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Blood hints at autism's source

Janet Raloff

From San Diego, at the Experimental Biology 2005 meeting

Researchers have identified a biochemical peculiarity in the blood of autistic children. The scientists say the finding could lead to earlier diagnosis of this neurological disorder and a better understanding of how certain genes may drive it.

Autism, which typically shows up in toddlers, is characterized by limited language skills, poor social interaction, repetitive behaviors, and limited interests. Autism often runs in families, which suggests a genetic cause.

However, "the incidence of autism has gone up dramatically in the last 15 years," notes S. Jill James, director of biochemical genetics at Arkansas Children's Hospital in Little Rock. "Because genes don't change that fast, this points to something in the environment as a trigger," she says.

In a study of the blood of some apparently healthy children, the biochemistry of one sample stood out. It came from an autistic boy. Curious, James got blood samples from 20 other autistic children. All exhibited a similar, unusual biochemical fingerprint, which James has now confirmed in an additional 75 autistic children. None in a comparison group of 75 neurologically healthy kids carried the fingerprint in his or her blood.

The autistic youngsters had unusually low concentrations of the antioxidant glutathione in their cells. Their ratio of active glutathione to its inactive breakdown products also was unusually low.

"This pattern is consistent with an inability to detoxify [poisons], especially heavy metals," such as mercury or lead, James says. That's because the antioxidant normally binds to heavy metals, and the body then targets the molecular complex for elimination.

Any of several combinations of genes may predispose the body to low glutathione concentrations. James suspects that autism develops under the combined effect of several gene mutations that deplete glutathione and of exposure of a child to heavy metals or other poisons. One of the most controversial theories about autism is that vaccines preserved with the mercury-containing chemical thimerosal can cause the condition (SN: 11/13/04, p. 311).

Dietary treatments could boost glutathione in children carrying genes that reduce the antioxidant, says James.

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Letters:

In this article researcher S. Jill James implicates low glutathione and heavy metal exposure in autism. This may be the case, but glutathione has a number of important functions that have nothing to do with heavy metal binding. As an antioxidant, glutathione reduces toxic free radicals. Glutathione is also a key factor in the maintenance of cellular redox poise. It goes without saying that it is also possible that low glutathione is correlated with, but not causative of, autism.

Todd P. Silverstein
Williamette University
Salem, OR

I would venture that at least part of the explanation for the rise in autism's incidence is related to its recent recognition. When I was a kid, there was no such thing as autism. You can't diagnose something you don't recognize.

Andrew Nelson
Santa Barbara, CA

Studies published in the past 2 years have investigated the extent to which autism's increasing incidence traces to changes in diagnosis. At least a few of these studies have found that incidence has increased even after accounting for better diagnosis.—J. Raloff

References:

James, S.J., S. Melnyk, and S. Jernigan. 2005. Low plasma methionine, cysteine, and glutathione levels are associated with increase frequency of common polymorphisms affecting methylation and glutathione pathways in children with autism. Experimental Biology 2005. April 2. San Diego.

James, S.J., et al. 2004. Metabolic biomarkers of increased oxidative stress and impaired methylation capacity in children with autism. American Journal of Clinical Nutrition 80(December):1611–1617. Abstract.

Further Readings:

Bower, B. 2004. Brain development disturbed in autism. Science News 166(July 31):78. Available at Science News.

______. 2002. Autism leaves kids lost in face. Science News 161(June 29):408. Available at Science News.

______. 2000. Gene implicated in development of autism. Science News 158(Dec. 16):390. Available at Science News.

______. 2000. When autism aids memory. Science News 158(July 29):72. Available at Science News.

Christensen, D. 2002. The persistent problem of cystic fibrosis. Science News 161(Jan. 26):59–60. Available at Science News.

Fackelmann, K. 1995. Variations on a theme. Science News 147(May 6):280–281. Available at Science News.

Parsell, D. 2004. Assault on autism. Science News 166(Nov. 13):311–312. Available at Science News.

Travis, J. 2004. Drug fails in autism study. Science News 166(Jan. 31):76. Available at Science News.

______. 2003. Autism advance: Mutated genes disrupt nerve cell proteins. Science News 163(April 5):212. Available at Science News.

Sources:

S. Jill James
University of Arkansas for Medical Sciences
Department of Pediatrics
1120 Marshall Street, Slot 512-40B
Little Rock, AR 72202-3591


From Science News, Volume 167, No. 16, April 16, 2005, p. 254.