December 1, 2010

Cellular Energy Defects Discovered In Autistic Children

Autistic children are more likely to have trouble producing cellular energy due to mitochondrial DNA abnormalities than their typically developing counterparts, claims a new study published Tuesday in the Journal of the American Medical Association (JAMA).

Researchers at the University of California-Davis Health System discovered that impaired mitochondrial function due to damage and oxidative stress could be linked to the autism. While they say that this does not identify the cause of autism, the discovery could lead to a new way of screening for the neural disorder by using blood samples, the nonprofit organization Autism Speaks, which funded the study, said in a Tuesday press release.

According to the authors of the JAMA paper, the brain is the body's second biggest consumer of energy, and if damage to the mitochondria prevents neurons from getting enough fuel to function properly, it could result in some of the cognitive impairments typically associated with autism. The same disorder has already been associated with several other neurological conditions, including Parkinson's disease, Alzheimer's disease, and schizophrenia, the researchers said in a separate press release.

"Children with mitochondrial diseases may present exercise intolerance, seizures and cognitive decline, among other conditions," lead author Cecilia Giulivi, a professor at the UC Davis School of Veterinary Medicine Department of Molecular Bioscience, said in a statement Tuesday. "Some will manifest disease symptoms and some will appear as sporadic cases"¦ Many of these characteristics are shared by children with autism."

"It is remarkable that evidence of mitochondrial dysfunction and changes in mitochondrial DNA were detected in the blood of these young children with autism," added Geraldine Dawson, chief science officer of Autism Speaks. "One of the challenges has been that it has been difficult to diagnose mitochondrial dysfunction because it usually requires a muscle biopsy. If we could screen for these metabolic problems with a blood test, it would be a big step forward."

As part of their research, Giulivi and her colleagues selected 10 autistic children between the ages of two and five, and then recruited non-autistic children of the same ages and similar backgrounds for comparison sake. They obtained blood samples from each subject, and then analyzed the metabolic pathways of mitochondria in lymphocytes, a type of immune cell.

The UC-Davis scientists found that the mitochondria of the autistic children consumed much less oxygen than those in the control group--which according the university's press release is "a sign of lowered mitochondrial activity." Eighty percent of the autistic subjects had reduced oxygen consumption in the mitochondrial enzyme complex NADH oxidase, while 60 percent had reduced succinate oxidase oxidation levels, and 40 percent had reduced ATPase oxygen levels.

Furthermore, they discovered elevated levels of pyruvate, the material which mitochondria transforms into cellular energy, in the plasma of autistic children. According to the UC-Davis press release, that discovery "suggests the mitochondria of children with autism are unable to process pyruvate fast enough to keep up with the demand for energy, pointing to a novel deficiency at the level of an enzyme named pyruvate dehydrogenase."

"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," the authors wrote in their paper. "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."


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