Elevated mitochondrial DNA copy number in peripheral blood cells is associated with childhood autism

Biomarkers of mitochondrial dysfunction in autism spectrum disorder: A systematic review and meta-analysis

Autism spectrum disorder (ASD) is a neurodevelopmental disorder affecting 1 in 36 children and is associated with physiological abnormalities, most notably mitochondrial dysfunction, at least in a subset of individuals. This systematic review and meta-analysis discovered 204 relevant articles which evaluated biomarkers of mitochondrial dysfunction in ASD individuals. Significant elevations (all p < 0.01) in the prevalence of lactate (17%), pyruvate (41%), alanine (15%) and creatine kinase (9%) were found in ASD. Individuals with ASD had significant differences (all p < 0.01) with moderate to large effect sizes (Cohen's d' ≥ 0.6) compared to controls in mean pyruvate, lactate-to-pyruvate ratio, ATP, and creatine kinase. Some studies found abnormal TCA cycle metabolites associated with ASD. Thirteen controlled studies reported mitochondrial DNA (mtDNA) deletions or variations in the ASD group in blood, peripheral blood mononuclear cells, lymphocytes, leucocytes, granulocytes, and brain. Meta-analyses discovered significant differences (p < 0.01) in copy number of mtDNA overall and in ND1, ND4 and CytB genes. Four studies linked specific mtDNA haplogroups to ASD. A series of studies found a subgroup of ASD with elevated mitochondrial respiration which was associated with increased sensitivity of the mitochondria to physiological stressors and neurodevelopmental regression. Lactate, pyruvate, lactate-to-pyruvate ratio, carnitine, and acyl-carnitines were associated with clinical features such as delays in language, social interaction, cognition, motor skills, and with repetitive behaviors and gastrointestinal symptoms, although not all studies found an association. Lactate, carnitine, acyl-carnitines, ATP, CoQ10, as well as mtDNA variants, heteroplasmy, haplogroups and copy number were associated with ASD severity. Variability was found across biomarker studies primarily due to differences in collection and processing techniques as well as the intrinsic heterogeneity of the ASD population. Several studies reported alterations in mitochondrial metabolism in mothers of children with ASD and in neonates who develop ASD. Treatments targeting mitochondria, particularly carnitine and ubiquinol, appear beneficial in ASD. The link between mitochondrial dysfunction in ASD and common physiological abnormalities in individuals with ASD including gastrointestinal disorders, oxidative stress, and immune dysfunction is outlined. Several subtypes of mitochondrial dysfunction in ASD are discussed, including one related to neurodevelopmental regression, another related to alterations in microbiome metabolites, and another related to elevations in acyl-carnitines. Mechanisms linking abnormal mitochondrial function with alterations in prenatal brain development and postnatal brain function are outlined. Given the multisystem complexity of some individuals with ASD, this review presents evidence for the mitochondria being central to ASD by contributing to abnormalities in brain development, cognition, and comorbidities such as immune and gastrointestinal dysfunction as well as neurodevelopmental regression. A diagnostic approach to identify mitochondrial dysfunction in ASD is outlined. From this evidence, it is clear that many individuals with ASD have alterations in mitochondrial function which may need to be addressed in order to achieve optimal clinical outcomes. The fact that alterations in mitochondrial metabolism may be found during pregnancy and early in the life of individuals who eventually develop ASD provides promise for early life predictive biomarkers of ASD. Further studies may improve the understanding of the role of the mitochondria in ASD by better defining subgroups and understanding the molecular mechanisms driving some of the unique changes found in mitochondrial function in those with ASD.

Developmental Dyslexia: Insights from EEG-Based Findings and Molecular Signatures-A Pilot Study

Developmental dyslexia (DD) is a learning disorder. Although risk genes have been identified, environmental factors, and particularly stress arising from constant difficulties, have been associated with the occurrence of DD by affecting brain plasticity and function, especially during critical neurodevelopmental stages. In this work, electroencephalogram (EEG) findings were coupled with the genetic and epigenetic molecular signatures of individuals with DD and matched controls. Specifically, we investigated the genetic and epigenetic correlates of key stress-associated genes (NR3C1, NR3C2, FKBP5, GILZ, SLC6A4) with psychological characteristics (depression, anxiety, and stress) often included in DD diagnostic criteria, as well as with brain EEG findings. We paired the observed brain rhythms with the expression levels of stress-related genes, investigated the epigenetic profile of the stress regulator glucocorticoid receptor (GR) and correlated such indices with demographic findings. This study presents a new interdisciplinary approach and findings that support the idea that stress, attributed to the demands of the school environment, may act as a contributing factor in the occurrence of the DD phenotype.

Mitochondrial DNA copy number in autism spectrum disorder and attention deficit hyperactivity disorder: a systematic review and meta-analysis

Background

Several reports suggest that altered mitochondrial DNA copy number (mtDNA-cn), a common biomarker for aberrant mitochondrial function, is implicated in autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), but the results are still elusive.

Methods

A meta-analysis was performed to summarize the current indication and to provide a more precise assessment of the mtDNA-cn in ASD and ADHD. A search in the MEDLINE-PubMed, Scopus, and EMBASE databases was done to identify related studies up to the end of February 2023. The meta-analysis was conducted according to recommendations of the Cochrane Handbook of Systematic Reviews.

Results

Fourteen studies involving 666 cases with ASD and ADHD and 585 controls were collected and judged relevant for the systematic review and meta-analysis. The pooled results by a random effects meta-analysis was reported as a geometric mean of the estimated average response ratio and 95% confidence interval. Overall analysis of studies reported differences in mtDNA-cn in blood samples (k = 10) and non-blood samples (brain tissues and oral samples; k = 4) suggested significantly higher mtDNA-cn in patients compared to controls (p = 0.0275). Sub-analysis by stratifying studies based on tissue type, showed no significant increase in mtDNA-cn in blood samples among patients and controls (p = 0.284). Conversely, higher mtDNA-cn was observed in non-blood samples in patients than in controls (p = 0.0122). Further stratified analysis based on blood-cell compositions as potential confounds showed no significant difference in mtDNA-cn in peripheral blood samples of patients comparted to controls (p = 0.074). In addition, stratified analysis of aged-matched ASD and ADHD patients and controls revealed no significant difference in mtDNA-cn in blood samples between patients and controls (p = 0.214), whereas a significant increase in mtDNA-cn was observed in non-blood samples between patients and controls (p < 0.001). Finally, when the mtDNA-cn was analyzed in blood samples of aged-matched patients with ASD (peripheral blood, leukocytes, and PBMCs) or ADHD (peripheral blood), no significant difference in mtDNA-cn was observed between ASD patients and controls (p = 0.385), while a significant increase in mtDNA-cn was found between ADHD patients and controls (p = 0.033).

Conclusion

In this first meta-analysis of the evaluation of mtDNA-cn in ASD/ADHD, our results show elevated mtDNA-cn in ASD and ADHD, further emphasizing the implication of mitochondrial dysfunction in neurodevelopmental disorders. However, our results indicate that the mtDNA-cn in blood is not reflected in other tissues in ASD/ADHD, and the true relationship between blood-derived mtDNA-cn and ASD/ADHD remains to be defined in future studies. The importance of blood-cell compositions as confounders of blood-based mtDNA-cn measurement and the advantages of salivary mtDNA-cn should be considered in future studies. Moreover, the potential of mtDNA-cn as a biomarker for mitochondrial malfunction in neurodevelopmental disorders deserves further investigations.

The Interplay between Dysregulated Metabolism and Epigenetics in Cancer

Cellular metabolism (or energetics) and epigenetics are tightly coupled cellular processes. It is arguable that of all the described cancer hallmarks, dysregulated cellular energetics and epigenetics are the most tightly coregulated. Cellular metabolic states regulate and drive epigenetic changes while also being capable of influencing, if not driving, epigenetic reprogramming. Conversely, epigenetic changes can drive altered and compensatory metabolic states. Cancer cells meticulously modify and control each of these two linked cellular processes in order to maintain their tumorigenic potential and capacity. This review aims to explore the interplay between these two processes and discuss how each affects the other, driving and enhancing tumorigenic states in certain contexts.

Mitochondrial dysfunction in cognitive neurodevelopmental disorders: Cause or effect?

Mitochondria have a crucial role in brain development and neurogenesis, both in embryonic and adult brains. Since the brain is the highest energy consuming organ, it is highly vulnerable to mitochondrial dysfunction. This has been implicated in a range of brain disorders including, neurodevelopmental conditions, psychiatric illnesses, and neurodegenerative diseases. Genetic variations in mitochondrial DNA (mtDNA), and nuclear DNA encoding mitochondrial proteins, have been associated with several cognitive disorders. However, it is not yet clear whether mitochondrial dysfunction is a primary cause of these conditions or a secondary effect. Our review article deals with this topic, and brings out recent advances in mitochondria-oriented therapies. Mitochondrial dysfunction could be involved in the pathogenesis of a subset of disorders involving cognitive impairment. In these patients, mitochondrial dysfunction could be the cause of the condition, rather than the consequence. There are vast areas in this topic that remains to be explored and elucidated.

Evidence for parent-of-origin effects in autism spectrum disorder: a narrative review

Autism spectrum disorder (ASD) is a heterogeneous group of early-onset neurodevelopmental disorders known to be highly heritable with a complex genetic architecture. Abnormal brain developmental trajectories that impact synaptic functioning, excitation-inhibition balance and brain connectivity are now understood to play a central role in ASD. Ongoing efforts to identify the genetic underpinnings still prove challenging, in part due to phenotypic and genetic heterogeneity.This review focuses on parent-of-origin effects (POEs), where the phenotypic effect of an allele depends on its parental origin. POEs include genomic imprinting, transgenerational effects, mitochondrial DNA, sex chromosomes and mutational transmission bias. The motivation for investigating these mechanisms in ASD has been driven by their known impacts on early brain development and brain functioning, in particular for the most well-documented POE, genomic imprinting. Moreover, imprinting is implicated in syndromes such as Angelman and Prader-Willi, which frequently share comorbid symptoms with ASD. In addition to other regions in the genome, this comprehensive review highlights the 15q11-q13 and 7q chromosomal regions as well as the mitochondrial DNA as harbouring the majority of currently identified POEs in ASD.

A molecular framework for autistic experiences: Mitochondrial allostatic load as a mediator between autism and psychopathology

Molecular autism research is evolving toward a biopsychosocial framework that is more informed by autistic experiences. In this context, research aims are moving away from correcting external autistic behaviors and toward alleviating internal distress. Autism Spectrum Conditions (ASCs) are associated with high rates of depression, suicidality and other comorbid psychopathologies, but this relationship is poorly understood. Here, we integrate emerging characterizations of internal autistic experiences within a molecular framework to yield insight into the prevalence of psychopathology in ASC. We demonstrate that descriptions of social camouflaging and autistic burnout resonate closely with the accepted definitions for early life stress (ELS) and chronic adolescent stress (CAS). We propose that social camouflaging could be considered a distinct form of CAS that contributes to allostatic overload, culminating in a pathophysiological state that is experienced as autistic burnout. Autistic burnout is thought to contribute to psychopathology via psychological and physiological mechanisms, but these remain largely unexplored by molecular researchers. Building on converging fields in molecular neuroscience, we discuss the substantial evidence implicating mitochondrial dysfunction in ASC to propose a novel role for mitochondrial allostatic load in the relationship between autism and psychopathology. An interplay between mitochondrial, neuroimmune and neuroendocrine signaling is increasingly implicated in stress-related psychopathologies, and these molecular players are also associated with neurodevelopmental, neurophysiological and neurochemical aspects of ASC. Together, this suggests an increased exposure and underlying molecular susceptibility to ELS that increases the risk of psychopathology in ASC. This article describes an integrative framework shaped by autistic experiences that highlights novel avenues for molecular research into mechanisms that directly affect the quality of life and wellbeing of autistic individuals. Moreover, this framework emphasizes the need for increased access to diagnoses, accommodations, and resources to improve mental health outcomes in autism.

Dissecting the multifaceted contribution of the mitochondrial genome to autism spectrum disorder

Autism spectrum disorder (ASD) is a clinically heterogeneous class of neurodevelopmental conditions with a strong, albeit complex, genetic basis. The genetic architecture of ASD includes different genetic models, from monogenic transmission at one end, to polygenic risk given by thousands of common variants with small effects at the other end. The mitochondrial DNA (mtDNA) was also proposed as a genetic modifier for ASD, mostly focusing on maternal mtDNA, since the paternal mitogenome is not transmitted to offspring. We extensively studied the potential contribution of mtDNA in ASD pathogenesis and risk through deep next generation sequencing and quantitative PCR in a cohort of 98 families. While the maternally-inherited mtDNA did not seem to predispose to ASD, neither for haplogroups nor for the presence of pathogenic mutations, an unexpected influence of paternal mtDNA, apparently centered on haplogroup U, came from the Italian families extrapolated from the test cohort (n = 74) when compared to the control population. However, this result was not replicated in an independent Italian cohort of 127 families and it is likely due to the elevated paternal age at time of conception. In addition, ASD probands showed a reduced mtDNA content when compared to their unaffected siblings. Multivariable regression analyses indicated that variants with 15%-5% heteroplasmy in probands are associated to a greater severity of ASD based on ADOS-2 criteria, whereas paternal super-haplogroups H and JT were associated with milder phenotypes. In conclusion, our results suggest that the mtDNA impacts on ASD, significantly modifying the phenotypic expression in the Italian population. The unexpected finding of protection induced by paternal mitogenome in term of severity may derive from a role of mtDNA in influencing the accumulation of nuclear de novo mutations or epigenetic alterations in fathers' germinal cells, affecting the neurodevelopment in the offspring. This result remains preliminary and needs further confirmation in independent cohorts of larger size. If confirmed, it potentially opens a different perspective on how paternal non-inherited mtDNA may predispose or modulate other complex diseases.

Association of mitochondrial DNA content, heteroplasmies and inter-generational transmission with autism

Mitochondria are essential for brain development. While previous studies linked dysfunctional mitochondria with autism spectrum disorder (ASD), the role of the mitochondrial genome (mtDNA) in ASD risk is largely unexplored. This study investigates the association of mtDNA heteroplasmies (co-existence of mutated and unmutated mtDNA) and content with ASD, as well as its inter-generational transmission and sex differences among two independent samples: a family-based study (n = 1,938 families with parents, probands and sibling controls) and a prospective birth cohort (n = 997 mother-child pairs). In both samples, predicted pathogenic (PP) heteroplasmies in children are associated with ASD risk (Meta-OR = 1.56, P = 0.00068). Inter-generational transmission of mtDNA reveals attenuated effects of purifying selection on maternal heteroplasmies in children with ASD relative to controls, particularly among males. Among children with ASD and PP heteroplasmies, increased mtDNA content shows benefits for cognition, communication, and behaviors (P ≤ 0.02). These results underscore the value of exploring maternal and newborn mtDNA in ASD.

Most genetic studies of autism spectrum disorder (ASD) have focused on the nuclear genome. Here, the authors show that variations in mitochondrial DNA, detectable at birth, are also associated with risk of ASD.

Mitochondrial DNA Copy Number in Rett Syndrome Caused by Methyl-CpG-Binding Protein-2 Variants

OBJECTIVE

To determine changes in mitochondrial DNA (mtDNA) copy number in peripheral blood in Rett syndrome caused by methyl-CpG-binding protein-2 (MECP2) variants and explore the mechanism of mitochondrial dysfunction in Rett syndrome.

STUDY DESIGN

Female patients who were diagnosed with Rett syndrome and had an MECP2 variant (n = 142) were recruited in this study, along with the same number of age- and sex-matched healthy controls. MtDNA copy number was quantified by real-time quantitative polymerase chain reaction with TaqMan probes. The differences in mtDNA copy number between the Rett syndrome group and the control group were analyzed using the independent-samples t test. Linear regression, biserial correlation analysis, and one-way ANOVA were applied for the correlations between mtDNA copy number and age, clinical severity, variant types, functional domains, and hot-spot variants.

RESULTS

MtDNA copy number was found to be significantly increased in the patients with Rett syndrome with MECP2 gene variants compared with the control subjects. Age, clinical severity, variant types, functional domains, and hot-spot variants were not related to mtDNA copy number in patients with Rett syndrome.

CONCLUSIONS

MtDNA copy number is increased significantly in patients with Rett syndrome, suggesting that changes in mitochondrial function in Rett syndrome trigger a compensatory increase in mtDNA copy number and providing new possibilities for treating Rett syndrome, such as mitochondria-targeted therapies.

The serotonin reuptake transporter modulates mitochondrial copy number and mitochondrial respiratory complex gene expression in the frontal cortex and cerebellum in a sexually dimorphic manner

Neuropsychiatric and neurodevelopmental disorders such as major depressive disorder (MDD) and autism spectrum disorder (ASD) are complex conditions attributed to both genetic and environmental factors. There is a growing body of evidence showing that serotonergic signaling and mitochondrial dysfunction contribute to the pathophysiology of these disorders and are linked as signaling through specific serotonin (5-HT) receptors drives mitochondrial biogenesis. The serotonin transporter (SERT) is important in these disorders as it regulates synaptic serotonin and therapeutically is the target of selective serotonin reuptake inhibitors which are a major class of anti-depressant drug. Human allelic variants of the serotonin transporter-linked polymorphic region (5-HTTLPR) such as the S/S variant, are associated with reduced SERT expression and increased susceptibility for developing neuropsychiatric disorders. Using a rat model that is haploinsufficient for SERT and displays reduced SERT expression similar to the human S/S variant, we demonstrate that reduced SERT expression modulates mitochondrial copy number and expression of respiratory chain electron transfer components in the brain. In the frontal cortex, genotype-related trends were opposing for males and females, such that reduced SERT expression led to increased expression of the Complex I subunit mt-Nd1 in males but reduced expression in females. Our findings suggest that SERT expression and serotonergic signaling have a role in regulating mitochondrial biogenesis and adenosine triphosphate (ATP) production in the brain. We speculate that the sexual dimorphism in mitochondrial abundance and gene expression contributes to the sex bias found in the incidence of neuropsychiatric disorders such as MDD and ASD.

Decreased mitochondrial DNA copy number in nerve cells and the hippocampus during nicotine exposure is mediated by autophagy

Cigarette smoke is a harmful air pollutant and nicotine dependence is the essential cause of the tobacco epidemic. Since mitochondrial abnormalities are associated with substance addiction, in this work we used mitochondrial DNA (mtDNA) copy number as an indicator of mitochondrial function to investigate whether nicotine addicts also exhibit mitochondrial abnormalities. We found significantly lower mtDNA copy number in the peripheral blood of healthy nicotine addicts than in non-smokers, indicating that long-term nicotine exposure through smoking has detrimental effects on mitochondria. We also examined the effects of nicotine on mtDNA levels in a rat conditioned place preference (CPP) model of addiction and in cultured neuron cells, which revealed that the mtDNA copy number was significantly reduced in the hippocampus of CPP rats, in human neuroblastoma SH-SY5Y cells, and in rat pheochromocytoma PC12 cells, suggesting that significantly reduced mtDNA copy number is a potential biomarker of nicotine addiction. In SH-SY5Y cells, nicotine treatment induced several mitochondrial defects, such as increased mtDNA damage, increased reactive oxygen species (ROS) levels, decreased mitochondrial membrane potential (△Ψm), and stimulation of autophagic flux via transcriptional up-regulation of several autophagy-related genes and elevated marker protein accumulation, although genes controlling mtDNA replication were unaffected. In addition, pretreatment with the autophagy inhibitor Bafilomycin A1 led to accumulation of microtubule-associated protein 1 light chain 3b-II (LC3B-II) and counteracted the nicotine-induced decrease in mtDNA copy number. These results were recapitulated in PC12 cells, which also showed significant down-regulation of the marker SQSTM1/P62, suggesting that the decrease in mtDNA copy number is mediated by autophagy. This study shows that prolonged nicotine exposure, such as that in nicotine addicts, leads to a decrease of mtDNA copy number in neurons due to enhanced induction of autophagy. CAPSULE: It was found that smoking or nicotine exposure decreased mtDNA copy number based on population, animal, and cell models, and these effects appear to be mediated by autophagy.

Inflammation and Mitochondrial Dysfunction in Autism Spectrum Disorder

Autism Spectrum Disorders (ASD) is a severe childhood psychiatric condition with an array of cognitive, language and social impairments that can significantly impact family life. ASD is classically characterized by reduced communication skills and social interactions, with limitations imposed by repetitive patterns of behavior, interests, and activities. The pathophysiology of ASD is thought to arise from complex interactions between environmental and genetic factors within the context of individual development. A growing body of research has raised the possibility of identifying the aetiological causes of the disorder. This review highlights the roles of immune-inflammatory pathways, nitro-oxidative stress and mitochondrial dysfunctions in ASD pathogenesis and symptom severity. The role of NK-cells, T helper, T regulatory and B-cells, coupled with increased inflammatory cytokines, lowered levels of immune-regulatory cytokines, and increased autoantibodies and microglial activation is elucidated. It is proposed that alterations in mitochondrial activity and nitrooxidative stress are intimately associated with activated immune-inflammatory pathways. Future research should determine as to whether the mitochondria, immune-inflammatory activity and nitrooxidative stress changes in ASD affect the development of amygdala-frontal cortex interactions. A number of treatment implications may arise, including prevention-orientated prenatal interventions, treatment of pregnant women with vitamin D, and sodium butyrate. Treatments of ASD children and adults with probiotics, sodium butyrate and butyrate-inducing diets, antipurinergic therapy with suramin, melatonin, oxytocin and taurine are also discussed.

DNA Methylation of PGC-1α Is Associated With Elevated mtDNA Copy Number and Altered Urinary Metabolites in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex disorder that is underpinned by numerous dysregulated biological pathways, including pathways that affect mitochondrial function. Epigenetic mechanisms contribute to this dysregulation and DNA methylation is an important factor in the etiology of ASD. We measured DNA methylation of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), as well as five genes involved in regulating mitochondrial homeostasis to examine mitochondrial dysfunction in an ASD cohort of South African children. Using targeted Next Generation bisulfite sequencing, we found differential methylation (p < 0.05) at six key genes converging on mitochondrial biogenesis, fission and fusion in ASD, namely PGC-1α, STOML2, MFN2, FIS1, OPA1, and GABPA. PGC-1α, the transcriptional regulator of biogenesis, was significantly hypermethylated at eight CpG sites in the gene promoter, one of which contained a putative binding site for CAMP response binding element 1 (CREB1) (p = 1 × 10^–6). Mitochondrial DNA (mtDNA) copy number, a marker of mitochondrial function, was elevated (p = 0.002) in ASD compared to controls and correlated significantly with DNA methylation at the PGC-1α promoter and there was a positive correlation between methylation at PGC-1α CpG#1 and mtDNA copy number (Spearman’s r = 0.2, n = 49, p = 0.04) in ASD. Furthermore, DNA methylation at PGC-1α CpG#1 and mtDNA copy number correlated significantly (p < 0.05) with levels of urinary organic acids associated with mitochondrial dysfunction, oxidative stress, and neuroendocrinology. Our data show differential methylation in ASD at six key genes converging on PGC-1α-dependent regulation of mitochondrial biogenesis and function. We demonstrate that methylation at the PGC-1α promoter is associated with elevated mtDNA copy number and metabolomic evidence of mitochondrial dysfunction in ASD. This highlights an unexplored role for DNA methylation in regulating specific pathways involved in mitochondrial biogenesis, fission and fusion contributing to mitochondrial dysfunction in ASD.

Dysfunction in Mitochondrial Electron Transport Chain Complex I, Pyruvate Dehydrogenase Activity, and Mutations in ND1 and ND4 Gene in Autism Spectrum Disorder Subjects from Tamil Nadu Population, India

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterised by impaired social interaction and behavioural abnormalities. Growing evidence proved that impairment in mitochondrial functions could inhibit energy production and may contribute to the onset of ASD. Genetic variants in the genes of mitochondrial DNA (mtDNA) could interrupt the normal energy metabolism and production in the brain which lead to a wide range of structural and functional changes in the brain resulting in ASD. The present study aims to compare the activities of mitochondrial electron transport chain (ETC) complex I, pyruvate dehydrogenase (PDH) and specific mitochondrial DNA gene (MT-ND1 and MT-ND4) variants associated with ASD subjects in the Tamil Nadu population. Mutational analysis revealed that most mutations in ASD subjects showed synonymous type followed by missense in both the ND1 and ND4 genes. Interestingly, we found that the complex I and PDH dysfunctions may have a role in ASD compared to the controls (p ≤ 0.0001). Hence, the results of the present study suggest that mitochondrial dysfunction, specifically the complex I genes, may play a major role in the onset of ASD, concluding that further research on mitochondrial genes are mandatory to unravel the mechanism behind ASD pathogenesis.

Mitochondria and early-life adversity

Early-life adversity (ELA), which includes maltreatment, neglect, or severe trauma in childhood, increases the life-long risk for negative health outcomes. Mitochondria play a key role in the stress response and may be an important mechanism by which stress is transduced into biological risk for disease. By responding to cues from stress-signaling pathways, mitochondria interact dynamically with physiological stress responses coordinated by the central nervous, endocrine, and immune systems. Preclinical evidence suggests that alterations in mitochondrial function and structure are linked to both early stress and systemic biological dysfunction. Early clinical studies support that increased mitochondrial DNA content and altered cellular energy demands may be present in individuals with a history of ELA. Further research should investigate mitochondria as a potential therapeutic target following ELA.

Mitochondrial DNA copy number may be associated with attention deficit/hyperactivity disorder severity in treatment: a one-year follow-up study

OBJECTIVE

Studies on etiopathogenesis of attention deficit/hyperactivity disorder (ADHD) are increasingly focussing on mitochondrial dysfunction. Children diagnosed with ADHD who had significantly higher mitochondrial DNA (mtDNA) copy numbers than healthy children in our first study were re-examined in 1-year follow-up to investigate effects of severity and treatment of ADHD on mtDNA.

METHODS

Twenty-eight patients who participated in previous study were included in this follow-up study. Patients were equally divided into two groups according to whether they had been receiving treatment. Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version, and Conners Parent Rating Scale (CPRS) were used. Polymerase chain reaction was performed.

RESULTS

Means of the first and second mtDNA copy were similar in all patients. mtDNA copy numbers did not change between two measurements in treated and non-treated groups. There was a correlation between CPRS ADHD index and inattention scores and mtDNA copy number in treated group. mtDNA copy number did not change in patients with ADHD over a period of 1 year regardless of treatment.

CONCLUSIONS

There may be a relationship between decreased ADHD severity with treatment and positive effects of mitochondrial functions. Mitochondrial dysfunction may play a role in pathophysiology of ADHD.KEY POINTSThis was the first study to follow up ADHD patients in order to investigate mitochondrial dysfunction by measuring mtDNA copy numbers 1 year after the initial measurements.mtDNA copy number, one of the best markers of mitochondrial dysfunction, did not change in ADHD patients over a period of 1 year regardless of treatment.Mitochondrial dysfunction may play a role in the pathophysiology of ADHD, where it may be involved with or without treatment.In the treated group, there was an association between decreased ADHD severity and reduced mtDNA copy numbers.There may be a relationship between decreased ADHD severity with treatment and the positive effects of mitochondrial functions.

Male preconception antioxidant supplementation may lower autism risk: a call for studies

Current research indicates that a sizable number of autism spectrum disorder (ASD) cases arise from de novo mutations (DNMs) occurring within the paternal germline, usually in an age-dependent manner. Andrologists have reported that somatic cells and gametes share the same pathologies that generate these DNMs-specifically, DNA hypomethylation caused by oxidative nucleoside base damage. Because many ASD researchers seek to identify genetic risk factors, teams are developing methods of assessing aberrant DNA patterns, such as parental gonadal mosaicism. Several studies propose antioxidant supplementation as a strategy to lower autism risk, and/or suggest connections between childhood neurodevelopmental disorders such as autism and paternally-derived DNMs. Actual data, however, are currently not available to determine whether male preconception antioxidant supplementation effectively lowers autism risk. The purpose of this paper is to (1) explore the mechanisms causing DNMs, specifically DNA hypomethylation; (2) explain how antioxidant supplementation may lower the risk of having a child with ASD; and, (3) advocate for the implementation of large prospective studies testing (2). These studies may very well find that male preconception supplementation with antioxidants prevents neurodevelopmental disorders in offspring, in much the same way that female prenatal consumption of folate was found to decrease the risk of birth defects. If this is indeed the case, the alarming rise in autism prevalence rates of the past few decades will slow-or even cease-upon the initiation of public awareness campaigns.

Developmental regression and mitochondrial function in children with autism

BACKGROUND

Developmental regression (DR) occurs in about one-third of children with Autism Spectrum Disorder (ASD) yet it is poorly understood. Current evidence suggests that mitochondrial function in not normal in many children with ASD. However, the relationship between mitochondrial function and DR has not been well-studied in ASD.

METHODS

This cross-sectional study of 32 children, 2 to 8 years old with ASD, with (n = 11) and without (n = 12) DR, and non-ASD controls (n = 9) compared mitochondrial respiration and mtDNA damage and copy number between groups and their relation to standardized measures of ASD severity.

RESULTS

Individuals with ASD demonstrated lower ND1, ND4, and CYTB copy number (Ps < 0.01) as compared to controls. Children with ASD and DR had higher maximal oxygen consumption rate (Ps < 0.02), maximal respiratory capacity (P < 0.05), and reserve capacity (P = 0.01) than those with ASD without DR. Coupling Efficiency and Maximal Respiratory Capacity were associated with disruptive behaviors but these relationships were different for those with and without DR. Higher ND1 copy number was associated with better behavior.

CONCLUSIONS

This study suggests that individuals with ASD and DR may represent a unique metabolic endophenotype with distinct abnormalities in respiratory function that may put their mitochondria in a state of vulnerability. This may allow physiological stress to trigger mitochondrial decompensation as is seen clinically as DR. Since mitochondrial function was found to be related to ASD symptoms, the mitochondria could be a potential target for novel therapeutics. Additionally, identifying those with vulnerable mitochondrial before DR could result in prevention of ASD.

Stress and Psychiatric Disorders: The Role of Mitochondria

In seeking to understand mental health and disease, it is fundamental to identify the biological substrates that draw together the experiences and physiological processes that underlie observed psychological changes. Mitochondria are subcellular organelles best known for their central role in energetics, producing adenosine triphosphate to power most cellular processes. Converging lines of evidence indicate that mitochondria play a key role in the biological embedding of adversity. Preclinical research documents the effects of stress exposure on mitochondrial structure and function, and recent human research suggests alterations constituting recalibrations, both adaptive and nonadaptive. Current research suggests dynamic relationships among stress exposure, neuroendocrine signaling, inflammation, and mitochondrial function. These complex relationships are implicated in disease risk, and their elucidation may inform prevention and treatment of stress- and trauma-related disorders. We review and evaluate the evidence for mitochondrial dysfunction as a consequence of stress exposure and as a contributing factor to psychiatric disease.

Mitochondrial DNA copy number, damage, repair and degradation in depressive disorder

Objectives: We aimed to explore mitochondrial DNA (mtDNA) copy number, damage, repair and degradation in peripheral blood mononuclear cells (PBMCs) of patients with depression and to compare the results with healthy subjects.Methods: Total genomic DNA was isolated from PBMCs of 25 depressed and 60 healthy subjects before, immediately after, and 3 h after the exposure to H₂O₂. Evaluation of mtDNA copy number was performed using real-time PCR and 2-ΔCt methods. Semi-long run real-time PCR was used to estimate the number of mtDNA lesions.Results: Baseline mtDNA copy number did not differ in cells of healthy and depressed subjects; however, it was negatively correlated with the severity of the episode. After a 10-min challenge with hydrogen peroxide (H₂O₂), depressed patients' PBMCs exhibited slower changes of the copy number, indicating a lower efficiency of mtDNA degradation compared to controls. Moreover, a significantly higher number of mtDNA lesions was found in depressed patients at the baseline as well as at other experimental time points. mtDNA lesions were also elevated in depressed patient cells immediately after H₂O₂ exposure. Induction of oxidative stress had no significant influence on the cells of controls.Conclusions: We are the first to show that impairment in repair and degradation of mtDNA may be involved in the pathophysiology of depression.

Mitochondrial DNA Copy Number in Peripheral Blood as a Potential Non-invasive Biomarker for Multiple Sclerosis

The impaired mitochondrial function has been implicated in the pathogenicity of multiple sclerosis (MS), a chronic inflammatory, demyelinating, and neurodegenerative disease of the CNS. Circulating mtDNA copy number in body fluids has been proposed as an indicator for several neurodegenerative diseases, and the altered cerebrospinal fluid mtDNA has been shown as a promising marker for MS. The aim of this study was to determine changes and biomarker potential of circulating mtDNA in peripheral blood in MS. The mtDNA copy number was quantified by real-time PCR in blood samples from 60 patients with relapsing-remitting MS (RRMS) and 64 healthy controls. The RRMS patients had significantly lower circulating mtDNA copy number compared to controls. Subgroup analysis with stratification of RRMS patients based on disease duration under or over 10 years revealed that the mtDNA copy number was significantly lower in the group with longer disease duration. A negative correlation was observed between mtDNA copy number and disease duration. The ROC curve analysis indicated a significant ability of mtDNA copy number to separate RRMS patients from controls with an AUC of 0.859. This is the first study to measure peripheral blood mtDNA copy number in MS patients. Current data suggest that the reduction in peripheral blood mtDNA copy number may be an early event in MS and correlate with the disease progression. The findings of this study indicate that circulating blood-based mtDNA copy number may be a potential non-invasive candidate biomarker for mitochondria-mediated neurodegeneration and MS. This can put forward the clinical applicability over other invasive markers.

Peripheral Blood Mitochondrial DNA Copy Number Obtained From Genome-Wide Genotype Data Is Associated With Neurocognitive Impairment in Persons With Chronic HIV Infection

BACKGROUND

Mitochondrial DNA (mtDNA) copy number varies by cell type and energy demands. Blood mtDNA copy number has been associated with neurocognitive function in persons without HIV. Low mtDNA copy number may indicate disordered mtDNA replication; high copy number may reflect a response to mitochondrial dysfunction. We hypothesized that blood mtDNA copy number estimated from genome-wide genotyping data is related to neurocognitive impairment (NCI) in persons with HIV.

METHODS

In the CNS HIV Antiretroviral Therapy Effects Research (CHARTER) study, peripheral blood mtDNA copy number was obtained from genome-wide genotyping data as a ratio of mtDNA single-nucleotide polymorphism probe intensities relative to nuclear DNA single-nucleotide polymorphisms. In a multivariable regression model, associations between mtDNA copy number and demographics, blood cell counts, and HIV disease and treatment characteristics were tested. Associations of mtDNA copy number with the global deficit score (GDS), GDS-defined NCI (GDS ≥ 0.5), and HIV-associated neurocognitive disorder (HAND) diagnosis were tested by logistic regression, adjusting for potential confounders.

RESULTS

Among 1010 CHARTER participants, lower mtDNA copy number was associated with longer antiretroviral therapy duration (P < 0.001), but not with d-drug exposure (P = 0.85). mtDNA copy number was also associated with GDS (P = 0.007), GDS-defined NCI (P < 0.001), and HAND (P = 0.002). In all analyses, higher mtDNA copy number was associated with poorer cognitive performance.

CONCLUSIONS

Higher mtDNA copy number estimated from peripheral blood genotyping was associated with worse neurocognitive performance in adults with HIV. These results suggest a connection between peripheral blood mtDNA and NCI, and may represent increased mtDNA replication in response to mitochondrial dysfunction.

Mitochondria, Metabolism, and Redox Mechanisms in Psychiatric Disorders

Significance: Our current knowledge of the pathophysiology and molecular mechanisms causing psychiatric disorders is modest, but genetic susceptibility and environmental factors are central to the etiology of these conditions. Autism, schizophrenia, bipolar disorder and major depressive disorder show genetic gene risk overlap and share symptoms and metabolic comorbidities. The identification of such common features may provide insights into the development of these disorders. Recent Advances: Multiple pieces of evidence suggest that brain energy metabolism, mitochondrial functions and redox balance are impaired to various degrees in psychiatric disorders. Since mitochondrial metabolism and redox signaling can integrate genetic and environmental environmental factors affecting the brain, it is possible that they are implicated in the etiology and progression of psychiatric disorders. Critical Issue: Evidence for direct links between cellular mitochondrial dysfunction and disease features are missing. Future Directions: A better understanding of the mitochondrial biology and its intracellular connections to the nuclear genome, the endoplasmic reticulum and signaling pathways, as well as its role in intercellular communication in the organism, is still needed. This review focuses on the findings that implicate mitochondrial dysfunction, the resultant metabolic changes and oxidative stress as important etiological factors in the context of psychiatric disorders. We also propose a model where specific pathophysiologies of psychiatric disorders depend on circuit-specific impairments of mitochondrial dysfunction and redox signaling at specific developmental stages.

Alterations of Mitochondrial Biology in the Oral Mucosa of Chilean Children with Autism Spectrum Disorder (ASD)

Autistic Spectrum Disorder (ASD) is characterized by the impairment of socio-communicative skills and the presence of restricted and stereotyped behavior patterns. Recent researches have revealed the influence of mitochondrial physiology on the development of ASD. Several research groups have identified defects in respiratory complexes, coenzyme-Q10 deficiency, increased oxidative damage, decreased of superoxide dismutase (SOD2). A study on the influence of mitochondrial physiology on the development of ASD can provide new alternatives and challenges. That is why we set ourselves the general objective to initiate studies of mitochondrial physiology in Chilean children with ASD. A sample of oral mucosa was collected in a group of 12 children diagnosed with ASD and 12 children without ASD. In children with ASD, we found a significant increase in mitochondrial DNA levels. Likewise, in these children, an increase in the protein oxidation was observed. Finally, a downward trend in the expression of the HIGD2A and SOD2 genes was observed, while DRP1, FIS1, MFN1, MFN2, and OPA1 gene expression show an upward trend. The increment of mitochondrial DNA, high oxidative stress, and high expression of the MFN2 gene could help as a scanner of the mitochondrial function in children with ASD.

A Pipeline for Faecal Host DNA Analysis by Absolute Quantification of LINE-1 and Mitochondrial Genomic Elements Using ddPCR

Stool contains DNA shed from cells of the gastrointestinal (GI) tract and has great potential as a bio-specimen for non-invasive, nucleic acid-based detection of GI diseases. Whereas methods for studying faecal microbiome DNA are plentiful, there is a lack of well-characterised procedures for stabilisation, isolation, and quantitative analysis of faecal host DNA. We report an optimised pipeline for faecal host DNA analysis from the point-of-collection to droplet digital PCR (ddPCR) absolute quantification of host-specific gene targets. We evaluated multiple methods for preservation and isolation of host DNA from stool to identify the highest performing methods. To quantify host DNA even if present in partially degraded form, we developed sensitive, human-specific short-amplicon ddPCR assays targeting repetitive nuclear genomic elements (LINE-1) and mitochondrial genes. We validated the ability of these optimised methods to perform absolute quantification of host DNA in 200 stool DNA extracts from samples that were serially collected from three healthy individuals and three hospitalised patients. These specimens allowed assessment of host DNA day-to-day variability in stool specimens with widely varying physical characteristics (i.e., Bristol scores). We further extended this approach to mouse stool analysis, to enable faecal host DNA studies in animal disease models as well.

Peripheral Mitochondrial DNA Copy Number is Increased in Korean Attention-Deficit Hyperactivity Disorder Patients

The involvement of mitochondrial dysfunction in the pathophysiology of attention-deficit hyperactivity disorder (ADHD) has been suggested in several reports. Mitochondrial DNA (mtDNA) copy number as well as methylation of the D-loop region and peroxisome-proliferator-activated receptor γ co-activator-1α (PPARGC1A) are considered biomarkers for mitochondrial dysfunction. We compared the mtDNA copy number and methylation ratio of the D-loop region and PPARGC1A between ADHD patients and controls and also among ADHD subtypes. The present study included 70 subjects with ADHD and 70 age- and gender-matched healthy controls (HCs). We measured the relative mtDNA copy number in peripheral blood cells using quantitative polymerase chain reaction (qPCR), and the methylation ratio was measured using methylation-specific PCR (MSP) after bisulfite conversion. The relative mtDNA copy number was significantly higher in ADHD patients than in HCs (p = 0.028). The mtDNA methylation ratio of PPARGC1A was decreased in ADHD patients compared with HCs (p = 0.008). After adjusting for IQ level, only the mtDNA copy number differed between the ADHD and HCs (p = 0.01). There was a significant difference in the methylation ratio of PPARGC1A among ADHD subtypes. These results suggest the possible involvement of mitochondrial dysfunction in the pathophysiology of ADHD. Further large cohort studies investigating the correlation between clinical markers and biomarkers of mitochondrial dysfunction are warranted.

Clinical and Molecular Characteristics of Mitochondrial Dysfunction in Autism Spectrum Disorder

Autism spectrum disorder (ASD) affects ~ 2% of children in the United States. The etiology of ASD likely involves environmental factors triggering physiological abnormalities in genetically sensitive individuals. One of these major physiological abnormalities is mitochondrial dysfunction, which may affect a significant subset of children with ASD. Here we systematically review the literature on human studies of mitochondrial dysfunction related to ASD. Clinical aspects of mitochondrial dysfunction in ASD include unusual neurodevelopmental regression, especially if triggered by an inflammatory event, gastrointestinal symptoms, seizures, motor delays, fatigue and lethargy. Traditional biomarkers of mitochondrial disease are widely reported to be abnormal in ASD, but appear non-specific. Newer biomarkers include buccal cell enzymology, biomarkers of fatty acid metabolism, non-mitochondrial enzyme function, apoptosis markers and mitochondrial antibodies. Many genetic abnormalities are associated with mitochondrial dysfunction in ASD, including chromosomal abnormalities, mitochondrial DNA mutations and large-scale deletions, and mutations in both mitochondrial and non-mitochondrial nuclear genes. Mitochondrial dysfunction has been described in immune and buccal cells, fibroblasts, muscle and gastrointestinal tissue and the brains of individuals with ASD. Several environmental factors, including toxicants, microbiome metabolites and an oxidized microenvironment are shown to modulate mitochondrial function in ASD tissues. Investigations of treatments for mitochondrial dysfunction in ASD are promising but preliminary. The etiology of mitochondrial dysfunction and how to define it in ASD is currently unclear. However, preliminary evidence suggests that the mitochondria may be a fruitful target for treatment and prevention of ASD. Further research is needed to better understand the role of mitochondrial dysfunction in the pathophysiology of ASD.

Frequency and association of mitochondrial genetic variants with neurological disorders

Mitochondria are small cytosolic organelles and the main source of energy production for the cells, especially in the brain. This organelle has its own genome, the mitochondrial DNA (mtDNA), and genetic variants in this molecule can alter the normal energy metabolism in the brain, contributing to the development of a wide assortment of Neurological Disorders (ND), including neurodevelopmental syndromes, neurodegenerative diseases and neuropsychiatric disorders. These ND are comprised by a heterogeneous group of syndromes and diseases that encompass different cognitive phenotypes and behavioral disorders, such as autism, Asperger's syndrome, pervasive developmental disorder, attention deficit hyperactivity disorder, Huntington disease, Leigh Syndrome and bipolar disorder. In this work we carried out a Systematic Literature Review (SLR) to identify and describe the mitochondrial genetic variants associated with the occurrence of ND. Most of genetic variants found in mtDNA were associated with Single Nucleotide Polimorphisms (SNPs), ~79%, with ~15% corresponding to deletions, ~3% to Copy Number Variations (CNVs), ~2% to insertions and another 1% included mtDNA replication problems and genetic rearrangements. We also found that most of the variants were associated with coding regions of mitochondrial proteins but were also found in regulatory transcripts (tRNA and rRNA) and in the D-Loop replication region of the mtDNA. After analysis of mtDNA deletions and CNV, none of them occur in the D-Loop region. This SLR shows that all transcribed mtDNA molecules have mutations correlated with ND. Finally, we describe that all mtDNA variants found were associated with deterioration of cognitive (dementia) and intellectual functions, learning disabilities, developmental delays, and personality and behavior problems.

Blood Mitochondrial DNA Content in HIV-Exposed Uninfected Children with Autism Spectrum Disorder

Long-term outcomes of perinatal exposure to maternal antiretroviral therapy in HIV-exposed uninfected (HEU) children are unknown. However, both HIV antiretroviral therapy and autism spectrum disorder (ASD) have been associated with mitochondrial alterations. Leukocyte mitochondrial DNA (mtDNA) content can serve as a marker for mitochondrial dysfunction. In this cross-sectional, nested case-control study, HEU children with ASD were matched approximately 1:3 on age, sex, and ethnicity to HEU children without ASD, HIV-unexposed uninfected (HUU) controls, and HUU children with ASD. Leukocyte mtDNA content was measured using quantitative PCR. Among 299 HEU in this study, 14 (4.7%) were diagnosed with ASD, which is higher than the general population prevalence estimates. HEU children without ASD and HUU children with ASD had higher mtDNA content than HUU controls. HEU children with ASD had significantly higher mtDNA content than all other study groups. Our results suggest a clear association between elevated leukocyte mtDNA content and both HEU and ASD status. This may implicate mitochondrial dysfunction as a contributor to the high ASD prevalence observed in our cohort.

Reference Intervals of Mitochondrial DNA Copy Number in Peripheral Blood for Chinese Minors and Adults

BACKGROUND

Mitochondrial DNA (mtDNA) content measured by different techniques cannot be compared between studies, and age- and tissue-related control values are hardly available. In the present study, we aimed to establish the normal reference range of mtDNA copy number in the Chinese population.

METHODS

Two healthy cohorts of 200 Chinese minors (0.1-18.0 years) and 200 adults (18.0-88.0 years) were recruited. Then, they were further categorized into eight age groups. The absolute mtDNA copy number per cell was measured by a quantitative real-time polymerase chain reaction. We subsequently used this range to evaluate mtDNA content in four patients (0.5-4.0 years) with molecularly proven mitochondrial depletion syndromes (MDSs) and 83 cases of mitochondrial disease patients harboring the m.3243A>G mutation.

RESULTS

The reference range of mtDNA copy number in peripheral blood was 175-602 copies/cell (mean: 325 copies/cell) in minors and 164-500 copies/cell (mean: 287 copies/cell) in adults. There was a decreasing trend in mtDNA copy number in blood with increasing age, especially in 0-2-year-old and >50-year-old donors. The mean mtDNA copy number level among the mitochondrial disease patients with m.3243A>G mutation was significantly higher than that of healthy controls. The mtDNA content of POLG, DGUOK, TK2, and SUCLA2 genes in blood samples from MDS patients was reduced to 25%, 38%, 32%, and 24%, respectively.

CONCLUSIONS

We primarily establish the reference intervals of mtDNA copy number, which might contribute to the clinical diagnosis and monitoring of mitochondrial disease.

The putative role of environmental aluminium in the development of chronic neuropathology in adults and children. How strong is the evidence and what could be the mechanisms involved?

The conceptualisation of autistic spectrum disorder and Alzheimer's disease has undergone something of a paradigm shift in recent years and rather than being viewed as single illnesses with a unitary pathogenesis and pathophysiology they are increasingly considered to be heterogeneous syndromes with a complex multifactorial aetiopathogenesis, involving a highly complex and diverse combination of genetic, epigenetic and environmental factors. One such environmental factor implicated as a potential cause in both syndromes is aluminium, as an element or as part of a salt, received, for example, in oral form or as an adjuvant. Such administration has the potential to induce pathology via several routes such as provoking dysfunction and/or activation of glial cells which play an indispensable role in the regulation of central nervous system homeostasis and neurodevelopment. Other routes include the generation of oxidative stress, depletion of reduced glutathione, direct and indirect reductions in mitochondrial performance and integrity, and increasing the production of proinflammatory cytokines in both the brain and peripherally. The mechanisms whereby environmental aluminium could contribute to the development of the highly specific pattern of neuropathology seen in Alzheimer's disease are described. Also detailed are several mechanisms whereby significant quantities of aluminium introduced via immunisation could produce chronic neuropathology in genetically susceptible children. Accordingly, it is recommended that the use of aluminium salts in immunisations should be discontinued and that adults should take steps to minimise their exposure to environmental aluminium.

Simultaneous quantification of DNA damage and mitochondrial copy number by long-run DNA-damage quantification (LORD-Q)

DNA damage and changes in the mitochondrial DNA content have been implicated in ageing and cancer development. To prevent genomic instability and tumorigenesis, cells must maintain the integrity of their nuclear and mitochondrial DNA. Advances in the research of DNA damage protection and genomic stability, however, also depend on the availability of techniques that can reliably quantify alterations of mitochondrial DNA copy numbers and DNA lesions in an accurate high-throughput manner. Unfortunately, no such method has been established yet. Here, we describe the high-sensitivity long-run real-time PCR technique for DNA-damage quantification (LORD-Q) and its suitability to simultaneously measure DNA damage rates and mitochondrial DNA copy numbers in cultured cells and tissue samples. Using the LORD-Q multiplex assay, we exemplarily show that the mitochondrial DNA content does not directly affect DNA damage susceptibility, but influences the efficacy of certain anticancer drugs. Hence, LORD-Q provides a fast and precise method to assess DNA lesions, DNA repair and mtDNA replication as well as their role in a variety of pathological settings.

Association of mitochondrial DNA in peripheral blood with depression, anxiety and stress- and adjustment disorders in primary health care patients

Mitochondrial dysfunction may result in a variety of diseases. The objectives here were to examine possible differences in mtDNA copy number between healthy controls and patients with depression, anxiety or stress- and adjustment disorders; the association between mtDNA copy number and disease severity at baseline; and the association between mtDNA copy number and response after an 8-week treatment (mindfulness, cognitive based therapy). A total of 179 patients in primary health care (age 20-64 years) with depression, anxiety and stress- and adjustment disorders, and 320 healthy controls (aged 19-70 years) were included in the study. Relative mtDNA copy number was measured using quantitative real-time PCR on peripheral blood samples. We found that the mean mtDNA copy number was significantly higher in patients compared to controls (84.9 vs 75.9, p<0.0001) at baseline. The difference in mtDNA copy number between patients and controls remained significant after controlling for age and sex (ß=8.13, p<0.0001; linear regression analysis). The mtDNA copy number was significantly associated with Patient Health Questionnaire (PHQ-9) scores (β=0.57, p=0.02) at baseline. After treatment, the change in mtDNA copy number was significantly associated with the treatment response, i.e., change in Hospital Anxiety and Depression Scale (HADS-D) and PHQ-9 scores (ß=1.00, p=0.03 and ß=0.65, p=0.04, respectively), after controlling for baseline scores, age, sex, BMI, smoking status, alcohol drinking and medication. Our findings show that mtDNA copy number is associated with symptoms of depression, anxiety and stress- and adjustment disorders and treatment response in these disorders.

Mitochondrial dysfunction in Autism Spectrum Disorder: clinical features and perspectives

Autism Spectrum Disorder (ASD) is a prototypic pervasive developmental disorder characterized by social interaction, and communication deficits, repetitive, stereotypic patterns of behavior, and impairments in language and development. Clinical studies have identified mitochondrial disturbances at the levels of DNA, activity, complexes, oxidative stress, and metabolites in blood and urine of ASD patients. However, these observations from postmortem brains or peripheral tissues do not provide a direct link between autism and mitochondria. The synaptic abnormality of autistic patients has not been investigated yet. Here we review the findings of clinical studies investigating mitochondrial involvement in ASD patients, focusing particularly on the brain and the limitations and future directions needed in order to fully understand the role of mitochondria in ASD pathology.

Difference in mitochondrial DNA copy number in peripheral blood cells between probands with autism spectrum disorders and their unaffected siblings

OBJECTIVES

Several reports suggest that mitochondrial dysfunction is involved in the pathophysiology of autism spectrum disorders (ASD). Therefore, mitochondrial DNA (mtDNA) copy number, a common biomarker for mitochondrial dysfunction, might be associated with ASD phenotypes.

METHODS

Relative mtDNA copy number in the peripheral blood cells of 100 Korean ASD patients and their unaffected sib-pairs was measured by quantitative polymerase chain reaction (qPCR).

RESULTS

ASD patients had significantly higher relative mtDNA copy numbers than their unaffected sibs (P = .042). In addition, there were statistically significant correlations between mtDNA copy number and clinical phenotypes for language and communication in ASD.

CONCLUSIONS

Our findings suggest that mitochondrial dysfunction and elevated mtDNA copy number may be a biological subtype of ASD that is related to the phenotype for communication.

Metabolic Dysfunction Underlying Autism Spectrum Disorder and Potential Treatment Approaches

Autism spectrum disorder (ASD) is characterized by deficits in sociability and communication, and increased repetitive and/or restrictive behaviors. While the etio-pathogenesis of ASD is unknown, clinical manifestations are diverse and many possible genetic and environmental factors have been implicated. As such, it has been a great challenge to identify key neurobiological mechanisms and to develop effective treatments. Current therapies focus on co-morbid conditions (such as epileptic seizures and sleep disturbances) and there is no cure for the core symptoms. Recent studies have increasingly implicated mitochondrial dysfunction in ASD. The fact that mitochondria are an integral part of diverse cellular functions and are susceptible to many insults could explain how a wide range of factors can contribute to a consistent behavioral phenotype in ASD. Meanwhile, the high-fat, low-carbohydrate ketogenic diet (KD), used for nearly a century to treat medically intractable epilepsy, has been shown to enhance mitochondrial function through a multiplicity of mechanisms and affect additional molecular targets that may address symptoms and comorbidities of ASD. Here, we review the evidence for the use of metabolism-based therapies such as the KD in the treatment of ASD as well as emerging co-morbid models of epilepsy and autism. Future research directions aimed at validating such therapeutic approaches and identifying additional and novel mechanistic targets are also discussed.

Relation of Mitochondrial DNA Copy Number in Peripheral Blood to Postoperative Atrial Fibrillation After Isolated Off-Pump Coronary Artery Bypass Grafting

Oxidative stress has been considered to be an important factor contributing to postoperative atrial fibrillation (PoAF). Mitochondrial DNA (mtDNA) copy number in peripheral blood has been found to be associated with a patient's oxidative stress. Therefore, we sought to determine whether there was association between mtDNA copy number and the onset of atrial fibrillation. mtDNA copy numbers were measured using the quantitative real-time polymerase chain reaction in peripheral blood from 485 consecutive patients with sinus rhythm undergoing coronary artery bypass grafting. The blood was collected before surgery. In the cohort, the incidence of PoAF was 20.8% (101/485). The mean mtDNA copy number was significantly higher in patents with PoAF than in those with sinus rhythm (36.43 vs 16.63, p <0.001). The receiver operating characteristic analysis proved that the mtDNA copy number could predict PoAF with good sensitivity and specificity (area under the curve = 0.814, cutoff = 20.91, sensitivity = 70.3%, specificity = 80.2%, p <0.001). On multivariate logistic and Cox regression analysis, mtDNA copy number was shown to be a significant independent risk factor for PoAF (odds ratio = 10.01, p <0.001 and hazard ratio = 7.011, p = 0.004). There was a strong positive correlation between mtDNA copy number and malondialdehyde in patients with PoAF (r = 0.449, p = 0.01). In conclusion, we showed that elevated mtDNA copy number in peripheral blood is associated with PoAF. Further investigation is needed to validate mtDNA copy number as a predictive biomarker for PoAF and to explore its potential role in arrhythmogenesis.

Identifying sensitive windows for prenatal particulate air pollution exposure and mitochondrial DNA content in cord blood

INTRODUCTION

Changes in mitochondrial DNA (mtDNA) can serve as a marker of cumulative oxidative stress (OS) due to the mitochondria's unique genome and relative lack of repair systems. In utero particulate matter ≤2.5μm (PM_2.5) exposure can enhance oxidative stress. Our objective was to identify sensitive windows to predict mtDNA damage experienced in the prenatal period due to PM_2.5 exposure using mtDNA content measured in cord blood.

MATERIAL AND METHODS

Women affiliated with the Mexican social security system were recruited during pregnancy in the Programming Research in Obesity, Growth, Environment and Social Stressors (PROGRESS) study. Mothers with cord blood collected at delivery and complete covariate data were included (n=456). Mothers' prenatal daily exposure to PM_2.5 was estimated using a satellite-based spatio-temporally resolved prediction model and place of residence during pregnancy. DNA was extracted from umbilical cord leukocytes. Quantitative real-time polymerase chain reaction (qPCR) was used to determine mtDNA content. A distributive lag regression model (DLM) incorporating weekly averages of daily PM_2.5 predictions was constructed to plot the association between exposure and OS over the length of pregnancy.

RESULTS

In models that included child's sex, mother's age at delivery, prenatal environmental tobacco smoke exposure, birth year, maternal education, and assay batch, we found significant associations between higher PM_2.5 exposure during late pregnancy (35-40weeks) and lower mtDNA content in cord blood.

CONCLUSIONS

Increased PM_2.5 during a specific prenatal window in the third trimester was associated with decreased mtDNA content suggesting heightened sensitivity to PM-induced OS during this life stage.

A Putative Blood-Based Biomarker for Autism Spectrum Disorder-Associated Ileocolitis

Gastrointestinal symptoms are common in children with autism spectrum disorder (ASD). A significant proportion of children with ASD and gastrointestinal symptoms have histologic evidence of ileocolitis (inflammation of the terminal ileum and/or colon). We previously reported the molecular characterization of gastrointestinal biopsy tissue from ASD children with ileocolitis (ASD^IC+) compared to anatomically similar inflamed tissue from typically developing children with inflammatory bowel disease (IBD; i.e. Crohn’s disease or ulcerative colitis) and typically developing children with gastrointestinal symptoms but no evidence of gastrointestinal mucosal inflammation (TD^IC−). ASD^IC+ children had a gene expression profile that, while primarily overlapping with known IBD, had distinctive differences. The present study confirms these findings and replicates this molecular characterization in a second cohort of cases (ASD^IC+) and controls (TD^IC−). In these two separate case/control mucosal-based cohorts, we have demonstrated overlap of 59 differentially expressed transcripts (DETs) unique to inflamed ileocolonic tissue from symptomatic ASD^IC+ children. We now report that 9 of these 59 transcripts are also differentially expressed in the peripheral blood of the second cohort of ASD^IC+ children. This set of transcripts represents a putative blood-based biomarker for ASD-associated ileocolonic inflammation.

Genetic Evidence for Elevated Pathogenicity of Mitochondrial DNA Heteroplasmy in Autism Spectrum Disorder

Increasing clinical and biochemical evidence implicate mitochondrial dysfunction in the pathophysiology of Autism Spectrum Disorder (ASD), but little is known about the biological basis for this connection. A possible cause of ASD is the genetic variation in the mitochondrial DNA (mtDNA) sequence, which has yet to be thoroughly investigated in large genomic studies of ASD. Here we evaluated mtDNA variation, including the mixture of different mtDNA molecules in the same individual (i.e., heteroplasmy), using whole-exome sequencing data from mother-proband-sibling trios from simplex families (n = 903) where only one child is affected by ASD. We found that heteroplasmic mutations in autistic probands were enriched at non-polymorphic mtDNA sites (P = 0.0015), which were more likely to confer deleterious effects than heteroplasmies at polymorphic mtDNA sites. Accordingly, we observed a ~1.5-fold enrichment of nonsynonymous mutations (P = 0.0028) as well as a ~2.2-fold enrichment of predicted pathogenic mutations (P = 0.0016) in autistic probands compared to their non-autistic siblings. Both nonsynonymous and predicted pathogenic mutations private to probands conferred increased risk of ASD (Odds Ratio, OR[95% CI] = 1.87[1.14-3.11] and 2.55[1.26-5.51], respectively), and their influence on ASD was most pronounced in families with probands showing diminished IQ and/or impaired social behavior compared to their non-autistic siblings. We also showed that the genetic transmission pattern of mtDNA heteroplasmies with high pathogenic potential differed between mother-autistic proband pairs and mother-sibling pairs, implicating developmental and possibly in utero contributions. Taken together, our genetic findings substantiate pathogenic mtDNA mutations as a potential cause for ASD and synergize with recent work calling attention to their unique metabolic phenotypes for diagnosis and treatment of children with ASD.

Mitochondrial Dysfunction in Autism Spectrum Disorders

Autism spectrum disorders (ASD) are classified as neurodevelopmental disorders characterised by diminished social communication and interaction. Recently, evidence has accrued that a significant proportion of individuals with autism have concomitant diseases such as mitochondrial disease and abnormalities of energy generation. This has therefore led to the hypothesis that autism may be linked to mitochondrial dysfunction. We review such studies reporting decreased activity of mitochondrial electron transport chain (ETC) complexes and reduced gene expression of mitochondrial genes, in particular genes of respiratory chain complexes, in individuals with autism. Overall, the findings support the hypothesis that there is an association of ASD with impaired mitochondrial function; however, many of the studies have small sample sizes and there is variability in the techniques utilised. There is therefore a vital need to utilise novel imaging techniques, such as near-infrared spectroscopy, that will allow non-invasive measurement of metabolic markers for neuronal activity such as cytochrome c oxidase, in order to better establish the link between autism and mitochondrial dysfunction.

Gut-Microbiota-Brain Axis and Its Effect on Neuropsychiatric Disorders With Suspected Immune Dysregulation

PURPOSE

Gut microbiota regulate intestinal function and health. However, mounting evidence indicates that they can also influence the immune and nervous systems and vice versa. This article reviews the bidirectional relationship between the gut microbiota and the brain, termed the microbiota-gut-brain (MGB) axis, and discusses how it contributes to the pathogenesis of certain disorders that may involve brain inflammation.

METHODS

Articles were identified with a search of Medline (starting in 1980) by using the key words anxiety, attention-deficit hypersensitivity disorder (ADHD), autism, cytokines, depression, gut, hypothalamic-pituitary-adrenal (HPA) axis, inflammation, immune system, microbiota, nervous system, neurologic, neurotransmitters, neuroimmune conditions, psychiatric, and stress.

FINDINGS

Various afferent or efferent pathways are involved in the MGB axis. Antibiotics, environmental and infectious agents, intestinal neurotransmitters/neuromodulators, sensory vagal fibers, cytokines, and essential metabolites all convey information to the central nervous system about the intestinal state. Conversely, the hypothalamic-pituitary-adrenal axis, the central nervous system regulatory areas of satiety, and neuropeptides released from sensory nerve fibers affect the gut microbiota composition directly or through nutrient availability. Such interactions seem to influence the pathogenesis of a number of disorders in which inflammation is implicated, such as mood disorder, autism-spectrum disorders, attention-deficit hypersensitivity disorder, multiple sclerosis, and obesity.

IMPLICATIONS

Recognition of the relationship between the MGB axis and the neuroimmune systems provides a novel approach for better understanding and management of these disorders. Appropriate preventive measures early in life or corrective measures such as use of psychobiotics, fecal microbiota transplantation, and flavonoids are discussed.

Traffic-Related Air Pollution, Blood Pressure, and Adaptive Response of Mitochondrial Abundance

BACKGROUND

Exposure to black carbon (BC), a tracer of vehicular-traffic pollution, is associated with increased blood pressure (BP). Identifying biological factors that attenuate BC effects on BP can inform prevention. We evaluated the role of mitochondrial abundance, an adaptive mechanism compensating for cellular-redox imbalance, in the BC-BP relationship.

METHODS AND RESULTS

At ≥ 1 visits among 675 older men from the Normative Aging Study (observations=1252), we assessed daily BP and ambient BC levels from a stationary monitor. To determine blood mitochondrial abundance, we used whole blood to analyze mitochondrial-to-nuclear DNA ratio (mtDNA/nDNA) using quantitative polymerase chain reaction. Every standard deviation increase in the 28-day BC moving average was associated with 1.97 mm Hg (95% confidence interval [CI], 1.23-2.72; P<0.0001) and 3.46 mm Hg (95% CI, 2.06-4.87; P<0.0001) higher diastolic and systolic BP, respectively. Positive BC-BP associations existed throughout all time windows. BC moving averages (5-day to 28-day) were associated with increased mtDNA/nDNA; every standard deviation increase in 28-day BC moving average was associated with 0.12 standard deviation (95% CI, 0.03-0.20; P=0.007) higher mtDNA/nDNA. High mtDNA/nDNA significantly attenuated the BC-systolic BP association throughout all time windows. The estimated effect of 28-day BC moving average on systolic BP was 1.95-fold larger for individuals at the lowest mtDNA/nDNA quartile midpoint (4.68 mm Hg; 95% CI, 3.03-6.33; P<0.0001), in comparison with the top quartile midpoint (2.40 mm Hg; 95% CI, 0.81-3.99; P=0.003).

CONCLUSIONS

In older adults, short-term to moderate-term ambient BC levels were associated with increased BP and blood mitochondrial abundance. Our findings indicate that increased blood mitochondrial abundance is a compensatory response and attenuates the cardiac effects of BC.