Autism spectrum disorders (ASDs) fall under the larger term “pervasive developmental disorder” (PDD). A PDD is a behavioral disorder that encompasses communication, speech, social interaction, and repetitive, compulsive behaviors.
Autistic Disorder
What most people think of when they think of autism is termed autistic disorder. This disorder is characterized by social and communication challenges, unusual behaviors and interests, and significant delays in language acquisition and usage. Many people who have autistic disorder also have an intellectual disability.
Asperger Syndrome
Asperger syndrome is usually thought of as mild autism. People with Asperger syndrome usually do not have language problems or an intellectual disability. They may, however, have social challenges, unusual interests, or unusual behaviors.
Rett Syndrome
Rett Syndrome is a neurodevelopmental disorder caused by mutations in a gene, causing genes not to produce proteins. Children with Rett Syndrome have problems with speech, hand use, and normal movement. Symptoms of autism such social and language impairments, as well as regression of behavioral milestones, are often seen in girls with Rett Syndrome.
Childhood disintegrative disorder
Childhood disintegrative disorder is often confused with late-onset autism because children with this condition develop normally until age 3 or 4, then exhibit a dramatic loss of communication, social, play, and motor skills.
Autism, however, typically occurs earlier than childhood disintegrative disorder. The loss of skills in those affected by childhood disintegrative disorder is also more dramatic. This condition is far less common than “classic” autism.
The severity of symptoms for any one individual with an ASD can range from mild to severe, but all disorders share the common symptom of social and communication difficulties.