Most researchers agree, the key symptom is the deficit in social interaction. Parents often report that as infants, their autistic children didn't smile or respond to voices, made almost no eye contact with them and stiffened when they were held. As the child grows, he may not respond to anyone around him and may not attempt to form friendships with peers. If he does involve someone else in his play, it's only as a tool. He may perform stereotypical motor movements, such as flapping the hands, rocking, pacing, repetitive finger movements or twirling on his feet.
Some repetitive actions are more complex, like flipping light switches or flushing toilets.
Another hallmark of the disorder is the lack of communication. About 40 to 50 percent of those with the disorder are mute. The rest run the gamut from echolalia, or mimicking the words of others without comprehension, to speaking coherently. Au- stic individuals won't initiate or sustain conversation, won't substitute nonverbal communication, such as pointing, and may continually repeat jingles or commercials. The pitch, intonation, rate, rhythm or stress of the speech may be abnormal, and the person doesn't understand questions, directions or jokes.