Autism is a developmental disorder characterized by troubles with social interaction and communication and by restricted and repetitive behavior. Parents usually notice signs in the first two or three years of their child's life. These signs often develop gradually, though some children with autism reach their developmental milestones at a normal pace and then worsen.
Autism is caused by a combination of genetic and environmental factors. Risk factors include certain infections during pregnancy, such as rubella, as well as valproic acid, alcohol or cocaine use during pregnancy. Controversies surround other proposed environmental causes, for example the vaccine hypotheses, which have been disproven. Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize; how this occurs is not well understood. In the DSM-5, autism is included within the autism spectrum (ASDs), along with Asperger syndrome, which is less severe, and pervasive developmental disorder not otherwise specified (PDD-NOS).