Fact sheet on intellectual disability, a comorbid disorder with Aspergers and Autism, also known as mental retardation


Most patients presenting in clinical settings with an Autism Spectrum Disorder, such as Aspergers syndrome or autism, have other comorbid disorders. Mental retardation is a possible comorbid disorder at the more severe end of the autism spectrum.


Mental retardation is a term for a pattern of persistently slow learning of basic motor and language skills ("milestones") during childhood, and a significantly below-normal global intellectual capacity as an adult. One common criterion for diagnosis of mental retardation is a tested intelligence quotient (IQ) of 70 or below.


People with mental retardation may be described as having developmental disabilities, global developmental delay, or learning difficulties.


Alternative terms

The term "Mental retardation" has acquired pejorative and shameful connotations over the last few decades and is now used almost exclusively in technical or scientific contexts where exactness is necessary. The term 'intellectual disability' is increasingly common, and used on this website where possible.


In North America the broad term developmental delay has become an increasingly preferred synonym by many parents and direct support professionals. 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.

Developmental disability is preferred by most physicians, but can also refer to any other physical or psychiatric delay, such as delayed puberty.

Both the phrases 'intellectual disability' and 'learning disability' are 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.


The American Association on Mental Retardation continues to use the term mental retardation. In June 2006 its members voted to change the name of the organization to the "American Association on Intellectual and Developmental Disabilities," rejecting the options to become the AAID or AADD. Part of the rationale for the double name was that many of the members worked with people with autism and Asperger's syndrome, also known as pervasive developmental disorders, not all of whom were also mentally retarded.


In the UK, "mental handicap" had become the common medical term, replacing "mental subnormality" in Scotland and "mental deficiency" in England and Wales, until Stephen Dorrell, Secretary of State for Health in England and Wales from 1995-7, changed the National Health Service's designation to "learning disability." The new term is not yet widely understood, and is often taken to refer to problems affecting schoolwork (the American usage): which are known in the UK as "learning difficulties." British social workers may use "learning difficulty" to refer to both people with MR and those with conditions such as dyslexia.



There are many signs. For example, children with developmental disabilities may learn to sit up, to crawl, or to walk later than other children, or they may learn to talk later. Both adults and children with intellectual disabilities may also:

• have trouble speaking
• find it hard to remember things
• have trouble understanding social rules
• have trouble discerning cause and effect
• have trouble solving problems
• have trouble thinking logically.


In early childhood mild disability (IQ 60–70) may not be obvious, and may not be diagnosed until they begin school. Even when poor academic performance is recognized, it may take expert assessment to distinguish mild mental disability from learning disability or behavior problems. As they become adults, many people can live independently and may be considered by others in their community as "slow" rather than retarded.


Moderate disability (IQ 50–60) is nearly always obvious within the first years of life. These people will encounter difficulty in school, at home, and in the community. In many cases they will need to join special, usually separate, classes in school, but they can still progress to become functioning members of society. As adults they may live with their parents, in a supportive group home, or even semi-independently with significant supportive services to help them, for example, manage their finances.


Among people with intellectual disabilities, only about one in eight will score below 50 on IQ tests. A person with a more severe disability will need more intensive support and supervision his or her entire life.


The limitations of cognitive function will cause a child to learn and develop more slowly than a typical child. Children may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. Learning will take them longer, require more repetition, and there may be some things they cannot learn. The extent of the limits of learning is a function of the severity of the disability.


Nevertheless, virtually every child is able to learn, develop, and grow to some extent.



According to the 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. It is formally diagnosed by professional assessment of intelligence and adaptive behavior.


IQ tests were created as an attempt to measure a person's abilities in several areas, including language, numeracy and problem-solving. The average score is 100. People with a score below 75 will often, but not always, have difficulties with daily living skills. Since factors other than mental ability (depression, anxiety, lack of adequate effort, etc.) can yield low IQ scores, it is important for the evaluator to rule them out prior to concluding that measured IQ is "significantly below average".


The following ranges, based on the Wechsler Adult Intelligence Scale (WAIS), are in standard use today:
Class IQ
Profound mental retardation Below 20
Severe mental retardation 20–34
Moderate mental retardation 35–49
Mild mental retardation 50–69
Borderline mental retardation 70–79


Significant limitations in two or more areas of adaptive behavior

Adaptive behavior, or adaptive functioning, refers to the skills needed to live independently (or at the minimally acceptable level for age). To assess adaptive behavior, professionals compare the functional abilities of a child to those of other children of similar age. To measure adaptive behavior, professionals use structured interviews, with which they systematically elicit information about the person's functioning in the community from someone who knows them well. There are many adaptive behavior scales, and accurate assessment of the quality of someone's adaptive behavior requires clinical judgment as well. Certain skills are important to adaptive behavior, such as:

• daily living skills, such as getting dressed, using the bathroom, and feeding oneself
• communication skills, such as understanding what is said and being able to answer
• social skills with peers, family members, spouses, adults, and others.


Evidence that the limitations became apparent in childhood

This third condition is used to distinguish it from dementing conditions such as Alzheimer's disease or is due to traumatic injuries that damaged the brain.



Down syndrome, fetal alcohol syndrome and Fragile X syndrome are the three most common inborn causes. However, doctors have found many other causes. The most common are:


Genetic conditions. Sometimes disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions include Down syndrome, Fragile X syndrome, and phenylketonuria (PKU).

Problems during pregnancy. Mental disability can result when the fetus does not develop inside the mother properly. For example, there may be a problem with the way the fetus's cells divide as it grows. A woman who drinks alcohol (see fetal alcohol syndrome) or gets an infection like rubella during pregnancy may also have a baby with mental disability.


Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have developmental disability due to brain damage.


Health problems. Diseases like whooping cough, measles, or meningitis can cause mental disability. It can also be caused by not getting enough medical care, or by being exposed to poisons like lead or mercury.


Iodine deficiency, affecting approximately 2 billion people worldwide, is the leading preventable cause of mental disability in areas of the developing world where iodine deficiency is endemic. Iodine deficiency also causes goiter, an enlargement of the thyroid gland. More common than full fledged cretinism, as retardation caused by severe iodine deficiency is called, is mild impairment of intelligence. Certain areas of the world due to natural deficiency and governmental inaction are severely affected. India is the most outstanding, with 500 million suffering from deficiency, 54 million from goiter, and 2 million from cretinism. Among other nations affected by iodine deficiency, China and Kazakhstan have begun taking action, while Russia has not.


Malnutrition is a common cause of reduced intelligence in parts of the world affected by famine such as Ethiopia.


The use of forceps during birth can lead to intellectual disability in an otherwise normal child. They can fracture the skull and cause brain damage.


Institutionalization at a young age can cause intellectual disability in normal children.


Sensory deprivation in the form of severe environmental restrictions (such as being locked in a basement), prolonged isolation, or severe atypical parent-child interactions.


Psycho-social disadvantage. Contributing factors are lack of reading material, use of language not common in that community, poor diet, poor health practices, and poor housing.


Treatment and assistance

By most definitions it is more accurately considered a disability rather than a disease. It can be distinguished in many ways from mental illness, such as schizophrenia or depression. Currently, there is no "cure" for an established disability, though with appropriate support and teaching, most individuals can learn to do many things.


There are usually a variety of agencies in the most countries that provide assistance for people with developmental disabilities. They will usually include state-run, for-profit, and non-profit, privately run agencies. Within one agency there could be departments that include fully staffed residential homes, day habilitation programs that approximate schools, workshops wherein people with disabilities can obtain jobs, programs that assist people with developmental disabilities in obtaining jobs in the community, programs that provide support for people with developmental disabilities who have their own apartments, programs that assist them with raising their children, and many more.


Although there is no specific medication for intellectual disability, many people with developmental disabilities have further medical complications and may take several medications. Beyond that there are specific programs that people with developmental disabilities can take part in wherein they learn basic life skills. These "goals" may take a much longer amount of time for them to accomplish, but the ultimate goal is independence. This may be anything from independence in tooth brushing to an independent residence. People with developmental disabilities learn throughout their lives and can obtain many new skills even late in life with the help of their families, caregivers, clinicians and the people who coordinate the efforts of all of these people.


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This autism fact sheet is licensed under the GNU Free Documentation. It is derivative of a Mental retardation article at http://en.wikipedia.org

Mental retardation is a term for a pattern of persistently slow learning of basic motor and language skills ("milestones") during childhood and can be a comorbid disorder with Asperger's syndrome and Autism