Autism spectrum

Overview
The autism spectrum, also called autism spectrum disorders (ASD) or autism spectrum conditions (ASC), with the word autistic sometimes replacing autism, is a spectrum of psychological conditions characterized by widespread abnormalities of social interactions and communication, as well as severely restricted interests and highly repetitive behavior.

The three main forms of ASD are autism, Asperger syndrome, and PDD-NOS. Autism forms the core of the autism spectrum disorders. Asperger syndrome is closest to autism in signs and likely causes. Pervasive developmental disorder not otherwise specified (PDD-NOS) is diagnosed when the criteria are not met for a more specific disorder. Some sources also include Rett syndrome and childhood disintegrative disorder, which share several signs with autism but may have unrelated causes. Unlike autism, Asperger's has no significant delay in language development.

The terminology of autism can be bewildering, with autism, Asperger's and PDD-NOS sometimes called the autistic disorders instead of ASD, whereas autism itself is often called autistic disorder, childhood autism, or infantile autism. ASD, in turn, is a subset of the broader autism phenotype (BAP), which describes individuals who may not have ASD but do have autistic-like traits, such as avoiding eye contact.

One review estimated a prevalence of at least 1.3 per 1,000 for autism and 6.0–6.5 per 1,000 for ASD; PDD-NOS was the vast majority of ASD, Asperger's was about 0.3 per 1,000 and the atypical forms childhood disintegrative disorder and Rett syndrome were much rarer.

Autistic traits
Behaviorally, certain characteristics identify the autism spectrum. The type, severity and/or 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 and computer programming. Some autistic individuals might show a marked proficiency in rote memorization which may help learn the foundation of these subjects; however, the exceptionally good aptitude (in these subjects) of high functioning autistic spectrum persons may be due to their ability to readily identify patterns and apply them consistently to new situations outside of established knowledge or teaching. These savant skills, although popularly considered to be a major part of autistic disorders, are evident only in a small fraction of autistic individuals, with estimates of the fraction ranging from 0.5% to 10%.

Diagnostic criteria and techniques
When the rising prevalence of autism spectrum disorders sparked research in the late 1990s, medical opinion initially attributed the increase to improved diagnostic screening or changes in the definition of autism. In 1994, the fourth major revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) was published with updated criteria for the diagnosis of autism and autism spectrum disorders. Professional medical associations, including the American Academy of Pediatrics, say that this revision was an important factor in increasing the apparent prevalence of autism and a 2005 study by Mayo Clinic researchers found increases in autistic spectrum disorder diagnoses followed the revisions in DSM criteria and changes in funding for special education programs.

An increased awareness of autistic spectrum disorders by parents and pediatricians may have also led to increased reporting of Autism due to 'case substitution', which occurs when children with other disorders are identified as autistic. This misdiagnosis may occur for several reasons including an increase in government funding for care of children diagnosed as autistic, but not for children with a similar degree of disability and need. If this is occurring, it means that children who in the past would probably have been diagnosed as having a learning disability or a psychiatric disorder, or not diagnosed at all, are recorded as cases of autistic spectrum disorder.

Children who are not primarily autistic, e.g. those with Fragile-X Syndrome (with characteristics that fit the criteria for autism) and even Down's Syndrome may have the diagnostic group with the best funding assigned. Dr. Fred Volkmar, a Yale University autism researcher, has said that "diagnostic substitution" was prompted by better services for autism.

ADHD and autism
Some research suggests a possible genetic and behavioral connection between ADHD and autism.