Oct. 17, 2002

(SACRAMENTO, Calif.) The unprecedented increase in autism in California is real and cannot be explained away by artificial factors, such as misclassification and criteria changes, according to the results of a large statewide epidemiological study.

"Speculation about the increase in autism in California has led some to try to explain it away as a statistical issue or with other factors that artificially inflated the numbers," said UC Davis pediatric epidemiologist Robert S. Byrd, who is the principal investigator on the study.

"Instead, we found that autism is on the rise in the state and we still do not know why. The results of this study are, without a doubt, sobering.

" Key findings of the study are that:

The observed increase in autism cases cannot be explained by a loosening in the criteria used to make the diagnosis.
Some children reported with mental retardation and not autism did meet criteria for autism, but this misclassification does not appear to have changed over time.
Because more than 90 percent of the children in the survey are native born, major migration of children into California does not contribute to the increase.
A diagnosis of mental retardation associated with autism had declined significantly between the two age groups.
The percentage of parent-reported regression (loss of developmental milestones) does not differ between two age groups.
Gastrointestinal symptoms, including constipation and vomiting, in the first 15 months are more commonly reported by parents in the younger group.

 "While this study does not identify the cause of autism, it does verify that autism has not been over-reported in the California Regional Center System and that some children diagnosed with mental retardation are, in fact, autistic," Byrd said. Byrd and his research team earlier this year enrolled 684 California children who received services from one of the California Regional Centers to participate in the study. They systematically gathered information for children in two age groups 7 to 9 years of age and 17 to 19 years of age from families of 375 children with a diagnosis of full syndrome autism and 309 children with a diagnosis of mental retardation without full syndrome autism.

Byrd, a pediatrician with UC Davis Children's Hospital, and his colleagues, conducted the study for the M.I.N.D. Institute at UC Davis to help explain reasons behind significant increases in the number of autistic children entering the state's 21 regional centers.

A 1999 report by the California Department of Developmental Services (DDS), which operates the centers, found a 273 percent increase in autism cases between 1987 and 1998. The report was the catalyst for the state Legislature and Gov. Gray Davis to direct DDS and the M.I.N.D. Institute to identify factors responsible for the increase, funding the effort with a $1 million appropriation. Autism is a complex and severe developmental disorder that affects a person's ability to communicate, form relationships with others, and respond appropriately to the environment. Those affected may avoid making eye contact and lack the ability to read faces for signs of emotion or other cues. Children typically do not engage in social play or games with their peers. Unusual behaviors such as rocking, hand-flapping or even self-injurious behavior may be present in some cases. Copies of all news releases from UC Davis Health System are available on the Web at

Editor's Note: Additional information available on these Web sites: Report to the Legislature at
Statistics of children entering the state Regional Center system at
1999 autism report at
Robert Byrd's biography at  
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