What's Causing the Autism Epidemic?

An explosion of new studies released during Autism Awareness Month offer tantalizing insights into potential causes of a disorder that’s been blamed on everything from bad parenting to vaccines and TV viewing.

Adding urgency to the quest, last month the Centers for Disease Control (CDC) reported that autism spectrum disorder (ASD) now affects an estimated one in 88 children, a sharp rise from 2002, when ASD was thought to strike one in 110 kids. That means ASD is more common in children than diabetes, AIDS, cancer, cerebral palsy and Down syndrome combined. 

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While some reports say autism diagnoses are rising at a rate of 10 to 17 percent a year, there’s hot medical debate as to whether the condition is actually striking more kids. Some experts contend that children who might have been labeled with other developmental disorders in the past—or not diagnosed at all—are now being classified as on the autistic spectrum, due to a broader definition of ASD.

A Puzzling Gender Gap

There continues to be a dramatic, still unexplained gender gap, with the CDC estimating that one in 54 boys have ASD, compared to one in 252 girls. Overall, more than two million Americans have been diagnosed with ASD—a spectrum of related developmental disabilities that can range from mild to severe.

Autism and ASD are umbrella terms for disorders marked by difficulties with social interactions, communication issues, and repetitive behavior. Some kids with ASD have mental and motor skill impairments, trouble sleeping, GI issues, and trouble paying attention, while others have normal or high IQs and may excel at math, music, or art.

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A $1 Billion Hunt for Autism Triggers

More than $1 billion has been poured into research investigating possible triggers for autism, which was once blamed on “refrigerator mothers,” the theory that cold, unfeeling moms prompted kids to retreat into autism due to psychological wounds. Another thoroughly discredited belief was that thimerosal, a mercury-based preservative used in childhood vaccines, such as the MMR (measles, mumps and rubella) shot, was the culprit.

The Institute of Medicine conducted a comprehensive safety review and found no link between thimerosal-containing vaccines and autism. Nearly two dozen other studies also failed to find any link. While scientists haven’t yet solved the autism riddle, they’ve made tantalizing discoveries about potential contributing factors:

Genes. It’s long been known that parents with one autistic child have a higher risk of having a second child with the condition. Now a new study published in Molecular Psychiatry shows that half siblings of autistic children have half the risk. That may not seem surprising, given that half siblings share about 25 percent of their genes, but the findings give new clues about how the condition is inherited.

Most of the half siblings in the study had the same mom, suggesting that even though ASD is far more common in males, women can inherit and pass along genetic risk. Earlier research suggests that in about 60 percent of ASD cases, genetic variations are inherited from unaffected moms and dads.

Poor health during pregnancy. Another new study reports that moms who are obese, diabetic, or suffer from high blood pressure during pregnancy were 61 percent more likely to have a child with autism, compared to healthy women with a normal body weight. These maternal conditions also more than doubled a child’s risk for development delays.

Two recent studies highlight the protective benefits of taking prenatal vitamins containing folic acid during the 12 weeks before and after conception. Norwegian researchers report that doing so cuts the risk of having a child with severe language delays or autism by more than 50 percent.

Older dads. New research suggests that a baby’s autism risk increases if the dad is over age 35. The scientists estimated that spontaneous genetic mutations may magnify the threat by up to 20-fold—and the older the father is, the greater the likelihood that his sperm will contain these mutations, according to CBC News.

Three independent studies published in Nature this month all made similar discoveries, with one team reporting that such mutations can occur with either parent, but happened four times more often with sperm cells than eggs.

Air pollution. Kids whose moms lived within 1,000 feet of a freeway when they were born had double the risk of autism as kids who live in areas with less traffic, a 2010 study found.  However, that doesn’t prove that air pollution causes autism, the researchers caution, just that it may be a factor contributing to rising rates.

High fructose corn syrup. A scary study published this week in Clinical Epigenetics links the autism epidemic to our eating habits. The scientists investigated how mineral deficiencies triggered by dietary factors—particularly consumption of high fructose corn syrup (HFCS)—might impair the body’s ability to rid itself of common environmental toxins, such as pesticides.

Eating HFCS—a widely used sweetener often made from genetically modified corn—is linked to dietary loss of zinc, the researchers report. Zinc deficiency reduces the body’s ability to eliminate such heavy metalsas arsenic, cadmium, and mercury, potent toxins that can impair a baby’s brain development.

Compounding the danger, HFCS also leads to a loss of healthy, protective minerals, like calcium. That may worsen the devastating impact of pesticide exposure on the developing brain, suggest the researchers, thus boosting boost autism risk.

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