Autism affects people of every age, and it occurs in every ethnic and socioeconomic group, says the National Institute of Neurological Disorders and Stroke. It occurs in males four times more often than females.
As of 2015, the exact causes of autism, or autism spectrum disorder, are unknown, but both environment and genetics appear to be involved, explains the National Institute of Neurological Disorders and Stroke. Several specific genes involved with the disorder have been identified, and in cases where one twin has the condition, there is a 90 percent chance that other twin will also be affected. In families with one child who has the disorder, the likelihood of a second child having it is greater than in the general population--roughly five percent. Some studies have implicated abnormal levels of neurotransmitters, such as serotonin, in the brain. The notion that parenting plays a role has been discredited.
Impaired social interaction is the primary characteristic of autism spectrum disorder, according to the National Institute of Neurological Disorders and Stroke. Behaviors such as avoiding eye contact, a lack of response to people, and focusing on one item when surrounded by several others, are all manifestations of autism. Physical signs include repetitive movements such as rocking back and forth or biting and head-banging. Children with autism spectrum disorder tend to lack empathy and don't understand social cues.