Even though everyone develops at slightly different paces, almost everyone hits the same general developmental milestones and learns the same sets of skills on about the same timeline.
These skills progress as the brain develops, and they include: language and communication; social interaction; cognitive skills, like problem solving; and physical milestones, like walking, crawling, and fine motor skills.
If one of these skills doesn’t develop as scheduled, it may, depending on the severity of the delay, be described as a type of neurodevelopmental disorder, neuro referring to the brain.
When certain skills related to socializing and communicating don’t proceed as expected, this can result in isolation.
This is where the name autism originated: auto means “self,” and so autism refers to a condition where somebody might be removed from social interaction and communication, leaving them alone or isolated.
Before 2013, the DSM-4 (which has since been updated to the DSM-5), described autism as one of several pervasive developmental disorders, a category that also includes Asperger’s syndrome, childhood disintegrative disorder, and those pervasive developmental disorders that are not otherwise specified, or PDD-NOS for short.
Asperger’s syndrome was used to describe children who appeared to have characteristics of autism, like difficulties with social interactions or non-verbal communication, but didn’t generally have significant delays in language or cognitive development.
Therefore, Asperger’s syndrome was sometimes referred to as a “high-functioning” form of autism.
Childhood disintegrative disorder was used to describe the late onset of developmental delays.
These children developed typically at first, but then they seemed to lose their acquired social and communication skills sometime between ages two and ten.
“Pervasive developmental disorder: not otherwise” specified is essentially a catch-all category in which patients meet some, but not all, diagnostic criteria of autism, Asperger’s syndrome, or childhood disintegrative disorder.
Researchers found, however, that because these pervasive developmental disorders tend to have similar signs and symptoms, their diagnoses weren’t consistent across different clinics.
As of 2013, the DSM-5, the new and revised edition, removed these terms and replaced them with autism spectrum disorder, or ASD.
The term ASD encompasses all the previous pervasive developmental disorders, but it’s measured on a scale, or a spectrum, that differentiates between patients in two major areas: social communication and interaction deficits, and restrictive or repetitive behavior, interests, and activities.