Wanted: Chemicals that Cause Autism

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Dr. Philip Landrigan is rounding up a posse in search of one of America's most elusive evildoers: The cause of autism, which afflicts as many as 1 in 80 American children. Though the soft-spoken, gentlemanly pediatrician doesn't cut the figure of a sheriff, he used Wild West language to describe the hunt he and his fellow scientists have embarked on.

"We want a 'Most Wanted Chemicals' list. We want a 'Dirty Dozen,'" he told the audience at Exploring the Causes of Autism and Learning Disabilities, a December 2010 conference organized by the Mount Sinai Children's Environmental Health Center, where Landrigan is dean of global health and chairman of the Department of Preventative Medicine. Landrigan received a 2010 Heart of Green Award from The Daily Green.

Diagnosis of Autism Spectrum Disorder, a developmental disability with a range of effects on intelligence and sociability, increased 57% between 2002 and 2006, according to Colleen Boyle, acting director of the National Center on Birth Defects and Developmental Disabilities. And while the center's last set of statistics drew alarming headlines about 1 in 110 children now being diagnosed with autism, she said that's an average; the rate could be as high as 1 in 80 (or as low as 1 in 240).

As recently as 2005, the increase in diagnoses was attributed to just that: An increase in diagnoses. Doctors and parents, it was thought, were more aware of the symptoms of the disease, the definition of the Autism Spectrum Disorder grew more expansive, government services were more widely available and the stigma associated with the illness was disappearing – all of which contributed to an increase in diagnosis that had little or no basis in actual increased illness.

But the rates of disease are actually increasing, not just the diagnosis or treatment of disease, according to research by Irva Hertz-Picciotto and colleagues at the Center for Children's Environmental Health at the University of California-Davis.

And that's just one reason genetics alone can't explain autism. Genetics clearly plays a role – if one identical twin has autism, 70% of his siblings do, too. But even scientists sometimes mistake a genetic basis of disease for an explanation of its causes: the environment is still the trigger for the expression of genes. (And scientists are only now exploring the epigenetics of disease – not just the genes themselves, in other words, but their place in the DNA sequence.)

The question is: What are those environmental triggers that cause autism? And when in the early development of a fetus does the trigger get pulled? The triggers may or may not be synthetic chemicals: Other aspects of the environment that may affect gene expression include nutrients in food, physical factors like heat or radiation, and exposure to medications, alcohol and drugs.

The trigger-happy culprits are on the lam. Landrigan and his colleagues are hunting them down.

"The human brain in the human fetus is exquisitely vulnerable to toxic chemicals – much more than in adults," Landrigan said. "The human brain is capable of doing calculus and writing symphonies and enjoying the beauty of the sunset, but the cost of that is exquisite vulnerability."

Scientists have identified some culprits that are known to be toxic to the developing brain in the first trimester of pregnancy, ranging from a mother's ingestion of a now-banned morning sickness medication (Thalidomide) to her exposure to the certain pesticides (chlorpyrifos) once used commonly around the house to combat insect infestations. But with 80,000 synthetic chemicals in use in the United States, few have undergone rigorous health safety testing. More than 1,000 are known to be neurotoxic to animals, about 200 of which are known to be neurotoxic to human adults; no one knows for sure which of those are also toxic to the unborn.

Photo: Dr. Philip Landrigan at the 2010 Heart of Green Awards ceremony.

"The number of new product formulations and chemicals and exposures coming online is just astronomical," said Hertz-Picciotto.

The good news is that scientists are closer than ever – perhaps just a few years away – from identifying environmental triggers for autism, which is the first step in halting the increase of the disease. In the U.S. four very large studies are underway that are, cooperatively, seeking the answers:

• CHARGE: In California the Childhood Autism Risks from Genetics and the Environment is tracking more than 1,000 children – some with autism or other developmental disabilities, and others without – and attempting to determine which exposures and susceptibilities define each group.
• EARLI: The Early Autism Risk Longitudinal Investigation will track 1,200 mothers of autistic children as they experience their second pregnancy. Mothers – and their homes and families – will be tested for various exposures before, during and after birth, and the second sibling will be tracked for three years.
• MARBLES: The Markers of Autism Risk in Babies – Learning Early Signs study has been assessing pre- and post-natal exposures to California mothers of autistic children during their second pregnancy.
• The National Children's Study: So big it doesn't need an acronym, the National Chidlren's Study is the mother of all studies, tracking 100,000 children from before birth until age 21 to attempt to understand the genetic and environmental cause of a range of childhood illnesses, including autism and other developmental abnormalities.

Finding the causes of autism and other possibly related chronic childhood diseases – from ADHD and asthma to obesity and diabetes – amounts to a huge effort at preventative medicine. It's the kind of thing that can save the U.S. economy enormously, not only in health treatment savings, but in the productivity of smart, skilled workers who might otherwise be relegated to the margins of society. Removing lead from gasoline, for instance, is estimated to be worth $200 billion annually because of the increased intelligence of each generation of children born without brain damage from lead exposure.

As Dr. Linda Birnbaum, the director of the National Institute of Environmental Health Sciences and the National Toxicology Program put it, "Our focus is not on cures and therapies, it's on prevention. Health and medicine are not the same thing."

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