Autism is not a disease, a mental illness, or a behavior problem. It is a complex disorder of the central nervous system that affects many different expressions of brain development, including social interactions and communications. Most people with autism have problems communicating, forming relationships, and interpreting and responding to the external world. Asperger syndrome is a condition similar to autism but without the problems in language development. Autism is classified by the American Psychiatric Association as one of a group of disorders known as pervasive development disorders, which includes, besides Asperger syndrome, the conditions childhood disintegrative disorder, Rett disorder, and general pervasive developmental disorder.
Autism occurs at all intelligence levels. Although about 75% of autistic individuals have an intelligence quotient (IQ) below average, the other 25% have average or above average intelligence. About 10% have high intelligence in a specific area such as mathematics.
Autism begins in early childhood. The signs and symptoms of autism may become apparent by the time the child reaches the age of 18 months, and they almost always become apparent by the time the child is 3 years old.
The person with autism appears to have difficulty understanding what he or she is experiencing. In people who are not autistic, the brain integrates input from the various senses (sights, sounds, smells, tastes, and touching sensations) to interpret experiences. Some experts theorize that the brain of a person with autism is unable to integrate the sensory inputs, thus making the person incapable of interpreting and responding to what is happening around him or her.
The cause of autism is unknown, but research findings indicate a strong genetic component. The tendency to autism runs in families, and people with autism appear to have an inborn predisposition to developing the disorder. Most likely, environmental, immunologic, and metabolic factors also influence the development of the disorder.
Autism is linked to certain medical conditions, including fragile X syndrome, untreated phenylketonuria (PKU), tuberous sclerosis, and congenital rubella syndrome. Fetal exposure to toxins, such as hazardous chemicals, may play a role in autism.
Over time, many different theories have been proposed about what causes autism. Some believed that emotional trauma at an early age, especially "bad parenting", was to blame. This theory has been rejected. A reaction to routine childhood vaccines has been blamed for autism. Although some research on this subject has revealed no link between vaccines and autism, the debate is ongoing. Many still believe that vaccines could be a factor.
The list of traits and behaviors associated with autism is long, and each affected person expresses his or her own combination of these behaviors. None of these behaviors is common to all people with autism, and many are occasionally exhibited by people who are not autistic. Some people with autism have more problems with communication, while others have more problems with social interactions. However, certain traits and behaviors are common to many people with autism, as follows:
Studies from Europe indicate that there may be a link between the MMR (measles/mumps/rubella) vaccine and autism. [Sara Solovitch, "Do vaccines spur autism in kids?", San Jose Mercury News, May 25th, 1999]