Autism is a developmental disability that can be present from birth or very early in development. It can significantly affect essential human behaviors such as social interaction, the ability to communicate ideas and feelings, imagination, and the establishment of relationships with others. It can has life-long effects on how children and adults learn, socialize, and participate in the community. Autism is a developmental disorder of neurobiological origin that is defined on the basis of behavioral and developmental features. Although precise neurobiological mechanisms have not yet been established, it is clear that autism reflects the operation of factors in the developing brain.
As yet, known direct links between pathophysiology and behavior in autism are still rare and have not yet had great influence on treatments or diagnosis. Nevertheless, current biological research, such as genetics, may already have important implications for families and children with autism spectrum disorders. Autism is best characterized as a spectrum of disorders that vary in severity of symptoms, age of onset, and associations with other disorders (e.g. specific language delay, epilepsy). The manifestations of autism vary considerably across children and within an individual child over time. There are strong and consistent commonalities, especially in social deficits. However, there is no single behavior that is always typical of autism and no behavior that would automatically exclude an individual child from diagnosis of autism.
Autism statistics from the U.S. Centers for Disease Control and Prevention (CDC) identify around 1 in 59 American children as on the autism spectrum. This is a 600 percent increase in prevalence over the past two decades. Careful research shows that this increase is only partly explained by improved diagnosis and awareness. Studies also show that autism is three to four times more common among boys than girls. An estimated 1 out of 42 boys is diagnosed with autism in the United States.
From Educating Children with Autism, by the National Research Council