The condition manifests before age three and can be particularly baffling and frustrating because some affected children appear to develop normally until the onset of the disorder.
While the severity of symptoms varies greatly, there are invariably impairments of social interaction, impairments in communication ability (many autistic children are do not talk at all and remain mute throughout life), and restriction of interests and presence of repetitive behaviors.
Parents may notice an avoidance of eye contact and lack of responsiveness in young infants, who have difficulty forming emotional bonds and displaying attachment.
Autistic children also exhibit many kinds of repetitive behaviors early in life, such as hand flapping, body rocking, and making sounds. They may arrange or stack objects over and over again. They show an early preference for unvarying routines of everyday life.
Many children inflict injury to themselves by repeated actions such as hand biting and head banging. A majority of autistic children have deficits in motor coordination and have poor muscle tone. They also have unusual responses to sensory experiences and may be highly sensitive to certain sounds, textures, tastes, or smells.