Autistic disorder, or classic autism, is the most severe form of autism spectrum disorders or ASD. Impaired social interaction is the distinguishing feature of ASD. Autism is more prevalent in boys than girls. The signs of autism appear during the first 3 years of a child’s life. An autistic child displays odd repetitive motions, uses repetitive or unusual language, is unable to make friends with peers, is unable to initiate or sustain a conversation with others, has difficulty regulating emotions, and has an inflexible adherence to routine. The exact cause of autistic disorder is unknown. However, ongoing research has linked autism to variations in the gene, CNTNAP2. Prenatal exposure to the chemicals thalidomide and valpoic acid has been linked to a greater risk of a child being born with autism. For many children, the symptoms improve with treatment and age. Educational behavioral intervention can help autistic children develop social and language skills. Medications are prescribed to treat specific autism-related symptoms such as depression, seizures, anxiety and obsessive-compulsive behavior.