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Tuesday, August 9, 2011

Causation and the Environment

The New York Times reports on recent studies suggesting environmental causes of autism:

But “environment” is a tricky word. To many scientists studying autism, it means “everything that’s not the inherited DNA,” said Irva Hertz-Picciotto, a professor of epidemiology at the University of California, Davis, MIND Institute. An environmental influence might be a chemical the fetus is exposed to via the placenta, or it might refer to aspects of nutrition, maternal health, stress — or perhaps exposure to a microbe.

The causal links most strongly supported by research include rubella infection during pregnancy and prenatal exposure to medications like thalidomide and valproic acid, an anti-seizure drug. Other environmental factors, like air pollution and exposure to certain pesticides and other chemicals, have been found to be associated with autism, but without evidence of causality.

In a 2010 paper in the journal NeuroToxicology, Dr. Amir Miodovnik, a pediatrician at the Mount Sinai School of Medicine, and his colleagues showed that children who had been exposed to high levels of phthalates prenatally were more likely to show social impairments at 7 to 9 years of age.

Phthalates, chemicals found in many consumer products, are so-called endocrine disruptors, hormonally active substances that can interfere with a variety of developmental processes, including brain development. Yet these data don’t demonstrate cause and effect, Dr. Miodovnik said, “only that these substances are associated with symptoms found in autism.” Conversely, taking prenatal vitamins around the time of conception has been associated with a lower risk of autism in a recent study.

These epidemiologic associations may point us in the direction of still other factors involved in the making of autism. “Every case is probably a result of the confluence of many factors,” Dr. Hertz-Picciotto said. “No case probably has one cause.”

The Brownsville Herald reports:

Researchers conducting a study in Harlingen hope to learn whether genetics or the environment are factors in the development of autism.

Twenty Mexican-American children 2 to 5 years old are participating in the pilot study under way at the Regional Academic Health Center here. They are being accompanied by their mothers.

Hispanics are less likely than non-Hispanic whites to be diagnosed with autism, according to a press release by the University of Texas Health Science Center at San Antonio, which is conducting the study.

Researchers are trying to learn whether Mexican-Americans have a genetic composition that makes them less susceptible to developing autism, or if diagnosis is being unrecognized, said Beatriz Tapia, field investigator for the study and a faculty associate with the Health Science Center’s Department of Family & Community Medicine of the School of Medicine.

Voice of America has a report on broader research on environmental influences on children's health, including autism, among others: