Asperger syndrome, also known as Asperger disorder or simply Asperger's, is an autism spectrum disorder that is characterized by significant difficulties in social interaction and nonverbal communication, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development. Although not required for diagnosis, physical clumsiness and atypical use of language are frequently reported. The syndrome is named after the Austrian pediatrician Hans Asperger who, in 1944, studied and described children in his practice who lacked nonverbal communication skills, demonstrated limited empathy with their peers, and were physically clumsy. The modern conception of Asperger syndrome came into existence in 1981 and went through a period of popularization, becoming standardized as a diagnosis in the early 1990s. Many questions remain about aspects of the disorder. There is doubt about whether it is distinct from high-functioning autism; partly because of this, its prevalence is not firmly established. The diagnosis of Asperger's was eliminated in the 2013 fifth edition of the Diagnostic and Statistical Manual of Mental Disorders and replaced by a diagnosis of autism spectrum disorder on a severity scale.