What the DSM 5 Says
In the DSM 5 Autism Spectrum Disorder (ASD) is currently classified as a neurodevelopmental disorder. What does that mean exactly? Here’s what the text of the DSM 5 says,
“The neurodevelopmental disorders are a group of conditions with onset in the developmental period. The disorders typically manifest early in development, often before the child enters grade school, and are characterized by developmental deficits that produce impairments of personal, social, academic, or occupational functioning. The range of developmental deficits varies from very specific limitation of learning or control of executive functions to global impairments of social skills or intelligence. The neurodevelopmental disorders frequently co-occur; for example, individuals with autism spectrum disorder often have intellectual disability (intellectual developmental disorder), and many children with attention-deficit/hyperactivity disorder (ADHD) also have a specific learning disorder. For some disorders, the clinical presentation includes symptoms of excess as well as deficits and delays in achieving expected milestones. For example autism spectrum disorder is diagnosed only when the characteristic deficits of social communication are accompanied by excessively repetitive behaviors, restricted interests, and insistence on sameness.”
(American Psychiatric Association, 2013)
The brain works differently, to varying degrees, and everything that the brain manages will also work differently, to varying degrees. These differences show up fairly early in life.