Autism rise tied to better diagnosis

CHICAGO -- The rise in autism cases is not evidence of an epidemic but reflects better diagnosis of autism by schools, according to a study released last week.

The number of children classified by US special education programs as mentally retarded or learning disabled has declined in tandem with the rise in autism cases between 1994 and 2003, the study's author said, suggesting a switch of diagnoses.

Government health authorities have been trying to allay widely publicized concerns that vaccines containing the mercury-containing preservative therimerosal, which is no longer used, were behind an autism epidemic.

There may be as yet unknown environmental triggers behind autism, study author Paul Shattuck of the University of Wisconsin at Madison said, but his research suggests that the past decade's rise in autism cases was more of a labeling issue.

Autism was fully recognized in 1994 by all US states as a behavioral classification for schoolchildren, who receive individualized attention whatever their diagnosis, he wrote in the journal Pediatrics.

Subsequent increases in the number of autism cases have varied widely by state, but the average prevalence among 6- to 11-year-olds enrolled in special education programs increased from 0.6 per 1,000 pupils in 1994 to 3.1 per 1,000 in 2003.

During the same period, diagnoses of mental retardation fell by 2.8 per 1,000 students, and diagnoses of learning disabilities dropped by 8.3 per 1,000 students.

Autism is a spectrum of disorders caused by abnormal brain development that can lead to diminished social skills as well as unusual ways of learning and reactions to sensations. As many as 6 in 1,000 children are ultimately diagnosed with it to some degree, according to the Autism Society of America.

Shattuck's analysis was challenged in an accompanying commentary by autism researcher Craig Newschaffer of Johns Hopkins Bloomberg School of Public Health in Baltimore.

''We do not know whether individual children have switched classifications, and, of course, we can never know whether a given child in a particular birth cohort would have been classified differently had they been born either earlier or later. At best, analyses of this type are merely trying to determine if trends in one classification have the potential to offset those in another," he wrote.

There is a clear need for definitive studies into the roles played by genetic susceptibility and environmental triggers in autism, Newschaffer wrote.

REUTERS