A nearly 300 percent increase in the number of California children with autism is a real phenomenon that cannot be explained away by improved diagnosis, greater awareness of the disease or families moving to the state in search of treatment, University of California researchers said Thursday.
But the cause of the drastic rise in cases is still a mystery to scientists, who say more study into the disease’s possible genetic and environmental causes is needed.
“The numbers appear to be real,” said lead researcher Dr. Robert Byrd, a UC-Davis pediatrician. “But we still have a lot to explain.”
The $1 million state-funded study grew out of a 1999 state report showing that the number of reported autism cases nearly quadrupled to 10,360 in 1998 from 2,778 in 1987. At the time, health officials and some clinicians speculated that an “overdiagnosis” of autism cases or an influx of families seeking services could be to blame.
Instead, Byrd and his colleagues were surprised to find that diagnosis of autism appeared to hold constant, and that 90 percent of children receiving services were born in California.
“There’s always been this discounting of the data: `It can’t be this bad, it can’t be that high,’ ” said Michael Nanko, executive director of Cure Autism Now, a Los Angeles-based advocacy group. “This study answers the skeptics and sends a message about the urgency for more funding for treatment and research.”
One autism expert disputed the survey’s results, however, noting that criteria for diagnosing autism have changed over time. “I don’t think there are more kids with autism,” said Bryna Siegel, a UC-San Francisco child psychiatrist who heads the university’s autism clinic. “There are more labels of autism.”
“There are a lot of problems with how autism is diagnosed in California,” Siegel added, noting that the state Department of Developmental Services is trying to standardize diagnoses.
In California, 18,460 children have been diagnosed with the disease, according to the most recent figures from the state.
Autism, first described by doctors in 1943, is a complex developmental disorder that can severely impair children’s social interactions, reasoning skills and ability to communicate. It is typically diagnosed at 2 to 4 years of age.
Some of the disease’s defining characteristics include abnormal responses to sensations, avoidance of eye contact, and repetitive behavior. According to the Autism Society of America, an estimated 500,000 to 1.5 million Americans are autistic or have a less severe form of autism known as pervasive development disorder.
The incidence rate of autism has been rising throughout the country, but not as dramatically as in California.
Autism has long been thought to have a genetic basis, but its rapid rise in California has suggested to researchers that other factors may be at work: Genes alone simply don’t change that quickly, they say.
Now, scientists hypothesize that an as-yet-undiscovered interaction between environmental triggers that “switch on” previously dormant, faulty genes might explain some autism cases. Some of those triggers could include environmental toxins or metabolic disorders. Some autism activists blame components of childhood vaccines, although many scientists say this theory is poorly supported.
To tease out the causes for California’s rapid rise in cases or at least remove some causes from consideration the researchers compared 375 autistic children in two groups. One group included 7- to 9-year-olds who were diagnosed in the 1990s. The other comprised 17- to 19-year-olds who had been diagnosed a decade earlier. The researchers looked at a similarly divided set of 309 children who had been diagnosed with mental retardation but not autism.
Researchers found that virtually the same proportion of autistic children in both groups were correctly diagnosed according to stringent psychiatric criteria. If more children were termed “autistic” because of overly generous or misguided diagnoses, Byrd said, researchers would have found fewer children in the younger group who met the criteria for autism.
The researchers also examined whether some autistic children had been mislabeled as mentally retarded. In contrast, they found that just under a fifth of both old and young children in the mentally retarded group met the criteria for autism as well as mental retardation.
Researchers also examined whether demographics of children with autism had changed over a decade, but found that the disease continued to cross all racial, ethnic and economic boundaries. There was one exception: Researchers found a slightly higher, but statistically insignificant, proportion of Latino children in the younger autistic group, Byrd said.
Research into the causes of California’s autism spike is ongoing. A state team will spend five years investigating new cases in six Bay Area counties with a $3.5 million grant from the U.S. Centers for Disease Control and Prevention.
The UC-Davis study was hailed by families of autistic children who have long sought additional government money for services.
“I’m very excited to see a scientifically rigorous study that says, `Yes, we have a problem,’ ” said Chris Bogert, a San Jose mother of a 6-year-old autistic boy. “Hopefully, it will really mobilize the scientific community and the policy community and the media to really address this issue. We’re in the middle of this huge national tragedy.”