Asperger syndrome (AS), also known as Asperger's, is a neurodevelopmental disorder characterized by significant difficulties in social interaction and nonverbal communication, along with restricted and repetitive patterns of behavior and interests. It is an autism spectrum disorder (ASD), but differs from other ASDs by relatively unimpaired 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 in many cases never resolve.