Rise in autism prevalence in CA likely due to environmental issues, suggests UC Davis study

This, according to journalist David Kirby of the Huffington Post, is big.

The prestigious MIND Institute of San Francisco, funded in part by a grant from the NIH, has concluded that the huge and continuing increase in autism diagnoses in California is NOT due to changes in diagnostic criteria or changes in record keeping. The study states that the increase is real, and suggests that there is a good chance that the causes are environmental rather than genetic. The study does leave open the possibility that there is a connection between increased awareness and increased numbers of diagnosed cases of autism.

Before reprinting a hefty portion of the UC Davis press release describing the study, though, I have to raise a question. I have been searching for years for any reliable statistics on diagnoses of "high functioning" autism versus "low functioning" autism. I have searched databases, asked major researchers - and it seems that such records are extremely hard to come by. California is the best record-keeping entity out there - but even there, there doesn't seem to be a simple way to know whether an "autism spectrum" or "PDD-NOS" diagnosis describes a child with "classic" or "high functioning" symptoms.

How, then, were these researchers able to provide us with a statistical analysis showing that changes in diagnostic criteria, reporting, and awareness cannot account for the rise in autism diagnoses?

Setting that question aside for the time being - and assuming that the difficulty is not as significant for MIND as it is for me - here is what the press release tells us:

A study by researchers at the UC Davis M.I.N.D. Institute has found that the seven- to eight-fold increase in the number children born in California with autism since 1990 cannot be explained by either changes in how the condition is diagnosed or counted — and the trend shows no sign of abating.

Published in the January 2009 issue of the journal Epidemiology, results from the study also suggest that research should shift from genetics to the host of chemicals and infectious microbes in the environment that are likely at the root of changes in the neurodevelopment of California’s children.

“It’s time to start looking for the environmental culprits responsible for the remarkable increase in the rate of autism in California,” said UC Davis M.I.N.D. Institute researcher Irva Hertz-Picciotto, a professor of environmental and occupational health and epidemiology and an internationally respected autism researcher.

The incidence of autism by age six in California has increased from fewer than nine in 10,000 for children born in 1990 to more than 44 in 10,000 for children born in 2000. Some have argued that this change could have been due to migration into California of families with autistic children, inclusion of children with milder forms of autism in the counting and earlier ages of diagnosis as consequences of improved surveillance or greater awareness.

Hertz-Picciotto and her co-author, Lora Delwiche of the UC Davis Department of Public Health Sciences, initiated the study to address these beliefs, analyzing data collected by the state of California Department of Developmental Services (DDS) from 1990 to 2006, as well as the United States Census Bureau and state of California Department of Public Health Office of Vital Records, which compiles and maintains birth statistics.

Hertz-Picciotto and Delwiche correlated the number of cases of autism reported between 1990 and 2006 with birth records and excluded children not born in California. They used Census Bureau data to calculate the rate of incidence in the population over time and examined the age at diagnosis of all children ages two to 10 years old.

The methodology eliminated migration as a potential cause of the increase in the number of autism cases. It also revealed that no more than 56 percent of the estimated 600-to-700 percent increase, that is, less than one-tenth of the increased number of reported autism cases, could be attributed to the inclusion of milder cases of autism. Only 24 percent of the increase could be attributed to earlier age at diagnosis.

Hertz-Picciotto said that the study is a clarion call to researchers and policy makers who have focused attention and money on understanding the genetic components of autism. She said that the rise in cases of autism in California cannot be attributed to the state’s increasingly diverse population because the disorder affects ethnic groups at fairly similar rates.

“Right now, about 10 to 20 times more research dollars are spent on studies of the genetic causes of autism than on environmental ones. We need to even out the funding,” Hertz-Picciotto said.

The study results are also a harbinger of things to come for public-health officials, who should prepare to offer services to the increasing number of children diagnosed with autism in the last decade who are now entering their late teen years, Hertz-Picciotto said.

...“We’re looking at the possible effects of metals, pesticides and infectious agents on neurodevelopment,” Hertz-Picciotto said. “If we’re going to stop the rise in autism in California, we need to keep these studies going and expand them to the extent possible.”