Preliminary research has found that children with autism are more likely to have impaired mitochondrial function (structures within cells responsible for energy production) and mitochondrial DNA abnormalities than typically developing children, according to a study in the December 1 issue of JAMA.
"Limited scientific advances have been made regarding the causes of autism, with general agreement that both genetic and environmental factors contribute to this disorder," the authors write. Some reports have suggested that mitochondrial dysfunction may influence processes highly dependent on energy, such as neurodevelopment, and contribute to autism. However, most reports involved only 1 or a few isolated cases, according to background information in the article.
Cecilia Giulivi, Ph.D., of the University of California, Davis, and colleagues tested the hypothesis that children with full syndrome autism would have dysfunctional mitochondria in peripheral blood lymphocytes (white blood cells). The researchers used data collected from patients ages 2 to 5 years who were a subset of children participating in the Childhood Autism Risk From Genes and Environment study, a population-based investigation with confirmed autism cases and age-matched, genetically unrelated, typically developing controls, that was launched in 2003 and is still ongoing. Mitochondrial dysfunction and mitochondrial DNA (mtDNA) abnormalities were evaluated in lymphocytes from 10 children with autism and 10 controls.
Findings of the researchers include mitochondrial-dependent oxygen consumption being impaired in peripheral blood lymphocytes from children with autism compared with control children; lymphocytic mitochondria in autism had a lower oxidative phosphorylation (a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate [ATP], a molecule that supplies energy to metabolism) capacity and contributed to the overall increased cellular oxidative stress; and mitochondrial DNA overreplication was found in 5 patients and deletions were observed in 2 patients.
"The high prevalence of mitochondrial dysfunction observed in this preliminary study performed with children presenting with full syndrome autism may or may not indicate an etiological [causal] role. Whether the mitochondrial dysfunction in children with autism is primary or secondary to an as-yet unknown event remains the subject of future work; however, mitochondrial dysfunction could greatly amplify and propagate brain dysfunction, such as that found in autism, given that the highest levels of mtDNA abnormalities are observed in postmitotic [a mature cell that is no longer capable of undergoing mitosis (cell division)] tissues with high energy demands (e.g., brain)," the authors write.
The researchers note that among the limitations of the study is the small number of children assessed, and that caution should be exercised with regard to the generalization of findings in a larger population.
"In this preliminary study, evidence of mitochondrial dysfunction was observed in children presenting with full syndrome autism. More research is needed to understand the molecular causes of the mitochondrial dysfunction and how this and other neurometabolic defects may contribute to autism ..."
(JAMA. 2010;304:2389-2396. Available pre-embargo to the media at www.jamamedia.org)
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