Autism belongs to a group of five pervasive developmental disorders (PDD), which are characterized by extensive deviations in social interaction and communication, as well as narrow interests and clearly repetitive behavior. These symptoms do not imply soreness, fragility, or emotional disturbance.
Of the five pervasive disorders, Asperger’s syndrome is the closest to autism in terms of signs and possible causes; Rett syndrome and childhood disintegrative disorder share some features with autism, but their causes are different; if symptoms do not match the criteria for a specific disease, a diagnosis of pervasive developmental disorder without further specification (PDD-NOS) is made. People with Asperger’s Syndrome, unlike autistic people, develop speech skills without significant delays.
Atypical autism is characterized by a later age of onset (from 3 years of age), as well as failure to fulfill at least one of the three ICD-10 criteria for childhood autism.
The terminology associated with autism can be confusing because autism, Asperger’s syndrome, and PDD-NOS are often lumped together as “autism spectrum disorders,” sometimes referred to as “autistic disorders,” and autism itself is often referred to as autistic disorder or childhood autism. Since 2013, in the DSM-5 classifier, autism (autistic disorder), Asperger’s syndrome, childhood disintegrative disorder and PDD-NOS are officially combined into one disorder – autism spectrum disorder.
In this article, “autism” corresponds to the classic autistic disorder, but in clinical practice the expressions “autism”, “autism spectrum disorder” and PDD are often used interchangeably. In turn, autism spectrum disorders are included in the broader autism phenotype (BAP), which also describes individuals with autistic behaviors such as those who avoid eye contact.
Individual manifestations of autism cover a wide spectrum: from persons with severe disabilities – dumb and mentally disabled, spending time swinging, constantly waving their hands – to socially active highly functional autists, whose disorder manifests itself in oddities in communication, narrow interests and verbose, pedantic speech. Sometimes the syndrome is subdivided into low-, medium- and high-functioning autism, using the IQ scale or by assessing the level of support that a person needs in everyday life; there is no standard for this typing, and there is a debate around it. Autism can also be subdivided into syndromic and non-syndromic – in the former case, the disorder is associated with severe or profound mental retardation, or a congenital syndrome with physical symptoms, such as tuberous sclerosis. Although the cognitive tests in people with Asperger’s syndrome are higher than in autists, the real degree of overlap between these two diagnoses with similar manifestations (high-functioning autism, non-syndromic autism) diagnoses is unclear.
Some studies report that the diagnosis of autism is not due to developmental arrest, but due to a child’s loss of language or social skills, usually between 15 and 30 months of age. So far, there is no consensus on this feature; perhaps regressive autism is a specific subtype of the disorder.
The inability to isolate biologically based subpopulations makes it difficult to investigate the causes of the disorder. Suggestions have been made to classify autism using both behavior and genetics, and it is suggested that the term “type 1 autism” be reserved for the rare cases in which testing confirms a mutation in the CNTNAP2 gene.