Scientists are not certain what causes autism, but it is likely that both genetics and environment play a role. Researchers have identified a number of genes associated with the disorder. Studies of people with autism have found irregularities in several regions of the brain. Other studies suggest that people with autism have abnormal levels of serotonin or other neurotransmitters in the brain.

Autism is a brain condition, present from birth, which affects the way the brain processes information. In 1995, the National Institutes of Health (NIH) concluded that autism probably results from a genetic susceptibility that involves multiple genes. A variety of factors could be associated with some forms of autism, including infectious, metabolic, genetic, neurological, and environmental factors. See similar questions...

Autism spectrum diagnoses are now known to be largely genetic in origin, and runs in families. Twin studies have uncovered many examples of identical (monozygotic) twins having autism spectrum diagnoses. One may have autism and the other AS, but when one identical twin is autistic, the other one is as well. If autistic conditions were not genetic, this would probably not happen. See similar questions...

Autism, part of a group of disorders known as Autism Spectrum Disorders (ASD), is a complex neurobiological disorder that typically lasts throughout a person's lifetime. The disorder is characterized by varying degrees of impairment in communication skills and social abilities, and also by repetitive behaviors. Symptoms range from mild to severe. One milder form of the disorder is known as Asperger Syndrome. See similar questions...