What's the real story? Health asked leading autism researchers to help us figure it out.

To say there's a big debate over autism is an understatement. More than 5,000 families have filed court claims blaming vaccine makers for their children's autism symptoms——including serious language delays, poor social skills, and repetitive movements——yet the research to date repeatedly shows no connection between vaccines and autism. A recent court decision added fuel to the fire by awarding compensation to the family of a young girl who developed autism symptoms after being vaccinated. What's the real story? Health asked leading autism researchers to help us figure it out.

Q: Why does there seem to be a sudden epidemic of autism?

A: Epidemic may be the wrong word. In the mid-1970s the reported rate of autism was 21 in 10,000 children, or 1 in 470. Today its 65 to 67 per 10,000, or 1 in 150—--about a threefold increase in 30 years. While any uptick in these numbers is worrisome, scientists aren't calling that an epidemic. Many experts believe the actual rise in autism cases (additions to the amount typically seen in the general population) is quite small. The surge in diagnoses, they say, is largely due to a broader understanding of what qualifies as autism, greater awareness of the disorder, and the increased availability of services for children with autism symptoms.

To better understand that argument, consider this: Many children who are classified as autistic today would have been diagnosed with speech disorders or mental retardation 30 years ago. Indeed, as the number of children with autism has climbed, the number diagnosed with mental retardation has dropped. “These factors could explain all of the increase in autism cases,” says autism expert Eric Fombonne, MD, head of the department of psychiatry at Montreal Childrens Hospital.

Q: What's behind the idea that vaccines are to blame for autism?

A: There are many theories—and theres not much scientific support for any of them. One blames the MMR (measles, mumps, and rubella) vaccine, suggesting that the measles proteins in the shot can damage a child's stomach; a leaky gut could allow protein fragments produced during diges­tion to travel to the brain and wreak havoc. Another theory implicates the vaccine preservative thimerosal, which con­tains a form of mercury known as ethylmercury. Some believe the heavy metal causes neurodevelopmental abnor­malities that lead to autism, in part, because methylmercury (a similar compound commonly found in some fish) can damage the brain.

However, more than 10 studies comparing hundreds of thousands of children who did or didn't receive MMR vac­cines consistently showed no increased risk of autism. And six studies comparing children who received thimerosal-based vaccines versus thimerosal-free vaccines also showed no increased risk. That said, some experts don't think the studies were rigorous or sensitive enough to pick up an effect in a fraction of susceptible children. “If 1 in 1,000 of the kids with autism had been affected by vaccines, you would not detect it in those studies,” says Isaac Pessah, PhD, director of the Center for Childrens Environmental Health at the University of California, Davis.

That means the debate is likely to go on. Pessah believes that many questions need to be answered, such as when to vaccinate and how many shots to give a child at once. “While we've increased the number of vaccines that are required, we haven't kept up the research on what is too many within a certain period of time,” he explains.

Q: Are some children more susceptible to autism after they've been vaccinated?

A: Most experts believe that autism has a strong genetic component, and a kid with a genetic predisposition may be susceptible to any number of insults, or “hits,” to his or her system—from vaccines, infections, or other environmental factors yet to be proven. But Pessah says its doubtful that vaccines alone could be the sole contributor to autism.

Q: If the vaccine-autism link isn't proven, why did the federal government recently settle a lawsuit alleging that a girl got autism from vaccines?

A: The reason for the settlement isn't entirely clear. While many autism advocates hailed the decision as an admission that vaccines can cause autism, the U.S. Centers for Disease Control and Prevention (CDC) went out of its way to dispute that notion. The agency insists that the research does not support a link between autism and vaccines.

The case concerned Hannah Poling, now 9, who was 18 months old when she received five shots at once that vaccinated her against nine diseases. Ten months later, she was diagnosed with mitochondrial-enzyme deficiency, a rare inheritable disease that causes brain damage and autism-like symptoms. The question put to the Vaccine Injury Compensation Program (VICP), a federal body established in 1988 to help control the slew of lawsuits against vaccine makers, was whether her vaccinations caused her autism symptoms, which didnt appear until after she was vaccinated. The VICP conceded it was biologically plausible that the vaccines worsened her underlying disorder, triggering her symptoms. However, the case did not prove that vaccines can trigger autism symptoms in children with mitochondrial disease, only that common infections can set off the symptoms in these kids. (Hannah had endured several ear infections and fevers before displaying autistic behavior.) In fact, many mitochondrial-disease experts say that instead of avoiding vaccines for kids with these problems, its critical that they get vaccines to prevent devastating infections.

Q: If vaccines aren't a root cause of autism, what is?

A: A range of environmental factors, including infections, medications, diet, and pollutants, may be to blame. For example, a lot of research fingers pesticides. One study measured markers of organophosphate pesticides like malathion or diazinon (commonly used in agriculture) in the blood or urine of children and their mothers, then checked the developmental abilities of the children; it found a higher rate of autism-like disorders in children with higher pesticide levels. Organochlorines seem to interfere with how the nervous system keeps from being overly excited, an issue in autistic children.

Q: How would diet contribute to autism—or prevent it?

A: Some experts believe that two proteins——gluten (found in barley, rye, oats, and wheat) and casein (in dairy products)——dont get broken down completely in the gastrointestinal tracts of children on the autism spectrum, and that could hurt brain development and function. A gluten-and-casein-free diet is the most widely used for autism. Many families report that it helps regulate bowel habits, sleep, and repetitive behaviors, and improves their kids overall progress, though no good research confirms that. Several large-scale studies of this diet are underway.

Fombonne warns that the improvement seen by parents after a treatment is often due to the placebo effect or their desire to see a benefit. The bottom line: Parents should do whatever they can to help their children, experts say, but its crucial to find proof that any stressful intervention like restrictive diets is worth the cost and time.