Mitochondrial Dysfunction In Autism Spectrum Disorder Research Articles

Altered markers of mitochondrial function in adults with autism spectrum disorder.

Previous research suggests potential mitochondrial dysfunction and changes in fatty acid metabolism in a subgroup of individuals with autism spectrum disorder (ASD), indicated by higher lactate, pyruvate levels, and mitochondrial disorder prevalence. This study aimed to further investigate potential mitochondrial dysfunction in ASD by assessing blood metabolite levels linked to mitochondrial metabolism. Blood levels of creatine kinase (CK), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate, pyruvate, free and total carnitine, as well as acylcarnitines were obtained in 73 adults with ASD (47 males, 26 females) and compared with those of 71 neurotypical controls (NTC) (44 males, 27 females). Correlations between blood parameters and psychometric ASD symptom scores were also explored. Lower CK (pcorr = 0.045) levels were found exclusively in males with ASD compared to NTC, with no such variation in females. ALT and AST levels did not differ significantly between both groups. After correction for antipsychotic and antidepressant medication, CK remained significant. ASD participants had lower serum lactate levels (pcorr = 0.036) compared to NTC, but pyruvate and carnitine concentrations showed no significant difference. ASD subjects had significantly increased levels of certain acylcarnitines, with a decrease in tetradecadienoyl-carnitine (C14:2), and certain acylcarnitines correlated significantly with autistic symptom scores. We found reduced serum lactate levels in ASD, in contrast to previous studies suggesting elevated lactate or pyruvate. This difference may reflect the focus of our study on high-functioning adults with ASD, who are likely to have fewer secondary genetic conditions associated with mitochondrial dysfunction. Our findings of significantly altered acylcarnitine levels in ASD support the hypothesis of altered fatty acid metabolism in a subset of ASD patients.

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.

Higher Lactate Level and Lactate-to-Pyruvate Ratio in Autism Spectrum Disorder.

Mitochondrial dysfunction is considered one of the pathophysiological mechanisms of autism spectrum disorder (ASD). However, previous studies of biomarkers associated with mitochondrial dysfunction in ASD have revealed inconsistent results. The objective of this study was to evaluate biochemical markers associated with mitochondrial dysfunction in subjects with ASD and their unaffected family members. Lactate and pyruvate levels, as well as the lactate-to-pyruvate ratio, were examined in the peripheral blood of probands with ASD (Affected Group, AG) and their unaffected family members (biological parents and unaffected siblings, Unaffected Group, UG). Lactate ≥22 mg/dl, pyruvate ≥1.4 mg/dl, and lactate-to-pyruvate ratio >25 were defined as abnormal. The clinical variables were compared between subjects with higher (>25) and lower (≤25) lactate-to-pyruvate ratios within the AG. The AG (n=59) had a significantly higher lactate and lactate-to-pyruvate ratio than the UG (n=136). The frequency of subjects with abnormally high lactate levels and lactate-to-pyruvate ratio was significantly higher in the AG (lactate 31.0% vs. 9.5%, ratio 25.9% vs. 7.3%, p<0.01). The relationship between lactate level and the repetitive behavior domain of the Autism Diagnostic Interview-Revised was statistically significant. These results suggest that biochemical markers related to mitochondrial dysfunction, especially higher lactate levels and lactate-to-pyruvate ratio, might be associated with the pathophysiology of ASD. Further larger studies using unrelated individuals are needed to control for the possible effects of age and sex on chemical biomarker levels.

Mitochondrial Dysfunction Is Inducible in Lymphoblastoid Cell Lines From Children With Autism and May Involve the TORC1 Pathway.

We previously developed a lymphoblastoid cell line (LCL) model of mitochondrial dysfunction in autism spectrum disorder (ASD); some individuals with ASD showed mitochondrial dysfunction (AD-A) while other individuals (AD-N) demonstrated mitochondrial respiration similar to controls (CNT). To test the hypothesis that mitochondrial dysfunction could be a consequence of environmental exposures through chronic elevations in reactive oxygen species (ROS), we exposed LCLs to prolonged ROS. We also examined expression of metabolic regulatory genes and the modulating effect of the mechanistic target of rapamycin (mTOR) pathway. Prolonged ROS exposure induced or worsened mitochondrial dysfunction in all LCL groups. Expression of genes associated with ROS protection was elevated in both AD-N and AD-A LCLs, but mitochondrial fission/fusion and mitoplasticity gene expression was only increased in AD-N LCLs. Partial least squares discriminant analysis showed that mTOR, UCP2 (uncoupling protein 2), SIRT1 (sirtuin 1), and MFN2 (mitofusin-2) gene expression differentiated LCL groups. Low-dose rapamycin (0.1 nM) normalized respiration with the magnitude of this normalization greater for AD-A LCLs, suggesting that the mammalian target of rapamycin complex 1 (mTORC1) pathway may have a different dynamic range for regulating mitochondrial activity in individuals with ASD with and without mitochondrial dysfunction, potentially related to S6K1 (S6 kinase beta-1) regulation. Understanding pathways that underlie mitochondrial dysfunction in ASD may lead to novel treatments.

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.

Genetic and clinical evidence of mitochondrial dysfunction in autism spectrum disorder and intellectual disability.

Clinical conditions commonly associated with mitochondrial disorders (CAMDs) are often present in autism spectrum disorders (ASD) and intellectual disability (ID). Therefore, the mitochondrial dysfunction hypothesis has been proposed as a transversal mechanism that may function in both disorders. Here, we investigated the presence of conditions associated with mitochondrial disorders and mitochondrial DNA (mtDNA) alterations in 122 subjects who presented ASD with ID (ASD group), 115 subjects who presented ID but not ASD (ID group) and 112 healthy controls (HC group). We assessed in the three study groups the presence of the clinical conditions through a questionnaire and the mtDNA content of two mitochondrial genes, MT-ND1 and MT-ND4, by qPCR. The mtDNA sequences of 98 ASD and 95 ID subjects were obtained by mtDNA-targeted next generation sequencing and analysed through the MToolBox pipeline to identify mtDNA mutations. Subjects with ASD and ID showed higher frequencies of constipation, edema, seizures, vision alterations, strabismus and sphincter incontinence than HCs subjects. ASD and ID subjects showed significantly lower mtDNA content than HCs in both MT-ND1 and MT-ND4 genes. In addition, we identified 49 putative pathogenic variants with a heteroplasmy level higher than 60%: 8 missense, 29 rRNA and 12 tRNA variants. A total of 28.6% of ASD and 30.5% of ID subjects carried at least one putative pathogenic mtDNA mutation. The high frequency of CAMDs, the low mtDNA content and the presence of putative pathogenic mtDNA mutations observed in both ASD and ID subjects are evidence of mitochondrial dysfunction in ASD and ID.

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.

Mitochondrial Dysfunction as a Neurobiological Subtype of Autism Spectrum Disorder

Impaired mitochondrial function impacts many biological processes that depend heavily on energy and metabolism and can lead to a wide range of neurodevelopmental disorders, including autism spectrum disorder (ASD). Although evidence that mitochondrial dysfunction is a biological subtype of ASD has grown in recent years, no study, to our knowledge, has demonstrated evidence of mitochondrial dysfunction in brain tissue in vivo in a large, well-defined sample of individuals with ASD. To assess brain lactate in individuals with ASD and typically developing controls using high-resolution, multiplanar spectroscopic imaging; to map the distribution of lactate in the brains of individuals with ASD; and to assess correlations of elevated brain lactate with age, autism subtype, and intellectual ability. Case-control study at Columbia University Medical Center and New York State Psychiatric Institute involving 75 children and adults with ASD and 96 age- and sex-matched, typically developing controls. Lactate doublets (present or absent) on brain magnetic resonance spectroscopic imaging. Lactate doublets were present at a significantly higher rate in participants with ASD (13%) than controls (1%) (P = .001). In the ASD group, the presence of lactate doublets correlated significantly with age (P = .004) and was detected more often in adults (20%) than in children (6%), though it did not correlate with sex, ASD subtype, intellectual ability, or the Autism Diagnostic Observation Schedule total score or subscores. In those with ASD, lactate was detected most frequently within the cingulate gyrus but it was also present in the subcortical gray matter nuclei, corpus callosum, superior temporal gyrus, and pre- and postcentral gyri. In vivo brain findings provide evidence for a possible neurobiological subtype of mitochondrial dysfunction in ASD.

Redox metabolism abnormalities in autistic children associated with mitochondrial disease

Research studies have uncovered several metabolic abnormalities associated with autism spectrum disorder (ASD), including mitochondrial disease (MD) and abnormal redox metabolism. Despite the close connection between mitochondrial dysfunction and oxidative stress, the relation between MD and oxidative stress in children with ASD has not been studied. Plasma markers of oxidative stress and measures of cognitive and language development and ASD behavior were obtained from 18 children diagnosed with ASD who met criteria for probable or definite MD per the Morava et al. criteria (ASD/MD) and 18 age and gender-matched ASD children without any biological markers or symptoms of MD (ASD/NoMD). Plasma measures of redox metabolism included reduced free glutathione (fGSH), oxidized glutathione (GSSG), the fGSH/GSSG ratio and 3-nitrotyrosine (3NT). In addition, a plasma measure of chronic immune activation, 3-chlorotyrosine (3CT), was also measured. Language was measured using the preschool language scale or the expressive one-word vocabulary test (depending on the age), adaptive behaviour was measured using the Vineland Adaptive Behavior Scale (VABS) and core autism symptoms were measured using the Autism Symptoms Questionnaire and the Social Responsiveness Scale. Children with ASD/MD were found to have lower scores on the communication and daily living skill subscales of the VABS despite having similar language and ASD symptoms. Children with ASD/MD demonstrated significantly higher levels of fGSH/GSSG and lower levels of GSSG as compared with children with ASD/NoMD, suggesting an overall more favourable glutathione redox status in the ASD/MD group. However, compare with controls, both ASD groups demonstrated lower fGSH and fGSH/GSSG, demonstrating that both groups suffer from redox abnormalities. Younger ASD/MD children had higher levels of 3CT than younger ASD/NoMD children because of an age-related effect in the ASD/MD group. Both ASD groups demonstrated significantly higher 3CT levels than control subjects, suggesting that chronic inflammation was present in both groups of children with ASD. Interestingly, 3NT was found to correlate positively with several measures of cognitive function, development and behavior for the ASD/MD group, but not the ASD/NoMD group, such that higher 3NT concentrations were associated with more favourable adaptive behaviour, language and ASD-related behavior. To determine whether difference in receiving medications and/or supplements could account for the differences in redox and inflammatory biomarkers across ASD groups, we examined differences in medication and supplements across groups and their effect of redox and inflammatory biomarkers. Overall, significantly more participants in the ASD/MD group were receiving folate, vitamin B12, carnitine, co-enzyme Q10, B vitamins and antioxidants. We then determined whether folate, carnitine, co-enzyme Q10, B vitamins and/or antioxidants influenced redox or inflammatory biomarkers. Antioxidant supplementation was associated with a significantly lower GSSG, whereas antioxidants, co-enzyme Q10 and B vitamins were associated with a higher fGSH/GSSG ratio. There was no relation between folate, carnitine, co-enzyme Q10, B vitamins and antioxidants with 3NT, 3CT or fGSH. Overall, our findings suggest that ASD/MD children with a more chronic oxidized microenvironment have better development. We interpret this finding in light of the fact that more active mitochondrial can create a greater oxidized microenvironment especially when dysfunctional. Thus, compensatory upregulation of mitochondria which are dysfunctional may both increase activity and function at the expense of a more oxidized microenvironment. Although more ASD/MD children were receiving certain supplements, the use of such supplements were not found to be related to the redox biomarkers that were related to cognitive development or behavior in the ASD/MD group but could possibly account for the difference in glutathione metabolism noted between groups. This study suggests that different subgroups of children with ASD have different redox abnormalities, which may arise from different sources. A better understanding of the relationship between mitochondrial dysfunction in ASD and oxidative stress, along with other factors that may contribute to oxidative stress, will be critical to understanding how to guide treatment and management of ASD children. This study also suggests that it is important to identify ASD/MD children as they may respond differently to specific treatments because of their specific metabolic profile.

Mitochondrial abnormalities in temporal lobe of autistic brain

Autism spectrum disorder (ASD) consists of a group of complex developmental disabilities characterized by impaired social interactions, deficits in communication and repetitive behavior. Multiple lines of evidence implicate mitochondrial dysfunction in ASD. In postmortem BA21 temporal cortex, a region that exhibits synaptic pathology in ASD, we found that compared to controls, ASD patients exhibited altered protein levels of mitochondria respiratory chain protein complexes, decreased Complex I and IV activities, decreased mitochondrial antioxidant enzyme SOD2, and greater oxidative DNA damage. Mitochondrial membrane mass was higher in ASD brain, as indicated by higher protein levels of mitochondrial membrane proteins Tom20, Tim23 and porin. No differences were observed in either mitochondrial DNA or levels of the mitochondrial gene transcription factor TFAM or cofactor PGC1α, indicating that a mechanism other than alterations in mitochondrial genome or mitochondrial biogenesis underlies these mitochondrial abnormalities. We further identified higher levels of the mitochondrial fission proteins (Fis1 and Drp1) and decreased levels of the fusion proteins (Mfn1, Mfn2 and Opa1) in ASD patients, indicating altered mitochondrial dynamics in ASD brain. Many of these changes were evident in cortical pyramidal neurons, and were observed in ASD children but were less pronounced or absent in adult patients. Together, these findings provide evidence that mitochondrial function and intracellular redox status are compromised in pyramidal neurons in ASD brain and that mitochondrial dysfunction occurs during early childhood when ASD symptoms appear.

Mitochondrial Dysfunction Can Connect the Diverse Medical Symptoms Associated With Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a devastating neurodevelopmental disorder. Over the past decade, evidence has emerged that some children with ASD suffer from undiagnosed comorbid medical conditions. One of the medical disorders that has been consistently associated with ASD is mitochondrial dysfunction. Individuals with mitochondrial disorders without concomitant ASD manifest dysfunction in multiple high-energy organ systems, such as the central nervous, muscular, and gastrointestinal (GI) systems. Interestingly, these are the identical organ systems affected in a significant number of children with ASD. This finding increases the possibility that mitochondrial dysfunction may be one of the keys that explains the many diverse symptoms observed in some children with ASD. This article will review the importance of mitochondria in human health and disease, the evidence for mitochondrial dysfunction in ASD, the potential role of mitochondrial dysfunction in the comorbid medical conditions associated with ASD, and how mitochondrial dysfunction can bridge the gap for understanding how these seemingly disparate medical conditions are related. We also review the limitations of this evidence and other possible explanations for these findings. This new understanding of ASD should provide researchers a pathway for understanding the etiopathogenesis of ASD and clinicians the potential to develop medical therapies.

Mitochondrial dysfunction in autism spectrum disorders: a systematic review and meta-analysis

A comprehensive literature search was performed to collate evidence of mitochondrial dysfunction in autism spectrum disorders (ASDs) with two primary objectives. First, features of mitochondrial dysfunction in the general population of children with ASD were identified. Second, characteristics of mitochondrial dysfunction in children with ASD and concomitant mitochondrial disease (MD) were compared with published literature of two general populations: ASD children without MD, and non-ASD children with MD. The prevalence of MD in the general population of ASD was 5.0% (95% confidence interval 3.2, 6.9%), much higher than found in the general population (∼0.01%). The prevalence of abnormal biomarker values of mitochondrial dysfunction was high in ASD, much higher than the prevalence of MD. Variances and mean values of many mitochondrial biomarkers (lactate, pyruvate, carnitine and ubiquinone) were significantly different between ASD and controls. Some markers correlated with ASD severity. Neuroimaging, in vitro and post-mortem brain studies were consistent with an elevated prevalence of mitochondrial dysfunction in ASD. Taken together, these findings suggest children with ASD have a spectrum of mitochondrial dysfunction of differing severity. Eighteen publications representing a total of 112 children with ASD and MD (ASD/MD) were identified. The prevalence of developmental regression (52%), seizures (41%), motor delay (51%), gastrointestinal abnormalities (74%), female gender (39%), and elevated lactate (78%) and pyruvate (45%) was significantly higher in ASD/MD compared with the general ASD population. The prevalence of many of these abnormalities was similar to the general population of children with MD, suggesting that ASD/MD represents a distinct subgroup of children with MD. Most ASD/MD cases (79%) were not associated with genetic abnormalities, raising the possibility of secondary mitochondrial dysfunction. Treatment studies for ASD/MD were limited, although improvements were noted in some studies with carnitine, co-enzyme Q10 and B-vitamins. Many studies suffered from limitations, including small sample sizes, referral or publication biases, and variability in protocols for selecting children for MD workup, collecting mitochondrial biomarkers and defining MD. Overall, this evidence supports the notion that mitochondrial dysfunction is associated with ASD. Additional studies are needed to further define the role of mitochondrial dysfunction in ASD.

Autism and mitochondrial disease

Autism spectrum disorder (ASD) as defined by the revised Diagnostic and Statistical Manual of Mental Disorders: DSM IVTR criteria (American Psychiatric Association [2000] Washington, DC: American Psychiatric Publishing) as impairment before the age of 3 in language development and socialization with the development of repetitive behaviors, appears to be increased in incidence and prevalence. Similarly, mitochondrial disorders are increasingly recognized. Although overlap between these disorders is to be expected, accumulating clinical, genetic, and biochemical evidence suggests that mitochondrial dysfunction in ASD is more commonly seen than expected. Some patients with ASD phenotypes clearly have genetic-based primary mitochondrial disease. This review will examine the data linking autism and mitochondria.