According to a preliminary analysis, proposed changes to the definition of autism would likely exclude higher functioning individuals, making it more difficult to obtain health, educational, and social services.

The American Psychiatric Association has appointed an expert panel to reassess the definition of autism, part of work being done to complete the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders. It’s the first time the standard reference has been updated in 17 years.

The preliminary analysis was presented on Thursday at a meeting of the Icelandic Medical Association by Dr. Fred R. Volkmar, who recently resigned from his position on the APA expert panel.

Volkmar used data from a 1993 study, focusing on 372 autistic patients among the highest functioning, and found that only 45 percent of them would qualify under the new definition.

The experts remaining on the APA panel disagree with Volkmar’s assertion that the new definition would have such drastic impact.

The new definition would place related disorders like Asperger syndrome and P.D.D.-N.O.S. under the same roof as autism, calling the new category autism spectrum disorder. A patient would have to exhibit three deficits in social interaction and communication and two repetitive behaviors - a much tighter control than current guidelines.

According to Volkmar, about a quarter of patients diagnosed with autism in 1993 would not be under the new definition, three-quarters of Asperger syndrome patients would no longer qualify, and up to 85 percent of those diagnosed with P.D.D.-N.O.S. would not.

The revisions to the APA manual will be final by December.