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.
"These are fairly small percentages compared to the size of the increase that we've seen in the state," Hertz-Picciotto said.
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.
"These children are now moving toward adulthood, and a sizeable percentage of them have not developed the life skills that would allow them to live independently," she said.
|Contact: Phyllis Brown|
University of California - Davis - Health System