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autism causes, autism environment, autism genetics

California’s Autism Increase Is No Myth, Study Says

January 12, 2009 01:01 PM
by Denis Cummings
A California study has determined that the state’s dramatic increase of autism cases is due to a genuine rise in autism, rather than to a change in criteria for diagnosis.

California Autism Rate Increases Sevenfold Since 1990

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California has had the largest increase of autism in the United States, up from 205 cases in 1990 to more than 3,000 in 2006. “For years,” writes Scientific American, “many medical officials have suspected that the trend is artificial—due to changes in diagnoses or migration patterns rather than a real rise in the disorder.”

In a study to be published in the January edition of the journal Epidemiology, researchers at the University of California-Davis’ M.I.N.D. Institute have determined that these factors account for only a fraction of the increase. “Younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases,” the study found.

Cal-Davis epidemiology professor Irva Hertz-Picciotto, who led the study, said in the study press release that more research should be performed on the effect of environmental factors. “Right now, about 10 to 20 times more research dollars are spent on studies of the genetic causes of autism than on environmental ones,” she said. “We need to even out the funding.”

The M.I.N.D. Institute is currently conducting the “first major investigation of environmental factors and gene-environment interactions” in autism. The CHARGE (Childhood Autism Risks from Genetics and the Environment) study is examining the effect of chemicals such as mercury, polychlorinated biphenyls (PCB’s), lead and pesticides.

Background: Causes of autism

Autism is a neurodevelopmental disorder that impairs a person’s ability to communicate and interact with others, and causes restricted and repetitive behavior. It is usually diagnosed in children between the ages of 18 months and three years old. Autism is the most serious of the three autism spectrum disorders (ASDs), which also includes Asperger syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS).

Little is known about what causes autism, though most studies focus on a genetic cause or an environmental cause. Research has shown that autism tends to reoccur in families and that there is a high concordance rate of autism in identical twins, suggesting a genetic cause. However, scientists have yet to discover a gene or arrangement of genes linked to ASDs.

Because there is a widespread increase in autism cases, many researchers believe that there must be a link to changes in the environment. Studies have shown a link between autism and prenatal exposure to thalidomide and valproic acid, though “the concordance rate is not 100%,” writes Michael Szpir in Environmental Health Perspectives, “which suggests that a genetic predisposition is necessary for chemical and microbial factors to act as triggers.”

“Given the complexity of autism, we will not find a magic bullet (genetic or environmental) to blame for most cases,” writes University of North Carolina professor of epidemiology and maternal and child health Julie L. Daniels. “There are probably many combinations of genes and environmental factors that contribute to the constellation of autistic traits.”

There has been a highly publicized debate over the effect of vaccinations in causing autism, based on the fact that the early signs of autism are seen soon after a child receives the MMR vaccine. Though there is little scientific evidence showing a link between vaccinations and autism, the U.S. federal government lost a lawsuit in March in which a child’s autism was blamed on vaccinations.

Reference: Autism

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