Disease impact in chronic progressive external ophthalmoplegia: More than meets the eye

Red Flags in Primary Mitochondrial Diseases: What Should We Recognize?

Primary mitochondrial diseases (PMDs) are complex group of metabolic disorders caused by genetically determined impairment of the mitochondrial oxidative phosphorylation (OXPHOS). The unique features of mitochondrial genetics and the pivotal role of mitochondria in cell biology explain the phenotypical heterogeneity of primary mitochondrial diseases and the resulting diagnostic challenges that follow. Some peculiar features ("red flags") may indicate a primary mitochondrial disease, helping the physician to orient in this diagnostic maze. In this narrative review, we aimed to outline the features of the most common mitochondrial red flags offering a general overview on the topic that could help physicians to untangle mitochondrial medicine complexity.

Identifying trajectories of fatigue in patients with primary mitochondrial disease due to the m.3243A > G variant

Severe fatigue is a common complaint in patients with primary mitochondrial disease. However, less is known about the course of fatigue over time. This longitudinal observational cohort study of patients with the mitochondrial DNA 3243 A>G variant explored trajectories of fatigue over 2 years, and characteristics of patients within these fatigue trajectories. Fifty-three adult patients treated at the Radboud University Medical Center Nijmegen were included. The majority of the patients reported consistent, severe fatigue (41%), followed by patients with a mixed pattern of severe and mild fatigue (36%). Then, 23% of patients reported stable mild fatigue levels. Patients with a stable high fatigue trajectory were characterized by higher disease manifestations scores, more clinically relevant mental health symptoms, and lower psychosocial functioning and quality of life compared to patients reporting stable low fatigue levels. Fatigue at baseline and disease manifestation scores predicted fatigue severity at the 2-year assessment (57% explained variance). This study demonstrates that severe fatigue is a common and stable complaint in the majority of patients. Clinicians should be aware of severe fatigue in patients with moderate to severe disease manifestation scores on the Newcastle Mitochondrial Disease Scale, the high prevalence of clinically relevant mental health symptoms and overall impact on quality of life in these patients. Screening of fatigue and psychosocial variables will guide suitable individualized treatment to improve the quality of life.

Cell-type-specific DNA methylation analysis of the frontal cortices of mutant Polg1 transgenic mice with neuronal accumulation of deleted mitochondrial DNA

Bipolar disorder (BD) is a severe psychiatric disorder characterized by repeated conflicting manic and depressive states. In addition to genetic factors, complex gene–environment interactions, which alter the epigenetic status in the brain, contribute to the etiology and pathophysiology of BD. Here, we performed a promoter-wide DNA methylation analysis of neurons and nonneurons derived from the frontal cortices of mutant Polg1 transgenic (n = 6) and wild-type mice (n = 6). The mutant mice expressed a proofreading-deficient mitochondrial DNA (mtDNA) polymerase under the neuron-specific CamK2a promoter and showed BD-like behavioral abnormalities, such as activity changes and altered circadian rhythms. We identified a total of 469 differentially methylated regions (DMRs), consisting of 267 neuronal and 202 nonneuronal DMRs. Gene ontology analysis of DMR-associated genes showed that cell cycle-, cell division-, and inhibition of peptide activity-related genes were enriched in neurons, whereas synapse- and GABA-related genes were enriched in nonneurons. Among the DMR-associated genes, Trim2 and Lrpprc showed an inverse relationship between DNA methylation and gene expression status. In addition, we observed that mutant Polg1 transgenic mice shared several features of DNA methylation changes in postmortem brains of patients with BD, such as dominant hypomethylation changes in neurons, which include hypomethylation of the molecular motor gene and altered DNA methylation of synapse-related genes in nonneurons. Taken together, the DMRs identified in this study will contribute to understanding the pathophysiology of BD from an epigenetic perspective.

Differences in mitochondrial DNA copy number between patients with bipolar I and II disorders

Mitochondria play a critical role in energy metabolism. Genetic, postmortem brain, and brain imaging studies of bipolar disorder (BD) patients indicated that mitochondrial dysfunction might explain BD pathophysiology. Mitochondrial function can be indirectly evaluated by measuring mitochondrial DNA (mtDNA) copy numbers. We recruited 186 bipolar I disorder (BD1) and 95 bipolar II disorder (BD2) patients, and age- and sex-matched controls. MtDNA copy numbers in peripheral blood cells were measured via quantitative polymerase chain reaction. We explored parameters (including age and clinical features) that might affect mtDNA copy numbers. We found that BD1 patients had a lower mtDNA copy number than controls and that mtDNA copy number was negatively associated with the number of mood episodes. BD2 patients had a higher mtDNA copy number than controls. Thus, changes in mitochondrial function may influence BD pathophysiology. The opposite directions of the association with mtDNA copy number in BD1 and BD2 patients suggests that the difference in pathophysiology may be associated with mitochondrial function.

Cardiovascular Involvement in mtDNA Disease: Diagnosis, Management, and Therapeutic Options

Mitochondrial diseases (MD) include an heterogenous group of systemic disorders caused by sporadic or inherited mutations in nuclear or mitochondrial DNA (mtDNA), causing impairment of oxidative phosphorylation system. Hypertrophic cardiomyopathy is the dominant pattern of cardiomyopathy in all forms of mtDNA disease, being observed in almost 40% of the patients. Dilated cardiomyopathy, left ventricular noncompaction, and conduction system disturbances have been also reported. In this article, the authors discuss the current clinical knowledge on MD, focusing on diagnosis and management of mitochondrial diseases caused by mtDNA mutations.

Mitochondrial Syndromes Revisited

In the last ten years, the knowledge of the genetic basis of mitochondrial diseases has significantly advanced. However, the vast phenotypic variability linked to mitochondrial disorders and the peculiar characteristics of their genetics make mitochondrial disorders a complex group of disorders. Although specific genetic alterations have been associated with some syndromic presentations, the genotype–phenotype relationship in mitochondrial disorders is complex (a single mutation can cause several clinical syndromes, while different genetic alterations can cause similar phenotypes). This review will revisit the most common syndromic pictures of mitochondrial disorders, from a clinical rather than a molecular perspective. We believe that the new phenotype definitions implemented by recent large multicenter studies, and revised here, may contribute to a more homogeneous patient categorization, which will be useful in future studies on natural history and clinical trials.

Cognitive functioning and mental health in mitochondrial disease: A systematic scoping review

Mitochondrial diseases (MDs) are rare, heterogeneous, hereditary and progressive in nature. In addition to the serious somatic symptoms, patients with MD also experience problems regarding their cognitive functioning and mental health. We provide an overview of all published studies reporting on any aspect of cognitive functioning and/or mental health in patients with MD and their relatives. A total of 58 research articles and 45 case studies were included and critically reviewed. Cognitive impairments in multiple domains were reported. Mental disorders were frequently reported, especially depression and anxiety. Furthermore, most studies showed impairments in self-reported psychological functioning and high prevalence of mental health problems in (matrilineal) relatives. The included studies showed heterogeneity regarding patient samples, measurement instruments and reference groups, making comparisons cautious. Results highlight a high prevalence of cognitive impairments and mental disorders in patients with MD. Recommendations for further research as well as tailored patientcare with standardized follow-up are provided. Key gaps in the literature are identified, of which studies on natural history are of highest importance.

Effects of psychoactive drugs on cellular bioenergetic pathways

OBJECTIVES

To investigate the actions of lithium, valproate, lamotrigine and quetiapine on bioenergetic pathways in cultured NT2-N neuronal-like cells and C8-B4 microglial cells.

METHODS

NT2-N and C8-B4 cells were cultured and treated with lithium (2.5 mM), valproate (0.5 mM), quetiapine (0.05 mM) or lamotrigine (0.05 mM) for 24 hours. Gene expression and the mitochondrial bioenergetic profile were measured in both cell lines.

RESULTS

In NT2-N cells, valproate increased oxidative phosphorylation (OXPHOS) gene expression, mitochondrial uncoupling and maximal respiratory capacity, while quetiapine decreased OXPHOS gene expression and respiration linked to ATP turnover, as well as decreasing the expression of genes in the citric acid cycle. Lamotrigine decreased OXPHOS gene expression but had no effect on respiration, while lithium reduced the expression of genes in the citric acid cycle. In C8-B4 cells, valproate and lithium increased OXPHOS gene expression, and valproate increased basal respiratory rate and maximal and spare respiratory capacities. In contrast, quetiapine significantly reduced basal respiratory rate and maximal and spare respiratory capacities.

CONCLUSIONS

Overall our data suggest that some drugs used to treat neuropsychiatric and affective disorders have actions on a range of cellular bioenergetic processes, which could impact their effects in patients.

Mitochondrial diseases: expanding the diagnosis in the era of genetic testing

Mitochondrial diseases are clinically and genetically heterogeneous. These diseases were initially described a little over three decades ago. Limited diagnostic tools created disease descriptions based on clinical, biochemical analytes, neuroimaging, and muscle biopsy findings. This diagnostic mechanism continued to evolve detection of inherited oxidative phosphorylation disorders and expanded discovery of mitochondrial physiology over the next two decades. Limited genetic testing hampered the definitive diagnostic identification and breadth of diseases. Over the last decade, the development and incorporation of massive parallel sequencing has identified approximately 300 genes involved in mitochondrial disease. Gene testing has enlarged our understanding of how genetic defects lead to cellular dysfunction and disease. These findings have expanded the understanding of how mechanisms of mitochondrial physiology can induce dysfunction and disease, but the complete collection of disease-causing gene variants remains incomplete. This article reviews the developments in disease gene discovery and the incorporation of gene findings with mitochondrial physiology. This understanding is critical to the development of targeted therapies.

Splice-Break: exploiting an RNA-seq splice junction algorithm to discover mitochondrial DNA deletion breakpoints and analyses of psychiatric disorders

Deletions in the 16.6 kb mitochondrial genome have been implicated in numerous disorders that often display muscular and/or neurological symptoms due to the high-energy demands of these tissues. We describe a catalogue of 4489 putative mitochondrial DNA (mtDNA) deletions, including their frequency and relative read rate, using a combinatorial approach of mitochondria-targeted PCR, next-generation sequencing, bioinformatics, post-hoc filtering, annotation, and validation steps. Our bioinformatics pipeline uses MapSplice, an RNA-seq splice junction detection algorithm, to detect and quantify mtDNA deletion breakpoints rather than mRNA splices. Analyses of 93 samples from postmortem brain and blood found (i) the 4977 bp ‘common deletion’ was neither the most frequent deletion nor the most abundant; (ii) brain contained significantly more deletions than blood; (iii) many high frequency deletions were previously reported in MitoBreak, suggesting they are present at low levels in metabolically active tissues and are not exclusive to individuals with diagnosed mitochondrial pathologies; (iv) many individual deletions (and cumulative metrics) had significant and positive correlations with age and (v) the highest deletion burdens were observed in major depressive disorder brain, at levels greater than Kearns–Sayre Syndrome muscle. Collectively, these data suggest the Splice-Break pipeline can detect and quantify mtDNA deletions at a high level of resolution.

Genotypes of chronic progressive external ophthalmoplegia in a large adult-onset cohort

Chronic progressive external ophthalmoplegia (CPEO) is a common presentation of mitochondrial disease. We performed a retrospective evaluation of the molecular genetic testing and genotype-phenotype correlations in a large cohort of adult-onset CPEO patients (N = 111). One hundred percent of patients tested had at least one mitochondrial DNA (mtDNA) deletion. Genetic testing of nuclear genes encoding mitochondrial proteins identified pathogenic/likely pathogenic variants likely to be associated with CPEO in 7.6% of patients. As expected, the nuclear gene most associated with DNA variation was POLG. A single likely pathogenic mitochondrial DNA variant (m.12278T>C) was identified in two unrelated patients. No significant differences were noted in the clinical phenotypes of patients with pathogenic or likely pathogenic nuclear variants in comparison to those with negative nuclear gene testing. Analysis of deletion size and heteroplasmy in muscle-derived mtDNA showed significant correlations with age of symptom onset but not disease severity (number of canonical CPEO features). Results suggest that smaller mtDNA deletions (p = 0.0127, r² = 0.1201) and higher heteroplasmy of single mtDNA deletions (p = 0.0112, r² = 0.2483) are associated with an earlier age of onset in CPEO patients.

Chronic Progressive External Ophthalmoplegia and Bilateral Vestibular Hypofunction: Balance, Gait, and Eye Movement Before and After Multimodal Chiropractic Care: A Case Study

Objective

The purpose of this report is to describe care of a patient with chronic progressive external ophthalmoplegia and bilateral vestibular hypofunction.

Clinical Features

A 66-year-old patient presented with limited eye movement and mild ptosis, which led to a diagnosis of chronic progressive external ophthalmoplegia. Rotary chair testing suggested vestibular involvement. Other symptoms included dizziness, problems with balance, and chronic stiffness in his cervical and thoracic regions. He had anxiety about loss of function and limited exercise habits because of fear of falling. Examination methods included balance assessment, kinetic aspects of walking, and videonystagmography.

Intervention and Outcome

He had already begun regular practice of vestibular rehabilitation exercises before receiving 18 sessions of manual and instrument-assisted chiropractic manipulation, along with mobilization, stretching, and transverse massage, over 37 weeks. In addition to self-reported improvements, there was substantially decreased postural sway during balance assessment and there were small improvements in eye movement, ptosis, and walking.

Conclusion

This patient showed improvements in balance, eye movements, and walking while undergoing multimodal chiropractic care and practicing eye and balance exercises.

What Can Mitochondrial DNA Analysis Tell Us About Mood Disorders?

Variants in mitochondrial DNA (mtDNA) and nuclear genes encoding mitochondrial proteins in bipolar disorder, depression, or other psychiatric disorders have been studied for decades, since mitochondrial dysfunction was first suggested in the brains of patients with these diseases. Candidate gene association studies initially resulted in findings compatible with the mitochondrial dysfunction hypothesis. Many of those studies, however, were conducted with modest sample sizes (N < 1000), which could cause false positive findings. Furthermore, the DNA samples examined in these studies, including genome-wide association studies, were generally derived from peripheral tissues. One key unanswered question is whether there is an association between mood disorders and somatic mtDNA mutations (deletions and point mutations) in brain regions that accumulate a high amount of mtDNA mutations and/or are involved in the regulation of mood. Two lines of robust evidence supporting the importance of mtDNA mutations in brain tissues for mood disorders have come from clinical observation of mitochondrial disease patients who carry primary mtDNA mutations or accumulate secondary mtDNA mutations due to nuclear mutations and an animal model study. More than half of mitochondrial disease patients have comorbid mood disorders, and mice with neuron-specific accumulation of mtDNA mutations show spontaneous depression-like episodes. In this review, we first summarize the current knowledge of mtDNA and its genetics and discuss what mtDNA analysis tells us about neuropsychiatric disorders based on an example of Parkinson's disease. We also discuss challenges and future directions beyond mtDNA analysis toward an understanding of the pathophysiology of "idiopathic" mood disorders.

Enrichment of deleterious variants of mitochondrial DNA polymerase gene (POLG1) in bipolar disorder

AIM

Rare missense variants, which likely account for a substantial portion of the genetic 'dark matter' for a common complex disease, are challenging because the impacts of variants on disease development are difficult to substantiate. This study aimed to examine the impacts of amino acid substitution variants in the POLG1 found in bipolar disorder, as an example and proof of concept, in three different modalities of assessment: in silico predictions, in vitro biochemical assays, and clinical evaluation. We then tested whether deleterious variants in POLG1 contributed to the genetics of bipolar disorder.

METHODS

We searched for variants in the POLG1 gene in 796 Japanese patients with bipolar disorder and 767 controls and comprehensively investigated all 23 identified variants in the three modalities of assessment. POLG1 encodes mitochondrial DNA polymerase and is one of the causative genes for a Mendelian-inheritance mitochondrial disease, which is occasionally accompanied by mood disorders. The healthy control data from the Tohoku Medical Megabank Organization were also employed.

RESULTS

Although the frequency of carriers of deleterious variants varied from one method to another, every assessment achieved the same conclusion that deleterious POLG1 variants were significantly enriched in the variants identified in patients with bipolar disorder compared to those in controls.

CONCLUSION

Together with mitochondrial dysfunction in bipolar disorder, the present results suggested deleterious POLG1 variants as a credible risk for the multifactorial disease.

Depression-like episodes in mice harboring mtDNA deletions in paraventricular thalamus

Depression is a common debilitating human disease whose etiology has defied decades of research. A critical bottleneck is the difficulty in modeling depressive episodes in animals. Here, we show that a transgenic mouse with chronic forebrain expression of a dominant negative mutant of Polg1, a mitochondrial DNA (mtDNA) polymerase, exhibits lethargic behavioral changes, which are associated with emotional, vegetative and psychomotor disturbances, and response to antidepression drug treatment. The results suggested a symptomatic similarity between the lethargic behavioral change that was recurrently and spontaneously experienced by the mutant mice and major depressive episode as defined by DSM-5. A comprehensive screen of mutant brain revealed a hotspot for mtDNA deletions and mitochondrial dysfunction in the paraventricular thalamic nucleus (PVT) with similar defects observed in postmortem brains of patients with mitochondrial disease with mood symptoms. Remarkably, the genetic inhibition of PVT synaptic output by Cre-loxP-dependent expression of tetanus toxin triggered de novo depression-like episodes. These findings identify a novel preclinical mouse model and brain area for major depressive episodes with mitochondrial dysfunction as its cellular mechanism.

Effect of L-carnitine on exercise performance in patients with mitochondrial myopathy

Exercise intolerance due to impaired oxidative metabolism is a prominent symptom in patients with mitochondrial myopathy (MM), but it is still uncertain whether L-carnitine supplementation is beneficial for patients with MM. The aim of our study was to investigate the effects of L-carnitine on exercise performance in MM. Twelve MM subjects (mean age±SD=35.4±10.8 years) with chronic progressive external ophthalmoplegia (CPEO) were first compared to 10 healthy controls (mean age±SD=29±7.8 years) before they were randomly assigned to receive L-carnitine supplementation (3 g/daily) or placebo in a double-blind crossover design. Clinical status, body composition, respiratory function tests, peripheral muscle strength (isokinetic and isometric torque) and cardiopulmonary exercise tests (incremental to peak exercise and at 70% of maximal), constant work rate (CWR) exercise test, to the limit of tolerance [Tlim]) were assessed after 2 months of L-carnitine/placebo administration. Patients with MM presented with lower mean height, total body weight, fat-free mass, and peripheral muscle strength compared to controls in the pre-test evaluation. After L-carnitine supplementation, the patients with MM significantly improved their Tlim (14±1.9 vs 11±1.4 min) and oxygen consumption (V˙O2) at CWR exercise, both at isotime (1151±115 vs 1049±104 mL/min) and at Tlim (1223±114 vs 1060±108 mL/min). These results indicate that L-carnitine supplementation may improve aerobic capacity and exercise tolerance during high-intensity CWRs in MM patients with CPEO.

Heterozygous Polg mutation causes motor dysfunction due to mtDNA deletions

Objective

Mutations in nuclear-encoded mitochondrial DNA (mtDNA) polymerase (POLG) are known to cause autosomal dominant chronic progressive external ophthalmoplegia (adCPEO) with accumulation of multiple mtDNA deletions in muscles. However, no animal model with a heterozygous Polg mutation representing mtDNA impairment and symptoms of CPEO has been established. To understand the pathogenic mechanism of CPEO, it is important to determine the age dependency and tissue specificity of mtDNA impairment resulting from a heterozygous mutation in the Polg gene in an animal model.

Methods

We assessed behavioral phenotypes, tissue-specific accumulation of mtDNA deletions, and its age dependency in heterozygous Polg^D257A knock-in mice carrying a proofreading-deficient mutation in the Polg.

Results

Heterozygous Polg^D257A knock-in mice exhibited motor dysfunction in a rotarod test. Polg^+/D257A mice had significant accumulation of multiple mtDNA deletions, but did not show significant accumulation of point mutations or mtDNA depletion in the brain. While mtDNA deletions increased in an age-dependent manner regardless of the tissue even in Polg^+/+ mice, the age-dependent accumulation of mtDNA deletions was enhanced in muscles and in the brain of Polg^+/D257A mice.

Interpretation

Heterozygous Polg^D257A knock-in mice showed tissue-specific, age-dependent accumulation of multiple mtDNA deletions in muscles and the brain which was likely to result in neuromuscular symptoms. Polg^+/D257A mice may be used as an animal model of adCPEO associated with impaired mtDNA maintenance.

A mitochondrial bioenergetic basis of depression

Major depressive disorder (MDD) is an important public health problem affecting 350 million people worldwide. After decades of study, the pathophysiology of MDD remains elusive, resulting in treatments that are only 30-60% effective. This review summarizes the emerging evidence that implicates impaired mitochondrial bioenergetics as a basis for MDD. It is suggested that impaired mitochondrial bioenergetic function contributes to the pathophysiology of MDD via several potential pathways including: genetics/genomics, inflammation, oxidative stress, and alterations in neuroplasticity. A discussion of mitochondrial bioenergetic pathways that lead to MDD is provided. Evidence is reviewed regarding the mito-toxic or mito-protective impact of various antidepressant medications currently in use. Opportunities for further research on novel therapeutic approaches, including mitochondrial modulators, as stand-alone or adjunct therapy for reducing depression are suggested. In conclusion, while there is substantial evidence linking mitochondrial bioenergetics and MDD, there are currently no clear mitochondrial phenotypes or biomarkers to use as guides in targeting therapies beyond individuals with MDD and known mitochondrial disorders toward the general population of individuals with MDD. Further study is needed to develop these phenotypes and biomarkers, to identify therapeutic targets, and to test therapies aimed at improving mitochondrial function in individuals whose MDD is to some extent symptomatic of impaired mitochondrial bioenergetics.

Twinkle mutation in an Italian family with external progressive ophthalmoplegia and parkinsonism: a case report and an update on the state of art

The objective is to describe the clinical phenotype and genetic basis of a family with autosomal dominant progressive external ophthalmoplegia and parkinsonism with a Twinkle mutation. The proband, an 82 years old female, reported since childhood bilateral eyelid ptosis, ophthalmoplegia, sensorineural hypoacusis, mild depression since she was 45, with a positive familiar anamnesis of eyelid ptosis (father, two sisters and a son). She developed mild bilateral parkinsonism with a moderate clinical response to levodopa. The (123)I-FP-CIT SCAN evidenced a marked bilateral putaminal reduction and moderate caudate uptake reduction. Her 79 years old sister reported eyelid ptosis since she was 45 with ophthalmoplegia and developed a mild bilateral rest and postural tremor with moderate right arm plastic hypertonia when she was 76. The parkinsonism was confirmed with (123)I-FP-CIT SCAN. One of the two sons presented eyelid ptosis since he was 30 years old, with peripheral neuropathy with biopsy evidence of myopathy. We identified a G1750A mutation in the c10orf2 gene in the three patients. Mitochondrial dysfunction has been implicated in the pathogenesis of sporadic, idiopathic Parkinson disease (PD). In some cases, mitochondrial DNA primary genetic abnormalities or more commonly secondary rearrangements due to polymerase gamma (POLG) gene mutation can directly cause parkinsonism. Parkinsonism has been reported as a rare symptom associated to Twinkle (c10orf2). Parkinsonism has to be investigated in patients with PEO with analysis of Twinkle mutation.

Mutations in human DNA polymerase γ confer unique mechanisms of catalytic deficiency that mirror the disease severity in mitochondrial disorder patients

Human mitochondrial DNA polymerase γ (pol γ) is solely responsible for the replication and repair of the mitochondrial genome. Unsurprisingly, alterations in pol γ activity have been associated with mitochondrial diseases such as Alpers syndrome and progressive external ophthalmoplegia. Thus far, predicting the severity of mitochondrial disease based the magnitude of deficiency in pol γ activity has been difficult. In order to understand the relationship between disease severity in patients and enzymatic defects in vitro, we characterized the molecular mechanisms of four pol γ mutations, A957P, A957S, R1096C and R1096H, which have been found in patients suffering from aggressive Alpers syndrome to mild progressive external ophthalmoplegia. The A957P mutant showed the most striking deficiencies in the incorporation efficiency of a correct deoxyribonucleotide triphosphate (dNTP) relative to wild-type pol γ, with less, but still significant incorporation efficiency defects seen in R1096H and R1096C, and only a small decrease in incorporation efficiency observed for A957S. Importantly, this trend matches the disease severity observed in patients very well (approximated as A957P ≫ R1096C ≥ R1096H ≫ A957S, from most severe disease to least severe). Further, the A957P mutation conferred a two orders of magnitude loss of fidelity relative to wild-type pol γ, indicating that a buildup of mitochondrial genomic mutations may contribute to the death in infancy seen with these patients. We conclude that characterizing the unique molecular mechanisms of pol γ deficiency for physiologically important mutant enzymes is important for understanding mitochondrial disease and for predicting disease severity.

Impaired mitochondrial function in psychiatric disorders

Major psychiatric illnesses such as mood disorders and schizophrenia are chronic, recurrent mental illnesses that affect the lives of millions of individuals. Although these disorders have traditionally been viewed as 'neurochemical diseases', it is now clear that they are associated with impairments of synaptic plasticity and cellular resilience. Although most patients with these disorders do not have classic mitochondrial disorders, there is a growing body of evidence to suggest that impaired mitochondrial function may affect key cellular processes, thereby altering synaptic functioning and contributing to the atrophic changes that underlie the deteriorating long-term course of these illnesses. Enhancing mitochondrial function could represent an important avenue for the development of novel therapeutics and also presents an opportunity for a potentially more efficient drug-development process.