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Autism presents in a wide degree, from those who are nearly dysfunctional and apparently mentally disabled to those whose symptoms are mild or remedied enough to appear unexceptional ("normal") to others. Although not used or accepted by professionals or within the literature, autistic individuals are often divided into those with an IQ<80 referred to as having "low-functioning autism" (LFA), while those with IQ>80 are referred to as having "high-functioning autism" (HFA). Low and high functioning are more generally applied to how well an individual can accomplish activities of daily living, rather than to IQ. The terms low and high functioning are controversial and not all autistics accept these labels. Additionally, a recent review questioned the validity of IQ testing of autistic people.
This discrepancy can lead to confusion among service providers who equate IQ with functioning and may refuse to serve high-IQ autistic people who are severely compromised in their ability to perform daily living tasks, or may fail to recognize the intellectual potential of many autistic people who are considered LFA. For example, some professionals refuse to recognize autistics who can speak or write as being autistic at all, because they still think of autism as a communication disorder so severe that no speech or writing is possible.
As a consequence, many "high-functioning" autistic persons, and autistic people with a relatively high IQ, are under diagnosed, thus making the claim that "autism implies retardation" self-fulfilling. The number of people diagnosed with LFA is not rising quite as sharply as HFA, indicating that at least part of the explanation for the apparent rise is probably better diagnostics. Many also think that ASD's are being over diagnosed: (1) because the growth in the number and complexity of symptoms associated with autism has increased the chances professionals will erroneously diagnose autism and (2) because the growth in services and therapies for autism has increased the number who falsely qualify for those often free services and therapies.
Asperger's and Kanner's syndromes
In the current Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), the most significant difference between Autistic Disorder (also known as Kanner's syndrome) and Asperger's syndrome is that a diagnosis of the former includes the observation of "delays or abnormal functioning in at least one of the following areas, with onset prior to age 3 years: (1) social interaction, (2) language as used in social communication, or (3) symbolic or imaginative play", while a diagnosis of Asperger's syndrome observes "no clinically significant delay" in the latter two of these areas.
While the DSM-IV does not include level of intellectual functioning in the diagnosis, the fact that those with Asperger's syndrome tend to perform better than those with Kanner's autism has produced a popular conception that Asperger's syndrome is synonymous with "higher-functioning autism", or that it is a lesser disorder than autism. Similarly, there is a popular conception that autistic individuals with a high level of intellectual functioning in fact have Asperger's syndrome, or that both types are merely 'geeks' with a medical label. The popular depiction of autism in the media has been of relatively severe cases (for example, as seen in the films Rain Man and Mercury Rising), and in turn many close friends and relatives of those who have been diagnosed in the autistic spectrum choose to speak of their loved ones as having Asperger's syndrome rather than autism.
The extent to which someone with higher functioning autism or Asperger's syndrome may excel is theoretically quite high. For example, Henry Cavendish, one of history's foremost scientists, may have been autistic. George Wilson, a notable chemist and physician, wrote a book about Cavendish entitled, "The Life of the Honourable Henry Cavendish", published in 1851. From Wilson's detailed description it seems that while Cavendish may have exhibited many classic signs of autism, he nevertheless had an extraordinary mind.
Autism as a spectrum disorder
For more details on this topic, see Autistic spectrum.
Another view of these disorders is that they are on a continuum known as autistic spectrum disorders. Autism spectrum disorder is an increasingly popular term that refers to a broad definition of autism including the classic form of the disorder as well as closely related conditions such as PDD-NOS and Asperger's syndrome. Although the classic form of autism can be easily distinguished from other forms of autism spectrum disorder, the terms are often used interchangeably.
A related continuum, Sensory Integration Dysfunction, involves how well humans integrate the information they receive from their senses. Autism, Asperger's syndrome, and Sensory Integration Dysfunction are all closely related and overlap.
Some people believe that there might be two manifestations of classical autism, regressive autism and early infantile autism. Early infantile autism is present at birth while regressive autism begins before the age of 3 and often around 18 months. Although this causes some controversy over when the neurological differences involved in autism truly begin, some speculate that an environmental influence or toxin triggers the disorder. This triggering could occur during gestation due to a toxin that enters the mother's body and is transferred to the fetus. The triggering could also occur after birth during the crucial early nervous system development of the child.
A paper published in 2006 concerning the behavioral, cognitive, and genetic bases of autism argues that autism should perhaps not be seen as a single disorder, but rather as a set of distinct symptoms (social difficulties, communicative difficulties and repetitive behaviors) that have their own distinct causes. An implication of this would be that a search for a "cure" for autism is unlikely to succeed if it is not examined as separate, albeit overlapping and commonly co-occurring, disorders.
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