Some children seem to live in a world all their own. They appear distant and closed-in, avoiding eye contact and shying away from their parents' hugs. They may exhibit strange behaviors, like flapping their arms or obsessively lining up their toys. They are among the approximately 1.5 million children in America who have autism -- a condition that interferes with a child's ability to communicate and interact socially.

Autism has up to now been very difficult to decipher. Scientists still don't fully understand the mystery that lies deep in the brains of children with autism. Although researchers have uncovered clues to what causes the condition, they have not yet discovered a way to prevent or cure autism.

Statistics from Idea Data and CDC
The number of autism cases in the United States continues to rise

What is concerning to many scientists is that autism appears to be on the rise. Today, one out of every 150 American children has the condition, according to the Centers for Disease Control and Prevention (CDC). Since the 1980s and early 1990s, the rate of autism has increased by approximately 10 to 17 percent annually. Doctors don't know whether this apparent increase is the result of some environmental factor -- such as greater exposure to toxic chemicals -- or simply that children are being diagnosed more effectively than they were two decades ago.

Autism is part of a cluster of conditions called autism spectrum disorders (ASDs), or known by the broader term, pervasive developmental disorders (PDDs). All of these conditions share similar symptoms. Although autism can affect children of any race and ethnicity, it is four times more common in boys than in girls.

Autism can range from mild to severe, but most children with the condition have difficulty in these three areas:

Learn More About Autism Now

For more information on autism and how you can get involved, visit AutismSpeaks.org.

Communication - Children with autism have trouble with both verbal and nonverbal communication. They may avoid making eye contact or smiling, and may not understand the meaning of a smile, wink or wave. About 40 percent of children with autism don't speak at all. Another 25 percent start talking at between 12 and 18 months, but then rapidly lose their language ability. Some children with autism have difficulty forming words into sentences, or repeat exactly what they hear -- a condition called echolalia. Because they can't communicate what they want, sometimes autistic children scream or cry out of frustration.

Social interaction - Children with autism have difficulty relating to other people, in part because they can't understand other people's feelings and social cues. As a result, they can appear distant or aloof. They may shy away from physical or emotional contact, avoiding hugs and eye contact. Because autism affects the senses, some everyday sounds or smells may be unbearable to autistic children. They may cover their ears and scream when the phone rings, or gag from the smell of a peach. Or they may be less sensitive to pain than other children, and not feel a thing when they get a cut or bruise.

Image © 2003 Nancy J. Price
Quinn, an 18-month-old boy with autism, obsessively
stacking cans

Repetitive behaviors - Autistic children often repeat the same behaviors (called stereotyped behaviors, or stereotypy) over and over, including waving their arms, banging their head against a wall, repeating the same words, or obsessively lining up toys, books or other objects. Repetition is a theme throughout an autistic child's life. Any change to their daily routine -- even something as simple as cutting a sandwich straight across rather than on a diagonal -- can lead to a meltdown.

The symptoms of autism can vary dramatically from child to child. While one child may be entirely unable to communicate, another may be able to recite entire Shakespearian plays. One child may be unable to add 3 + 4, another may be able to perform advanced calculus functions.

In addition to autism, four other conditions fall under the header of ASDs:

Thank YouThanks to Scott Bernstein, M.D., for his assistance with this article.

Asperger syndrome - Children with this condition have some symptoms of autism, including poor social skills and a lack of empathy, but they have age-appropriate language skills and a normal or high IQ.
Rett syndrome - This condition affects only 1 out of every 10,000 to 15,000 children, the vast majority of them girls. Those with Rett syndrome shy away from social contact. They may wring their hands and be unable to control the movement of their feet.
Childhood Disintegrative Disorder (CDD) - This rare disorder affects only about two out of every 100,000 children with ASDs, most of them male. Children with CDD will develop normally until about age 3 or 4, then will suddenly and dramatically lose their motor, language and social skills.
Pervasive Developmental Disorder - Not Otherwise Specified (PDD-NOS) - This condition shares some of the same symptoms with autism (communication and social delays), but does not meet the full criteria for diagnosis.

Autism is much more common in people with certain genetic, chromosomal, and metabolic disorders, such as fragile X syndrome (an inherited form of mental retardation whose name refers to a damaged and fragile-looking X chromosome), phenylketonuria (an inherited condition in which the body lacks the enzyme needed to process the amino acid phenylalanine, leading to mental retardation) and tuberous sclerosis (a rare genetic disorder that causes benign tumors to grow throughout the body and brain). Epileptic seizures, mental retardation and vision and/or hearing loss are also common in children who have autism.

Next, we'll look at some of the potential causes of autism.