DALLAS, May 4 (UPI) -- Autism spectrum disorders cover a wide span of conditions and symptoms, making a quick definitive diagnosis difficult, a U.S. expert says.

Dr. Catherine Karni of the University of Texas Southwestern Medical Center, who is also medical director of outpatient services at the Center for Pediatric Psychiatry at Children's Medical Center Dallas, says it wasn't until 1980 that autism became an official clinical diagnosis, separate from childhood schizophrenia or retardation. Patients often display a distinctive pattern of symptoms rather than just one.

The main characteristics include impairments in social interaction, impairments in communication, restricted interests and repetitive behavior, Karni says. Parents are usually the first to notice the unusual behaviors, while pediatricians initially hear their concerns.

"Autism cannot be diagnosed with a simple diagnostic test," Karni says in a statement. "Having a team of specialists conduct specific assessments means there is a better chance for children to be diagnosed correctly and for the right treatments to be enacted."

Many parents take their child to a pediatrician because the child is not talking, Karni says.

"But there are many possibilities for this behavior," she says. "Autism is only one."

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