IMMUNITY ROLE?

IMMUNITY ROLE?

Support is growing for the idea that immune system problems in a pregnant woman or developing child set the stage for autism.

Zimmerman and his colleagues recently found that rheumatoid arthritis and other autoimmune disorders, in which the immune system attacks parts of the body, are unexpectedly common in families of autistic children. Zimmerman says that other studies have shown that from 30 to 70 percent of autistic children have subtle immune system abnormalities, although such children aren't exceptionally vulnerable to everyday infections.

To study whether impaired immunity might put some children at risk of developing autism after being exposed to thimerosal, Mady Hornig of Columbia University and her colleagues did experiments using mice vulnerable to autoimmune diseases. The researchers injected newborns of this susceptible strain and of two other strains with thimerosal alone, with a thimerosal-vaccine combination, or saline solution. The doses were comparable to those that children receive in typical vaccinations.

In the September Molecular Psychiatry, Hornig's team reports that virtually all the mice in the immune-compromised strain that received either form of thimerosal showed autismlike symptoms. They behaved oddly and had delayed growth and brain abnormalities. The other two strains of mice showed no such effects.

Some scientists caution against reading too much into the findings. Epidemiologist Craig Newschaffer of Johns Hopkins says that animal experiments such as this are important to determine the physiological effects of exposure to toxic substances. But, he notes, it's impossible to say with certainty that lab animals exhibiting certain kinds of behavior have autism or that what happens in lab animals translates to people. "We have to keep in mind that these are largely preliminary studies," he says.