Investigation of antioxidant enzymes in children with autistic disorder

Glucocorticoids alter neuronal differentiation of human neuroepithelial-like cells by inducing long-lasting changes in the reactive oxygen species balance

Prenatal exposure to excess glucocorticoid has been shown to have adverse effects on the developing nervous system that may lead to alterations of fetal and adult neurogenesis, resulting in behavioral changes. In addition, an imbalance of the redox state, with an increased susceptibility to oxidative stress, has been observed in rodent neural stem cells exposed to the synthetic glucocorticoid analog dexamethasone (Dex). In the present study, we used the induced pluripotent stem cells (IPSC)-derived lt-NES AF22 cell line, representative of the neuroepithelial stage in central nervous system development, to investigate the heritable effects of Dex on reactive oxygen species (ROS) balance and its impact on neuronal differentiation. By analysing gene expression in daughter cells that were never directly exposed to Dex, we could observe a downregulation of four key antioxidant enzymes, namely Catalase, superoxide dismutase 1, superoxide dismutase 2 and glutathione peroxidase7, along with an increased intracellular ROS concentration. The imbalance in the intracellular REDOX state was associated to a significant downregulation of major neuronal markers and a concomitant increase of glial cells. Interestingly, upon treatment with the antioxidant N-acetyl-cysteine (NAC), the misexpression of both neuronal and glial markers analyzed was recovered. These novel findings point to the increased ROS concentration playing a direct role in the heritable alterations of the differentiation potential induced by Dex exposure. Moreover, the data support the hypothesis that early insults may have detrimental long-lasting consequences on neurogenesis. Based on the positive effects exerted by NAC, it is conceivable that therapeutic strategies including antioxidants may be effective in the treatment of neuropsychiatric disorders that have been associated to increased ROS and impaired neurogenesis.

Increased ω-3 polyunsaturated fatty acid/arachidonic acid ratios and upregulation of signaling mediator in individuals with autism spectrum disorders

AIMS

The investigation of links between the ratio of omega-3/omega-6 PUFAs and neuronal signaling is a research priority in autism spectrum disorders (ASD).

MAIN METHODS

We examine the relationships between the plasma ratios of docosahexaenoid acid (DHA)/arachidonic acid (AA) and eicopentaenoic acid (EPA)/AA and biomarkers of AA-related signaling mediators such as ceruloplasmin, transferrin and superoxide dismutase, in the behavioral symptoms of 28 individuals with ASD (mean age 13.5±4.6years) and 21 age- and gender-matched normal healthy controls (mean age 13.9±5.7years). Behavioral symptoms were assessed using the Aberrant Behavior Checklists (ABC). We conducted controlling for dietary intake and assessed the dietary intake of nutrients.

KEY FINDINGS

There were no significant differences in intake of nutrients such as omega-3 and omega-6 PUFAs, saturated and unsaturated fatty acid, DHA, AA, iron and copper. Plasma EPA, DHA, and arachidic acid levels, and plasma DHA/AA and EPA/AA ratios were significantly higher, while plasma AA and adrenic acid were significantly lower in the 28 individuals with ASD than in the 21 normal controls. The ABC scores were significantly higher in the ASD group compared to the control group. The plasma ceruloplasmin levels in the ASD group were significantly reduced compared to those in the control group.

SIGNIFICANCE

Increased plasma DHA/AA and EPA/AA ratios may be related to low plasma levels of ceruloplasmin which has neuroprotective properties. Reduced plasma ceruloplasmin levels may diminish the protective capacity against brain damage, and may contribute to the pathophysiology of behavioral symptoms in individuals with ASD.

Exploring the Validity of Valproic Acid Animal Model of Autism

The valproic acid (VPA) animal model of autism spectrum disorder (ASD) is one of the most widely used animal model in the field. Like any other disease models, it can't model the totality of the features seen in autism. Then, is it valid to model autism? This model demonstrates many of the structural and behavioral features that can be observed in individuals with autism. These similarities enable the model to define relevant pathways of developmental dysregulation resulting from environmental manipulation. The uncovering of these complex pathways resulted to the growing pool of potential therapeutic candidates addressing the core symptoms of ASD. Here, we summarize the validity points of VPA that may or may not qualify it as a valid animal model of ASD.

Active ribosomal genes, translational homeostasis and oxidative stress in the pathogenesis of schizophrenia and autism

BACKGROUND

Infantile autism and schizophrenia are severe multifactorial disorders with a pronounced genetic predisposition. Their pathogeneses are often associated with oxidative stress in the brain. Previously, we established that a cell's resistance to oxidative stress depended on the copy number of transcriptionally active genes for rRNA (ribosomal genes) in the cell's genome. The feature is measured cytogenetically in cultured lymphocytes derived from patients. It varies from 120 up to 190 copies per diploid genome, with an arithmetic mean of 150±4 (SE) copies in a healthy population (n=239), being considerably lower, according to our previous results, in a sample of patients with rheumatoid arthritis (n=49), another multifactorial disease with a proven significant role of oxidative stress in its pathogenesis: from 115 to 165 copies, with a mean of 140±4 (SE). Conversely, a sample of schizophrenic patients (n=42) previously showed a higher value of copy number of active rRNA genes compared with a healthy population: from 145 to 190 copies, with a mean of 170±4. This fact is of special interest in the context of the well-known, but still unexplained phenomenon of the reduced comorbidity rate of schizophrenia and rheumatoid arthritis.

RESULTS

The copy number of active ribosomal genes was estimated in a sample of autistic children (n=51). In contrast with the schizophrenic patients studied previously, we found that the values were significantly lower than those in the healthy population: from 125 to 160 copies, with a mean of 142±5. In this work, we suggest a mathematical model of the oxidative stress dynamics on the basis of Lotka-Volterra's approach to predator-prey interactions. In our model, the 'prey' represents reactive oxygen species, whereas the 'predator' simulates molecules of the antioxidant enzymes. The rate of biosynthesis of the latter is limited by the number of ribosomes available, which, in turn, is determined by the copy number of active rRNA genes. Analysis of the model showed the existence of a unique equilibrium point that makes biological sense. The reactive oxygen species level oscillatory approaches this equilibrium value, which inversely depends on the copy number of active rRNA genes.

DISCUSSION

Our findings confirm the hypothesis of disturbance of the 'translational homeostasis' in the pathogeneses of autism and schizophrenia, and would help explain why oxidative stress markers are discovered in most autism studies, whereas similar reports related to schizophrenia are far less consistent.

Are ASD and ADHD a Continuum? A Comparison of Pathophysiological Similarities Between the Disorders

OBJECTIVE

The objective of this study was to review and compare the similarities between autism spectrum disorder (ASD) and ADHD with regard to symptomatology, neurological deficits, metabolic and endocrine-related conditions, and brain pathology.

METHOD

A comprehensive review of the relevant research literature was carried out.

RESULTS

A number of important similarities between ASD and ADHD were identified, including recent increases in prevalence, male-biased incidence, shared involvement of sensory processing, motor and impulse control, abnormal patterns of neural connectivity, and sleep disturbances. Studies suggest involvement of androgen metabolism, impaired methylation, and heavy metal toxicity as possible contributing factors for both disorders.

CONCLUSION

ASD and ADHD share a number of features and pathophysiological conditions, which suggests that the two disorders may be a continuum and have a common origin.

Evaluation of Oxidative Metabolism in Child and Adolescent Patients with Attention Deficit Hyperactivity Disorder

OBJECTIVE

Oxidative metabolism is impaired in several medical conditions including psychiatric disorders, and this imbalance may be involved in the etiology of these diseases. The present study evaluated oxidative balance in pediatric and adolescent patients with attention deficit hyperactivity disorder (ADHD).

METHODS

The study included 48 children and adolescents (34 male, 14 female) with ADHD who had no neurological, systemic, or comorbid psychiatric disorders, with the exception of oppositional defiant disorder (ODD), and 24 sex- and age-matched healthy controls (17 male and seven female).

RESULTS

TAS was significantly lower, and TOS and OSI were significantly higher in patients with ADHD than in healthy controls. Total antioxidant levels were lower in patients with comorbid ODD than in those with no comorbidity. No difference was found in TOS or OSI among the ADHD subtypes; however, TAS was higher in the attention-deficient subtype.

CONCLUSION

Our findings demonstrated that oxidative balance is impaired and oxidative stress is increased in children and adolescents with ADHD. This results are consistent with those of previous studies.

Oxidative stress as an etiological factor and a potential treatment target of psychiatric disorders. Part 2. Depression, anxiety, schizophrenia and autism

The pathophysiology of psychiatric diseases, including depression, anxiety, schizophrenia and autism, is far from being fully elucidated. In recent years, a potential role of the oxidative stress has been highlighted in the pathogenesis of neuropsychiatric disorders. A body of clinical and preclinical evidence indicates that psychiatric diseases are characterized by higher levels of oxidative biomarkers and with lower levels of antioxidant defense biomarkers in the brain and peripheral tissues. In this article, we review current knowledge on the role of the oxidative stress in psychiatric diseases, based on clinical trials and animal studies, in addition, we analyze the effects of drug-induced modulation of oxidative balance and explore pharmacotherapeutic strategies for oxidative stress reduction.

Eicosanoids Derived From Arachidonic Acid and Their Family Prostaglandins and Cyclooxygenase in Psychiatric Disorders

Arachidonic acid (AA)-derived lipid mediators are called eicosanoids. Eicosanoids have emerged as key regulators of a wide variety of physiological responses and pathological processes, and control important cellular processes. AA can be converted into biologically active compounds by metabolism by cyclooxygenases (COX). Beneficial effect of COX-2 inhibitor celecoxib add-on therapy has been reported in early stage of schizophrenia. Moreover, add-on treatment of celecoxib attenuated refractory depression and bipolar depression. Further, the COX/prostaglandin E pathway play an important role in synaptic plasticity and may be included in pathophysiology in autism spectrum disorders (ASD). In this regard, plasma transferrin, which is an iron mediator related to eicosanoid signaling, may be related to social impairment of ASD. COX-2 is typically induced by inflammatory stimuli in the majority of tissues, and the only isoform responsible for propagating the inflammatory response. Thus, COX-2 inhibitors considered as the best target for Alzheimer's disease.

Bisphenol A induces oxidative stress and mitochondrial dysfunction in lymphoblasts from children with autism and unaffected siblings

Autism is a behaviorally defined neurodevelopmental disorder. Although there is no single identifiable cause for autism, roles for genetic and environmental factors have been implicated in autism. Extensive evidence suggests increased oxidative stress and mitochondrial dysfunction in autism. In this study, we examined whether bisphenol A (BPA) is an environmental risk factor for autism by studying its effects on oxidative stress and mitochondrial function in the lymphoblasts. When lymphoblastoid cells from autistic subjects and age-matched unaffected sibling controls were exposed to BPA, there was an increase in the generation of reactive oxygen species (ROS) and a decrease in mitochondrial membrane potential in both groups. A further subdivision of the control group into two subgroups-unaffected nontwin siblings and twin siblings-showed significantly higher ROS levels without any exposure to BPA in the unaffected twin siblings compared to the unaffected nontwin siblings. ROS levels were also significantly higher in the autism vs the unaffected nontwin siblings group. The effect of BPA on three important mtDNA genes-NADH dehydrogenase 1, NADH dehydrogenase 4, and cytochrome b-was analyzed to observe any changes in the mitochondria after BPA exposure. BPA induced a significant increase in the mtDNA copy number in the lymphoblasts from the unaffected siblings group and in the unaffected twin siblings group vs the unaffected nontwin siblings. In all three genes, the mtDNA increase was seen in 70% of the subjects. These results suggest that BPA exposure results in increased oxidative stress and mitochondrial dysfunction in the autistic subjects as well as the age-matched sibling control subjects, particularly unaffected twin siblings. Therefore, BPA may act as an environmental risk factor for autism in genetically susceptible children by inducing oxidative stress and mitochondrial dysfunction.

Escape from homeostasis

Many physiological systems, from gene networks to biochemistry to whole organism physiology, exhibit homeostatic mechanisms that keep certain variables within a fairly narrow range. Because homeostatic mechanisms buffer traits against environmental and genetic variation they allow the accumulation of cryptic genetic variation. Homeostatic mechanisms are never perfect and can be destabilized by mutations in genes that alter the kinetics of the underlying mechanism. We use mathematical models to study five diverse mechanisms of homeostasis: thermoregulation; maintenance of homocysteine concentration; neural control by a feed forward circuit; the myogenic response in the kidney; and regulation of extracellular dopamine levels in the brain. In all these cases there are homeostatic regions where the trait is relatively insensitive to genetic or environmental variation, flanked by regions where it is sensitive. Moreover, mutations or environmental changes can place an individual closer to the edge of the homeostatic region, thus predisposing that individual to deleterious effects caused by additional mutations or environmental changes. Mutations and environmental variables can also reduce the size of the homeostatic region, thus releasing potentially deleterious cryptic genetic variation. These considerations of mutations, environment, homeostasis, and escape from homeostasis help to explain why the etiology of so many diseases is complex.

Evidence linking oxidative stress, mitochondrial dysfunction, and inflammation in the brain of individuals with autism

Autism spectrum disorders (ASDs) are a heterogeneous group of neurodevelopmental disorders that are defined solely on the basis of behavioral observations. Therefore, ASD has traditionally been framed as a behavioral disorder. However, evidence is accumulating that ASD is characterized by certain physiological abnormalities, including oxidative stress, mitochondrial dysfunction and immune dysregulation/inflammation. While these abnormalities have been reported in studies that have examined peripheral biomarkers such as blood and urine, more recent studies have also reported these abnormalities in brain tissue derived from individuals diagnosed with ASD as compared to brain tissue derived from control individuals. A majority of these brain tissue studies have been published since 2010. The brain regions found to contain these physiological abnormalities in individuals with ASD are involved in speech and auditory processing, social behavior, memory, and sensory and motor coordination. This manuscript examines the evidence linking oxidative stress, mitochondrial dysfunction and immune dysregulation/inflammation in the brain of ASD individuals, suggesting that ASD has a clear biological basis with features of known medical disorders. This understanding may lead to new testing and treatment strategies in individuals with ASD.

The need for a comprehensive molecular characterization of autism spectrum disorders

Autism spectrum disorders (ASD) are a heterogeneous group of disorders which have complex behavioural phenotypes. Although ASD is a highly heritable neuropsychiatric disorder, genetic research alone has not provided a profound understanding of the underlying causes. Recent developments using biochemical tools such as transcriptomics, proteomics and cellular models, will pave the way to gain new insights into the underlying pathological pathways. This review addresses the state-of-the-art in the search for molecular biomarkers for ASD. In particular, the most important findings in the biochemical field are highlighted and the need for establishing streamlined interaction between behavioural studies, genetics and proteomics is stressed. Eventually, these approaches will lead to suitable translational ASD models and, therefore, a better disease understanding which may facilitate novel drug discovery efforts in this challenging field.

Potential Role of Selenoenzymes and Antioxidant Metabolism in relation to Autism Etiology and Pathology

Autism and autism spectrum disorders (ASDs) are behaviorally defined, but the biochemical pathogenesis of the underlying disease process remains uncharacterized. Studies indicate that antioxidant status is diminished in autistic subjects, suggesting its pathology is associated with augmented production of oxidative species and/or compromised antioxidant metabolism. This suggests ASD may result from defects in the metabolism of cellular antioxidants which maintain intracellular redox status by quenching reactive oxygen species (ROS). Selenium-dependent enzymes (selenoenzymes) are important in maintaining intercellular reducing conditions, particularly in the brain. Selenoenzymes are a family of ~25 genetically unique proteins, several of which have roles in preventing and reversing oxidative damage in brain and endocrine tissues. Since the brain's high rate of oxygen consumption is accompanied by high ROS production, selenoenzyme activities are particularly important in this tissue. Because selenoenzymes can be irreversibly inhibited by many electrophiles, exposure to these organic and inorganic agents can diminish selenoenzyme-dependent antioxidant functions. This can impair brain development, particularly via the adverse influence of oxidative stress on epigenetic regulation. Here we review the physiological roles of selenoproteins in relation to potential biochemical mechanisms of ASD etiology and pathology.

Ubiquinol improves symptoms in children with autism

BACKGROUND

Autism is a spectrum of neurodevelopmental disorders with manifestation within 3 years after birth. Manifestations of autism include behavior problems (hyperactivity, toys destruction, self-harm, and aggression) and sleep and eating disorders. Etiology of autism is poorly understood. Oxidative stress and antioxidants can participate in pathobiochemical mechanisms of autism.

METHODS

Twenty-four children, aged 3-6 years, with autism according to the DSM IV criteria and using CARS were included in the study. Concentrations of CoQ10-TOTAL, γ- and α-tocopherol, β-carotene, and lipid peroxidation were determined in plasma before and after three months of supportive therapy with ubiquinol at a daily dose 2 × 50 mg. Data on behavior of the children were collected from parents at the same time.

RESULTS

Ubiquinol supportive therapy improved symptoms in children with autism, as communication with parents (in 12%), verbal communication (in 21%), playing games of children (in 42%), sleeping (in 34%), and food rejection (in 17%), with CoQ10-TOTAL plasma level above 2.5 μmol/L.

CONCLUSIONS

Beneficial effect of ubiquinol in children with autism has been demonstrated for the first time. We assume that plasma concentration of CoQ10-TOTAL and lipid peroxidation could be used as relevant biomarkers of ubiquinol supportive therapy.

Necrosis is increased in lymphoblastoid cell lines from children with autism compared with their non-autistic siblings under conditions of oxidative and nitrosative stress

Autism spectrum disorders are a heterogeneous group of neurodevelopmental conditions characterised by impairments in reciprocal social interaction, communication and stereotyped behaviours. As increased DNA damage events have been observed in a range of other neurological disorders, it was hypothesised that they would be elevated in lymphoblastoid cell lines (LCLs) obtained from children with autism compared with their non-autistic siblings. Six case-sibling pairs of LCLs from children with autistic disorder and their non-autistic siblings were obtained from the Autism Genetic Resource Exchange (AGRE) and cultured in standard RPMI-1640 tissue culture medium. Cells were exposed to medium containing either 0, 25, 50, 100 and 200 µM hydrogen peroxide (an oxidative stressor) or 0, 5, 10, 20 and 40 µM s-nitroprusside (a nitric oxide producer) for 1h. Following exposure, the cells were microscopically scored for DNA damage, cytostasis and cytotoxicity biomarkers as measured using the cytokinesis-block micronucleus cytome assay. Necrosis was significantly increased in cases relative to controls when exposed to oxidative and nitrosative stress (P = 0.001 and 0.01, respectively). Nuclear division index was significantly lower in LCLs from children with autistic disorder than their non-autistic siblings when exposed to hydrogen peroxide (P = 0.016), but there was no difference in apoptosis, micronucleus frequency, nucleoplasmic bridges or nuclear buds. Exposure to s-nitroprusside significantly increased the number of micronuclei in non-autistic siblings compared with cases (P = 0.003); however, other DNA damage biomarkers, apoptosis and nuclear division did not differ significantly between groups. The findings of this study show (i) that LCLs from children with autism are more sensitive to necrosis under conditions of oxidative and nitrosative stress than their non-autistic siblings and (ii) refutes the hypothesis that children with autistic disorder are abnormally susceptible to DNA damage.

Impaired synthesis and antioxidant defense of glutathione in the cerebellum of autistic subjects: alterations in the activities and protein expression of glutathione-related enzymes

Autism is a neurodevelopmental disorder associated with social deficits and behavioral abnormalities. Recent evidence in autism suggests a deficit in glutathione (GSH), a major endogenous antioxidant. It is not known whether the synthesis, consumption, and/or regeneration of GSH is affected in autism. In the cerebellum tissues from autism (n=10) and age-matched control subjects (n=10), the activities of GSH-related enzymes glutathione peroxidase (GPx), glutathione-S-transferase (GST), glutathione reductase (GR), and glutamate cysteine ligase (GCL) involved in antioxidant defense, detoxification, GSH regeneration, and synthesis, respectively, were analyzed. GCL is a rate-limiting enzyme for GSH synthesis, and the relationship between its activity and the protein expression of its catalytic subunit GCLC and its modulatory subunit GCLM was also compared between the autistic and the control groups. Results showed that the activities of GPx and GST were significantly decreased in autism compared to that of the control group (P<0.05). Although there was no significant difference in GR activity between autism and control groups, 40% of autistic subjects showed lower GR activity than 95% confidence interval (CI) of the control group. GCL activity was also significantly reduced by 38.7% in the autistic group compared to the control group (P=0.023), and 8 of 10 autistic subjects had values below 95% CI of the control group. The ratio of protein levels of GCLC to GCLM in the autism group was significantly higher than that of the control group (P=0.022), and GCLM protein levels were reduced by 37.3% in the autistic group compared to the control group. A positive strong correlation was observed between GCL activity and protein levels of GCLM (r=0.887) and GCLC (r=0.799) subunits in control subjects but not in autistic subjects, suggesting that regulation of GCL activity is affected in autism. These results suggest that enzymes involved in GSH homeostasis have impaired activities in the cerebellum in autism, and lower GCL activity in autism may be related to decreased protein expression of GCLM.

Body mass index, dietary intake and feeding problems of Turkish children with autism spectrum disorder (ASD)

The body mass index of 164 children (aged 4-18 years) attending four autism rehabilitation centers in Istanbul, Turkey, was determined and assessed using the BMI-for-age percentile charts by the World Health Organization (WHO). The mean intake of energy and nutrients of 115 children were calculated using three-day food records. The feeding assessment surveys filled in by the parents/caregivers indicated that the major feeding problem among children was food selectivity. The majority of the children were overweight or obese (58.5%). A total of 11% of children were found to be severely thin and thin. The calcium, zinc, vitamin B6 and folate intake of the majority of children were inadequate. The salt consumption in all age groups and cholesterol intake in normal, overweight and obese children were high.

Rare single nucleotide polymorphisms in the regulatory regions of the superoxide dismutase genes in autism spectrum disorder

Oxidative stress is suspected to be one of the several contributing factors in the etiology of autism spectrum disorder (ASD). We analyzed genes of the superoxide dismutase family (SOD1, SOD2, and SOD3) that are part of a major antioxidative stress system in human in order to detect the genetic variants contributing to the development of ASD. Using the optimized high-resolution melting (HRM) analysis, we identified two rare single nucleotide polymorphisms (SNPs) associated with the etiology of ASD. Both are located in the superoxide dismutase 1 (SOD1) gene and have a minor allele frequency in healthy population ~5%. The SNP c.239 + 34A>C (rs2234694) and SNP g.3341C>G (rs36233090) were detected with an odds ratio of 2.65 and P < 0.01. Both are located in the noncoding potentially regulatory regions of the SOD1 gene. This adds to the importance of rare SNPs in the etiology of complex diseases as well as to the importance of noncoding genetic variants analysis with a potential influence on the regulation of gene expression.

Air pollution and newly diagnostic autism spectrum disorders: a population-based cohort study in Taiwan

There is limited evidence that long-term exposure to ambient air pollution increases the risk of childhood autism spectrum disorder (ASD). The objective of the study was to investigate the associations between long-term exposure to air pollution and newly diagnostic ASD in Taiwan. We conducted a population-based cohort of 49,073 children age less than 3 years in 2000 that were retrieved from Taiwan National Insurance Research Database and followed up from 2000 through 2010. Inverse distance weighting method was used to form exposure parameter for ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particles with aerodynamic diameter less than 10 µm (PM10). Time-dependent Cox proportional hazards (PH) model was performed to evaluate the relationship between yearly average exposure air pollutants of preceding years and newly diagnostic ASD. The risk of newly diagnostic ASD increased according to increasing O3, CO, NO2, and SO2 levels. The effect estimate indicating an approximately 59% risk increase per 10 ppb increase in O3 level (95% CI 1.42–1.79), 37% risk increase per 100 ppb in CO (95% CI 1.31–1.44), 340% risk increase per 10 ppb increase in NO2 level (95% CI 3.31–5.85), and 17% risk increase per 1 ppb in SO2 level (95% CI 1.09–1.27) was stable with different combinations of air pollutants in the multi-pollutant models. Our results provide evident that children exposure to O3, CO, NO2, and SO2 in the preceding 1 year to 4 years may increase the risk of ASD diagnosis.

Camel Milk as a Potential Therapy as an Antioxidant in Autism Spectrum Disorder (ASD)

Extensive studies have demonstrated that oxidative stress plays a vital role in the pathology of several neurological diseases, including autism spectrum disorder (ASD); those studies proposed that GSH and antioxidant enzymes have a pathophysiological role in autism. Furthermore, camel milk has emerged to have potential therapeutic effects in autism. The aim of the current study was to evaluate the effect of camel milk consumption on oxidative stress biomarkers in autistic children, by measuring the plasma levels of glutathione, superoxide dismutase, and myeloperoxidase before and 2 weeks after camel milk consumption, using the ELISA technique. All measured parameters exhibited significant increase after camel milk consumption (P < 0.5). These findings suggest that camel milk could play an important role in decreasing oxidative stress by alteration of antioxidant enzymes and nonenzymatic antioxidant molecules levels, as well as the improvement of autistic behaviour as demonstrated by the improved Childhood Autism Rating Scale (CARS).

Role of NAD(+), Oxidative Stress, and Tryptophan Metabolism in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a pervasive neuro-developmental disorder characterized by impaired social interaction, reduced/absent verbal and non-verbal communication, and repetitive behavior during early childhood. The etiology of this developmental disorder is poorly understood, and no biomarkers have been identified. Identification of novel biochemical markers related to autism would be advantageous for earlier clinical diagnosis and intervention. Studies suggest that oxidative stress-induced mechanisms and reduced antioxidant defense, mitochondrial dysfunction, and impaired energy metabolism (NAD(+), NADH, ATP, pyruvate, and lactate), are major causes of ASD. This review provides renewed insight regarding current autism research related to oxidative stress, mitochondrial dysfunction, and altered tryptophan metabolism in ASD.

Age-dependent decrease and alternative splicing of methionine synthase mRNA in human cerebral cortex and an accelerated decrease in autism

The folate and vitamin B12-dependent enzyme methionine synthase (MS) is highly sensitive to cellular oxidative status, and lower MS activity increases production of the antioxidant glutathione, while simultaneously decreasing more than 200 methylation reactions, broadly affecting metabolic activity. MS mRNA levels in postmortem human cortex from subjects across the lifespan were measured and a dramatic progressive biphasic decrease of more than 400-fold from 28 weeks of gestation to 84 years was observed. Further analysis revealed alternative splicing of MS mRNA, including deletion of folate-binding domain exons and age-dependent deletion of exons from the cap domain, which protects vitamin B12 (cobalamin) from oxidation. Although three species of MS were evident at the protein level, corresponding to full-length and alternatively spliced mRNA transcripts, decreasing mRNA levels across the lifespan were not associated with significant changes in MS protein or methionine levels. MS mRNA levels were significantly lower in autistic subjects, especially at younger ages, and this decrease was replicated in cultured human neuronal cells by treatment with TNF-α, whose CSF levels are elevated in autism. These novel findings suggest that rather than serving as a housekeeping enzyme, MS has a broad and dynamic role in coordinating metabolism in the brain during development and aging. Factors adversely affecting MS activity, such as oxidative stress, can be a source of risk for neurological disorders across the lifespan via their impact on methylation reactions, including epigenetic regulation of gene expression.

Non-protein-bound iron and 4-hydroxynonenal protein adducts in classic autism

A link between oxidative stress and autism spectrum disorders (ASDs) remains controversial with opposing views on its role in the pathogenesis of the disease. We investigated for the first time the levels of non-protein-bound iron (NPBI), a pro-oxidant factor, and 4-hydroxynonenal protein adducts (4-HNE PAs), as a marker of lipid peroxidation-induced protein damage, in classic autism. Patients with classic autism (n=20, mean age 12.0±6.2years) and healthy controls (n=18, mean age 11.7±6.5years) were examined. Intraerythrocyte and plasma NPBI were measured by high performance liquid chromatography (HPLC), and 4-HNE PAs in erythrocyte membranes and plasma were detected by Western blotting. The antioxidant defences were evaluated as erythrocyte glutathione (GSH) levels using a spectrophotometric assay. Intraerythrocyte and plasma NPBI levels were significantly increased (1.98- and 3.56-folds) in autistic patients, as compared to controls (p=0.0019 and p<0.0001, respectively); likewise, 4-HNE PAs were significantly higher in erythrocyte membranes and in plasma (1.58- and 1.6-folds, respectively) from autistic patients than controls (p=0.0043 and p=0.0001, respectively). Erythrocyte GSH was slightly decreased (-10.34%) in patients compared to controls (p=0.0215). Our findings indicate an impairment of the redox status in classic autism patients, with a consequent imbalance between oxidative stress and antioxidant defences. Increased levels of NPBI could contribute to lipid peroxidation and, consequently, to increased plasma and erythrocyte membranes 4-HNE PAs thus amplifying the oxidative damage, potentially contributing to the autistic phenotype.

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.

Metabolic perturbance in autism spectrum disorders: a metabolomics study

Autism spectrum disorders (ASD) are a group of biological disorders with associated metabolic derangement. This study aimed to identify a pattern of metabolic perturbance in ASD using metabolomics in urinary specimens from 48 children with ASD and 53 age matched controls. Using a combination of liquid- and gas-chromatography-based mass spectrometry, we detected the levels of 82 metabolites (53 of which were increased) that were significantly altered between the ASD and the control groups using osmolality normalized data. Pattern analysis showed that the levels of several amino acids such as glycine, serine, threonine, alanine, histidine, glutamyl amino acids and the organic acid, taurine were significantly (p≤0.05) lower in ASD children. The levels of antioxidants such as carnosine were also reduced in ASD (p=0.054). Furthermore, several gut bacterial metabolites were significantly altered in ASD children who had gastrointestinal dysfunction. Overall, this study detected abnormal amino acid metabolism, increased oxidative stress, and altered gut microbiomes in ASD. The relationship of altered gut microbial co-metabolism and the disrupted metabolisms requires further investigation.

Metabolic imbalance associated with methylation dysregulation and oxidative damage in children with autism

Oxidative stress and abnormal DNA methylation have been implicated in the pathophysiology of autism. We investigated the dynamics of an integrated metabolic pathway essential for cellular antioxidant and methylation capacity in 68 children with autism, 54 age-matched control children and 40 unaffected siblings. The metabolic profile of unaffected siblings differed significantly from case siblings but not from controls. Oxidative protein/DNA damage and DNA hypomethylation (epigenetic alteration) were found in autistic children but not paired siblings or controls. These data indicate that the deficit in antioxidant and methylation capacity is specific for autism and may promote cellular damage and altered epigenetic gene expression. Further, these results suggest a plausible mechanism by which pro-oxidant environmental stressors may modulate genetic predisposition to autism.

A randomized controlled pilot trial of oral N-acetylcysteine in children with autism

BACKGROUND

An imbalance in the excitatory/inhibitory systems with abnormalities in the glutamatergic pathways has been implicated in the pathophysiology of autism. Furthermore, chronic redox imbalance was also recently linked to this disorder. The goal of this pilot study was to assess the feasibility of using oral N-acetylcysteine (NAC), a glutamatergic modulator and an antioxidant, in the treatment of behavioral disturbance in children with autism.

METHODS

This was a 12-week, double-blind, randomized, placebo-controlled study of NAC in children with autistic disorder. Subjects randomized to NAC were initiated at 900 mg daily for 4 weeks, then 900 mg twice daily for 4 weeks and 900 mg three times daily for 4 weeks. The primary behavioral measure (Aberrant Behavior Checklist [ABC] irritability subscale) and safety measures were performed at baseline and 4, 8, and 12 weeks. Secondary measures included the ABC stereotypy subscale, Repetitive Behavior Scale-Revised, and Social Responsiveness Scale.

RESULTS

Thirty-three subjects (31 male subjects, 2 female subjects; aged 3.2-10.7 years) were randomized in the study. Follow-up data was available on 14 subjects in the NAC group and 15 in the placebo group. Oral NAC was well tolerated with limited side effects. Compared with placebo, NAC resulted in significant improvements on ABC irritability subscale (F = 6.80; p < .001; d = .96).

CONCLUSIONS

Data from this pilot investigation support the potential usefulness of NAC for treating irritability in children with autistic disorder. Large randomized controlled investigations are warranted.

Oxidative stress-related biomarkers in autism: systematic review and meta-analyses

Autism spectrum disorders (ASDs) are rarely diagnosed in children younger than 2 years, because diagnosis is based entirely on behavioral tests. Oxidative damage may play a central role in this pathogenesis, together with the interconnected transmethylation cycle and transsulfuration pathway. In an attempt to clarify and quantify the relationship between oxidative stress-related blood biomarkers and ASDs, a systematic literature review was carried out. For each identified study, mean biomarker levels were compared in cases and controls providing a point estimate, the mean ratio, for each biomarker. After meta-analysis, the ASD patients showed decreased blood levels of reduced glutathione (27%), glutathione peroxidase (18%), methionine (13%), and cysteine (14%) and increased concentrations of oxidized glutathione (45%) relative to controls, whereas superoxide dismutase, homocysteine, and cystathionine showed no association with ASDs. For the C677T allele in the methylene tetrahydrofolate reductase gene (MTHFR), homozygous mutant subjects (TT) showed a meta-OR of 2.26 (95% CI 1.30-3.91) of being affected by ASD with respect to the homozygous nonmutant (CC). Case-control studies on blood levels of vitamins suggest a lack of association (folic acid and vitamin B12) or rare association (vitamins A, B6, C, D, E). Sparse results were available for other biomarkers (ceruloplasmin, catalase, cysteinylglycine, thiobarbituric acid-reactive substances, nitric oxide) and for polymorphisms in other genes. Existing evidence is heterogeneous and many studies are limited by small sample size and effects. In conclusion, existing evidence suggests a role for glutathione metabolism, the transmethylation cycle, and the transsulfuration pathway, although these findings should be interpreted with caution, and larger, more standardized studies are warranted.

The potential role of the antioxidant and detoxification properties of glutathione in autism spectrum disorders: a systematic review and meta-analysis

BACKGROUND

Glutathione has a wide range of functions; it is an endogenous anti-oxidant and plays a key role in the maintenance of intracellular redox balance and detoxification of xenobiotics. Several studies have indicated that children with autism spectrum disorders may have altered glutathione metabolism which could play a key role in the condition.

METHODS

A systematic literature review and meta-analysis was conducted of studies examining metabolites, interventions and/or genes of the glutathione metabolism pathways i.e. the γ-glutamyl cycle and trans-sulphuration pathway in autism spectrum disorders.

RESULTS

Thirty nine studies were included in the review comprising an in vitro study, thirty two metabolite and/or co-factor studies, six intervention studies and six studies with genetic data as well as eight studies examining enzyme activity.

CONCLUSIONS

The review found evidence for the involvement of the γ-glutamyl cycle and trans-sulphuration pathway in autistic disorder is sufficiently consistent, particularly with respect to the glutathione redox ratio, to warrant further investigation to determine the significance in relation to clinical outcomes. Large, well designed intervention studies that link metabolites, cofactors and genes of the γ-glutamyl cycle and trans-sulphuration pathway with objective behavioural outcomes in children with autism spectrum disorders are required. Future risk factor analysis should include consideration of multiple nutritional status and metabolite biomarkers of pathways linked with the γ-glutamyl cycle and the interaction of genotype in relation to these factors.

Etiology of autistic features: the persisting neurotoxic effects of propionic acid

BACKGROUND

Recent clinical observations suggest that certain gut and dietary factors may transiently worsen symptoms in autism. Propionic acid (PA) is a short chain fatty acid and an important intermediate of cellular metabolism. Although PA has several beneficial biological effects, its accumulation is neurotoxic.

METHODS

Two groups of young Western albino male rats weighing about 45 to 60 grams (approximately 21 days old) were used in the present study. The first group consisted of oral buffered PA-treated rats that were given a neurotoxic dose of 250 mg/kg body weight/day for three days, n = eight; the second group of rats were given only phosphate buffered saline and used as a control. Biochemical parameters representing oxidative stress, energy metabolism, neuroinflammation, neurotransmission, and apoptosis were investigated in brain homogenates of both groups.

RESULTS

Biochemical analyses of brain homogenates from PA-treated rats showed an increase in oxidative stress markers (for example, lipid peroxidation), coupled with a decrease in glutathione (GSH) and glutathione peroxidase (GPX) and catalase activities. Impaired energy metabolism was ascertained through the decrease of lactate dehydrogenase and activation of creatine kinase (CK). Elevated IL-6, TNFα, IFNγ and heat shock protein 70 (HSP70) confirmed the neuroinflammatory effect of PA. Moreover, elevation of caspase3 and DNA fragmentation proved the pro-apoptotic and neurotoxic effect of PA to rat pups

CONCLUSION

By comparing the results obtained with those from animal models of autism or with clinical data on the biochemical profile of autistic patients, this study showed that the neurotoxicity of PA as an environmental factor could play a central role in the etiology of autistic biochemical features.

Plasma antioxidant capacity is reduced in Asperger syndrome

Recent evidence suggests that children with autism have impaired detoxification capacity and may suffer from chronic oxidative stress. To our knowledge, there has been no study focusing on oxidative metabolism specifically in Asperger syndrome (a milder form of autism) or comparing this metabolism with other psychiatric disorders. In this study, total antioxidant status (TAOS), non-enzymatic (glutathione and homocysteine) and enzymatic (catalase, superoxide dismutase, and glutathione peroxidase) antioxidants, and lipid peroxidation were measured in plasma or erythrocyte lysates in a group of adolescent patients with Asperger syndrome, a group of adolescents with a first episode of psychosis, and a group of healthy controls at baseline and at 8-12 weeks. TAOS was also analyzed at 1 year. TAOS was reduced in Asperger individuals compared with healthy controls and psychosis patients, after covarying by age and antipsychotic treatment. This reduced antioxidant capacity did not depend on any of the individual antioxidant variables measured. Psychosis patients had increased homocysteine levels in plasma and decreased copper and ceruloplasmin at baseline. In conclusion, Asperger patients seem to have chronic low detoxifying capacity. No impaired detoxifying capacity was found in the first-episode psychosis group in the first year of illness.

A review of candidate urinary biomarkers for autism spectrum disorder

CONTEXT

Autism is a complex, heterogeneous neurodevelopmental condition with a strong genetic component potentially impacted by various environmental factors influencing susceptibility. There are no reliable laboratory tests available to confirm an autism diagnosis.

OBJECTIVE

To examine the published literature and identify putative urinary biomarkers of autism.

METHODS

A comprehensive literature search was conducted using electronic bibliographic databases.

RESULTS

Putative autism biomarkers were identified that could be categorized according to the key theories that exist regarding the etiology of autism: gastrointestinal factors, immune dysregulation, heavy metal toxicity, neurotransmitter abnormalities, and oxidative stress.

CONCLUSION

There is scope for specific urinary biomarkers to be useful for identification of autistic metabolic phenotypes.

Novel metabolic biomarkers related to sulfur-dependent detoxification pathways in autistic patients of Saudi Arabia

BACKGROUND

Xenobiotics are neurotoxins that dramatically alter the health of the child. In addition, an inefficient detoxification system leads to oxidative stress, gut dysbiosis, and immune dysfunction. The consensus among physicians who treat autism with a biomedical approach is that those on the spectrum are burdened with oxidative stress and immune problems. In a trial to understand the role of detoxification in the etiology of autism, selected parameters related to sulfur-dependent detoxification mechanisms in plasma of autistic children from Saudi Arabia will be investigated compared to control subjects.

METHODS

20 males autistic children aged 3-15 years and 20 age and gender matching healthy children as control group were included in this study. Levels of reduced glutathione (GSH), total (GSH+GSSG), glutathione status (GSH/GSSG), glutathione reductase (GR), glutathione- s-transferase (GST), thioredoxin (Trx), thioredoxin reductase (TrxR) and peroxidoxins (Prxs I and III) were determined.

RESULTS

Reduced glutathione, total glutathione, GSH/GSSG and activity levels of GST were significantly lower, GR shows non-significant differences, while, Trx, TrxR and both Prx I and III recorded a remarkably higher values in autistics compared to control subjects.

CONCLUSION

The impaired glutathione status together with the elevated Trx and TrxR and the remarkable over expression of both Prx I and Prx III, could be used as diagnostic biomarkers of autism.

Discovery of carboxyethylpyrroles (CEPs): critical insights into AMD, autism, cancer, and wound healing from basic research on the chemistry of oxidized phospholipids

Basic research, exploring the hypothesis that 2-(ω-carboxyethyl)pyrrole (CEP) modifications of proteins are generated nonenzymatically in vivo is delivering a bonanza of molecular mechanistic insights into age-related macular degeneration, autism, cancer, and wound healing. CEPs are produced through covalent modification of protein lysyl ε-amino groups by γ-hydroxyalkenal phospholipids that are formed by oxidative cleavage of docosahexaenate-containing phospholipids. Chemical synthesis of CEP-modified proteins and the production of highly specific antibodies that recognize them preceded and facilitated their detection in vivo and enabled exploration of their biological occurrence and activities. This investigational approach, from the chemistry of biomolecules to disease phenotype, is proving to be remarkably productive.

Evaluation of oxidative stress in autism: defective antioxidant enzymes and increased lipid peroxidation

Autism is a neurodevelopmental disorder of childhood with poorly understood etiology and pathology. This pilot study aims to evaluate the levels of antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and levels of malondialdehyde (MDA), a marker of lipid peroxidation, in Egyptian autistic children. Autism is a neurodevelopmental disorder of childhood with poorly understood etiology and pathology. The present study included 20 children with autism diagnosed by DSM-IV-TR criteria and Childhood Autism Rating Scale. Controls included 25 age-matched healthy children. Cases were referred to Outpatient Clinic of Children with Special Needs Department, National Research Center, Cairo, Egypt. We compared levels of SOD, GSH-Px, and MDA in children with autism and controls. In children less than 6 years of age, levels of SOD, and GSH-Px were significantly lower in autistic children compared with their controls, while MDA was significantly higher among patients than controls. In children older than 6 years, there was no significant difference in any of these values between cases and controls. We concluded that children with autism are more vulnerable to oxidative stress in the form of increased lipid peroxidation and deficient antioxidant defense mechanism especially at younger children. We highlight that autistic children might benefit from antioxidants supplementation coupled with polyunsaturated fatty acids. Moreover, early assessment of antioxidant status would have better prognosis as it may decrease the oxidative stress before inducing more irreversible brain damage.

Glutathione pathway gene variation and risk of autism spectrum disorders

Despite evidence that autism is highly heritable with estimates of 15 or more genes involved, few studies have directly examined associations of multiple gene interactions. Since inability to effectively combat oxidative stress has been suggested as a mechanism of autism, we examined genetic variation 42 genes (308 single-nucleotide polymorphisms (SNPs)) related to glutathione, the most important antioxidant in the brain, for both marginal association and multi-gene interaction among 318 case–parent trios from The Autism Genetic Resource Exchange. Models of multi-SNP interactions were estimated using the trio Logic Regression method. A three-SNP joint effect was observed for genotype combinations of SNPs in glutaredoxin, glutaredoxin 3 (GLRX3), and cystathione gamma lyase (CTH); OR = 3.78, 95% CI: 2.36, 6.04. Marginal associations were observed for four genes including two involved in the three-way interaction: CTH, alcohol dehydrogenase 5, gamma-glutamylcysteine synthetase, catalytic subunit and GLRX3. These results suggest that variation in genes involved in counterbalancing oxidative stress may contribute to autism, though replication is necessary.

The neurobiology of lipid metabolism in autism spectrum disorders

Autism is a neurodevelopmental disorder characterized by impairments in communication and reciprocal social interaction, coupled with repetitive behavior, which typically manifests by 3 years of age. Multiple genes and early exposure to environmental factors are the etiological determinants of the disorder that contribute to variable expression of autism-related traits. Increasing evidence indicates that altered fatty acid metabolic pathways may affect proper function of the nervous system and contribute to autism spectrum disorders. This review provides an overview of the reported abnormalities associated with the synthesis of membrane fatty acids in individuals with autism as a result of insufficient dietary supplementation or genetic defects. Moreover, we discuss deficits associated with the release of arachidonic acid from the membrane phospholipids and its subsequent metabolism to bioactive prostaglandins via phospholipase A(2)-cyclooxygenase biosynthetic pathway in autism spectrum disorders. The existing evidence for the involvement of lipid neurobiology in the pathology of neurodevelopmental disorders such as autism is compelling and opens up an interesting possibility for further investigation of this metabolic pathway.

Oxidative pathways as a drug target for the treatment of autism

IMPORTANCE OF THE FIELD

Autism is a severe, pervasive developmental disorder, the aetiology of which is poorly understood. Current pharmacological treatment options for autism are often focused on addressing comorbid behavioural problems, rather than core features of the disorder. Investigation of a new treatment approach is needed.

AREAS COVERED IN THIS REVIEW

Recent research has indicated a possible role of abnormalities in oxidative homeostasis in the pathophysiology of autism, based on reports that a range of oxidative biomarkers are significantly altered in people with autism. This article reviews the current findings on oxidative stress in autism, including genetic links to oxidative pathways, changes in antioxidant levels and other oxidative stress markers. We conducted a search of the literature up to June 2010, using Medline, Pubmed, PsycINFO, CINAHL PLUS and BIOSIS Previews.

WHAT THE READER WILL GAIN

This review provides an overview of the current understanding of the role of oxidative stress in autism. This will assist in highlighting areas of future therapeutic targets and potential underlying pathophysiology of this disorder.

TAKE HOME MESSAGE

Abnormalities in oxidative homeostasis may play a role in the pathophysiology of autism. Antioxidant treatment may form a potential therapeutic pathway for this complex disorder.

Improving the prediction of response to therapy in autism

Autism is a heterogeneous disorder involving complex mechanisms and systems occurring at diverse times. Because an individual child with autism may have only a subset of all possible abnormalities at a specific time, it may be challenging to identify beneficial effects of an intervention in double-blind, randomized, controlled trials, which compare the mean responses to treatments. Beneficial effects in a small subset of children may be obscured by the lack of effect in the majority. We review the evidence for several potential model systems of biochemical abnormalities that may contribute to the etiology of autism, we describe potential biomarkers or treatment targets for each of these abnormalities, and we provide illustrative treatment trials using this methodology. Potential model systems include immune over and under reactivity, inflammation, oxidative stress, free fatty acid metabolism, mitochondrial dysfunction, and excitotoxicity. Including potential biomarkers and targeted treatments in clinical trials for autism provides a potential method for limiting the heterogeneity of enrolled subjects, which may improve the power of studies to identify beneficial effects of treatments while also improving the understanding of the disease.

Chromium, cadmium, and lead levels in urine of children with autism and typically developing controls

Although potentially harmful effects of heavy metals are well known, limited numbers of studies exist regarding their relationship with autism. The aim of this study was to investigate urine levels of some heavy metals such as of chromium (Cr), cadmium (Cd), and lead (Pb) in children with autism and healthy subjects. Urine levels of Cr, Cd, and Pb were measured by atomic absorption spectrometry in 30 children with autism and compared with 20 healthy controls. Urine Cd and Pb levels were found as significantly decreased in children with autism compared to healthy subjects (p < 0.05). On the other hand, urine Cr levels were significantly higher in children with autism than healthy subjects (p < 0.05). This study suggested that autism may be associated with significant decrease in excretion rate of Cd and Pb and a significant increase excretion rate in the levels of Cr in the urine. These results have indicated that further studies are warranted for investigation of possible roles of heavy metals in autism.

Mitochondrial dysfunction in autism spectrum disorders: cause or effect?

Autism Spectrum Disorders encompass severe developmental disorders characterized by variable degrees of impairment in language, communication and social skills, as well as by repetitive and stereotypic patterns of behaviour. Substantial percentages of autistic patients display peripheral markers of mitochondrial energy metabolism dysfunction, such as (a) elevated lactate, pyruvate, and alanine levels in blood, urine and/or cerebrospinal fluid, (b) serum carnitine deficiency, and/or (c) enhanced oxidative stress. These biochemical abnormalities are accompanied by highly heterogeneous clinical presentations, which generally (but by no means always) encompass neurological and systemic symptoms relatively unusual in idiopathic autistic disorder. In some patients, these abnormalities have been successfully explained by the presence of specific mutations or rearrangements in their mitochondrial or nuclear DNA. However, in the majority of cases, abnormal energy metabolism cannot be immediately linked to specific genetic or genomic defects. Recent evidence from post-mortem studies of autistic brains points toward abnormalities in mitochondrial function as possible downstream consequences of dysreactive immunity and altered calcium (Ca(2+)) signalling.