Friday, January 9, 2009
UC Davis researchers who analyzed 16 years of records concluded that California’s dramatic rise in autism cases since 1990 cannot be blamed on population increases or the way the disability is classified or diagnosed.
The study’s authors, from the university’s MIND Institute, called for a switch in research emphasis from a genetic cause to possible environmental triggers including chemicals, medications, fertility treatments and childhood vaccines.
The incidence of autism in children 6 or younger increased from less than nine per 10,000 children born in California in 1990 to more than 44 in 10,000 children born in 2000.
Many experts contend that other factors account for the increase, such as greater awareness among parents and pediatricians, and therefore a greater likelihood of a diagnosis.
But that accounts for only a fraction of the more than 600 percent jump, said Irva Hertz-Picciotto, whose work was published this month in the journal Epidemiology.
“It’s still climbing. Five years from now it’s going to be even higher than that,” Hertz-Picciotto said in a telephone interview Friday. “Once you’re left with this idea that part of this is due to a true increase, it has to have something to do with the environment because genetics don’t change that quickly.”
Looking at birth records from 1990 through 2006, the researchers excluded children not born in California, thus eliminating migration as a possible cause for the increase. They also used census data to calculate incidence of autism over time and the age at diagnosis.
Hertz-Picciotto and her colleague, Lora Delwiche, found that less than 10 percent of the estimated increase could be attributed to the inclusion — after 1993 — of milder forms of autism, and about 4 percent of the increase was attributed to a trend toward earlier diagnosis.
“These are fairly small percentages compared to the size of the increase that we’ve seen in the state,” said Hertz-Picciotto, a professor of environmental and occupational health and epidemiology.
Many scientists think people have a genetic predisposition to autism that is triggered by some environmental factor. Hertz-Picciotto believes it’s probably multiple genetic susceptibilities and more than one environmental trigger.
People with autism have trouble with communication and social interaction. They often play with toys in unusual ways and have repetitive patterns of behavior such as hand flapping and spinning.
Stanley Swartz, an autism researcher and professor of special education at Cal State San Bernardino, said it will be hard to get a consensus on causes for the increase.
“The problem is we’re operating almost completely on theories,” he said. “What we have to consider is that this is not a single syndrome with a single cause. … There’s more going on than just one thing because you do see such a wide variety of cases of autism.”
Becky White, of Riverside, agreed. Her 14-year-old son Cameron, a triplet, has such severe autism that she had to put him in a group home full time last spring. Cameron speaks little and is prone to aggressive behaviors. Even before he was diagnosed at age 3, White knew he was different from his brothers, especially with his lack of eye contact.
A deeply devout woman, White said she doesn’t waste time or energy figuring out where to place blame for Cameron’s autism. She believes it was God at work and not environment, since her other sons are developing normally.
“It lessens the odds (of it being an environmental trigger) when you have multiples raised in the same place, exposed to the same things, the same food, and one of them isn’t just a little different, but profoundly different,” she said.