Autism is one of five disorders that fall under the umbrella term of autism spectrum disorders (ASD)—also called pervasive developmental disorders (PDD). The other four disorders are Asperger syndrome (also called Asperger’s, Asperger’s syndrome, or Asperger’s disorder), Rett syndrome (also called Rett’s disorder), childhood disintegrative disorder, and pervasive development disorder-not otherwise specified (PDD-NOS;Diagnostic and Statistical Manual, 2000, p. 74).

Comparing signs and symptoms of disorders to distinguish between them is known as differential diagnosis. The following chart pinpoints the differences between autism and other autism spectrum disorders.

Autism	Asperger Syndrome
Significant language delay—difficulty understanding and using language	No significant language delay
May or may not have cognitive delays—problems with thinking or mental retardation	No significant delay in cognition—no mental retardation

Autism	Rett Syndrome
More frequent in males	More frequent in females
Delays in development from birth	Normal development through pregnancy and the first five months—then a loss of skills including: social interaction hand and body coordination language
Normal head growth	Head growth reduces between the ages of five months and 48 months

Autism	Childhood Disintegrative Disorder
Delays in development from birth	Normal development through at least two years of life—then a loss of skills, including: language social interaction play motor bowel or bladder control before age ten

Some children show (severe) difficulties in social communication, language, and/or cognition (thinking skills), and behaviors and emotions, but do not "fit" the diagnostic criteria above for autism. The diagnosis for such children is pervasive development disorder-not otherwise specified (PDD-NOS). (DSM-IV-TR®, 2000)