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Fillano, J. J., M. J. Goldenthal, et al. (2002). "Mitochondrial dysfunction in patients with hypotonia, epilepsy, autism, and developmental delay: HEADD syndrome." J Child Neurol 17(6): 435-9.
A group of 12 children clinically presenting with hypotonia, intractable epilepsy, autism, and developmental delay, who did not fall into previously described categories of mitochondrial encephalomyopathy, were evaluated for mitochondrial respiratory enzyme activity levels, mitochondrial DNA, and mitochondrial structural abnormalities. Reduced levels in specific respiratory activities were found solely in enzymes with subunits encoded by mitochondrial DNA in seven of eight biopsied skeletal muscle specimens evaluated. Five cases exhibited increased levels of large-scale mitochondrial DNA deletions, whereas pathogenic point mutations previously described in association with mitochondrial encephalomyopathies were not found. Mitochondrial structural abnormalities were present in three of four patients examined. Our findings suggest that mitochondrial dysfunction, including extensive abnormalities in specific enzyme activities, mitochondrial structure, and mitochondrial DNA integrity, may be present in children with a clinical constellation including hypotonia, epileptic seizures, autism, and developmental delay. The acronym HEADD is presented here to facilitate pursuit of mitochondrial defects in patients with this clinical constellation after other causes have been excluded.
Gargus, J. J. and F. Imtiaz (2008). "Mitochondrial energy-deficient endophenotype in autism." American Journal of Biochemistry and Biotechnology 4(2): 198-207.
While evidence points to a multigenic etiology of most autism, the pathophysiology of the disorder has yet to be defined and the underlying genes and biochemical pathways they subserve remain unknown. Autism is considered to be influenced by a combination of various genetic, environmental and immunological factors; more recently, evidence has suggested that increased vulnerability to oxidative stress may be involved in the etiology of this multifactorial disorder. Furthermore, recent studies have pointed to a subset of autism associated with the biochemical endophenotype of mitochondrial energy deficiency, identified as a subtle impairment in fat and carbohydrate oxidation. This phenotype is similar, but more subtle than those seen in classic mitochondrial defects. In some cases the beginnings of the genetic underpinnings of these mitochondrial defects are emerging, such as mild mitochondrial dysfunction and secondary carnitine deficiency observed in the subset of autistic patients with an inverted duplication of chromosome 15q11-q13. In addition, rare cases of familial autism associated with sudden infant death syndrome (SIDS) or associated with abnormalities in cellular calcium homeostasis, such as malignant hyperthermia or cardiac arrhythmia, are beginning to emerge. Such special cases suggest that the pathophysiology of autism may comprise pathways that are directly or indirectly involved in mitochondrial energy production and to further probe this connection three new avenues seem worthy of exploration: 1) metabolomic clinical studies provoking controlled aerobic exercise stress to expand the biochemical phenotype, 2) high-throughput expression arrays to directly survey activity of the genes underlying these biochemical pathways and 3) model systems, either based upon neuronal stem cells or model genetic organisms, to discover novel genetic and environmental inputs into these pathways.
Graf, W. D., J. Marin-Garcia, et al. (2000). "Autism associated with the mitochondrial DNA G8363A transfer RNA(Lys) mutation." J Child Neurol 15(6): 357-61.
We report a family with a heterogeneous group of neurologic disorders associated with the mitochondrial DNA G8363A transfer ribonucleic acid (RNA)Lys mutation. The phenotype of one child in the family was consistent with autism. During his second year of life, he lost previously acquired language skills and developed marked hyperactivity with toe-walking, abnormal reciprocal social interaction, stereotyped mannerisms, restricted interests, self-injurious behavior, and seizures. Brain magnetic resonance imaging (MRI) and repeated serum lactate studies were normal. His older sister developed signs of Leigh syndrome with progressive ataxia, myoclonus, seizures, and cognitive regression. Her laboratory studies revealed increased MRI T2-weighted signal in the putamen and posterior medulla, elevated lactate in serum and cerebrospinal fluid, and absence of cytochrome c oxidase staining in muscle histochemistry. Molecular analysis in her revealed the G8363A mutation of the mitochondrial transfer RNA(Lys) gene in blood (82% mutant mitochondrial DNA) and muscle (86%). The proportions of mutant mitochondrial DNA from her brother with autism were lower (blood 60%, muscle 61%). It is likely that the origin of his autism phenotype is the pathogenic G8363A mitochondrial DNA mutation. This observation suggests that certain mitochondrial point mutations could be the basis for autism in some individuals.
Lerman-Sagie, T., E. Leshinsky-Silver, et al. (2004). "Should autistic children be evaluated for mitochondrial disorders?" J Child Neurol 19(5): 379-81.
Autism is etiologically heterogeneous; medical conditions are implicated in only a minority of cases, whereas metabolic disorders are even less common. Recently, there have been articles describing the association of autism with mitochondrial abnormalities. We critically review the current literature and conclude that mitochondrial disorders are probably a rare and insignificant cause of pure autism; however, evidence is accumulating that both autosomal recessive and maternally inherited mitochondrial disorders can present with autistic features. Most patients will present with multisystem abnormalities associated with autistic behavior. Finding biochemical or structural mitochondrial abnormalities in an autistic child does not necessarily imply a primary mitochondrial disorder but can also be secondary to technical inaccuracies or another genetic disorder. Clinicians should be careful in diagnosing a mitochondrial disorder in an autistic child because it has important implications for accurate genetic counseling, prognosis, and therapy.
Lombard, J. (1998). "Autism: a mitochondrial disorder?" Med Hypotheses 50(6): 497-500.
Autism is a developmental disorder characterized by disturbance in language, perception and socialization. A variety of biochemical, anatomical and neuroradiographical studies imply a disturbance of brain energy metabolism in autistic patients. The underlying etiology of a disturbed bioenergetic metabolism in autism is unknown. A likely etiological possibility may involve mitochondrial dysfunction with concomitant defects in neuronal oxidative phosphorylation within the central nervous system. This hypothesis is supported by a frequent association of lactic acidosis and carnitine deficiency in autistic patients. Mitochondria are vulnerable to a wide array of endogenous and exogenous factors which appear to be linked by excessive nitric oxide production. Strategies to augment mitochondrial function, either by decreasing production of endogenous toxic metabolites, reducing nitric oxide production, or stimulating mitochondrial enzyme activity may be beneficial in the treatment of autism.
Oliveira, G., A. Ataide, et al. (2007). "Epidemiology of autism spectrum disorder in Portugal: prevalence, clinical characterization, and medical conditions." Dev Med Child Neurol 49(10): 726-33.
The objective of this study was to estimate the prevalence of autistic spectrum disorder (ASD) and identify its clinical characterization, and medical conditions in a paediatric population in Portugal. A school survey was conducted in elementary schools, targeting 332,808 school-aged children in the mainland and 10,910 in the Azores islands. Referred children were directly assessed using the Diagnostic and Statistical Manual of Mental Disorders (4th edn), the Autism Diagnostic Interview-Revised, and the Childhood Autism Rating Scale. Clinical history and a laboratory investigation was performed. In parallel, a systematic multi-source search of children known to have autism was carried out in a restricted region. The global prevalence of ASD per 10,000 was 9.2 in mainland, and 15.6 in the Azores, with intriguing regional differences. A diversity of associated medical conditions was documented in 20%, with an unexpectedly high rate of mitochondrial respiratory chain disorders.
Oliveira, G., L. Diogo, et al. (2005). "Mitochondrial dysfunction in autism spectrum disorders: a population-based study." Dev Med Child Neurol 47(3): 185-9.
A minority of cases of autism has been associated with several different organic conditions, including bioenergetic metabolism deficiency. In a population-based study, we screened associated medical conditions in a group of 120 children with autism (current age range 11y 5mo to 14y 4mo, mean age 12y 11mo [SD 9.6mo], male:female ratio 2.9:1). Children were diagnosed using Diagnostic and Statistical Manual of Mental Disorders criteria, the Autism Diagnostic Interview--Revised, and the Childhood Autism Rating Scale; 76% were diagnosed with typical autism and 24% with atypical autism. Cognitive functional level was assessed with the Griffiths scale and the Wechsler Intelligence Scale for Children and was in the normal range in 17%. Epilepsy was present in 19 patients. Plasma lactate levels were measured in 69 patients, and in 14 we found hyperlactacidemia. Five of 11 patients studied were classified with definite mitochondrial respiratory chain disorder, suggesting that this might be one of the most common disorders associated with autism (5 of 69; 7.2%) and warranting further investigation.
Poling, J. S., R. E. Frye, et al. (2006). "Developmental regression and mitochondrial dysfunction in a child with autism." J Child Neurol 21(2): 170-2.
Autistic spectrum disorders can be associated with mitochondrial dysfunction. We present a singleton case of developmental regression and oxidative phosphorylation disorder in a 19-month-old girl. Subtle abnormalities in the serum creatine kinase level, aspartate aminotransferase, and serum bicarbonate led us to perform a muscle biopsy, which showed type I myofiber atrophy, increased lipid content, and reduced cytochrome c oxidase activity. There were marked reductions in enzymatic activities for complex I and III. Complex IV (cytochrome c oxidase) activity was near the 5% confidence level. To determine the frequency of routine laboratory abnormalities in similar patients, we performed a retrospective study including 159 patients with autism (Diagnostic and Statistical Manual of Mental Disorders-IV and Childhood Autism Rating Scale) not previously diagnosed with metabolic disorders and 94 age-matched controls with other neurologic disorders. Aspartate aminotransferase was elevated in 38% of patients with autism compared with 15% of controls (P <.0001). The serum creatine kinase level also was abnormally elevated in 22 (47%) of 47 patients with autism. These data suggest that further metabolic evaluation is indicated in autistic patients and that defects of oxidative phosphorylation might be prevalent.
Pons, R., A. L. Andreu, et al. (2004). "Mitochondrial DNA abnormalities and autistic spectrum disorders." J Pediatr 144(1): 81-5.
OBJECTIVES: To further characterize mtDNA defects associated with autistic features, especially the A3243G mtDNA mutation and mtDNA depletion.Study design Five patients with autistic spectrum disorders and family histories of mitochondrial DNA diseases were studied. We performed mtDNA analysis in all patients and magnetic resonance spectroscopy in three. RESULTS: Three patients manifested isolated autistic spectrum features and two had additional neurologic symptoms. Two patients harbored the A3243G mutation. In two others, the A3243G mutation was not found in accessible tissues but was present in tissues from their mothers. The fifth patient had 72% mtDNA depletion in skeletal muscle. CONCLUSIONS: Autistic spectrum disorders with or without additional neurologic features can be early presentations of the A3243G mtDNA mutation and can be a prominent clinical manifestation of mtDNA depletion. Mitochondrial dysfunction should be considered in patients who have autistic features and associated neurologic findings or who have evidence of maternal inheritance.
Ramoz, N., J. G. Reichert, et al. (2004). "Linkage and association of the mitochondrial aspartate/glutamate carrier SLC25A12 gene with autism." Am J Psychiatry 161(4): 662-9.
OBJECTIVE: Autism/autistic disorder (MIM number 209850) is a complex, largely genetic psychiatric disorder. The authors recently mapped a susceptibility locus for autism to chromosome region 2q24-q33 (MIM number 606053). In the present study, genes across the 2q24-q33 interval were analyzed to identify an autism susceptibility gene in this region. METHOD: Mutation screening of positional candidate genes was performed in two stages. The first stage involved identifying, in unrelated subjects showing linkage to 2q24-q33, genetic variants in exons and flanking sequence within candidate genes and comparing the frequency of the variants between autistic and unrelated nonautistic subjects. Two single nucleotide polymorphisms (SNPs) that showed evidence for divergent distribution between autistic and nonautistic subjects were identified, both within SLC25A12, a gene encoding the mitochondrial aspartate/glutamate carrier (AGC1). In the second stage, the two SNPs in SLC25A12 were further genotyped in 411 autistic families, and linkage and association tests were carried out in the 197 informative families. RESULTS: Linkage and association were observed between autistic disorder and the two SNPs, rs2056202 and rs2292813, found in SLC25A12. Using either a single affected subject per family or all affected subjects, evidence for excess transmission was found by the Transmission Disequilibrium Test for rs2056202, rs2292813, and a two-locus G*G haplotype. Similar results were observed using TRANSMIT for the analyses. Evidence for linkage was supported by linkage analysis with the two SNPs, with a maximal multipoint nonparametric linkage score of 1.57 and a maximal multipoint heterogeneity lod score of 2.11. Genotype relative risk could be estimated to be between 2.4 and 4.8 for persons homozygous at these loci. CONCLUSIONS: A strong association of autism with SNPs within the SLC25A12 gene was demonstrated. Further studies are needed to confirm this association and to decipher any potential etiological role of AGC1 in autism.
Rossignol, D. A. and J. J. Bradstreet (2008). "Evidence of mitochondrial dysfunction in autism and implications for treatment." American Journal of Biochemistry and Biotechnology 4(2): 208-217.
Classical mitochondrial diseases occur in a subset of individuals with autism and are usually caused by genetic anomalies or mitochondrial respiratory pathway deficits. However, in many cases of autism, there is evidence of mitochondrial dysfunction (MtD) without the classic features associated with mitochondrial disease. MtD appears to be more common in autism and presents with less severe signs and symptoms. It is not associated with discernable mitochondrial pathology in muscle biopsy specimens despite objective evidence of lowered mitochondrial functioning. Exposure to environ-mental toxins is the likely etiology for MtD in autism. This dysfunction then contributes to a number of diagnostic symptoms and comorbidities observed in autism including: cognitive impairment, language deficits, abnormal energy metabolism, chronic gastrointestinal problems, abnormalities in fatty acid oxidation, and increased oxidative stress. MtD and oxidative stress may also explain the high male to female ratio found in autism due to increased male vulnerability to these dysfunctions. Biomarkers for mitochondrial dysfunction have been identified, but seem widely under-utilized despite available therapeutic interventions. Nutritional supplementation to decrease oxidative stress along with factors to improve reduced glutathione, as well as hyperbaric oxygen therapy (HBOT) represent supported and rationale approaches. The underlying pathophysiology and autistic symptoms of affected individuals would be expected to either improve or cease worsening once effective treatment for MtD is implemented.
Segurado, R., J. Conroy, et al. (2005). "Confirmation of association between autism and the mitochondrial aspartate/glutamate carrier SLC25A12 gene on chromosome 2q31." Am J Psychiatry 162(11): 2182-4.
OBJECTIVE: Autism is a neurodevelopmental disorder with childhood onset and a known major genetic component. A recent study identified a highly significant association between autism and a two-single-nucleotide-polymorphism haplotype in the SLC25A12 gene, with a homozygote genotype relative risk between 2.4 and 4.8. The authors' goal was to investigate this association with autism in Irish affected child-parent trios because replication in an independent sample is essential in the validation of such potentially important findings. METHOD: Markers rs2056202 and rs2292813 were genotyped in a total of 158 trios (442 individuals). The Transmission Disequilibrium Test was used to examine these markers for association with autism. RESULTS: In agreement with the recent study, the authors found significant association between autism and the C alleles of both rs2056202 and rs2292813 as well as the two-marker haplotype. CONCLUSIONS: These findings provide replication of the association between autism and SLC25A12.
Silverman, J. M., J. D. Buxbaum, et al. (2007). "Autism-related routines and rituals associated with a mitochondrial aspartate/glutamate carrier SLC25A12 polymorphism." Am J Med Genet B Neuropsychiatr Genet.
Evidence for a genetic association between autism and two single nucleotide polymorphisms (SNPs), rs2056202 and rs2292813, in the mitochondrial aspartate/glutamate carrier (SLC25A12) gene led us to ask whether any of the four previously identified familial traits in autism spectrum disorders (ASD) varied by these SNPs. In 355 ASD cases from 170 sibships we examined levels of the four traits in these SNPs using ANCOVA models. The primary models selected unrelated affected cases and used age and sex as covariates. An ancillary set of models used all affected siblings and included "sibship" as a random effects independent variable. We found significantly lower levels of routines and rituals associated with the presence of the less frequent A allele in rs2056206. No other significant differences were observed. The rs2056202 polymorphism may be associated with levels of routines and rituals in autism and related disorders. (c) 2007 Wiley-Liss, Inc.
Trushina, E. and C. T. McMurray (2007). "Oxidative stress and mitochondrial dysfunction in neurodegenerative diseases." Neuroscience 145(4): 1233-48.
In recent years, it has become increasingly clear that mitochondrial dysfunction and oxidative damage are major contributors to neuronal loss. Free radicals, typically generated from mitochondrial respiration, cause oxidative damage of nucleic acids, lipids, carbohydrates and proteins. Despite enormous amount of effort, however, the mechanism by which oxidative damage causes neuronal death is not well understood. Emerging data from a number of neurodegenerative diseases suggest that there may be common features of toxicity that are related to oxidative damage. In this review, while focusing on Huntington's disease (HD), we discuss similarities among HD, Friedreich ataxia and xeroderma pigmentosum, which provide insight into shared mechanisms of neuronal death.
Tsao, C. Y. and J. R. Mendell (2007). "Autistic disorder in 2 children with mitochondrial disorders." J Child Neurol 22(9): 1121-3.
Autistic disorder is a heterogeneous disorder. The majority of the cases are idiopathic, and only a small number of the autistic children have associated secondary diagnosis. This article reports 2 children with mitochondrial disorders associated with autistic disorder fulfilling the diagnostic criteria of the American Psychiatric Association Manual of Psychiatric Diseases, 4th edition, and briefly reviews the literature on autistic disorder associated with mitochondrial disorders.
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