Faulty brain 'switch' linked to autism

August 05, 2005|By Sandy Kleffman | Sandy Kleffman,Knight Ridder / Tribune

Providing one more clue for solving the autism mystery, researchers have discovered that the brain mechanism that stops or slows nerve impulses contributes to the disorder.

A team at Duke University Medical Center in Durham, N.C., found that genes that serve as "off switches" in the brain's neurons play a role.

Exactly how such genes interact and what happens in the brains of autistic children remains unknown. But the findings are sure to intrigue the many parents of autistic children who have long suspected that their children suffer from a sensory overload.

The study will be published in the September issue of the American Journal of Human Genetics.

Autism remains one of the great mysteries of modern times. Once a rare disorder, it has drawn increased attention as the number of diagnosed cases jumped greatly in recent years, sending scientists scrambling in search of a cause.

The latest study focused on gamma aminobutyric acid or GABA, a chemical that inhibits brain nerve cells from firing, thus telling the body to slow down. It acts as a sort of information filter, preventing the brain from becoming overstimulated.

"If it's not working or something's wrong with the GABA system, then you would think that there may be sensory overload," said Margaret Pericak-Vance, a lead researcher on the study and director of the Duke Center for Human Genetics. "This is what we think might be going on."

Most scientists believe there is a strong genetic component to autism. At least 10 genes and as many as 100 may be involved.

But thus far, researchers have been stymied in their attempt to find a single gene that plays a major role, Pericak-Vance said.

The latest study found that one GABA receptor gene interacting with a second GABA gene appeared to increase the risk of developing autism. That led researchers to conclude that it may be a complex interaction of several genes that make children susceptible to the disorder.

"There's probably a minimum of 10 genes involved and it's going to be a challenge to try to decipher what they all are and the size of their effect," Pericak-Vance said.

The study sheds no light on one of the most controversial issues surrounding autism today -- whether environmental factors trigger the disorder in genetically susceptible children.

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