TUESDAY, Jan. 5, 2010 (HealthDay News) -- Highly educated, older parents are more likely to have a child diagnosed with autism, a new study finds.
Using data on about 2.5 million births in California in a five-year period, researchers identified 10 autism clusters, or geographical areas in which there was a higher than usual incidence of children diagnosed with the neurodevelopmental disability that's marked by impaired social and communication skills, and repetitive behaviors.
The rate of autism in the clusters was about twice that of the surrounding areas.
The parents' educational attainment was classified into one of four levels: less than 12 years of school, high school graduate, some college (13 to 15 years) or 16-plus years of school (college graduate or advanced degree).
Parents who lived in the areas where autism was more prevalent were more likely to be college graduates or hold advanced degrees than parents who lived outside the clusters.
"It confirms what we already knew, which is that highly educated parents are more likely to have children with autism," said the study's lead author, Karla Van Meter, an epidemiologist with the Sonoma County Department of Public Health who was a doctoral student in public health sciences at the University of California, Davis, when she conducted the research.
Mothers and fathers who were older when their child was born were also more likely to have autistic children, but parental age was not linked as strongly with autism as educational attainment, Van Meter said.
The study is in the Jan. 6 online issue of Autism Research.
The researchers identified 9,900 children born between 1996 and 2000 who were diagnosed with autism by age 6, according to the study. Data came from the California Department of Developmental Services, which coordinates services for children with autism.
Just why there appears to be a link between parents' educational level and autism is unclear, but theories abound.
"Nobody really knows for sure, but some think there may be something genetic going on, some believe better-educated parents are more successful in seeking services for their children or may have different expectations for the kids, some believe there could be some physical or chemical exposure in those households," Van Meter said. "It could be all of the above or some combination of factors. All are being studied."
Though the data did not include information on household incomes, areas with highly educated residents also tend to be higher-income areas, the researchers said. For example, the cluster in San Diego County ran along the coast between Del Mar and La Jolla, one of the nation's wealthiest areas.
Other clusters were found in the Los Angeles area, the San Francisco Bay area and the Central Valley.
Andy Shih, vice president for scientific affairs at Autism Speaks, said that highly educated parents tend to know more about autism, are more successful in getting their children treatment and are more likely to have the resources to move to be closer to treatment centers. The clusters tended to be near regional autistic treatment centers, the study found.
"The unanswered question is, 'What about the parents who don't have the means to move to a place where there are better services, or who don't have the information on early signs of autism?'" Shih said. "This study points to a potential health disparity in our population."
Lee Grossman, president and chief executive of the Autism Society of America, described the study as interesting but said that, in his experience, autism cuts across demographic and socioeconomic lines.
"It seems to occur at the same rate no matter where you are and who you are," Grossman said. "We really aren't seeing well-educated parents having a greater tendency to have children with autism."
Better-educated parents may be more likely to seek out services sooner, however. Previous research has suggested that children from white and more-affluent families tend to have their children diagnosed sooner than minority children or poorer children, Grossman said.
At the same time, the number of children with autism continues to rise. A report in December from the U.S. Centers for Disease Control and Prevention found that one in every 110 children in the United States has been diagnosed with autism.
The number of 8-year-olds with autism rose an average of 57 percent between 2002 and 2006, the CDC reported.
The U.S. National Institute of Neurological Disorders and Stroke has more on autism.