Table 1.

Differential diagnostic features of autism spectrum disorders

	Autism	Asperger’s syndrome	Pervasive developmental disorder- not otherwise specified (PDD-NOS)
Age of recognition (diagnosis*)	0–3 years (3–5 years)	>3 years (6–8 years)	Variable
Regression	About 25% (social or communication)	No	Variable
Sex ratio (male:female)	2:1	4:1	Male>female (variable)
Socialisation	Poor; >2 DSM-IV criteria	Poor	Variable
Communication	Delayed, deviant; might be non-verbal	No early delay; qualitative and pragmatic difficulties later	Variable
Behaviour	More impaired than in Asperger’s syndrome or PDD-NOS (includes stereotypy)	Variable (circumscribed interests)	Variable
Intellectual disability	>60%	Mild to none	Mild to severe
Cause	More likely to establish genetic or other cause than in Asperger’s syndrome or PDD-NOS	Variable	Variable
Seizures	25% over lifespan	Roughly 10%	Roughly 10%
Outcome	Poor to fair	Fair to good	Fair to good

DSM-IV=Diagnostic and Statistical Manual of Mental Disorders, 4th edition.

^*Average age at diagnosis. Data adapted from Volkmar and Pauls.¹²