Autism is a complex developmental disorder that appears in the first 3 years of life, though it is some times diagnosed much later. It affects the brain's normal development of social and communication skills.

Autism is a spectrum that encompasses a wide continuum of behavior. Core features include impaired social interactions, impaired verbal and nonverbal communication and restricted and repetitive patterns of behavior.

Symptoms may vary from quite mild to quite severe. Mild autism is known as Asberger's syndrome.

Autism is a physical condition linked to abnormal biology and neurochemistry in the brain. The exact causes of these abnormalities remain unknown, but this is a very active area of research.

In the past, autism was thought to be a mental illness caused by bad parenting. No scientific evidence supports this idea, which has since been rejected.

Genetic factors seem to be important. Language and cognitive abnormalities are more common in relatives of autistic children. Chromosomal abnormalities and other neurological problems are also more common in families with autism.

In the general population, autism affects up to 0.2% of children, but the risk of a couple having a second autistic child increases more than 50 times -- to 10-20%. An identical twin is far more likely to also have autism than a fraternal twin or another sibling would be -- all of these facts suggest a strong genetic influence on the condition.

Autism affects boys 3 to 4 times more often than girls. Family income, education, and lifestyle do not seem to affect the risk of autism.

Some parents be concerned that the MMR vaccine that children receive at 1 year of age may cause autism. This theory was based on the fact that the incidence of autism has increased steadily since around the same time MMR vaccination began and on the fact that children with the regressive form of autism tend to regress at around the time the MMR vaccine is given.

Several major studies have found no connection between the vaccine and autism, however, and the American Academy of Pediatrics has officially stated there does not appear to be a causal link.

Some doctors attribute the increased incidence in autism to our newer definitions of autism. The term "autism" now includes a wider spectrum of children. For example a child who is diagnosed with high-functioning autism today may have been thought to simply be odd or strange 30 years ago.