The connection between developmental delay and autism can be understood in that autism spectrum disorders (ASDs) are a category of neurological challenges that present as delays in development. Other categories of developmental delay disorders can include such challenges as mental retardation and other cognitive disabilities, aside from autism. A person, therefore, would be absolutely correct in describing autism and related disorders as forms of developmental delay. Classic autism and similar ASDs, such as Asperger's or Rett syndrome, are classified for research purposes as neurodevelopmental disorders. Neurodevelopment refers to the development of certain functions and systems within the brain as a child matures from infancy to adulthood.
Medical and therapeutic professionals, as well as parents and advocacy groups, refer to the various types of developmental delay and autism disorders by different terms. Autism and similar disorders were classified under the heading of Pervasive Developmental Disorders (PDDs) in the 1990s. At the beginning of the 21st century, however, parents, certain professionals, and advocacy groups began arguing for classification changes. Re-classification to a heading such as autism spectrum disorder, according to advocates of the change, more accurately reflected the range of severity involved in the different types of developmental delay and autism disorders associated with such delays. Regardless of specific nomenclature, all forms of autism can be classified as a type of developmental delay.
Typically, a child diagnosed with a disorder on the autism spectrum does not follow the same neurodevelopmental time line as other children of the same age. Specifically, children diagnosed on the spectrum present with marked delays in the development of cognitive abilities, a common connection between developmental delay and autism. For children with ASDs, developmental delays present primarily in areas of language and articulation, gross and fine motor skills, and social skills. Which ASD a child is diagnosed with depends on the specific developmental delays present, as well as the severity of those delays.
Determining the presence of a developmental delay and autism spectrum disorder requires a professional to evaluate a child based on three key processes: notable delay, the rate of dissociation, and deviance from average norms. In simple terms, the child must present with some form of marked and noticeable delay in a key developmental area commonly associated with an autism spectrum diagnosis. Delays must be present in one neurological domain, while other areas of neurodevelopment appear within normal range — a concept known as dissociation. Finally, the child's development must demonstrate deviancy, or a lack of reaching normal developmental milestones compared to other children of similar age.