U.S. researchers have identified 10 locations in California that have double the rates of autism found in surrounding areas, and these clusters were located in neighborhoods with high concentrations of white, highly educated parents.
Researchers at the University of California Davis had hoped to uncover pockets of autism that might reveal clues about triggers in the environment that could explain rising rates of autism, which affects as many as one in 110 U.S. children.
But the findings likely say more about the U.S. health care system than the causes of autism, said researcher Irva Hertz-Picciotto of UC Davis' MIND Institute, whose study will be released online Wednesday in the journal Autism Research.
Dr. Keith's Blog: Autism and Anxiety
Advocacy groups have been clamoring for treatment options and for better research to show what might be causing an apparent increase in autism cases.
Hertz-Picciotto and colleagues used a research technique that has been effective at identifying cancer clusters.
"This kind of analysis sometimes turns up clues about environmental factors," she said in a telephone interview.
The researchers looked at about 2.5 million births recorded in California from 1996 through 2000. About 10,000 of those children were later diagnosed with an autism spectrum disorder, according to the state's department of developmental services.
Using data from birth records, the team found a strong link between parental education and the high rates of autism.
"In this particular case, we found 10 clusters of autism across the state of California. When we looked further, we discovered virtually all of them were areas where there was a higher level of education among the parents who were giving birth in those years," Hertz-Picciotto said.
"We already know that people with a higher education in the United States are more likely to get a diagnosis of autism for their child. It doesn't necessarily mean that autism occurs more frequently in those families," she said.
"It was also a greater likelihood to be white, non-Hispanic, and for the parents to be a little bit older."
Access to Health Care
Hertz-Picciotto said studies in Denmark, which offers universal access to healthcare, have found no link between autism and race or socioeconomic status.
"In this country, we have a lot of people who are uninsured. They may not have someone to go to if they have suspicions about their child," she said.
She said some communities with lower education levels and fewer resources may have higher rates of undiagnosed autism. But the study did offer new clues about autism.
"What it tells us is if we want to go looking for environmental factors, they are not going to be these focused fixed points of contamination, for example," she said.
"It is probably going to be something much more widespread — common sorts of exposures that are more across the board."
Hertz-Picciotto said her team is now undertaking two different kinds of studies to look for environmental causes of autism, a spectrum of diseases ranging from severe and profound inability to communicate and mental retardation to relatively mild symptoms called Asperger's syndrome.
In one, her team plans to collect dust samples from the homes of 1,300 families with autistic children to look for common chemicals, such as flame retardants, that might be playing a role.
In another, the researchers are following pregnant women who have already given birth to a child with autism, to see if there are any common exposures that might be a factor in developing autism.