Autism - Definition & Incidence

In the diagnostic manual used to classify disabilities, the DSM-IV (American Psychiatric Association, 1994), “autistic disorder” is listed as a category under the heading of “Pervasive Developmental Disorders.” A diagnosis of autistic disorder is made when an individual displays 6 or more of 12 symptoms listed across three major areas: social interaction, communication, and behavior. When children display similar behaviors but do not meet the criteria for autistic disorder, they may receive a diagnosis of Pervasive Developmental Disorder-NOS (PDD not otherwise specified). Although the diagnosis is referred to as PDD-NOS, throughout the remainder of this fact sheet, we will refer to the diagnosis as PDD, as it is more commonly known.

Autistic disorder is one of the disabilities specifically defined in the Individuals with Disabilities Education Act (IDEA), the federal legislation under which children and youth with disabilities receive special education and related services. IDEA, which uses the term “autism,” defines the disorder as “a developmental disability significantly affecting verbal and nonverbal communication and social interaction, usually evident before age 3, that adversely affects a child’s educational performance. Other characteristics often associated with autism are engagement in repetitive activities and stereotyped movements, resistance to environmental change or change in daily routines, and unusual responses to sensory experiences.” (In keeping with the IDEA and the way in which this disorder is generally referred to in the field, we will use the term autism throughout the remainder of this fact sheet.)

Due to the similarity of behaviors associated with autism and PDD, use of the term pervasive developmental disorder has caused some confusion among parents and professionals. However, the treatment and educational needs are similar for both diagnoses.

Incidence

Autism and PDD occur in approximately 5 to 15 per 10,000 births. These disorders are four times more common in boys than girls.

The causes of autism and PDD are unknown. Currently, researchers are investigating areas such as neurological damage and biochemical imbalance in the brain. These disorders are not caused by psychological factors.

Adapted from information published by the National Information Center for Children and Youth with Disabilities