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Examining Autism Prevalence

NAAR-funded Researcher Leads New Study
April 23, 2007

A NAAR-funded researcher is the lead author of a new study that suggests the apparent rise in the number of children in the United States with autism is not the result of “diagnosis shifting.”

Dr. Craig J. Newschaffer, director of the Center for Autism and Developmental Disabilities Epidemiology at Johns Hopkins University in Baltimore, led the study, which indicates that autism prevalence is increasing with successively younger children, particularly those born between 1987 and 1992. The results of the study have been published in the March issue of

“Using a birth-cohort analysis approach, we saw, to no one's surprise, strong indications that the prevalence of the autism special education classification has been increasing dramatically over the past decade,” said Dr. Newschaffer, who serves as a mentor to a NAAR Pre-doctoral fellow focusing in autism epidemiology.

The study also refutes the theory that the rising rate of autism can be attributed to "diagnosis shifting," which suggested that children who in past years might have been classified as having mental retardation or speech/language difficulties are now being diagnosed as having autism. However, according to Dr. Newschaffer, the available data cannot address the question of whether children who previously would not have received special education services no receive the services under an autism special education classification.

“We used the same approach to look at other special education classifications and found that many, including mental retardation and speech/language impairment, showed little to no change over time, which clearly illustrates that there is not a "rising tide lifting all boats,"” said Dr. Newschaffer.

He added that it is still hard to determine whether the rate of increase in autism special education prevalence classification is slowing.

“Because of recent changes in the way the developmental delay classification can be
used, we need to wait for more data to confirm that this is real,” said Dr. Newschaffer.

Examining the epidemiology of autism is a critical part of efforts to better understand autism. But, unlike some areas of medical research such as cancer and cardiovascular diseases, there are no federal funds earmarked to support the training of autism epidemiologists.

“It is critical that we find ways to attract bright young scholars to the field,” said Dr. Newschaffer. “The NAAR Fellowship Program has allowed my center to help usher one such scholar, Keely Cheslack-Postova. The NAAR fellowship has enabled Keely to become involved in our center's major research efforts and, more importantly, to cultivate her own research interests.”

One project Ms. Cheslack-Postova has taken the lead on is a candidate gene study looking at the potential role of B2AR polymorphisms in autism. She is scheduled to present her findings, which suggest that a high activity of the B2AR genotype is associated with increased autism risk, at the International Meeting for Autism Research (IMFAR) this May in Boston.

“I think these results are important, as they support a very intriguing hypothesis developed by investigators here at Hopkins that over-stimulation of the B2AR receptor early in development (due to genetic predisposition, environmental exposure, or both) might be part of a mechanistic pathway leading to autism,” said Dr. Newschaffer.

Ms. Cheslack-Postova has also taken the lead on a comprehensive review paper focusing on screening for autism spectrum disorders from the epidemiologic perspective.

“While there certainly is widespread consensus that we need to identify children with autism at the earliest possible ages, determining the best way to do this is a formidable challenge,” said Dr. Newschafer. “I believe that epidemiologic thinking can assist us with this challenge.”

In addition, Ms. Cheslack-Postova has played an integral role in the development of a comprehensive research proposal to study autism, autoimmunity, and the environment.

“This project will provide the basis for her doctoral thesis research which will address, epidemiologically, the question of whether certain chemical exposures might induce or promote the formation of maternal antibodies to CNS protiens, thereby increasing autism risk,” said Dr. Newschaffer. “Through these projects and other experiences in our center, Ms. Cheslack-Postova has had a chance to experience first hand, even before completing her Ph.D., virtually the full range of issues challenging epidemiologists concerned with autism.”