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New Intensity to Debate Over Autism Cause

Parents and Researchers Grapple With Claims That Autism Is Linked to Thimerosal in Vaccines

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In 1994, the diagnosis changed again. Kids diagnosed with autism from 1980 through 1993 had to meet six mandatory criteria. The new 1994 definition offered 16 optional criteria, only eight of which had to be met. Gernsbacher says the 1994 diagnosis made it much easier for a child to be labeled autistic.

The federal Individuals with Disabilities Education Act, passed in 1991, assures appropriate public education for children with autism. Soon after, schools began reporting high numbers of students with autism. Those numbers keep going up. But that doesn't mean there's an autism epidemic, Gernsbacher says, any more than increased sales of petite clothing means women are getting smaller.

"My hunch is that if we looked at the production and purchase of petite-sized clothing we'd see a greatly increasing trend in the number of petite-sized garments produced and purchased over the past two decades," she says. "Should we therefore conclude that U.S. women are getting increasingly more petite? Probably not. There was probably always a contingent of petite-sized women, and their needs are being increasingly better met."

Gernsbacher points to data from Fombonne and others suggesting that there are 5.8 to 6.7 autism cases among every 1,000 U.S. children. If that's so, we haven't found them all yet. Even Oregon, which led the nation with 4.3 autism cases per 1,000 children in 2002-2003, still has a way to go. Other states lag much farther behind.

Oft-Cited Study Questioned

A 2002 pilot study by the MIND Institute of the University of California, Davis, looked at the issue of whether autism rates are really getting higher -- or whether we're just getting better at finding kids with autism.

Study leader Robert Byrd, MD, MPH, associate professor of clinical pediatrics at the University of California, Davis, says the study data suggest that any "loosening" of diagnostic criteria had no effect on autism rates in California. This study, despite shortcomings Byrd readily admits, is widely cited as proof that the autism epidemic is real.

The MIND study compared autistic kids born in 1982-1985 to kids born in 1993-1995. Using the current criteria for diagnosis, Byrd's team found that the more recently diagnosed kids were nearly as severely autistic as those in the earlier group.

"In both groups, they on average aren't just barely meeting the threshold to be called autism -- they are almost double the threshold," Byrd tells WebMD.

MIND Institute executive director Robert Hendren, DO, also defends the study findings.

"This study is just one data point that exists, not the final word on the subject," Hendren says. "But based on this study, we say the increase in autism incidence is not a matter of changing diagnostic practices."

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