Study challenges drug's role in autism

Study challenges drug's role in autism
The use of mercury-based preservative thimerosal may not be linked with autism as previously thought, according to a new study.
The prevalence of autism in California children continued to rise after many vaccine manufacturers started to remove the mercury-based preservative thimerosal in 1999, suggesting that the chemical was not a primary cause of the disorder, according to the study published in the January issue of the Archives of General Psychiatry.
The analysis found that from 2004 to 2007, when exposure to thimerosal dropped significantly for 3- to 5-year-olds, the rate continued to increase in that group from 3.0 to 4.1 per 1,000 children, according to the study.
"If mercury exposure in vaccines was a major cause of autism, then the number of ... affected kids should have diminished once they were no longer exposed to thimerosal," said Dr. Robert Schechter, lead author of the study and a medical officer at the state Department of Public Health. "That is not what we found."
The study is the latest in a series that has investigated the connection between thimerosal and autism. The majority have found no association.
The latest study was based on data from the California Department of Developmental Services, which provides services to about 36,000 people with autism and has one of the country's best reporting systems.
The researchers looked at all reported cases in the state of California starting with children born in 1989. They found the number of cases per 1,000 children has been steadily increasing from that point to March 2007, the end point of the study.
Steve M. Edelson, an experimental psychologist who is director of the Autism Research Institute, a nonprofit organization in San Diego of California, said the study, along with evidence from previous research, argued against thimerosal as the major culprit in autism.
But, he added, it still does not rule out all blame. Edelson said such large-scale analysis could overlook smaller groups of children, who for whatever reasons have a particular vulnerability to mercury. He said more solid evidence can only come from laboratory studies, such as postmortem analyses of the brains of autistic children.