Asperger syndrome (AS), also known as Asperger's, is a developmental disorder characterised by significant difficulties in social interaction and nonverbal communication, along with restricted and repetitive patterns of behavior and interests. As a milder autism spectrum disorder (ASD), it differs from other ASDs by relatively normal language and intelligence. Although not required for diagnosis, physical clumsiness and unusual use of language are common. Signs usually begin before two years of age and typically last for a person's entire life.
The exact cause of Asperger's is unknown. While it is largely inherited, the underlying genetics have not been determined conclusively. Environmental factors are also believed to play a role. Brain imaging has not identified a common underlying condition. In 2013, the diagnosis of Asperger's was removed from the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), and people with these symptoms are now included within the autism spectrum disorder along with autism and pervasive developmental disorder not otherwise specified (PDD-NOS). It remains within the International Classification of Diseases (ICD-11) as of 2019 as a subtype of autism spectrum disorder.