Autism is not a disease, but a developmental disorder of brain function. People with classical autism show three types of symptoms: impaired social interaction, problems with verbal and nonverbal communication and imagination, and unusual or severely limited activities and interests. Symptoms of autism usually appear during the first three years of childhood and continue throughout life. Although there is no cure, appropriate management may foster relatively normal development and reduce undesirable behaviors. People with autism have a normal life expectancy. Autism affects an estimated two to 10 of every 10,000 people, depending on the diagnostic criteria used. Most estimates that include people with similar disorders are two to three times greater. Autism strikes males about four times as often as females, and has been found throughout the world in people of all racial and social backgrounds. Autism varies a great deal in severity. The most severe cases are marked by extremely repetitive, unusual, self-injurious, and aggressive behavior. This behavior may persist over time and prove very difficult to change, posing a tremendous challenge to those who must live with, treat, and teach these individuals. The mildest forms of autism resemble a personality disorder associated with a perceived learning disability. The most distinct feature of autism is impaired social interaction. Children with autism may fail to respond to their names and often avoid looking at other people. Such children often have difficulty interpreting tone of voice or facial expressions and do not respond to others' emotions or watch other peoples faces for cues about appropriate behavior. They appear unaware of others' feelings toward them and of the negative impact of their behavior on other people. Many children with autism engage in repetitive movements such as rocking and hair twirling, or in self-injurious behavior such as biting or head-banging...
