Autism Spectrum Disorder (ASD) is characterized by severe and sustained impairment in social interaction and restricted, repetitive patterns of behavior, interests, and activities—both of which interfere with social, educational, and occupational functioning. ASD varies in severity depending on the symptoms. Development of the person with mild ASD (previously called Asperger's Disorder or High Functioning Autism), is typically normal in many respects, including language, general intelligence, age-appropriate self-help skills, curiosity about the environment, and adaptive behavior exclusive of socialization.
Moderate to severe ASD is distinguished from mild ASD by delayed language development and more severe communication problems (e.g., odd speech mannerisms, odd use of words or expressions, poor reading comprehension, or difficulty exchanging oral communication with others). People on the spectrum have in common impaired social interaction and repetitive/stereotyped patterns of behavior/interests.