Startling rise in autism stirs questions about the cause

Once considered rare, autism — a collection of neurologically based developmental disorders characterized by social withdrawal and repetitive behaviors — now afflicts 1 in 166 American children.

What’s more, the Autism Society of America estimates that the number of autistic children is growing by 10 percent to 17 percent every year.

U.S. Department of Education statistics show that in the past decade the number of children ages 6-21 who were diagnosed with autism and served under the federal Individuals with Disabilities Education Act increased more than 500 percent.

In Kansas, the number of children served in 1993 was 147. In 2003, the number was 993, a 575 percent increase. In Missouri, 399 children were served in 1993, compared with 2,664 in 2003, a 568 percent increase.

“It is obvious from all accounts that there is a crisis in the United States regarding the dramatic rise in autism rates and the resulting strain placed on families, the education system, and state Medicaid and disability programs,” a congressional report concluded in 2003. “A further crisis will ensue in the next two decades when we see an explosion in the need for adult services and long-term housing.”

The cause of autism has been hotly debated for years. Many experts think it involves a combination of genetic and environmental factors.

One theory is that the increase of mercury in childhood vaccines may have triggered a response in children who were genetically predisposed to being more vulnerable to neurological damage from mercury. But government health officials say that research indicates no connection between mercury in vaccines and neurodevelopmental disorders.

The issue intensified in 1999, when health officials announced that thimerosal — a compound that is 49.6 percent mercury by weight — no longer would be used as a preservative in children’s vaccines. They stressed, however, that the action was merely precautionary.

But those who think there is a correlation between mercury and autism note that the alarming growth in autism cases coincided with an increase in the number of recommended childhood vaccines that contained thimerosal.

Throughout most of the 20th century, children were not required to receive many vaccines. The only vaccine routinely given to infants that contained thimerosal was the DTP vaccine. It contained 25 micrograms of ethylmercury and was administered three times in the first six months of life, with a total of four times in two years.

But in 1991, when the federal Centers for Disease Control and Prevention began recommending the hepatitis B vaccine and increased the doses of Haemophilus influenzae type b (Hib) vaccine, the amount of mercury exposure to infants increased significantly.

Many Hib vaccines contained 25 micrograms of mercury and, like the DTP vaccines, were given three times in the first six months and a total of four times in the first two years. The hepatitis B vaccine contained 12.5 micrograms of mercury and was given shortly after birth, then two more times in the first six months of life.

That means babies receiving the recommended vaccines at their checkups went from getting 25 micrograms of mercury in one day to up to 62.5 micrograms in one day.

The daily limit set by the U.S. Environmental Protection Agency is 0.1 microgram of methylmercury for every kilogram of body weight. For an 11-pound baby — about the weight of a 2-month old — the daily limit would have been about 0.5 micrograms. So that baby would have received 125 times the EPA’s daily threshold.

How did this happen?

In 1997, Congress ordered the U.S. Food and Drug Administration to determine the effects of mercury on the human body through foods and drugs.

But when the agency examined the amounts of ethylmercury being injected into children, it faced a problem: The effects of ethylmercury had not been studied as extensively as methylmercury — the kind found in seafood — and the government had not established safety limits for ethylmercury exposure.

As a result, the agency ended up comparing the exposure from the vaccines with the federal limits for methylmercury exposure. And what they found was that the cumulative amount of mercury in the vaccines exceeded the EPA’s threshold.

“For years, nobody sat down to do the math to figure it out,” said U.S. Rep. Dave Weldon, a Florida Republican who has introduced legislation in Congress to ban the use of mercury in childhood vaccines.

That delayed discovery led the FDA and other agencies in 1999 to recommend, but not order, the removal of thimerosal from most childhood vaccines.

A June 29, 1999, e-mail sent to colleagues by a former senior FDA official said the news would “raise questions about FDA being ‘asleep at the switch’ for decades by allowing a potentially hazardous compound to remain in many childhood vaccines, and not forcing manufacturers to exclude it from new products.”

“We must keep in mind that the dose of ethylmercury was not generated by ‘rocket science’: conversion of the percentage of thimerosal to actual ug (micrograms) of mercury involves 9th grade algebra,” the FDA official wrote. “What took the FDA so long to do the calculations? Why didn’t CDC and the advisory bodies do these calculations while rapidly expanding the childhood immunization schedule?”

Those who have studied the issue say it could take a few more years before it is known whether thimerosal causes autism.

“Time will tell,” said David Kirby, author of Evidence of Harm, a new book about the controversy over mercury in vaccines. “One way or another, this is all going to come out.”

Posted by Becca

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