What Autism is Not
Autism is not Mental Retardation or a Lack of Intelligence
As intelligence is communicated through skillful use of language, people with autism's social and communication deficits can easily make them appear unintelligent. This is not necessarily the case, however. People with autism vary in intelligence more or less as normal people do, only their language and social problems can make that intelligence harder to discover. It should be kept in mind that there are multiple kinds of intelligence and not all of them involve language.
Historically, autism was confused with Mental Retardation (MR). Today, MR and autism are considered to be distinct conditions. Contemporary diagnostic criteria for MR are as follows: 1) an Intelligence Quotient score (IQ, a standard measure of intelligence) of 70 or less (representing the bottom two percent of IQ scores), 2) significant problems in functioning on their own in work and/or personal settings, and 3) onset of problems before age 18.
The third (early age of onset) criterion for the mental retardation diagnosis obviously overlaps with autism, which itself appears within the first three years of life. People with autism may also fit the second (poor adaptive functioning and independent living skills) criteria for MR as their social deficits may make it very difficult for them to take care of themselves or find gainful employment as adults. However, people with autism sometimes do not meet the first (low intelligence) criteria for MR. The bulk of people diagnosed with MR show a uniformly even pattern of low performance on IQ tests. In contrast, autistic people often show variable IQ test performance that suggests severe deficits in the midst of preserved or even strong abilities. There may be other evidence available to suggest that islands of ability are present, but difficult to demonstrate because of communication problems. A minority of people with autism's total IQ scores will be greater than 70, making the diagnosis of MR inappropriate. However, in most cases of moderate to severe autism (some seventy percent of all autism cases), IQ scores of 70 or below are achieved, and both autism and MR diagnoses are appropriate. Though both diagnoses may be present at the same time, they are still considered distinct conditions.
Autism is not Obsessive-Compulsive Disorder
People with autism's ritual preoccupations and behaviors are similar to the obsessions and compulsions characteristic of Obsessive Compulsive Disorder (OCD), and with the need for order and perfection characteristic of Obsessive Compulsive Personality Disorder (OCPD). Obsessions are intrusive thoughts that reoccur constantly and which cannot be suppressed or escaped. Though they may not be worries in-of-themselves, their very incessant and unrelenting quality causes affected people to become anxious and to behave in ways that will reduce that anxiety. For example, someone might develop an obsession concerning whether a door handle is dirty. Anxiety around that contamination fear would motivate action; once the door handle was cleaned, some anxiety relief might be experienced. In this manner are born compulsions, which are anxiety motivated behaviors that once performed, help to reduce distress (however short lived that relief might be). OCPD is a distinct condition from OCD. People with OCPD do not experience true obsessions or compulsions, but are instead basically very uptight, rule-governed, inflexible people rigidly concerned with their position within their social hierarchy, and with the orderliness and perfection of their personal environments and projects.
Thought there are similarities between autism and the obsessive compulsive disorders, these disorders are also distinct from one another. Autism begins in early childhood while the other disorders do not tend to manifest until early adulthood. There is also the matter of motivation to be considered. Autism is a brain disease reducing affected people's capability for appreciating the existence of the social world populated by other feeling human beings. People with moderate and severe autism have difficulty appreciating that other people have different agendas than they do; it is in question whether they appreciate other people as having independent existences at all. This is in contrast to people with OCPD who are hyper-aware of their social position. Though both those with OCD and those with autism engage in repetitive obsessive behaviors, OCD compulsiveness appears to be motivated more by anxious attempts to self-sooth, while autistic compulsiveness may be motivated by their need to self-stimulate. At any rate, the disease process that creates obsessions and compulsions in OCD appears to have a different mechanism than the one responsible for autistic deficits. This means that people with autism could develop OCD as well as autism and receive both diagnoses. However, if this were to be the case, both disease processes would be occurring simultaneously. One diagnosis does not reduce to the other.