Autistic spectrum disorder

The autistic spectrum (sometimes referred to as the autism spectrum) is the idea that autism is a developmental and behavioral syndrome that results from certain combinations of traits. Although these traits may be normally distributed in the population, some individuals inherit or otherwise manifest more autistic traits. At the severe end of the spectrum is low-functioning autism which has profound impairments in many areas, to Asperger's syndrome and high-functioning autism, to "normal" behaviour and perhaps hypersocialization on the high end of the spectrum.

In the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and the International Statistical Classification of Diseases and Related Health Problems (ICD-10), autism spectrum disorders (ASD) are classified as pervasive developmental disorders (PDD), as opposed to specific developmental disorders like dyslexia or dyspraxia.

Autistic spectrum and pervasive development disorders
In practice, autistic spectrum disorder and pervasive developmental disorder are synonymous, but making a distinction is valuable. Pervasive developmental disorders refer to those psychological and behavioral developmental disorders encompassing many areas of functioning: language and communication, self-help skills, motor coordination executive function, and scholastic achievement. The nosological category of pervasive developmental disorders includes syndromes that may be etiologically unrelated to autism, with autistic-like behavior being only one part of the disorder: Rett's syndrome and childhood disintegrative disorder.

Autistic traits
Behaviorally, certain characteristics identify the autism spectrum:

Social impairment

 * Lack of observed desire for friendship
 * Poor ability to make friends
 * Social awkwardness
 * Indiscriminate social interaction
 * Lack of eye contact
 * Brief response to questions
 * Gullibility

Language impairment

 * Odd or monotonous prosody of speech
 * Overly formal and pedantic language
 * Pronoun reversal
 * Visuospatial thinking sometimes preferred
 * Use of rote chunks of language
 * Late or no development of language
 * Poor use and understanding of nonverbal communication (i.e., facial expressions and body language)

Imaginative impairment and repetitive adherence

 * Concrete and literal use of language
 * Poor understanding of abstract thought, metaphors, and symbolism
 * Preference for routine
 * Absorption in detail; inability to understand meaning or the whole of a concept
 * Perseverative interest or focus

Sensory integration dysfunction

 * Hyper- or hyposensitivity of the various senses
 * Peculiar clothing and food preferences
 * Self-stimulating mannerisms
 * Fine or gross motor discoordination

The number of autistic traits present determines the severity of autism in the individual. These autistic traits may be beneficial for some disciplines like science, mathematics, engineering.

ADHD and autism
Some research has indicated a possible genetic and behavioral connection between ADHD and autism. As a result, some clinicians have suggested that ADHD be included under the category of autism spectrum disorders. Others disagree. 

Diagnoses of ADHD together with autism spectrum disorder are becoming increasingly common in children. In young children, the two conditions can appear similar. However, as children age, differences emerge between the two conditions. Children with typical autism become more withdrawn, while with a suitable environment hyperactivity reduces. In either event, problems with social skills can develop.

By contrast, children with ADHD rarely become calmer with age but often develop social and communication skills to a normal level. Any issues with social skills experienced by children with ADHD may have other causes. Examples include low self-esteem or difficulty with quiet, constructive social interaction.