dehydrogenase deficiency is a rare leukoencephalopathy, for which improved recognition by magnetic resonance imaging (MRI) in combination with advanced sequencing technologies allows noninvasive diagnostic confirmation. The MRI pattern is characterized by cerebral hemispheric white matter abnormalities with sparing of the U fibers, corpus callosum involvement with sparing of the outer blades, and involvement of corticospinal tracts, thalami, and spinal cord. In individuals with infantile regression and this pattern of MRI abnormalities, the differential diagnosis should include succinate dehydrogenase deficiency, in particular if MRS shows elevated succinate.

Leigh syndrome with Fukuyama congenital muscular dystrophy: a case report

We report the first case of Leigh syndrome (LS) with Fukuyama congenital muscular dystrophy (FCMD). A neonate suffered from lactic acidosis and subsequently presented with poor feeding, muscle weakness, hypotonia, cardiopulmonary dysfunction, and hydrocephalus. He died at 17 months. The findings of brain magnetic resonance imaging indicated some specific features of both LS and FCMD, and FCMD gene mutation was detected. Decreased mitochondrial respiratory complex I and II activity was noted. Mitochondrial DNA sequencing showed no pathogenic mutation. A case with complex I+II deficiency has rarely been reported, suggesting a nuclear gene mutation.

Type II Fp of human mitochondrial respiratory complex II and its role in adaptation to hypoxia and nutrition-deprived conditions

The flavoprotein (Fp) subunit of human mitochondrial succinate-ubiquinone reductase (SQR, complex II) has isoforms (type I, type II). Type II Fp is predominantly expressed in some cancer and fetal tissues and those tissues are often exposed to ischemia. The present study shows that complex II with type II Fp has lower optimal pH than complex II with type I Fp, and type II Fp mRNA expression was induced by ischemia. The result suggests complex II with type II Fp may function in cells with low mitochondrial matrix pH caused by ischemia and its function is related to cellular adaptation to ischemia.

Q-site inhibitor induced ROS production of mitochondrial complex II is attenuated by TCA cycle dicarboxylates

The impact of complex II (succinate:ubiquinone oxidoreductase) on the mitochondrial production of reactive oxygen species (ROS) has been underestimated for a long time. However, recent studies with intact mitochondria revealed that complex II can be a significant source of ROS. Using submitochondrial particles from bovine heart mitochondria as a system that allows the precise setting of substrate concentrations we could show that mammalian complex II produces ROS at subsaturating succinate concentrations in the presence of Q-site inhibitors like atpenin A5 or when a further downstream block of the respiratory chain occurred. Upon inhibition of the ubiquinone reductase activity, complex II produced about 75% hydrogen peroxide and 25% superoxide. ROS generation was attenuated by all dicarboxylates that are known to bind competitively to the substrate binding site of complex II, suggesting that the oxygen radicals are mainly generated by the unoccupied flavin site. Importantly, the ROS production induced by the Q-site inhibitor atpenin A5 was largely unaffected by the redox state of the Q pool and the activity of other respiratory chain complexes. Hence, complex II has to be considered as an independent source of mitochondrial ROS in physiology and pathophysiology.

Advances in the diagnosis of leukoencephalopathies

Introduction : Leukoencephalopathies (LEs) are a diverse group of diseases involving cerebral white matter. Some of the disorders may be infectious or immunologically mediated and, therefore, tend to be more amenable to treatment. Most of these disorders have a genetic basis, for which genetic counseling becomes important as currently very few of them have effective therapies. Areas covered : This review calls attention to the diagnostic dilemmas, highlights the diagnostic tests of choice for separating conditions with similar clinical, laboratory or neuroimaging findings, and describes several LEs that have been newly discovered within the last 20 years. Imaging of LEs has progressed rapidly since the introduction of magnetic resonance imaging (MRI) and spectroscopy (MRS), allowing recognition of new diseases, with and without identifiable corresponding biochemical or genetic defects. The distinguishing MRI and MRS features of LEs are described, as well as the resources available for biochemical, CSF and blood sample testing for diagnosis and differentiation from previously known LEs. Expert opinion : Although there is no treatment at present for many of the LEs, their detection as a cause of intellectual and motor disabilities, and as inherited disorders, makes it necessary to accurately categorize them. This knowledge will then allow further elucidation of the etiology, understanding the biological underpinnings, and eventually progress toward rational therapies.

Complex II deficiency--a case report and review of the literature

Complex II deficiency is a rare cause of mitochondrial respiratory chain defects with a prevalence of 2-23%. It is exclusively nuclear encoded and functions in the citric acid cycle by oxidizing succinate to fumarate and in the mitochondrial electron transport chain (ETC) by transferring electrons to ubiquinone. Of the four subunits, SDHA and SDHB are catalytic and SDHC and SDHD are anchoring. Mutations in SDHA and SDHAF1 (assembly factor) have been found in patients with CII deficiency and a mitochondrial phenotype. We present a patient with CII deficiency with a previously undescribed phenotype of dilated cardiomyopathy, left ventricular noncompaction, failure to thrive, hypotonia, and developmental delay. Also, a comprehensive review of 36 cases published in the literature was undertaken. The results show that CII deficiency has a variable phenotype with no correlation with residual complex activity in muscle although the phenotype and enzyme activities are comparable within a family. For some, the condition was fatal in infancy, others had multisystem involvement and some had onset in adulthood with mild symptoms and normal cognition. Neurological involvement is most commonly observed and brain imaging commonly shows leukoencephalopathy, Leigh syndrome, or cerebellar atrophy. Mutations in SDHAF1 are associated with leukoencephalopathy. Other organ systems like heart, muscle, and eyes are only involved in about 50% of the cases but cardiomyopathy is associated with high mortality and morbidity. In some patients, riboflavin has provided clinical improvement.

Clinical and imaging diagnosis for heredodegenerative diseases

Clinical features (progressive psychomotor retardation, seizures, movement disorders and motor signs in both central and peripheral systems, sensorineural defects, and psychiatric symptoms) and brain imaging are the keys to diagnosis. CT is indicated for the detection of calcifications and blood, and for angiography. MRI in all three axes requires T1, T2, FLAIR (from 1 year on), eventually T2* or contrast administration, and diffusion in any acute condition. MR spectroscopy allows the dectection of lactate and creatine deficiency, elevated choline in high membrane turnover, and low NAA in neuronal death. The normal sequence of myelination needs to be taken into account. Pre- and neonatal anomalies include cystic and basal ganglia lesions, gyral and myelin anomalies, callosal agenesis, and large subdural spaces. Anomalies disclosed after 3 months of age include basal ganglia appearing hyper- or hypointense on T2, hypointense on T2*, or calcified white matter anomalies mainly periventricular or subcortical, or with contrast enhancement, associated with macrocephaly and/or large or very small cysts, and hypomyelination; there may be "vascular" or pseudostroke disorders, cortical atrophy, hypoplasia, or abnormal signal of the brainstem and/or cerebellum. Spectroscopy should investigate basal ganglia, white matter, and the cerebellum. MRI may reveal typical alterations of the brain at the preclinical stage in siblings of affected children.

Leukoencephalopathy with accumulated succinate is indicative of SDHAF1 related complex II deficiency

BACKGROUND

Deficiency of complex II (succinate dehydrogenase, SDH) represents a rare cause of mitochondrial disease and is associated with a wide range of clinical symptoms. Recently, mutations of SDHAF1, the gene encoding for the SDH assembly factor 1, were reported in SDH-defective infantile leukoencephalopathy. Our goal was to identify SDHAF1 mutations in further patients and to delineate the clinical phenotype.

METHODS

In a retrospective data collection study we identified nine children with biochemically proven complex II deficiency among our cohorts of patients with mitochondrial disorders. The cohort comprised five patients from three families affected by SDH-defective infantile leukoencephalopathy with accumulation of succinate in disordered cerebral white matter, as detected by in vivo proton MR spectroscopy. One of these patients had neuropathological features of Leigh syndrome. Four further unrelated patients of the cohort showed diverse clinical phenotypes without leukoencephalopathy. SDHAF1 was sequenced in all nine patients.

RESULTS

Homozygous mutations of SDHAF1 were detected in all five patients affected by leukoencephalopathy with accumulated succinate, but not in any of the four patients with other, diverse clinical phenotypes. Two sisters had a mutation reported previously, in three patients two novel mutations were found.

CONCLUSION

Leukoencephalopathy with accumulated succinate is a key symptom of defective complex II assembly due to SDHAF1 mutations.

Gene expression suggests spontaneously hypertensive rats may have altered metabolism and reduced hypoxic tolerance

Cerebral small vessel disease (SVD) is an important cause of stroke, cognitive decline and vascular dementia (VaD). It is associated with diffuse white matter abnormalities and small deep cerebral ischemic infarcts. The molecular mechanisms involved in the development and progression of SVD are unclear. As hypertension is a major risk factor for developing SVD, Spontaneously Hypertensive Rats (SHR) are considered an appropriate experimental model for SVD. Prior work suggested an imbalance between the number of blood microvessels and astrocytes at the level of the neurovascular unit in 2-month-old SHR, leading to neuronal hypoxia in the brain of 9-month-old animals. To identify genes and pathways involved in the development of SVD, we compared the gene expression profile in the cortex of 2 and 9-month-old of SHR with age-matched normotensive Wistar Kyoto (WKY) rats using microarray-based technology. The results revealed significant differences in expression of genes involved in energy and lipid metabolisms, mitochondrial functions, oxidative stress and ischemic responses between both groups. These results strongly suggest that SHR suffer from chronic hypoxia, and therefore are unable to tolerate ischemia-like conditions, and are more vulnerable to high-energy needs than WKY. This molecular analysis gives new insights about pathways accounting for the development of SVD.

Mitochondrial ('mild') uncoupling and ROS production: physiologically relevant or not?

During the last decade, the possibility that 'mild' uncoupling could be protective against oxidative damage by diminishing ROS (reactive oxygen species) production has attracted much interest. In the present paper, we briefly examine the evidence for this possibility. It is only ROS production from succinate under reverse electron-flow conditions that is sensitive to membrane potential fluctuations, and so only this type of ROS production could be affected; however, the conditions under which succinate-supported ROS production is observed include succinate concentrations that are supraphysiological. Any decrease in membrane potential, even 'mild uncoupling', must necessarily lead to large increases in respiration, i.e. it must be markedly thermogenic. Mitochondria within cells are normally ATP-producing and thus already have a diminished membrane potential, and treatment of cells, organs or animals with small amounts of artificial uncoupler does not seem to have beneficial effects that are explainable via reduced ROS production. Although it has been suggested that members of the uncoupling protein family (UCP1, UCP2 and UCP3) may mediate a mild uncoupling, present evidence does not unequivocally support such an effect, e.g. the absence of the truly uncoupling protein UCP1 is not associated with increased oxidative damage. Thus present evidence does not support mild uncoupling as a physiologically relevant alleviator of oxidative damage.

Metabolic changes in early childhood using LCModel with corrected water scaling method

PURPOSE

To examine metabolic changes of the brain in early infancy measured by the LCModel with the water scaling method (LCModel-WS), and to determine whether the unsuppressed water signal (UWS) on the MR console and the area of the unsuppressed water peak (AUW) in the LCModel can be used to correct metabolite concentrations.

MATERIALS AND METHODS

MR spectroscopy was performed on a 1.5 Tesla MR scanner. To determine whether UWS and AUW increases linearly with PD and exp(-TE/T2), these values were measured using three phantoms with different PD and T2 values. UWS and AUW were also measured (PRESS, TR = 5000 ms, TE = 30 ms, VOI = 4.5 mL) in 57 pediatric controls (aged 2 weeks to 15 years).

RESULTS

Phantom studies revealed UWS and AUW increases linearly with PD and exp(-TE/T2). UWS and AUW were high in controls younger than 2 years of age, but gradually decreased to become almost constant after 4 years (UWS = 504 × 10(3) , AUW = 2.05 × 10(7)). AUW was linearly proportional to UWS in controls. These indicated that metabolite concentrations should be multiplied by the ratio of UWS/504 × 10(3) or AUW/2.05 × 10(7). Age dependent metabolite concentrations corrected by the ratio were obtained.

CONCLUSION

Both UWS and AUW can be used to correct metabolite concentrations; these corrections can significantly improve quantification of metabolites' concentration in early childhood.

A metabolic model of the mitochondrion and its use in modelling diseases of the tricarboxylic acid cycle

Background

Mitochondria are a vital component of eukaryotic cells and their dysfunction is implicated in a large number of metabolic, degenerative and age-related human diseases. The mechanism or these disorders can be difficult to elucidate due to the inherent complexity of mitochondrial metabolism. To understand how mitochondrial metabolic dysfunction contributes to these diseases, a metabolic model of a human heart mitochondrion was created.

Results

A new model of mitochondrial metabolism was built on the principle of metabolite availability using MitoMiner, a mitochondrial proteomics database, to evaluate the subcellular localisation of reactions that have evidence for mitochondrial localisation. Extensive curation and manual refinement was used to create a model called iAS253, containing 253 reactions, 245 metabolites and 89 transport steps across the inner mitochondrial membrane. To demonstrate the predictive abilities of the model, flux balance analysis was used to calculate metabolite fluxes under normal conditions and to simulate three metabolic disorders that affect the TCA cycle: fumarase deficiency, succinate dehydrogenase deficiency and α-ketoglutarate dehydrogenase deficiency.

Conclusion

The results of simulations using the new model corresponded closely with phenotypic data under normal conditions and provided insight into the complicated and unintuitive phenotypes of the three disorders, including the effect of interventions that may be of therapeutic benefit, such as low glucose diets or amino acid supplements. The model offers the ability to investigate other mitochondrial disorders and can provide the framework for the integration of experimental data in future studies.

Mitochondrial respiratory chain complexes: apoptosis sensors mutated in cancer?

Mutations in cancer cells affecting subunits of the respiratory chain (RC) indicate a central role of oxidative phosphorylation for tumourigenesis. Recent studies have suggested that such mutations of RC complexes impact apoptosis induction. We review here the evidence for this hypothesis, which in particular emerged from work on how complex I and II mediate signals for apoptosis. Both protein aggregates are specifically inhibited for apoptosis induction through different means by exploiting with protease activation and pH change, two widespread but independent features of dying cells. Nevertheless, both converge on forming reactive oxygen species for the demise of the cell. Investigations into these mitochondrial processes will remain a rewarding area for unravelling the causes of tumourigenesis and for discovering interference options.

Advances in molecular diagnostics for mitochondrial diseases

BACKGROUND

Mitochondrial disorders (MD) are diseases caused by impairment of the mitochondrial respiratory chain. Phenotypes are polymorphous and may range from pure myopathy to multisystemic disorders. The genetic defect can be located on mitochondrial or nuclear DNA. At present, diagnosis of MD requires a complex approach: measurement of serum lactate, electromyography, muscle histology and enzymology, and genetic analysis. Magnetic resonance spectroscopy allows the assessment of tissue metabolic alterations, thus providing useful information for the diagnosis and monitoring of MD. Molecular soluble markers of mitochondrial dysfunction, at rest and during exercise, can identify the impairment of the aerobic system in MD, but a reliable biomarker for the screening or diagnosis of MD is still needed.

OBJECTIVE

Molecular and genetic characterization of MD, together with other experimental approaches, contribute to add new insights to these diseases. Here, the role and advances of diagnostic techniques for MD are reviewed.

CONCLUSION

Possible applications of the results obtained by new molecular investigative approaches could in future guide therapeutic strategies.

In vivo magnetic resonance spectroscopy: basic methodology and clinical applications

The clinical use of in vivo magnetic resonance spectroscopy (MRS) has been limited for a long time, mainly due to its low sensitivity. However, with the advent of clinical MR systems with higher magnetic field strengths such as 3 Tesla, the development of better coils, and the design of optimized radio-frequency pulses, sensitivity has been considerably improved. Therefore, in vivo MRS has become a technique that is routinely used more and more in the clinic. In this review, the basic methodology of in vivo MRS is described-mainly focused on (1)H MRS of the brain-with attention to hardware requirements, patient safety, acquisition methods, data post-processing, and quantification. Furthermore, examples of clinical applications of in vivo brain MRS in two interesting fields are described. First, together with a description of the major resonances present in brain MR spectra, several examples are presented of deviations from the normal spectral pattern associated with inborn errors of metabolism. Second, through examples of MR spectra of brain tumors, it is shown that MRS can play an important role in oncology.

SDHAF1, encoding a LYR complex-II specific assembly factor, is mutated in SDH-defective infantile leukoencephalopathy

We report mutations in SDHAF1, encoding a new LYR-motif protein, in infantile leukoencephalopathy with defective succinate dehydrogenase (SDH, complex II). Disruption of the yeast homolog or expression of variants corresponding to human mutants caused SDH deficiency and failure of OXPHOS-dependent growth, whereas SDH activity and amount were restored in mutant fibroblasts proportionally with re-expression of the wild-type gene. SDHAF1 is the first bona fide SDH assembly factor reported in any organism.

High throughput lipidomic profiling of schizophrenia and bipolar disorder brain tissue reveals alterations of free fatty acids, phosphatidylcholines, and ceramides

A mass spectrometry based high throughput approach was employed to profile white and gray matter lipid levels in the prefrontal cortex (Brodmann area 9) of 45 subjects including 15 schizophrenia and 15 bipolar disorder patients as well as 15 controls samples. We found statistically significant alterations in levels of free fatty acids and phosphatidylcholine in gray and white matter of both schizophrenia and bipolar disorder samples compared to controls. Also, ceramides were identified to be significantly increased in white matter of both neuropsychiatric disorders as compared to control levels. The patient cohort investigated in this study includes a number of drug naive as well as untreated patients, allowing the assessment of drug effects on lipid levels. Our findings indicate that while gray matter phosphatidylcholine levels were influenced by antipsychotic medication, this was not the case for phosphatidylcholine levels in white matter. Changes in free fatty acids or ceramides in either white or gray matter also did not appear to be influenced by antipsychotic treatment. To assess lipid profiles in the living patient, we also profiled lipids of 40 red blood cell samples, including 7 samples from drug naive first onset patients. We found significant alterations in the concentrations of free fatty acids as well as ceramide. Overall, our findings suggest that lipid abnormalities may be a disease intrinsic feature of both schizophrenia and bipolar disorder reflected by significant changes in the central nervous system as well as peripheral tissues.

Neuroimaging of mitochondrial disease

Mitochondrial disease represents a heterogeneous group of genetic disorders that require a variety of diagnostic tests for proper determination. Neuroimaging may play a significant role in diagnosis. The various modalities of nuclear magnetic resonance imaging (MRI) allow for multiple independent detection procedures that can give important anatomical and metabolic clues for diagnosis. The non-invasive nature of neuroimaging also allows for longitudinal studies. To date, no pathonmonic correlation between specific genetic defect and neuroimaging findings have been described. However, certain neuroimaging results can give important clues that a patient may have a mitochondrial disease. Conventional MRI may show deep gray structural abnormalities or stroke-like lesions that do not respect vascular territories. Chemical techniques such as proton magnetic resonance spectroscopy (MRS) may demonstrate high levels of lactate or succinate. When found, these results are suggestive of a mitochondrial disease. MRI and MRS studies may also show non-specific findings such as delayed myelination or non-specific leukodystrophy picture. However, in the context of other biochemical, structural, and clinical findings, even non-specific findings may support further diagnostic testing for potential mitochondrial disease. Once a diagnosis has been established, these non-invasive tools can also aid in following disease progression and evaluate the effects of therapeutic interventions.

The in-depth evaluation of suspected mitochondrial disease

Mitochondrial disease confirmation and establishment of a specific molecular diagnosis requires extensive clinical and laboratory evaluation. Dual genome origins of mitochondrial disease, multi-organ system manifestations, and an ever increasing spectrum of recognized phenotypes represent the main diagnostic challenges. To overcome these obstacles, compiling information from a variety of diagnostic laboratory modalities can often provide sufficient evidence to establish an etiology. These include blood and tissue histochemical and analyte measurements, neuroimaging, provocative testing, enzymatic assays of tissue samples and cultured cells, as well as DNA analysis. As interpretation of results from these multifaceted investigations can become quite complex, the Diagnostic Committee of the Mitochondrial Medicine Society developed this review to provide an overview of currently available and emerging methodologies for the diagnosis of primary mitochondrial disease, with a focus on disorders characterized by impairment of oxidative phosphorylation. The aim of this work is to facilitate the diagnosis of mitochondrial disease by geneticists, neurologists, and other metabolic specialists who face the challenge of evaluating patients of all ages with suspected mitochondrial disease.

High rates of superoxide production in skeletal-muscle mitochondria respiring on both complex I- and complex II-linked substrates

Despite the considerable interest in superoxide as a potential cause of pathology, the mechanisms of its deleterious production by mitochondria remain poorly understood. Previous studies in purified mitochondria have found that the highest rates of superoxide production are observed with succinate-driven reverse-electron transfer through complex I, although the physiological importance of this pathway is disputed because it necessitates high concentrations of succinate and is thought not to occur when NAD is in the reduced state. However, very few studies have examined the rates of superoxide production with mitochondria respiring on both NADH-linked (e.g. glutamate) and complex II-linked substrates. In the present study, we find that the rates of superoxide production (measured indirectly as H2O2) with glutamate+succinate (approximately 1100 pmol of H2O2 x min(-1) x mg(-1)) were unexpectedly much higher than with succinate (approximately 400 pmol of H2O2 x min(-1) x mg(-1)) or glutamate (approximately 80 pmol of H2O2 x min(-1) x mg(-1)) alone. Superoxide production with glutamate+succinate remained high even at low substrate concentrations (<1 mM), was decreased by rotenone and was completely eliminated by FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone), indicating that it must in large part originate from reverse-electron transfer through complex I. Similar results were obtained when glutamate was replaced with pyruvate, alpha-ketoglutarate or palmitoyl carnitine. In contrast, superoxide production was consistently lowered by the addition of malate (malate+succinate approximately 30 pmol of H2O2 x min(-1) x mg(-1)). We propose that the inhibitory action of malate on superoxide production can be explained by oxaloacetate inhibition of complex II. In summary, the present results indicate that reverse-electron transfer-mediated superoxide production can occur under physiologically realistic substrate conditions and suggest that oxaloacetate inhibition of complex II may be an adaptive mechanism to minimize this.

Brain Magnetic Resonance in the Diagnostic Evaluation of Mitochondrial Encephalopathies

Brain MR imaging techniques are important ancillary tests in the diagnosis of a suspected mitochondrial encephalopathy since they provide details on brain structural and metabolic abnormalities. This is particularly true in children where non-specific neurologic symptoms are common, biochemical findings can be marginal and genetic defects may be not discovered. MR imaging modalities include conventional, or structural, imaging (MRI) and functional, or ultrastructural, imaging (spectroscopy, MRS; diffusion, DWI-ADC; perfusion, DSCI—ASL). Among them MRI and MRS are the main tools for diagnosis and work up of MD, and this review will focus mainly on them. The MRI findings of MD are very heterogeneous, as they depend on the metabolic brain defects, age of the patient, stage and severity of the disease. No correlation has been found between genetic defects and neuroimaging picture; however, some relationships between MR findings and clinical phenotypes may be identified. Different combinations of MRI signal abnormalities are often encountered but the most common findings may be summarized into three main MR patterns: (i) non-specific; (ii) specific; (iii) leukodystrophic-like. Regarding the functional MR techniques, only proton MRS plays an important role in demonstrating an oxidative metabolism impairment in the brain since it can show the accumulation of lactate, present as a doublet peak at 1.33 ppm. Assessment of lactate should be always performed on brain tissue and on the ventricular cerebral spinal fluid. As for MRI, metabolic MRS abnormalities can be of different types, and two distinct patterns can be recognized: non-specific and specific. The specific metabolic profiles, although not frequent to find, are highly pathognomonic of MD. The un-specific metabolic profiles add value to structural images in allowing to define the lesion load and to monitor the response to therapy trials.

NMR spectroscopic studies on the late onset form of 3-methylglutaconic aciduria type I and other defects in leucine metabolism

A diagnosis of 3-methylglutaconic aciduria type I (OMIM: 250950) based on elevated urinary excretion of 3-methylglutaconic acid (3MGA), 3-methylglutaric acid (3MG) and 3-hydroxyisovaleric acid (3HIVA) was made in a 61-year-old female patient presenting with leukoencephalopathy slowly progressing over more than 30 years. The diagnosis was confirmed at the enzymatic and molecular level. In vivo brain MR spectroscopic imaging (MRSI) was performed at 3.0 T, and one-dimensional and two-dimensional in vitro NMR spectroscopy of body fluids of the patient was performed at 11.7 T. Additionally, we measured 1D (1)H-NMR spectra of urine of seven patients with a total of four different inborn errors of leucine metabolism. Increased concentrations of 3HIVA, 3MGA (cis and trans) and 3MG were observed in the NMR spectra of the patient's urine. In the cerebrospinal fluid, the 3HIVA concentration was 10 times higher than in the plasma of the patient and only the cis isomer of 3MGA was observed. In vivo brain MRSI showed an abnormal resonance at 1.28 ppm that may be caused by 3HIVA. Comparison of (1)H-NMR spectra of urine samples from all eight patients studied, representing five different inborn errors of leucine metabolism, showed that each disease has typical NMR characteristics. Our leukoencephalopathy patient suffers from a late-onset form of 3-methylglutaconic aciduria type I. In the literature, only very few adult patients with this conditions have been described, and 3HIVA accumulation in white matter in the brain has not been presented before in these patients. Our data demonstrate that (1)H-NMR spectroscopy of urine can easily discriminate between the known inborn errors of leucine metabolism and provide the correct diagnosis.

Are mitochondria critical in the pathogenesis of Alzheimer's disease?

This review summarizes recent findings that suggest a causal connection between mitochondrial abnormalities and sporadic Alzheimer's disease (AD). Genetic causes of AD are known only for a small proportion of familial AD patients, but for a majority of sporadic AD patients, genetic causal factors are still unknown. Currently, there are no early detectable biomarkers for sporadic AD, and there is a lack of understanding of the pathophysiology of the disease. Findings from recent genetic studies of AD pathogenesis suggest that mitochondrial defects may play an important role in sporadic AD progression, and that mitochondrial abnormalities and oxidative damage may play a significant role in the progression of familial AD. Findings from biochemical studies, in vitro studies, gene expression studies, and animal model studies of AD are reviewed, and the possible contribution of mitochondrial mutations to late-onset sporadic AD is discussed.

Succinate causes oxidative damage through N-methyl-d-aspartate-mediated mechanisms

In this study we investigated whether succinate, the accumulating substrate in succinate dehydrogenase (SDH) deficiencies and SDH inhibitor intoxication, causes lipoperoxidation and protein carbonylation, and if NMDA receptors are involved in the succinate-induced oxidative damage. Adult male mice (30-40 g) received an intracerebroventricular injection of succinic acid (0.7, 1.0 and 1.7 micromol/5 microl) or 0.9% NaCl (5 microl) and had their exploratory behavior assessed in an open field for 10 min. Succinate (0.7 and 1.0 micromol/5 microl) decreased locomotor activity behavior and increased thiobarbituric acid reactive substances (TBARS) and protein carbonylation in the forebrain. Conversely, 1.7 micromol of succinate did not alter locomotor activity or oxidative damage parameters. The involvement of NMDA receptors in the succinate-induced increase of total protein carbonylation content and exploratory behavior inhibition was assessed by co-administrating MK-801 (7 nmol/2.5 microl icv), a noncompetitive NMDA receptor antagonist, with succinate (1 micromol/2.5 microl icv). The co-administration of MK-801 protected against succinate-induced increase of total protein carbonylation and decrease of locomotor activity. These results suggest the involvement of NMDA receptors in these effects of succinate, which may of particular relevance for succinate-accumulating conditions, such as SDH inhibitors intoxication and inherited SDH deficiencies.

Cerebrospinal fluid neurone-specific enolase in mitochondrial encephalomyopathies

Whether cerebrospinal fluid (CSF) neurone-specific enolase (NSE) contributes to the diagnosis of mitochondrial encephalomyopathies (MEMs) is unknown. Aim of the present study was thus to assess the validity of CSF-NSE in the diagnosis of MEM. CSF-NSE was determined in 24 controls, aged 28-88 years; and 23 MEM patients, aged 47-81 years. In controls, CSF-NSE was independent of sex (p = 0.849) and age (p = 0.346). Twenty-one MEM patients had clinical CNS involvement and two CNS abnormalities on imaging investigations exclusively. CSF cells were increased in 7, CSF protein in 17, CSF glucose in 1, and CSF lactate in 2 MEM patients. The upper reference limit of CSF-NSE was 14.66 ng/mL. CSF-NSE was elevated in 6 (26%) MEM patients. CSF-NSE was increased in a single MEM patient with subclinical CNS involvement. This study shows that CSF-NSE is elevated in only one quarter of the MEM patients. Determination of CSF-NSE appears to be of minor importance for the assessment of clinical or subclinical CNS involvement in MEM.

White matter involvement in mitochondrial diseases

White matter involvement is recently being realized as a common finding in mitochondrial disorders. It is considered an inherent part of the classical mitochondrial syndromes which are usually associated with alterations in the mitochondrial DNA such as: Leigh disease, Kearns-Sayre syndrome, mitochondrial encephalomyopathy lactic acidosis, and stroke like episodes, mitochondrial neuro-gastro-intestinal encephalomyopathy and Leber's hereditary optic neuropathy. White matter involvement is also described in mitochondrial disorders due to mutations in the nuclear DNA which are transmitted in an autosomal pattern. MRI findings suggestive of a mitochondrial disease are: small cyst-like lesions in abnormal white matter, involvement of both cerebral and cerebellar white matter, and a combination of a leukoencephalopathy with bilateral basal ganglia lesions. The clinical manifestations may be disproportionate to the extent of white matter involvement. Other organs may frequently be involved. The onset is often in infancy with a neurodegenerative course. The finding of a leukoencephalopathy in a patient with a complex neurologic picture and multisystem involvement should prompt a thorough mitochondrial evaluation.

Neuroimaging in leukodystrophies

The application of techniques based on in vivo magnetic resonance to the study of leukodystrophies is evaluated. Magnetic resonance imaging (MRI), the most important neuroimaging modality for patients with leukodystrophies, has proven invaluable for the detection of the extent and etiology of white-matter involvement, diagnosis, and monitoring of disease progression. Proton magnetic resonance spectroscopy, which can detect several brain metabolites, including those related to axonal function and myelination, can provide additional diagnostic and prognostic information and, in some cases, allows a rare insight into the biochemical pathology of leukodystrophies. The potential of other advanced magnetic resonance techniques, including diffusion tensor imaging, magnetization transfer contrast, and molecular imaging, is also discussed. In the future, anatomic and physiologic magnetic resonance techniques are expected to be integrated into a single examination that will provide a detailed characterization of white-matter diseases in children.

Mitochondrial dysfunction in schizophrenia: evidence for compromised brain metabolism and oxidative stress

The etiology and pathophysiology of schizophrenia remain unknown. A parallel transcriptomics, proteomics and metabolomics approach was employed on human brain tissue to explore the molecular disease signatures. Almost half the altered proteins identified by proteomics were associated with mitochondrial function and oxidative stress responses. This was mirrored by transcriptional and metabolite perturbations. Cluster analysis of transcriptional alterations showed that genes related to energy metabolism and oxidative stress differentiated almost 90% of schizophrenia patients from controls, while confounding drug effects could be ruled out. We propose that oxidative stress and the ensuing cellular adaptations are linked to the schizophrenia disease process and hope that this new disease concept may advance the approach to treatment, diagnosis and disease prevention of schizophrenia and related syndromes.