Intellectual Disability

Some autistic children have some degree of mental impairment. When tested, some areas of ability may be normal or superior, while others may be especially weak. For example, an autistic child may do well on the parts of the test that measure visual skills but earn low scores on the language subtests.

Mental disability isn't a mandatory feature of autism, but probably about 50% of autistic children score in the mentally disabled (IQ 70 or lower) range on IQ tests. There is great variation on IQ tests among those who have autism, with a common finding being that those with autism have a higher nonverbal IQ and a much lower verbal IQ. Often this pattern is reversed in those who have Asperger syndrome. In the past, the percentage of children with mental disability was higher (70%) because the diagnosis of autism was only used in more severely affected children. As more children get included on the autism spectrum, the percentage of those with normal IQs also increases.

IQ test results are much more uneven in the sub-categories than normal, frequently showing a peak in visuo-spatial tasks and those that require rote memory. Because of this, an autistic person may have much more skill in doing certain things than his/her IQ seems to indicate, and when taken to the extreme, the person may be called an autistic savant.

There are things like echolalia that separate autistic children from non-autistic intellectually disabled children.

More about the Autism Spectrum Test

Additionally, a recent review also questioned the validity of IQ testing of autistic people.

Alternative terms
Although the American Association on Mental Retardation continues to use the term mental retardation, it has acquired extremely pejorative and shameful connotations over the last few decades and is now used almost exclusively (and very rarely) in technical or scientific contexts. Some of the alternative terms to describe the condition are:

Medical practitioners and others are advised to avoid using "the r word" as it can be very hurtful and evoke feelings of fear or distrust in disabled people.
 * In North America the broad term developmental delay has become an increasingly preferred synonym. Elsewhere, however, developmental delay is generally used to imply that appropriate intervention will improve or completely eliminate the condition, allowing for "catching up." Importantly, this term carries the emotionally powerful idea that the individual's current difficulties are likely to be temporary. This may place unrealistic demands on autistic people and be a great source of stress.
 * Developmental disability is preferred by most physicians. However, the term also refers to any other physical or psychiatric delay, such as delayed puberty.
 * The phrase intellectual disability is increasingly being used as a synonym for people with significantly below-average IQ. These terms are sometimes used as a means of separating general intellectual limitations from specific, limited deficits as well as indicating that it is not an emotional or psychological disability. Intellectual disability is also used to describe the outcome of traumatic brain injury or lead poisoning or dementing conditions such as Alzheimer's disease. It is not specific to congenital conditions like Down syndrome.

Diagnosis
According to the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), there are three criteria before a person is considered to have a developmental disability:


 * An IQ below 70,
 * Significant limitations in two or more areas of adaptive behavior (i.e., ability to function at age level in an ordinary environment), and
 * Evidence that the limitations became apparent in childhood.


 * An IQ below 70
 * An IQ below 70

Difficulties in Diagnosis
Intellectual disability may be over-diagnosed in autistic people. Because autistic people's brains work differently, IQ tests designed for neurotypicals may fail to provide an accurate or meaningful score.

One autistic writer uses personal examples to show how intellectual development and social/emotional development may be different in autistic people:"'At two, I could describe the life cycle of the aphid, but I didn’t reliably answer direct questions for some years after that.  Not long ago, I asked my mom how old I was when I finally began to greet others with “how are you?” reliably, and she said that she was still awaiting that day. [...]""'In the standard-human way of thinking, an IQ in the 50s and enjoyment of Disney means that Clara must only understand certain words and ideas.  To upend that thinking, she and I met six years ago and our friendship exists almost exclusively via online chat, as in, fully in writing, which she does with ability much beyond the average adult. [...] This young lady used the word “impudent” in casual conversation the other day."This also does not take into account the possibility of communication difficulties. For example, an autistic child with dyspraxia may touch the wrong card while trying to touch the right one, or an underestimated autistic child may get bored with the test because it is too simple. A child who is presumed not to hear anything her parents say might hear it perfectly, just not have a way to respond.

Causes
Causes of intellectual include:


 * Genetic factors
 * Problems during pregnancy and at birth, and use of forceps during birth
 * General health problems, malnutrition, and iodine deficiency
 * Institutionalisation
 * Sensory deprivation
 * Psycho-social disadvantage

Treatment
Mental disability is not a disease - it is a disability, and is distinct from conditions of mental illness like schizophrenia or depression. There is no medicine to remove this disability, though there are many programs available to reduce the impact of this disability to assist the children to improve their condition and for adults to live a better life and find some sort of work which they may perform.

Programs may focus on an autistic person's strengths, such as good memory, honesty, and intense focus.