Is There Really an Epidemic?
Rates of autism have been growing 10 to 17 percent each year, according to the Autism Society of America. Worrisome? Yes. But experts stress that much of this increase is due to doctors simply getting better at identifying this disorder. "Kids who are getting diagnosed as autistic today would simply have been dismissed as mentally retarded 20 years ago," explains Johnson. "Mild cases of autism were most likely missed completely."
Scientists are still teasing out autism's causes, but the consensus is that genetics -- not environment -- play the larger role. "If an identical twin has autism, the chance is about 90 percent that the other does as well; with fraternal twins, that number drops to about 10 percent," explains Scott Myers, MD, a neurodevelopmental pediatrician at the Geisinger Medical Center, in Philadelphia. While experts caution there's no one "autism gene," researchers at the Mount Sinai School of Medicine, in New York City, recently screened more than 400 families that have members with autism and found that most shared a common genetic mutation. Children with autism also are more likely to come from families with anxiety or mood disorders, although researchers are still puzzled as to why.
Vaccines and Autism
One worry you can cross off your list: any possible association between vaccines and autism. "We've looked at several hundred thousand children all over the world and found no link between any type of vaccine and this disorder," stresses John Iskander, MD, a medical epidemiologist and pediatrician at the CDC. One recent review published last October analyzed more than 30 studies and found that the rate of autism among kids who received the MMR (measles-mumps-rubella) vaccine is no higher than in kids who never got the vaccine. After concerns arose in the 1990s that vaccines containing thimerosal (mercury) as a preservative could cause the disorder, it was removed (for the most part) from the market in 1999, despite the fact that study after study found no link between thimerosal and autism.
"It appears that the brain changes that lead to autism occur well before birth," explains Johnson. "When we've done autopsies of people with autism, we find abnormalities in areas of the brain that develop during the second trimester. There's no way that vaccines could cause any of these changes."