Characteristics
Autism is characterized by delays or abnormal functioning before the age of three years in one or more of the following domains: (1) social interaction; (2) communication; and (3) restricted, repetitive, and stereotyped patterns of behavior, interests, and activities.
Asperger syndrome can be distinguished from autism by the lack of delay or deviance in early language development. Additionally, individuals with Asperger syndrome do not have significant cognitive delays. Other symptoms include repetitive routines or rituals, peculiarities in speech and language, inappropriate affect or social behavior, problems with non-verbal communication, and clumsy or uncoordinated motor movements.
PDD-NOS is considered "subthreshold autism" and "atypical autism" because it is often characterized by milder symptoms of autism or symptoms in only one domain (such as social difficulties). People with PDD-NOS may demonstrate pervasive deficits in the development of reciprocal social interaction or stereotyped behaviors, but do not meet the criteria for a specific pervasive developmental disorder or other psychological disorders (such as schizophrenia or avoidant personality disorder).
Read more about this topic: Autism Spectrum