In 1943 Leo Kanner wrote about a small group of children he had seen in his clinical practice who exhibited severe language abnormalities, social isolation, and unusual responses to their physical environment. He described these individuals as being unable to relate to people and situations in an ordinary way from the beginning of life. He reported that from the start, it appeared that these individuals exhibited an “extreme autistic aloneness” and often appeared to “shut out” their external environment (Kanner, 1943). He suggested "autism" from the Greek autos, meaning "self", to describe the fact that the children seemed to lack interest in other people.
Currently Autistic Disorder is classified under the category of Pervasive Developmental Disorders in the DSM-IV-TR. Other conditions falling under the category of Pervasive Developmental Disorders include Asperger Syndrome, and Pervasive Developmental Disorder – Not Otherwise Specified (PDD-NOS). Collectively, these disorders are often referred to as the Autism Spectrum Disorders (ASD). These three conditions have similar characteristics but differ in the age of onset and severity of symptoms.
Two other very rare conditions are also included in the category of Pervasive Developmental Disorders; Rett Syndrome and Childhood Disintegrative Disorder.
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