Autism spectrum disorder is a serious developmental disorder that severely affects an individual's ability to understand, communicate, and interact with other people. It is usually diagnosed in early childhood. The causes of autism are not known. Defining criteria for diagnosing autism spectrum disorder include communication problems, repetitive and restrictive behaviors, and social deficits, which are normally seen by age three but have been detected as early as 18 months of age. There is no cure for autism spectrum disorder but there are medical, non-medical, behavioral treatments, and family therapies that may reduce symptoms and support development and learning.