Cell Dysfunction May Play Part in Autism11/30/10
TUESDAY, Nov. 30 (HealthDay News) -- Autistic children are much
more likely to have defects in a cellular structure called the
mitochondria, which is responsible for producing the energy used by
brain cells, preliminary research finds.
These defects may help to explain the onset or the severity of
autism in some children, according to the study in the Dec. 1 issue
Journal of the American Medical Association.
"In this report, children with full syndrome autism were more likely to have mitochondrial dysfunction than healthy, age-matched control children," said study author Cecilia Giulivi, a professor of biochemistry at the University of California, Davis. "But we don't know if mitochondrial dysfunction is a cause of autism or a consequence of autism."
Mitochondria, sometimes called cellular "powerhouses," produce
energy that's used to fuel a cell's activity -- an especially
important function in the brain, Giulivi said.
When mitochondria don't function properly, the results can be
devastating. Mitochondrial dysfunction been implicated in
neurological conditions ranging from Parkinson's and Alzheimer's
disease to schizophrenia and bipolar disorder.
Mitochondrial disease can lead to symptoms including muscle
weakness, exercise intolerance (pain and muscle cramps during
exercise), gastrointestinal disorders, seizures, liver disease,
vision and hearing problems, developmental delays and increased
susceptibility to infection.
While previous small studies have suggested some children with
autism may also have mitochondrial dysfunction, measuring the
function of mitochondria isn't easy because brain biopsies are out
of the question, Giulivi said.
Another area of the body in which mitochondria are active is in
the muscles, but biopsying muscle tissue is also invasive, she
In the new study, Giulivi analyzed the mitochondria in
lymphocyte cells, an immune system component found in the blood, of
10 children aged 2 to 5 with "full syndrome" autism and 10 normally
They found children with autism were far more likely to have
mitochondrial dysfunction, including defects in mitochondrial DNA
and abnormalities in the levels of various enzymes produced by the
"There has been evidence before that some children with autism have a mitochondrial disorder, but we haven't been able to do routine screening because a muscle biopsy is quite invasive," said Geraldine Dawson, chief science officer for Autism Speaks, which helped fund the research. "This study suggests we might be able to do a blood sample, which would allow us to do routine screening."
Still the findings come with caveats. While the study suggests
mitochondrial dysfunction plays a role in at least come cases of
autism, the researchers stressed that the results are preliminary
and more studies in larger numbers of children are needed.
And there are many unknowns, including how mitochondrial
dysfunction in brain cells might alter brain function in a way that
leads to some of the symptoms of autism, including communication
and social difficulties.
The researchers also don't know when the mitochondrial
dysfunction starts -- in the womb, in infancy or later, and how
that might impact the onset of autism or what other environmental
or genetic factors may also contribute.
Parents should also keep in mind that autism is a "heterogenous"
disorder, Dawson said. In the new study, only one child met the
clinical threshold for a mitochondrial disorder, while others
showed varying degrees of mitochondrial abnormalities.
"The fact that so many were showing some evidence of a mitochondrial dysfunction is remarkable because that has never been shown before," Dawson said. "This could be a subtype of autism, or could be a contributing factor to many types. It could be a cause or a consequence. We really don't know at this point, but the important thing is there really is something different about the way the mitochondria are functioning in some children with autism."
The 10 children with autism in the study all had "full syndrome"
autism. Children on the less severe end of the autism spectrum were
not included in the study.
Among the various mitochondrial defects, researchers found that
mitochondria from children with autism consumed less oxygen than
mitochondria from the children without autism, suggesting less
The cells of children with autism also produced twice as much
hydrogen peroxide, which can lead to oxidative stress, which can
Giulivi urged pediatricians to be on the lookout for symptoms
that might indicate mitochondrial dysfunction in autistic children,
including vision or hearing problems, seizures or exercise
intolerance such as muscle cramps during intensive physical
United Mitochondrial Disease Foundation has more
on mitochondrial disease.
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