Blood hints at autism’s source

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: Assault on Autism).

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

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